diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3a1810b..4810b04 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,7 +31,8 @@ set(WEBCC_ENABLE_GZIP 0 CACHE STRING "Enable gzip compression (need Zlib)? (1:Ye
 
 set(WEBCC_LOG_LEVEL 2 CACHE STRING "Log level (0:VERB, 1:INFO, 2:USER, 3:WARN or 4:ERRO)")
 
-set(WEBCC_USE_STD_FILESYSTEM 1 CACHE STRING "Use C++17 filesystem? (1:Yes, 0:No)")
+set(WEBCC_USE_STD_FILESYSTEM 1 CACHE STRING "Use std::filesystem? (1:Yes, 0:No)")
+set(WEBCC_USE_STD_STRING_VIEW 1 CACHE STRING "Use std::string_view? (1:Yes, 0:No)")
 
 if(BUILD_UNITTEST)
     enable_testing()
@@ -45,7 +46,7 @@ endif()
 
 # C++ standard requirements.
 
-if(WEBCC_USE_STD_FILESYSTEM)
+if(WEBCC_USE_STD_FILESYSTEM OR WEBCC_USE_STD_STRING_VIEW)
     set(CMAKE_CXX_STANDARD 17)
 else()
     set(CMAKE_CXX_STANDARD 11)
diff --git a/autotest/client_autotest/client_autotest.cc b/autotest/client_autotest/client_autotest.cc
index 400f8e7..4c58dd4 100644
--- a/autotest/client_autotest/client_autotest.cc
+++ b/autotest/client_autotest/client_autotest.cc
@@ -20,7 +20,7 @@ static Json::Value StringToJson(const std::string& str) {
   Json::Value json;
 
   Json::CharReaderBuilder builder;
-  std::stringstream stream(str);
+  std::istringstream stream{ str };
   std::string errors;
   if (!Json::parseFromStream(builder, stream, &json, &errors)) {
     std::cerr << errors << std::endl;
diff --git a/examples/book_client/book_json.cc b/examples/book_client/book_json.cc
index e8213b7..8481432 100644
--- a/examples/book_client/book_json.cc
+++ b/examples/book_client/book_json.cc
@@ -16,7 +16,7 @@ Json::Value StringToJson(const std::string& str) {
   Json::Value json;
 
   Json::CharReaderBuilder builder;
-  std::stringstream stream(str);
+  std::istringstream stream{ str };
   std::string errs;
   if (!Json::parseFromStream(builder, stream, &json, &errs)) {
     std::cerr << errs << std::endl;
diff --git a/examples/book_server/book_json.cc b/examples/book_server/book_json.cc
index 206983e..d20e111 100644
--- a/examples/book_server/book_json.cc
+++ b/examples/book_server/book_json.cc
@@ -16,7 +16,7 @@ Json::Value StringToJson(const std::string& str) {
   Json::Value json;
 
   Json::CharReaderBuilder builder;
-  std::stringstream stream(str);
+  std::istringstream stream{ str };
   std::string errs;
   if (!Json::parseFromStream(builder, stream, &json, &errs)) {
     std::cerr << errs << std::endl;
diff --git a/examples/book_server/main.cc b/examples/book_server/main.cc
index fe07d0a..792d12b 100644
--- a/examples/book_server/main.cc
+++ b/examples/book_server/main.cc
@@ -39,11 +39,11 @@ int main(int argc, char* argv[]) {
                  std::make_shared<BookListView>(),
                  { "GET", "POST" });
 
-    server.Route(webcc::R("/books/(\\d+)"),
+    server.Route(webcc::R{ "/books/(\\d+)" },
                  std::make_shared<BookDetailView>(photo_dir),
                  { "GET", "PUT", "DELETE" });
 
-    server.Route(webcc::R("/books/(\\d+)/photo"),
+    server.Route(webcc::R{ "/books/(\\d+)/photo" },
                  std::make_shared<BookPhotoView>(photo_dir),
                  { "GET", "PUT", "DELETE" });
 
diff --git a/examples/form_client.cc b/examples/form_client.cc
index 614a0c6..a0655bd 100644
--- a/examples/form_client.cc
+++ b/examples/form_client.cc
@@ -17,7 +17,7 @@ int main(int argc, char* argv[]) {
     std::cout << "  $ ./form_client path/to/webcc/data/upload" << std::endl;
     std::cout << "  $ ./form_client path/to/webcc/data/upload "
               << "http://httpbin.org/post" << std::endl;
-    std::cout << "(Post the example 'form_server')" << std::endl;
+    std::cout << "(Post to the example 'form_server')" << std::endl;
     std::cout << "  $ ./form_client path/to/webcc/data/upload "
                  "http://localhost:8080/upload"
               << std::endl;
@@ -43,8 +43,7 @@ int main(int argc, char* argv[]) {
   webcc::ClientSession session;
 
   try {
-    auto r = session.Send(webcc::RequestBuilder{}
-                              .Post(url)
+    auto r = session.Send(WEBCC_POST(url)
                               .FormFile("file", upload_dir / "remember.txt")
                               .FormData("json", "{}", "application/json")());
 
diff --git a/examples/github_client.cc b/examples/github_client.cc
index e2ca213..b04d493 100644
--- a/examples/github_client.cc
+++ b/examples/github_client.cc
@@ -20,7 +20,7 @@ Json::Value StringToJson(const std::string& str) {
   Json::Value json;
 
   Json::CharReaderBuilder builder;
-  std::stringstream stream(str);
+  std::istringstream stream{ str };
   std::string errors;
   if (!Json::parseFromStream(builder, stream, &json, &errors)) {
     std::cerr << errors << std::endl;
diff --git a/unittest/router_unittest.cc b/unittest/router_unittest.cc
index bc7dab5..ddc8710 100644
--- a/unittest/router_unittest.cc
+++ b/unittest/router_unittest.cc
@@ -17,8 +17,7 @@ public:
 TEST(RouterTest, URL_RegexBasic) {
   webcc::Router router;
 
-  router.Route(webcc::R("/instance/(\\d+)"),
-               std::make_shared<MyView>());
+  router.Route(webcc::R{ "/instance/(\\d+)" }, std::make_shared<MyView>());
 
   std::string url = "/instance/12345";
   webcc::UrlArgs args;
@@ -40,7 +39,7 @@ TEST(RouterTest, URL_RegexBasic) {
 TEST(RouterTest, URL_RegexMultiple) {
   webcc::Router router;
 
-  router.Route(webcc::R("/study/(\\d+)/series/(\\d+)/instance/(\\d+)"),
+  router.Route(webcc::R{ "/study/(\\d+)/series/(\\d+)/instance/(\\d+)" },
                std::make_shared<MyView>());
 
   std::string url = "/study/1/series/2/instance/3";
diff --git a/unittest/string_unittest.cc b/unittest/string_unittest.cc
index f54ca5a..f8652f0 100644
--- a/unittest/string_unittest.cc
+++ b/unittest/string_unittest.cc
@@ -6,8 +6,36 @@
 
 #include "webcc/string.h"
 
+TEST(StringTest, Trim) {
+  std::string str = "   trim me  ";
+  webcc::string_view sv = str;
+  webcc::Trim(sv);
+  EXPECT_EQ("trim me", sv);
+}
+
+TEST(StringTest, Trim_Left) {
+  std::string str = "   trim me";
+  webcc::string_view sv = str;
+  webcc::Trim(sv);
+  EXPECT_EQ("trim me", sv);
+}
+
+TEST(StringTest, Trim_Right) {
+  std::string str = "trim me  ";
+  webcc::string_view sv = str;
+  webcc::Trim(sv);
+  EXPECT_EQ("trim me", sv);
+}
+
+TEST(StringTest, Trim_Empty) {
+  std::string str = "";
+  webcc::string_view sv = str;
+  webcc::Trim(sv);
+  EXPECT_EQ("", sv);
+}
+
 TEST(StringTest, Split) {
-  std::vector<boost::string_view> parts;
+  std::vector<webcc::string_view> parts;
   webcc::Split("GET /path/to HTTP/1.1", ' ', false, &parts);
 
   EXPECT_EQ(3, parts.size());
@@ -18,12 +46,11 @@ TEST(StringTest, Split) {
 
 TEST(StringTest, Split_TokenCompressOff) {
   std::string str = "one,two,,three,,";
-  std::vector<boost::string_view> parts;
+  std::vector<webcc::string_view> parts;
 
   // Same as:
   //   boost::split(parts, str, boost::is_any_of(","),
   //                boost::token_compress_off);
-
   webcc::Split(str, ',', false, &parts);
 
   EXPECT_EQ(6, parts.size());
@@ -37,7 +64,7 @@ TEST(StringTest, Split_TokenCompressOff) {
 
 TEST(StringTest, Split_TokenCompressOn) {
   std::string str = "one,two,,three,,";
-  std::vector<boost::string_view> parts;
+  std::vector<webcc::string_view> parts;
 
   // Same as:
   //   boost::split(parts, str, boost::is_any_of(","),
@@ -51,8 +78,28 @@ TEST(StringTest, Split_TokenCompressOn) {
   EXPECT_EQ("", parts[3]);
 }
 
+TEST(StringTest, Split_TokensOnly) {
+  std::string str = ",,,,,";
+  std::vector<webcc::string_view> parts;
+
+  // Token compress on
+  webcc::Split(str, ',', true, &parts);
+  EXPECT_EQ(2, parts.size());
+  EXPECT_EQ("", parts[0]);
+  EXPECT_EQ("", parts[1]);
+  
+  parts.clear();
+
+  // Token compress off
+  webcc::Split(str, ',', false, &parts);
+  EXPECT_EQ(6, parts.size());
+  EXPECT_EQ("", parts[0]);
+  EXPECT_EQ("", parts[1]);
+  EXPECT_EQ("", parts[5]);
+}
+
 TEST(StringTest, Split_NewLine) {
-  std::vector<boost::string_view> lines;
+  std::vector<webcc::string_view> lines;
   webcc::Split("line one\nline two\nline 3", '\n', false, &lines);
 
   EXPECT_EQ(3, lines.size());
@@ -64,8 +111,8 @@ TEST(StringTest, Split_NewLine) {
 TEST(StringTest, SplitKV) {
   const std::string str = "key=value";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', true, &key, &value);
 
   EXPECT_EQ(true, ok);
@@ -76,8 +123,8 @@ TEST(StringTest, SplitKV) {
 TEST(StringTest, SplitKV_OtherDelim) {
   const std::string str = "key:value";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, ':', true, &key, &value);
 
   EXPECT_TRUE(ok);
@@ -89,8 +136,8 @@ TEST(StringTest, SplitKV_OtherDelim) {
 TEST(StringTest, SplitKV_Spaces) {
   const std::string str = " key =  value ";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', true, &key, &value);
 
   EXPECT_TRUE(ok);
@@ -102,8 +149,8 @@ TEST(StringTest, SplitKV_Spaces) {
 TEST(StringTest, SplitKV_SpacesNoTrim) {
   const std::string str = " key =  value ";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', false, &key, &value);
 
   EXPECT_TRUE(ok);
@@ -115,8 +162,8 @@ TEST(StringTest, SplitKV_SpacesNoTrim) {
 TEST(StringTest, SplitKV_NoKey) {
   const std::string str = "=value";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', true, &key, &value);
 
   EXPECT_TRUE(ok);
@@ -128,8 +175,8 @@ TEST(StringTest, SplitKV_NoKey) {
 TEST(StringTest, SplitKV_NoValue) {
   const std::string str = "key=";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', true, &key, &value);
 
   EXPECT_TRUE(ok);
@@ -141,8 +188,8 @@ TEST(StringTest, SplitKV_NoValue) {
 TEST(StringTest, SplitKV_NoKeyNoValue) {
   const std::string str = "=";
 
-  std::string key;
-  std::string value;
+  webcc::string_view key;
+  webcc::string_view value;
   bool ok = webcc::SplitKV(str, '=', true, &key, &value);
 
   EXPECT_TRUE(ok);
diff --git a/webcc/client.cc b/webcc/client.cc
index 19a1e96..93ae0a0 100644
--- a/webcc/client.cc
+++ b/webcc/client.cc
@@ -114,10 +114,10 @@ void Client::AsyncConnect() {
   }
 }
 
-void Client::AsyncResolve(const std::string& default_port) {
+void Client::AsyncResolve(string_view default_port) {
   std::string port = request_->port();
   if (port.empty()) {
-    port = default_port;
+    port = ToString(default_port);
   }
 
   LOG_VERB("Resolve host (%s)", request_->host().c_str());
diff --git a/webcc/client.h b/webcc/client.h
index 8481aa3..4da2e16 100644
--- a/webcc/client.h
+++ b/webcc/client.h
@@ -89,7 +89,7 @@ private:
 
   void AsyncConnect();
 
-  void AsyncResolve(const std::string& default_port);
+  void AsyncResolve(string_view default_port);
 
   void OnResolve(boost::system::error_code ec,
                  boost::asio::ip::tcp::resolver::results_type endpoints);
diff --git a/webcc/client_session.cc b/webcc/client_session.cc
index d04ebe9..bddd2a1 100644
--- a/webcc/client_session.cc
+++ b/webcc/client_session.cc
@@ -128,7 +128,7 @@ void ClientSession::Stop() {
   started_ = false;
 }
 
-void ClientSession::Accept(const std::string& content_types) {
+void ClientSession::Accept(string_view content_types) {
   if (!content_types.empty()) {
     headers_.Set(headers::kAccept, content_types);
   }
@@ -168,18 +168,18 @@ void ClientSession::AcceptGzip(bool gzip) {
 
 #endif  // WEBCC_ENABLE_GZIP
 
-void ClientSession::Auth(const std::string& type,
-                         const std::string& credentials) {
-  headers_.Set(headers::kAuthorization, type + " " + credentials);
+void ClientSession::Auth(string_view type, string_view credentials) {
+  headers_.Set(headers::kAuthorization,
+               ToString(type) + " " + ToString(credentials));
 }
 
-void ClientSession::AuthBasic(const std::string& login,
-                              const std::string& password) {
-  auto credentials = Base64Encode(login + ":" + password);
+void ClientSession::AuthBasic(string_view login, string_view password) {
+  auto credentials =
+      Base64Encode(ToString(login) + ":" + ToString(password));
   return Auth("Basic", credentials);
 }
 
-void ClientSession::AuthToken(const std::string& token) {
+void ClientSession::AuthToken(string_view token) {
   return Auth("Token", token);
 }
 
diff --git a/webcc/client_session.h b/webcc/client_session.h
index ce8e5f6..3fca3a1 100644
--- a/webcc/client_session.h
+++ b/webcc/client_session.h
@@ -52,7 +52,7 @@ public:
     buffer_size_ = buffer_size;
   }
 
-  void SetHeader(const std::string& key, const std::string& value) {
+  void SetHeader(string_view key, string_view value) {
     headers_.Set(key, value);
   }
 
@@ -60,14 +60,13 @@ public:
   // Only applied when:
   //   - the request to send has no `Content-Type` header, and
   //   - the request has a body.
-  void SetContentType(const std::string& media_type,
-                      const std::string& charset = "") {
-    media_type_ = media_type;
-    charset_ = charset;
+  void SetContentType(string_view media_type, string_view charset = "") {
+    media_type_ = ToString(media_type);
+    charset_ = ToString(charset);
   }
 
   // Set content types to accept.
-  void Accept(const std::string& content_types);
+  void Accept(string_view content_types);
 
 #if WEBCC_ENABLE_GZIP
 
@@ -77,13 +76,13 @@ public:
 #endif  // WEBCC_ENABLE_GZIP
 
   // Set authorization.
-  void Auth(const std::string& type, const std::string& credentials);
+  void Auth(string_view type, string_view credentials);
 
   // Set Basic authorization.
-  void AuthBasic(const std::string& login, const std::string& password);
+  void AuthBasic(string_view login, string_view password);
 
   // Set Token authorization.
-  void AuthToken(const std::string& token);
+  void AuthToken(string_view token);
 
   // Send a request.
   // Please use RequestBuilder to build the request.
diff --git a/webcc/common.cc b/webcc/common.cc
index 570c995..ab52254 100644
--- a/webcc/common.cc
+++ b/webcc/common.cc
@@ -12,41 +12,26 @@ namespace webcc {
 
 // -----------------------------------------------------------------------------
 
-bool Headers::Set(const std::string& key, const std::string& value) {
+bool Headers::Set(string_view key, string_view value) {
   if (value.empty()) {
     return false;
   }
 
   auto it = Find(key);
   if (it != headers_.end()) {
-    it->second = value;
+    it->second = ToString(value);
   } else {
-    headers_.push_back({ key, value });
+    headers_.push_back({ ToString(key), ToString(value) });
   }
 
   return true;
 }
 
-bool Headers::Set(std::string&& key, std::string&& value) {
-  if (value.empty()) {
-    return false;
-  }
-
-  auto it = Find(key);
-  if (it != headers_.end()) {
-    it->second = std::move(value);
-  } else {
-    headers_.push_back({ std::move(key), std::move(value) });
-  }
-
-  return true;
-}
-
-bool Headers::Has(const std::string& key) const {
+bool Headers::Has(string_view key) const {
   return const_cast<Headers*>(this)->Find(key) != headers_.end();
 }
 
-const std::string& Headers::Get(const std::string& key, bool* existed) const {
+const std::string& Headers::Get(string_view key, bool* existed) const {
   auto it = const_cast<Headers*>(this)->Find(key);
 
   if (existed != nullptr) {
@@ -61,7 +46,7 @@ const std::string& Headers::Get(const std::string& key, bool* existed) const {
   return s_no_value;
 }
 
-std::vector<Header>::iterator Headers::Find(const std::string& key) {
+std::vector<Header>::iterator Headers::Find(string_view key) {
   auto it = headers_.begin();
   for (; it != headers_.end(); ++it) {
     if (boost::iequals(it->first, key)) {
@@ -73,25 +58,23 @@ std::vector<Header>::iterator Headers::Find(const std::string& key) {
 
 // -----------------------------------------------------------------------------
 
-static bool ParseValue(const std::string& str, const std::string& expected_key,
-                       std::string* value) {
-  std::string key;
+static bool ParseValue(const std::string& str, const char* expected_key,
+                       string_view* value) {
+  string_view key;
   if (!SplitKV(str, '=', true, &key, value)) {
     return false;
   }
-
   if (key != expected_key) {
     return false;
   }
-
   return !value->empty();
 }
 
-ContentType::ContentType(const std::string& str) {
+ContentType::ContentType(string_view str) {
   Init(str);
 }
 
-void ContentType::Parse(const std::string& str) {
+void ContentType::Parse(string_view str) {
   Reset();
   Init(str);
 }
@@ -114,15 +97,15 @@ bool ContentType::Valid() const {
   return true;
 }
 
-void ContentType::Init(const std::string& str) {
+void ContentType::Init(string_view str) {
   std::string other;
 
   std::size_t pos = str.find(';');
-  if (pos == std::string::npos) {
-    media_type_ = str;
+  if (pos == str.npos) {
+    media_type_ = ToString(str);
   } else {
-    media_type_ = str.substr(0, pos);
-    other = str.substr(pos + 1);
+    media_type_ = ToString(str.substr(0, pos));
+    other = ToString(str.substr(pos + 1));
   }
 
   boost::trim(media_type_);
@@ -130,26 +113,31 @@ void ContentType::Init(const std::string& str) {
 
   if (media_type_ == "multipart/form-data") {
     multipart_ = true;
-    if (!ParseValue(other, "boundary", &additional_)) {
-      LOG_ERRO("Invalid 'multipart/form-data' content-type (no boundary).");
+    string_view boundary;
+    if (ParseValue(other, "boundary", &boundary)) {
+      additional_ = ToString(boundary);
+      LOG_INFO("Content-type multipart boundary: %s", additional_.c_str());
     } else {
-      LOG_INFO("Content-type multipart boundary: %s.", additional_.c_str());
+      LOG_ERRO("Invalid 'multipart/form-data' content-type (no boundary)");
     }
   } else {
-    if (ParseValue(other, "charset", &additional_)) {
-      LOG_INFO("Content-type charset: %s.", additional_.c_str());
+    string_view charset;
+    if (ParseValue(other, "charset", &charset)) {
+      additional_ = ToString(charset);
+      LOG_INFO("Content-type charset: %s", additional_.c_str());
     }
   }
 }
 
 // -----------------------------------------------------------------------------
 
+// TODO: Use string_view
 static inline void Unquote(std::string& str) {
   boost::trim_if(str, boost::is_any_of("\""));
 }
 
-bool ContentDisposition::Init(const std::string& str) {
-  std::vector<boost::string_view> parts;
+bool ContentDisposition::Init(string_view str) {
+  std::vector<string_view> parts;
   Split(str, ';', false, &parts);
 
   if (parts.empty()) {
@@ -160,18 +148,18 @@ bool ContentDisposition::Init(const std::string& str) {
     return false;
   }
 
-  std::string key;
-  std::string value;
+  string_view key;
+  string_view value;
   for (std::size_t i = 1; i < parts.size(); ++i) {
-    if (!SplitKV(parts[i].to_string(), '=', true, &key, &value)) {
+    if (!SplitKV(parts[i], '=', true, &key, &value)) {
       return false;
     }
 
     if (key == "name") {
-      name_ = value;
+      name_ = ToString(value);
       Unquote(name_);
     } else if (key == "filename") {
-      file_name_ = value;
+      file_name_ = ToString(value);
       Unquote(file_name_);
     }
   }
@@ -181,24 +169,24 @@ bool ContentDisposition::Init(const std::string& str) {
 
 // -----------------------------------------------------------------------------
 
-FormPartPtr FormPart::New(const std::string& name, std::string&& data,
-                          const std::string& media_type) {
+FormPartPtr FormPart::New(string_view name, std::string&& data,
+                          string_view media_type) {
   auto form_part = std::make_shared<FormPart>();
 
-  form_part->name_ = name;
+  form_part->name_ = ToString(name);
   form_part->data_ = std::move(data);
-  form_part->media_type_ = media_type;
+  form_part->media_type_ = ToString(media_type);
 
   return form_part;
 }
 
-FormPartPtr FormPart::NewFile(const std::string& name, const fs::path& path,
-                              const std::string& media_type) {
+FormPartPtr FormPart::NewFile(string_view name, const fs::path& path,
+                              string_view media_type) {
   auto form_part = std::make_shared<FormPart>();
 
-  form_part->name_ = name;
+  form_part->name_ = ToString(name);
   form_part->path_ = path;
-  form_part->media_type_ = media_type;
+  form_part->media_type_ = ToString(media_type);
 
   // Determine file name from file path.
   // TODO: encoding
@@ -288,7 +276,7 @@ std::size_t FormPart::GetDataSize() {
   return size;
 }
 
-void FormPart::Dump(std::ostream& os, const std::string& prefix) const {
+void FormPart::Dump(std::ostream& os, string_view prefix) const {
   for (auto& h : headers_.data()) {
     os << prefix << h.first << ": " << h.second << std::endl;
   }
diff --git a/webcc/common.h b/webcc/common.h
index 5a85905..751035b 100644
--- a/webcc/common.h
+++ b/webcc/common.h
@@ -29,11 +29,9 @@ public:
     return headers_;
   }
 
-  bool Set(const std::string& key, const std::string& value);
+  bool Set(string_view key, string_view value);
 
-  bool Set(std::string&& key, std::string&& value);
-
-  bool Has(const std::string& key) const;
+  bool Has(string_view key) const;
 
   // Get header by index.
   const Header& Get(std::size_t index) const {
@@ -44,14 +42,14 @@ public:
   // Get header value by key.
   // If there's no such header with the given key, besides return empty, the
   // optional |existed| parameter will be set to false.
-  const std::string& Get(const std::string& key, bool* existed = nullptr) const;
+  const std::string& Get(string_view key, bool* existed = nullptr) const;
 
   void Clear() {
     headers_.clear();
   }
 
 private:
-  std::vector<Header>::iterator Find(const std::string& key);
+  std::vector<Header>::iterator Find(string_view key);
 
   std::vector<Header> headers_;
 };
@@ -64,9 +62,9 @@ private:
 //   Content-Type: multipart/form-data; boundary=something
 class ContentType {
 public:
-  explicit ContentType(const std::string& str = "");
+  explicit ContentType(string_view str = "");
 
-  void Parse(const std::string& str);
+  void Parse(string_view str);
 
   void Reset();
 
@@ -91,7 +89,7 @@ public:
   }
 
 private:
-  void Init(const std::string& str);
+  void Init(string_view str);
 
 private:
   std::string media_type_;
@@ -109,7 +107,7 @@ private:
 // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition
 class ContentDisposition {
 public:
-  explicit ContentDisposition(const std::string& str) {
+  explicit ContentDisposition(string_view str) {
     valid_ = Init(str);
   }
 
@@ -126,7 +124,7 @@ public:
   }
 
 private:
-  bool Init(const std::string& str);
+  bool Init(string_view str);
 
 private:
   std::string name_;
@@ -151,14 +149,14 @@ public:
   // The data will be moved, no file name is needed.
   // The media type is optional. If the data is a JSON string, you can specify
   // media type as "application/json".
-  static FormPartPtr New(const std::string& name, std::string&& data,
-                         const std::string& media_type = "");
+  static FormPartPtr New(string_view name, std::string&& data,
+                         string_view media_type = "");
 
   // Construct a file part.
   // The file name will be extracted from path.
   // The media type, if not provided, will be inferred from file extension.
-  static FormPartPtr NewFile(const std::string& name, const fs::path& path,
-                             const std::string& media_type = "");
+  static FormPartPtr NewFile(string_view name, const fs::path& path,
+                             string_view media_type = "");
 
   // API: SERVER
   const std::string& name() const {
@@ -214,7 +212,7 @@ public:
   std::size_t GetDataSize();
 
   // Dump to output stream for logging purpose.
-  void Dump(std::ostream& os, const std::string& prefix) const;
+  void Dump(std::ostream& os, string_view prefix) const;
 
 private:
   // Generate headers from properties.
diff --git a/webcc/config.h.example b/webcc/config.h.example
index 14ff92c..367a524 100644
--- a/webcc/config.h.example
+++ b/webcc/config.h.example
@@ -17,7 +17,10 @@
 // Set 1/0 to enable/disable GZIP compression.
 #define WEBCC_ENABLE_GZIP 0
 
-// Set 1 to use C++17 filesystem or 0 to use Boost filesystem.
+// Set 1 to use std::filesystem or 0 to use boost::filesystem.
 #define WEBCC_USE_STD_FILESYSTEM 1
 
+// Set 1 to use std::string_view or 0 to use boost::string_view.
+#define WEBCC_USE_STD_STRING_VIEW 1
+
 #endif  // WEBCC_CONFIG_H_
diff --git a/webcc/config.h.in b/webcc/config.h.in
index 7d3974c..2a9af52 100644
--- a/webcc/config.h.in
+++ b/webcc/config.h.in
@@ -19,7 +19,10 @@
 // Set 1/0 to enable/disable GZIP compression.
 #define WEBCC_ENABLE_GZIP @WEBCC_ENABLE_GZIP@
 
-// Set 1 to use C++17 filesystem or 0 to use Boost filesystem.
+// Set 1 to use std::filesystem or 0 to use boost::filesystem.
 #define WEBCC_USE_STD_FILESYSTEM @WEBCC_USE_STD_FILESYSTEM@
 
+// Set 1 to use std::string_view or 0 to use boost::string_view.
+#define WEBCC_USE_STD_STRING_VIEW @WEBCC_USE_STD_STRING_VIEW@
+
 #endif  // WEBCC_CONFIG_H_
diff --git a/webcc/connection.cc b/webcc/connection.cc
index 8cb1812..076492e 100644
--- a/webcc/connection.cc
+++ b/webcc/connection.cc
@@ -24,10 +24,11 @@ void Connection::Start() {
   boost::system::error_code ec;
   auto endpoint = socket_.remote_endpoint(ec);
   if (!ec) {
-    request_->set_ip(endpoint.address().to_string());
+    request_->set_address(endpoint.address().to_string());
   }
 
   request_parser_.Init(request_.get(), view_matcher_);
+
   AsyncRead();
 }
 
diff --git a/webcc/globals.h b/webcc/globals.h
index 7ef01aa..6747c72 100644
--- a/webcc/globals.h
+++ b/webcc/globals.h
@@ -12,10 +12,32 @@
 
 #include "webcc/config.h"
 
+#if WEBCC_USE_STD_STRING_VIEW
+#include <string_view>
+#else
+#include "boost/utility/string_view.hpp"
+#endif  // WEBCC_USE_STD_STRING_VIEW
+
 namespace webcc {
 
 // -----------------------------------------------------------------------------
 
+#if WEBCC_USE_STD_STRING_VIEW
+using string_view = std::string_view;
+#else
+using string_view = boost::string_view;
+#endif  // WEBCC_USE_STD_STRING_VIEW
+
+inline std::string ToString(string_view sv) {
+#if WEBCC_USE_STD_STRING_VIEW
+  return std::string{ sv.begin(), sv.end() };
+#else
+  return sv.to_string();
+#endif  // WEBCC_USE_STD_STRING_VIEW
+}
+
+// -----------------------------------------------------------------------------
+
 using Strings = std::vector<std::string>;
 
 // Regex sub-matches of the URL (usually resource ID's).
@@ -169,7 +191,7 @@ public:
   };
 
 public:
-  explicit Error(Code code = kOK, const std::string& message = "")
+  explicit Error(Code code = kOK, string_view message = "")
       : code_(code), message_(message) {
   }
 
@@ -186,9 +208,9 @@ public:
     return message_;
   }
 
-  void Set(Code code, const std::string& message) {
+  void Set(Code code, string_view message) {
     code_ = code;
-    message_ = message;
+    message_ = ToString(message);
   }
 
   bool timeout() const {
diff --git a/webcc/logger.cc b/webcc/logger.cc
index 715636a..42a2b48 100644
--- a/webcc/logger.cc
+++ b/webcc/logger.cc
@@ -135,7 +135,7 @@ static const bool g_terminal_has_color = []() {
 static std::string DoGetThreadID() {
 #if (defined(_WIN32) || defined(_WIN64))
   auto thread_id = std::this_thread::get_id();
-  std::stringstream ss;
+  std::ostringstream ss;
   ss << thread_id;
   return ss.str();
 #else
@@ -184,7 +184,7 @@ static std::string GetTimestamp() {
   auto now = system_clock::now();
   std::time_t t = system_clock::to_time_t(now);
 
-  std::stringstream ss;
+  std::ostringstream ss;
   ss << std::put_time(std::localtime(&t), "%Y-%m-%d %H:%M:%S");
 
   milliseconds milli_seconds =
diff --git a/webcc/message.cc b/webcc/message.cc
index 031782f..5305836 100644
--- a/webcc/message.cc
+++ b/webcc/message.cc
@@ -31,6 +31,7 @@ void Message::SetBody(BodyPtr body, bool set_length) {
 
 const std::string& Message::data() const {
   static const std::string kEmptyData;
+
   auto string_body = std::dynamic_pointer_cast<StringBody>(body_);
   if (!string_body) {
     return kEmptyData;
@@ -43,54 +44,42 @@ std::shared_ptr<FileBody> Message::file_body() const {
 }
 
 bool Message::IsConnectionKeepAlive() const {
-  using headers::kConnection;
-
   bool existed = false;
-  const std::string& connection = GetHeader(kConnection, &existed);
+  const auto& connection = GetHeader(headers::kConnection, &existed);
 
   if (!existed) {
     // Keep-Alive is by default for HTTP/1.1.
     return true;
   }
 
-  if (boost::iequals(connection, "Keep-Alive")) {
-    return true;
-  }
-
-  return false;
+  return boost::iequals(connection, "Keep-Alive");
 }
 
 ContentEncoding Message::GetContentEncoding() const {
-  using headers::kContentEncoding;
-
-  const std::string& encoding = GetHeader(kContentEncoding);
+  const auto& encoding = GetHeader(headers::kContentEncoding);
 
   if (encoding == "gzip") {
     return ContentEncoding::kGzip;
-  }
-
-  if (encoding == "deflate") {
+  } else if (encoding == "deflate") {
     return ContentEncoding::kDeflate;
+  } else {
+    return ContentEncoding::kUnknown;
   }
-
-  return ContentEncoding::kUnknown;
 }
 
 bool Message::AcceptEncodingGzip() const {
-  using headers::kAcceptEncoding;
-
-  return GetHeader(kAcceptEncoding).find("gzip") != std::string::npos;
+  return GetHeader(headers::kAcceptEncoding).find("gzip") != std::string::npos;
 }
 
-void Message::SetContentType(const std::string& media_type,
-                             const std::string& charset) {
-  using headers::kContentType;
-
+void Message::SetContentType(string_view media_type, string_view charset) {
   if (!media_type.empty()) {
     if (charset.empty()) {
-      SetHeader(kContentType, media_type);
+      SetHeader(headers::kContentType, media_type);
     } else {
-      SetHeader(kContentType, media_type + "; charset=" + charset);
+      std::string value = ToString(media_type);
+      value += "; charset=";
+      value += ToString(charset);
+      SetHeader(headers::kContentType, value);
     }
   }
 }
@@ -116,21 +105,21 @@ Payload Message::GetPayload() const {
 }
 
 void Message::Dump(std::ostream& os) const {
-  const std::string prefix = "    > ";
+  static const char* const s_prefix = "    > ";
 
-  os << prefix << start_line_ << std::endl;
+  os << s_prefix << start_line_ << std::endl;
 
   for (const Header& h : headers_.data()) {
-    os << prefix << h.first << ": " << h.second << std::endl;
+    os << s_prefix << h.first << ": " << h.second << std::endl;
   }
 
-  os << prefix << std::endl;
+  os << s_prefix << std::endl;
 
-  body_->Dump(os, prefix);
+  body_->Dump(os, s_prefix);
 }
 
 std::string Message::Dump() const {
-  std::stringstream ss;
+  std::ostringstream ss;
   Dump(ss);
   return ss.str();
 }
diff --git a/webcc/message.h b/webcc/message.h
index 6728343..def0ddc 100644
--- a/webcc/message.h
+++ b/webcc/message.h
@@ -21,51 +21,30 @@ public:
 
   virtual ~Message() = default;
 
-  // ---------------------------------------------------------------------------
-
-  void SetBody(BodyPtr body, bool set_length);
-
-  BodyPtr body() const {
-    return body_;
+  const std::string& start_line() const {
+    return start_line_;
   }
 
-  // Get the data from the (string) body.
-  // Return empty string if the body is not a StringBody.
-  const std::string& data() const;
-
-  // Get the body as a FileBody.
-  // Return null if the body is not a FileBody.
-  std::shared_ptr<FileBody> file_body() const;
-
-  // ---------------------------------------------------------------------------
+  void set_start_line(string_view start_line) {
+    start_line_ = ToString(start_line);
+  }
 
   void SetHeader(Header&& header) {
     headers_.Set(std::move(header.first), std::move(header.second));
   }
 
-  void SetHeader(const std::string& key, const std::string& value) {
+  void SetHeader(string_view key, string_view value) {
     headers_.Set(key, value);
   }
 
-  const std::string& GetHeader(const std::string& key,
-                               bool* existed = nullptr) const {
+  const std::string& GetHeader(string_view key, bool* existed = nullptr) const {
     return headers_.Get(key, existed);
   }
 
-  bool HasHeader(const std::string& key) const {
+  bool HasHeader(string_view key) const {
     return headers_.Has(key);
   }
 
-  // ---------------------------------------------------------------------------
-
-  const std::string& start_line() const {
-    return start_line_;
-  }
-
-  void set_start_line(const std::string& start_line) {
-    start_line_ = start_line;
-  }
-
   std::size_t content_length() const {
     return content_length_;
   }
@@ -74,7 +53,19 @@ public:
     content_length_ = content_length;
   }
 
-  // ---------------------------------------------------------------------------
+  void SetBody(BodyPtr body, bool set_length);
+
+  BodyPtr body() const {
+    return body_;
+  }
+
+  // Get the data from the (string) body.
+  // Return empty string if the body is not a StringBody.
+  const std::string& data() const;
+
+  // Get the body as a FileBody.
+  // Return null if the body is not a FileBody.
+  std::shared_ptr<FileBody> file_body() const;
 
   // Check `Connection` header to see if it's "Keep-Alive".
   bool IsConnectionKeepAlive() const;
@@ -88,16 +79,13 @@ public:
 
   // Set `Content-Type` header. E.g.,
   //   SetContentType("application/json; charset=utf-8")
-  void SetContentType(const std::string& content_type) {
+  void SetContentType(string_view content_type) {
     SetHeader(headers::kContentType, content_type);
   }
 
   // Set `Content-Type` header. E.g.,
   //   SetContentType("application/json", "utf-8")
-  void SetContentType(const std::string& media_type,
-                      const std::string& charset);
-
-  // ---------------------------------------------------------------------------
+  void SetContentType(string_view media_type, string_view charset);
 
   // Make the message complete in order to be sent.
   virtual void Prepare() = 0;
@@ -106,8 +94,6 @@ public:
   // This doesn't include the payload(s) of the body!
   Payload GetPayload() const;
 
-  // ---------------------------------------------------------------------------
-
   // Dump to output stream for logging purpose.
   void Dump(std::ostream& os) const;
 
diff --git a/webcc/request.h b/webcc/request.h
index dedaacf..4f8aa07 100644
--- a/webcc/request.h
+++ b/webcc/request.h
@@ -23,8 +23,8 @@ public:
     return method_;
   }
 
-  void set_method(const std::string& method) {
-    method_ = method;
+  void set_method(string_view method) {
+    method_ = ToString(method);
   }
 
   const Url& url() const {
@@ -44,23 +44,23 @@ public:
   }
 
   UrlQuery query() const {
-    return UrlQuery(url_.query());
+    return UrlQuery{ url_.query() };
   }
 
   const UrlArgs& args() const {
     return args_;
   }
 
-  void set_args(const UrlArgs& args) {
-    args_ = args;
+  void set_args(UrlArgs&& args) {
+    args_ = std::move(args);
   }
 
-  const std::string& ip() const {
-    return ip_;
+  const std::string& address() const {
+    return address_;
   }
 
-  void set_ip(const std::string& ip) {
-    ip_ = ip;
+  void set_address(std::string&& address) {
+    address_ = std::move(address);
   }
 
   // Check if the body is a multi-part form data.
@@ -83,7 +83,7 @@ private:
   UrlArgs args_;
 
   // Client IP address.
-  std::string ip_;
+  std::string address_;
 };
 
 using RequestPtr = std::shared_ptr<Request>;
diff --git a/webcc/request_builder.cc b/webcc/request_builder.cc
index be484e5..d87402e 100644
--- a/webcc/request_builder.cc
+++ b/webcc/request_builder.cc
@@ -19,7 +19,7 @@ RequestPtr RequestBuilder::operator()() {
   request->set_url(std::move(url_));
 
   for (std::size_t i = 1; i < headers_.size(); i += 2) {
-    request->SetHeader(std::move(headers_[i - 1]), std::move(headers_[i]));
+    request->SetHeader(headers_[i - 1], headers_[i]);
   }
 
   // If no Keep-Alive, explicitly set `Connection` to "Close".
@@ -34,7 +34,7 @@ RequestPtr RequestBuilder::operator()() {
     if (gzip_ && body_->Compress()) {
       request->SetHeader(headers::kContentEncoding, "gzip");
     }
-#endif
+#endif  // WEBCC_ENABLE_GZIP
   } else if (!form_parts_.empty()) {
     // Another choice to generate the boundary is like what Apache does.
     // See: https://stackoverflow.com/a/5686863
@@ -77,41 +77,41 @@ RequestBuilder& RequestBuilder::File(const fs::path& path,
   return *this;
 }
 
-RequestBuilder& RequestBuilder::FormFile(const std::string& name,
+RequestBuilder& RequestBuilder::FormFile(string_view name,
                                          const fs::path& path,
-                                         const std::string& media_type) {
+                                         string_view media_type) {
   assert(!name.empty());
   return Form(FormPart::NewFile(name, path, media_type));
 }
 
-RequestBuilder& RequestBuilder::FormData(const std::string& name,
+RequestBuilder& RequestBuilder::FormData(string_view name,
                                          std::string&& data,
-                                         const std::string& media_type) {
+                                         string_view media_type) {
   assert(!name.empty());
   return Form(FormPart::New(name, std::move(data), media_type));
 }
 
-RequestBuilder& RequestBuilder::Header(const std::string& key,
-                                       const std::string& value) {
-  headers_.push_back(key);
-  headers_.push_back(value);
+RequestBuilder& RequestBuilder::Header(string_view key, string_view value) {
+  headers_.push_back(ToString(key));
+  headers_.push_back(ToString(value));
   return *this;
 }
 
-RequestBuilder& RequestBuilder::Auth(const std::string& type,
-                                     const std::string& credentials) {
+RequestBuilder& RequestBuilder::Auth(string_view type,
+                                     string_view credentials) {
   headers_.push_back(headers::kAuthorization);
-  headers_.push_back(type + " " + credentials);
+  headers_.push_back(ToString(type) + " " + ToString(credentials));
   return *this;
 }
 
-RequestBuilder& RequestBuilder::AuthBasic(const std::string& login,
-                                          const std::string& password) {
-  auto credentials = Base64Encode(login + ":" + password);
+RequestBuilder& RequestBuilder::AuthBasic(string_view login,
+                                          string_view password) {
+  auto credentials =
+      Base64Encode(ToString(login) + ":" + ToString(password));
   return Auth("Basic", credentials);
 }
 
-RequestBuilder& RequestBuilder::AuthToken(const std::string& token) {
+RequestBuilder& RequestBuilder::AuthToken(string_view token) {
   return Auth("Token", token);
 }
 
diff --git a/webcc/request_builder.h b/webcc/request_builder.h
index 11ceb5c..aacb92b 100644
--- a/webcc/request_builder.h
+++ b/webcc/request_builder.h
@@ -39,44 +39,44 @@ public:
   RequestBuilder(const RequestBuilder&) = delete;
   RequestBuilder& operator=(const RequestBuilder&) = delete;
 
-  // Build
+  // Build and return the request object.
   RequestPtr operator()();
 
-  RequestBuilder& Method(const std::string& method) {
-    method_ = method;
+  RequestBuilder& Method(string_view method) {
+    method_ = ToString(method);
     return *this;
   }
 
-  RequestBuilder& Get(const std::string& url, bool encode = false) {
+  RequestBuilder& Get(string_view url, bool encode = false) {
     return Method(methods::kGet).Url(url, encode);
   }
 
-  RequestBuilder& Head(const std::string& url, bool encode = false) {
+  RequestBuilder& Head(string_view url, bool encode = false) {
     return Method(methods::kHead).Url(url, encode);
   }
 
-  RequestBuilder& Post(const std::string& url, bool encode = false) {
+  RequestBuilder& Post(string_view url, bool encode = false) {
     return Method(methods::kPost).Url(url, encode);
   }
 
-  RequestBuilder& Put(const std::string& url, bool encode = false) {
+  RequestBuilder& Put(string_view url, bool encode = false) {
     return Method(methods::kPut).Url(url, encode);
   }
 
-  RequestBuilder& Delete(const std::string& url, bool encode = false) {
+  RequestBuilder& Delete(string_view url, bool encode = false) {
     return Method(methods::kDelete).Url(url, encode);
   }
 
-  RequestBuilder& Patch(const std::string& url, bool encode = false) {
+  RequestBuilder& Patch(string_view url, bool encode = false) {
     return Method(methods::kPatch).Url(url, encode);
   }
 
-  RequestBuilder& Url(const std::string& url, bool encode = false) {
+  RequestBuilder& Url(string_view url, bool encode = false) {
     url_ = webcc::Url{ url, encode };
     return *this;
   }
 
-  RequestBuilder& Port(const std::string& port) {
+  RequestBuilder& Port(string_view port) {
     url_.set_port(port);
     return *this;
   }
@@ -87,25 +87,25 @@ public:
   }
 
   // Append a piece to the path.
-  RequestBuilder& Path(const std::string& path, bool encode = false) {
+  RequestBuilder& Path(string_view path, bool encode = false) {
     url_.AppendPath(path, encode);
     return *this;
   }
 
   // Append a parameter to the query.
-  RequestBuilder& Query(const std::string& key, const std::string& value,
+  RequestBuilder& Query(string_view key, string_view value,
                         bool encode = false) {
     url_.AppendQuery(key, value, encode);
     return *this;
   }
 
-  RequestBuilder& MediaType(const std::string& media_type) {
-    media_type_ = media_type;
+  RequestBuilder& MediaType(string_view media_type) {
+    media_type_ = ToString(media_type);
     return *this;
   }
 
-  RequestBuilder& Charset(const std::string& charset) {
-    charset_ = charset;
+  RequestBuilder& Charset(string_view charset) {
+    charset_ = ToString(charset);
     return *this;
   }
 
@@ -123,7 +123,7 @@ public:
 
   // Set (comma separated) content types to accept.
   // E.g., "application/json", "text/html, application/xhtml+xml".
-  RequestBuilder& Accept(const std::string& content_types) {
+  RequestBuilder& Accept(string_view content_types) {
     return Header(headers::kAccept, content_types);
   }
 
@@ -156,26 +156,25 @@ public:
   }
 
   // Add a form part of file.
-  RequestBuilder& FormFile(const std::string& name, const fs::path& path,
-                           const std::string& media_type = "");
+  RequestBuilder& FormFile(string_view name, const fs::path& path,
+                           string_view media_type = "");
 
   // Add a form part of string data.
-  RequestBuilder& FormData(const std::string& name, std::string&& data,
-                           const std::string& media_type = "");
+  RequestBuilder& FormData(string_view name, std::string&& data,
+                           string_view media_type = "");
 
-  RequestBuilder& Header(const std::string& key, const std::string& value);
+  RequestBuilder& Header(string_view key, string_view value);
 
   RequestBuilder& KeepAlive(bool keep_alive = true) {
     keep_alive_ = keep_alive;
     return *this;
   }
 
-  RequestBuilder& Auth(const std::string& type, const std::string& credentials);
+  RequestBuilder& Auth(string_view type, string_view credentials);
 
-  RequestBuilder& AuthBasic(const std::string& login,
-                            const std::string& password);
+  RequestBuilder& AuthBasic(string_view login, string_view password);
 
-  RequestBuilder& AuthToken(const std::string& token);
+  RequestBuilder& AuthToken(string_view token);
 
   // Add the `Date` header to the request.
   RequestBuilder& Date();
diff --git a/webcc/request_parser.cc b/webcc/request_parser.cc
index e0512d8..daeec34 100644
--- a/webcc/request_parser.cc
+++ b/webcc/request_parser.cc
@@ -36,15 +36,15 @@ bool RequestParser::OnHeadersEnd() {
 }
 
 bool RequestParser::ParseStartLine(const std::string& line) {
-  std::vector<boost::string_view> parts;
+  std::vector<string_view> parts;
   Split(line, ' ', true, &parts);
 
   if (parts.size() != 3) {
     return false;
   }
 
-  request_->set_method(parts[0].to_string());
-  request_->set_url(Url{ parts[1].to_string() });
+  request_->set_method(parts[0]);
+  request_->set_url(Url{ parts[1] });
 
   // HTTP version is ignored.
 
@@ -198,7 +198,7 @@ bool RequestParser::ParsePartHeaders(bool* need_more_data) {
 
     // Parse Content-Disposition.
     if (boost::iequals(header.first, headers::kContentDisposition)) {
-      ContentDisposition content_disposition(header.second);
+      ContentDisposition content_disposition{ header.second };
       if (!content_disposition.valid()) {
         LOG_ERRO("Invalid content-disposition header: %s",
                  header.second.c_str());
diff --git a/webcc/request_parser.h b/webcc/request_parser.h
index a753fb2..31493fe 100644
--- a/webcc/request_parser.h
+++ b/webcc/request_parser.h
@@ -42,21 +42,22 @@ private:
                   std::size_t count, bool* end = nullptr) const;
 
 private:
-  Request* request_;
+  // The result request message.
+  Request* request_ = nullptr;
 
   // A function for matching view once the headers of a request has been
   // received. The parsing will stop and fail if no view can be matched.
   ViewMatcher view_matcher_;
 
   // Form data parsing steps.
-  enum Step {
+  enum class Step {
     kStart,
     kBoundaryParsed,
     kHeadersParsed,
     kEnded,
   };
 
-  Step step_ = kStart;
+  Step step_ = Step::kStart;
 
   // The current form part being parsed.
   FormPartPtr part_;
diff --git a/webcc/response_builder.cc b/webcc/response_builder.cc
index 3b488be..3cc1845 100644
--- a/webcc/response_builder.cc
+++ b/webcc/response_builder.cc
@@ -55,6 +55,12 @@ ResponseBuilder& ResponseBuilder::File(const fs::path& path,
   return *this;
 }
 
+ResponseBuilder& ResponseBuilder::Header(string_view key, string_view value) {
+  headers_.push_back(ToString(key));
+  headers_.push_back(ToString(value));
+  return *this;
+}
+
 ResponseBuilder& ResponseBuilder::Date() {
   headers_.push_back(headers::kDate);
   headers_.push_back(utility::HttpDate());
diff --git a/webcc/response_builder.h b/webcc/response_builder.h
index 5bacfc5..c5266a8 100644
--- a/webcc/response_builder.h
+++ b/webcc/response_builder.h
@@ -61,13 +61,13 @@ public:
     return *this;
   }
 
-  ResponseBuilder& MediaType(const std::string& media_type) {
-    media_type_ = media_type;
+  ResponseBuilder& MediaType(string_view media_type) {
+    media_type_ = ToString(media_type);
     return *this;
   }
 
-  ResponseBuilder& Charset(const std::string& charset) {
-    charset_ = charset;
+  ResponseBuilder& Charset(string_view charset) {
+    charset_ = ToString(charset);
     return *this;
   }
 
@@ -98,11 +98,7 @@ public:
   ResponseBuilder& File(const fs::path& path, bool infer_media_type = true,
                         std::size_t chunk_size = 1024);
 
-  ResponseBuilder& Header(const std::string& key, const std::string& value) {
-    headers_.push_back(key);
-    headers_.push_back(value);
-    return *this;
-  }
+  ResponseBuilder& Header(string_view key, string_view value);
 
   // Add the `Date` header to the response.
   ResponseBuilder& Date();
diff --git a/webcc/router.cc b/webcc/router.cc
index d16caea..a87d68f 100644
--- a/webcc/router.cc
+++ b/webcc/router.cc
@@ -8,13 +8,12 @@
 
 namespace webcc {
 
-bool Router::Route(const std::string& url, ViewPtr view,
-                   const Strings& methods) {
+bool Router::Route(string_view url, ViewPtr view, const Strings& methods) {
   assert(view);
 
   // TODO: More error check
 
-  routes_.push_back({ url, {}, view, methods });
+  routes_.push_back({ ToString(url), {}, view, methods });
 
   return true;
 }
@@ -26,7 +25,6 @@ bool Router::Route(const UrlRegex& regex_url, ViewPtr view,
   // TODO: More error check
 
   try {
-
     routes_.push_back({ "", regex_url(), view, methods });
 
   } catch (const std::regex_error& e) {
diff --git a/webcc/router.h b/webcc/router.h
index 0efb8ae..b4ee47e 100644
--- a/webcc/router.h
+++ b/webcc/router.h
@@ -15,7 +15,7 @@ public:
 
   // Route a URL to a view.
   // The URL should start with "/". E.g., "/instances".
-  bool Route(const std::string& url, ViewPtr view,
+  bool Route(string_view url, ViewPtr view,
              const Strings& methods = { "GET" });
 
   // Route a URL (as regular expression) to a view.
diff --git a/webcc/server.cc b/webcc/server.cc
index 927ade4..3cbc13e 100644
--- a/webcc/server.cc
+++ b/webcc/server.cc
@@ -300,7 +300,7 @@ void Server::Handle(ConnectionPtr connection) {
   }
 
   // Save the (regex matched) URL args to request object.
-  request->set_args(args);
+  request->set_args(std::move(args));
 
   // Ask the matched view to process the request.
   ResponsePtr response = view->Handle(request);
diff --git a/webcc/string.cc b/webcc/string.cc
index 265fea9..ed630b8 100644
--- a/webcc/string.cc
+++ b/webcc/string.cc
@@ -36,19 +36,19 @@ bool ToSizeT(const std::string& str, int base, std::size_t* size) {
   return true;
 }
 
-void Split(boost::string_view input, char delim, bool compress_token,
-           std::vector<boost::string_view>* output) {
+void Split(string_view input, char delim, bool compress_token,
+           std::vector<string_view>* output) {
   std::size_t i = 0;
   std::size_t p = 0;
 
   i = input.find(delim);
 
-  while (i != boost::string_view::npos) {
+  while (i != string_view::npos) {
     output->emplace_back(input.substr(p, i - p));
     p = i + 1;
 
     if (compress_token) {
-      while (input[p] == delim) {
+      while (p < input.size() && input[p] == delim) {
         ++p;
       }
     }
@@ -59,10 +59,19 @@ void Split(boost::string_view input, char delim, bool compress_token,
   output->emplace_back(input.substr(p, i - p));
 }
 
-bool SplitKV(const std::string& input, char delim, bool trim_spaces,
-             std::string* key, std::string* value) {
+void Trim(string_view& sv, const char* spaces) {
+  sv.remove_prefix(std::min(sv.find_first_not_of(spaces), sv.size()));
+
+  std::size_t pos = sv.find_last_not_of(spaces);
+  if (pos != sv.npos) {
+    sv.remove_suffix(sv.size() - pos - 1);
+  }
+}
+
+bool SplitKV(string_view input, char delim, bool trim_spaces, string_view* key,
+             string_view* value) {
   std::size_t pos = input.find(delim);
-  if (pos == std::string::npos) {
+  if (pos == input.npos) {
     return false;
   }
 
@@ -70,11 +79,23 @@ bool SplitKV(const std::string& input, char delim, bool trim_spaces,
   *value = input.substr(pos + 1);
 
   if (trim_spaces) {
-    boost::trim(*key);
-    boost::trim(*value);
+    Trim(*key);
+    Trim(*value);
   }
 
   return true;
 }
 
+bool SplitKV(string_view input, char delim, bool trim_spaces, std::string* key,
+             std::string* value) {
+  string_view key_view;
+  string_view value_view;
+  if (SplitKV(input, delim, trim_spaces, &key_view, &value_view)) {
+    *key = ToString(key_view);
+    *value = ToString(value_view);
+    return true;
+  }
+  return false;
+}
+
 }  // namespace webcc
diff --git a/webcc/string.h b/webcc/string.h
index 880c628..67e9635 100644
--- a/webcc/string.h
+++ b/webcc/string.h
@@ -4,7 +4,7 @@
 #include <string>
 #include <vector>
 
-#include "boost/utility/string_view.hpp"
+#include "webcc/globals.h"  // for string_view
 
 namespace webcc {
 
@@ -15,15 +15,21 @@ std::string RandomString(std::size_t length);
 // Just a wrapper of std::stoul.
 bool ToSizeT(const std::string& str, int base, std::size_t* size);
 
+void Trim(string_view& sv, const char* spaces = " ");
+
 // Split string without copy.
 // |compress_token| is the same as boost::token_compress_on for boost::split.
-void Split(boost::string_view input, char delim, bool compress_token,
-           std::vector<boost::string_view>* output);
+void Split(string_view input, char delim, bool compress_token,
+           std::vector<string_view>* output);
+
+// Split a key-value string.
+// E.g., split "Connection: Keep-Alive".
+bool SplitKV(string_view input, char delim, bool trim_spaces, string_view* key,
+             string_view* value);
 
 // Split a key-value string.
 // E.g., split "Connection: Keep-Alive".
-// TODO: Use string_view (blocked by trim)
-bool SplitKV(const std::string& input, char delim, bool trim_spaces,
+bool SplitKV(string_view input, char delim, bool trim_spaces,
              std::string* key, std::string* value);
 
 }  // namespace webcc
diff --git a/webcc/url.cc b/webcc/url.cc
index 86b5c8c..e7a006f 100644
--- a/webcc/url.cc
+++ b/webcc/url.cc
@@ -29,7 +29,7 @@ bool HexToDecimal(char hex, int* decimal) {
   return true;
 }
 
-bool Decode(const std::string& encoded, std::string* raw) {
+bool Decode(string_view encoded, std::string* raw) {
   for (auto iter = encoded.begin(); iter != encoded.end(); ++iter) {
     if (*iter == '%') {
       if (++iter == encoded.end()) {
@@ -67,16 +67,16 @@ bool Decode(const std::string& encoded, std::string* raw) {
 
 // Unsafe decode.
 // Return the original string on failure.
-std::string DecodeUnsafe(const std::string& encoded) {
+std::string DecodeUnsafe(string_view encoded) {
   std::string raw;
   if (Decode(encoded, &raw)) {
     return raw;
   }
-  return encoded;
+  return ToString(encoded);
 }
 
 // Encode all characters which should be encoded.
-std::string EncodeImpl(const std::string& raw,  // UTF8
+std::string EncodeImpl(string_view raw,  // UTF8
                        std::function<bool(int)> should_encode) {
   const char kHex[] = "0123456789ABCDEF";
 
@@ -102,14 +102,16 @@ std::string EncodeImpl(const std::string& raw,  // UTF8
 // Our own implementation of alpha numeric instead of std::isalnum to avoid
 // taking locale into account.
 inline bool IsAlNum(int c) {
-  return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+  return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') ||
+         (c >= 'a' && c <= 'z');
 }
 
 // Characters that are allowed in a URI but do not have a reserved purpose are
 // are called unreserved. These include uppercase and lowercase letters, decimal
 // digits, hyphen, period, underscore, and tilde.
 inline bool IsUnreserved(int c) {
-  return IsAlNum((unsigned char)c) || c == '-' || c == '.' || c == '_' || c == '~';
+  return IsAlNum((unsigned char)c) || c == '-' || c == '.' || c == '_' ||
+         c == '~';
 }
 
 // General delimiters serve as the delimiters between different uri components.
@@ -171,23 +173,23 @@ inline bool IsQueryChar(int c) {
 
 // -----------------------------------------------------------------------------
 
-std::string Url::EncodeHost(const std::string& utf8_str) {
+std::string Url::EncodeHost(string_view utf8_str) {
   return EncodeImpl(utf8_str, [](int c) -> bool { return c > 127; });
 }
 
-std::string Url::EncodePath(const std::string& utf8_str) {
+std::string Url::EncodePath(string_view utf8_str) {
   return EncodeImpl(utf8_str, [](int c) -> bool {
     return !IsPathChar(c) || c == '%' || c == '+';
   });
 }
 
-std::string Url::EncodeQuery(const std::string& utf8_str) {
+std::string Url::EncodeQuery(string_view utf8_str) {
   return EncodeImpl(utf8_str, [](int c) -> bool {
     return !IsQueryChar(c) || c == '%' || c == '+';
   });
 }
 
-std::string Url::EncodeFull(const std::string& utf8_str) {
+std::string Url::EncodeFull(string_view utf8_str) {
   return EncodeImpl(utf8_str, [](int c) -> bool {
     return !IsUnreserved(c) && !IsReserved(c);
   });
@@ -195,7 +197,7 @@ std::string Url::EncodeFull(const std::string& utf8_str) {
 
 // -----------------------------------------------------------------------------
 
-Url::Url(const std::string& str, bool encode) {
+Url::Url(string_view str, bool encode) {
   if (encode) {
     Parse(Url::EncodeFull(str));
   } else {
@@ -203,7 +205,7 @@ Url::Url(const std::string& str, bool encode) {
   }
 }
 
-void Url::AppendPath(const std::string& piece, bool encode) {
+void Url::AppendPath(string_view piece, bool encode) {
   if (piece.empty() || piece == "/") {
     return;
   }
@@ -222,24 +224,23 @@ void Url::AppendPath(const std::string& piece, bool encode) {
   if (encode) {
     path_.append(Url::EncodePath(piece));
   } else {
-    path_.append(piece);
+    path_.append(ToString(piece));
   }
 }
 
-void Url::AppendQuery(const std::string& key, const std::string& value,
-                      bool encode) {
+void Url::AppendQuery(string_view key, string_view value, bool encode) {
   if (!query_.empty()) {
     query_ += "&";
   }
   if (encode) {
     query_ += Url::EncodeQuery(key) + "=" + Url::EncodeQuery(value);
   } else {
-    query_ += key + "=" + value;
+    query_ += ToString(key) + "=" + ToString(value);
   }
 }
 
-void Url::Parse(const std::string& str) {
-  std::string tmp = str;
+void Url::Parse(string_view str) {
+  std::string tmp = ToString(str);
   boost::trim_left(tmp);
 
   std::size_t p = std::string::npos;
@@ -314,8 +315,8 @@ UrlQuery::UrlQuery(const std::string& encoded_str) {
         i = j + 1;
       }
 
-      std::string key;
-      std::string value;
+      string_view key;
+      string_view value;
       if (SplitKV(kv, '=', false, &key, &value)) {
         parameters_.push_back({ DecodeUnsafe(key), DecodeUnsafe(value) });
       }
diff --git a/webcc/url.h b/webcc/url.h
index bcd7efb..0f81b07 100644
--- a/webcc/url.h
+++ b/webcc/url.h
@@ -17,15 +17,15 @@ namespace webcc {
 class Url {
 public:
   // Encode URL different components.
-  static std::string EncodeHost(const std::string& utf8_str);
-  static std::string EncodePath(const std::string& utf8_str);
-  static std::string EncodeQuery(const std::string& utf8_str);
-  static std::string EncodeFull(const std::string& utf8_str);
+  static std::string EncodeHost(string_view utf8_str);
+  static std::string EncodePath(string_view utf8_str);
+  static std::string EncodeQuery(string_view utf8_str);
+  static std::string EncodeFull(string_view utf8_str);
 
 public:
   Url() = default;
 
-  explicit Url(const std::string& str, bool encode = false);
+  explicit Url(string_view str, bool encode = false);
 
   const std::string& scheme() const {
     return scheme_;
@@ -47,19 +47,18 @@ public:
     return query_;
   }
 
-  void set_port(const std::string& port) {
-    port_ = port;
+  void set_port(string_view port) {
+    port_ = ToString(port);
   }
 
   // Append a piece of path.
-  void AppendPath(const std::string& piece, bool encode = false);
+  void AppendPath(string_view piece, bool encode = false);
 
   // Append a query parameter.
-  void AppendQuery(const std::string& key, const std::string& value,
-                   bool encode = false);
+  void AppendQuery(string_view key, string_view value, bool encode = false);
 
 private:
-  void Parse(const std::string& str);
+  void Parse(string_view str);
 
   void Clear();
 
@@ -125,12 +124,11 @@ private:
 // Used by Server::Route().
 class UrlRegex {
 public:
-  explicit UrlRegex(const std::string& url) : url_(url) {
+  explicit UrlRegex(string_view url) : url_(url) {
   }
 
   std::regex operator()() const {
     std::regex::flag_type flags = std::regex::ECMAScript | std::regex::icase;
-
     return std::regex{ url_, flags };
   }
 
diff --git a/webcc/utility.cc b/webcc/utility.cc
index 0134f8c..8c6ab4b 100644
--- a/webcc/utility.cc
+++ b/webcc/utility.cc
@@ -10,6 +10,8 @@
 #include "webcc/string.h"
 #include "webcc/version.h"
 
+using boost::asio::ip::tcp;
+
 namespace webcc {
 namespace utility {
 
@@ -22,7 +24,7 @@ std::string HttpDate() {
   std::time_t t = std::time(nullptr);
   std::tm gmt = *std::gmtime(&t);
 
-  std::stringstream date;
+  std::ostringstream date;
   date.imbue(std::locale::classic());  // Use classic C locale
   date << std::put_time(&gmt, "%a, %d %b %Y %H:%M:%S GMT");
   return date.str();
@@ -54,9 +56,8 @@ bool ReadFile(const fs::path& path, std::string* output) {
   return true;
 }
 
-void DumpByLine(const std::string& data, std::ostream& os,
-                const std::string& prefix) {
-  std::vector<boost::string_view> lines;
+void DumpByLine(const std::string& data, std::ostream& os, string_view prefix) {
+  std::vector<string_view> lines;
   Split(data, '\n', false, &lines);
 
   std::size_t size = 0;
@@ -75,18 +76,17 @@ void DumpByLine(const std::string& data, std::ostream& os,
   }
 }
 
-void PrintEndpoint(std::ostream& ostream,
-                   const boost::asio::ip::tcp::endpoint& endpoint) {
+void PrintEndpoint(std::ostream& ostream, const tcp::endpoint& endpoint) {
   ostream << endpoint;
-  if (endpoint.protocol() == boost::asio::ip::tcp::v4()) {
+  if (endpoint.protocol() == tcp::v4()) {
     ostream << ", v4";
-  } else if (endpoint.protocol() == boost::asio::ip::tcp::v6()) {
+  } else if (endpoint.protocol() == tcp::v6()) {
     ostream << ", v6";
   }
 }
 
-std::string EndpointToString(const boost::asio::ip::tcp::endpoint& endpoint) {
-  std::stringstream ss;
+std::string EndpointToString(const tcp::endpoint& endpoint) {
+  std::ostringstream ss;
   PrintEndpoint(ss, endpoint);
   return ss.str();
 }
diff --git a/webcc/utility.h b/webcc/utility.h
index 528c454..4270ade 100644
--- a/webcc/utility.h
+++ b/webcc/utility.h
@@ -29,8 +29,7 @@ bool ReadFile(const fs::path& path, std::string* output);
 
 // Dump the string data line by line to achieve more readability.
 // Also limit the maximum size of the data to be dumped.
-void DumpByLine(const std::string& data, std::ostream& os,
-                const std::string& prefix);
+void DumpByLine(const std::string& data, std::ostream& os, string_view prefix);
 
 // Print TCP endpoint.
 // Usage: PrintEndpoint(std::cout, endpoint)