上篇寫了一個簡單的Java web伺服器實現,只能處理一些靜態資源的請求,本篇文章實現的Servlet容器基於前面的伺服器做了個小改造,增加了Servlet請求的處理。 程式執行步驟 代碼實現: 添加依賴: 伺服器代碼: 常量類: Request: package ex02.pyrmont; imp ...
上篇寫了一個簡單的Java web伺服器實現,只能處理一些靜態資源的請求,本篇文章實現的Servlet容器基於前面的伺服器做了個小改造,增加了Servlet請求的處理。
程式執行步驟
- 創建一個ServerSocket對象;
- 調用ServerSocket對象的accept方法,等待連接,連接成功會返回一個Socket對象,否則一直阻塞等待;
- 從Socket對象中獲取InputStream和OutputStream位元組流,這兩個流分別對應request請求和response響應;
- 處理請求:讀取InputStream位元組流信息,轉成字元串形式,並解析,這裡的解析比較簡單,僅僅獲取uri(統一資源標識符)信息;
- 處理響應(分兩種類型,靜態資源請求響應或servlet請求響應):如果是靜態資源請求,則根據解析出來的uri信息,從WEB_ROOT目錄中尋找請求的資源資源文件, 讀取資源文件,並將其寫入到OutputStream位元組流中;如果是Servlet請求,則首先生成一個URLClassLoader類載入器,載入請求的servlet類,創建servlet對象,執行service方法(往OutputStream寫入響應的數據);
- 關閉Socket對象;
- 轉到步驟2,繼續等待連接請求;
代碼實現:
添加依賴:
<!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api --> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.3</version> </dependency>
伺服器代碼:
package ex02.pyrmont.first; import java.net.Socket; import java.net.ServerSocket; import java.net.InetAddress; import java.io.InputStream; import java.io.OutputStream; import java.io.IOException; import ex02.pyrmont.Request; import ex02.pyrmont.Response; import ex02.pyrmont.StaticResourceProcessor; public class HttpServer1 { // 關閉服務命令 private static final String SHUTDOWN_COMMAND = "/SHUTDOWN"; public static void main(String[] args) { HttpServer1 server = new HttpServer1(); //等待連接請求 server.await(); } public void await() { ServerSocket serverSocket = null; int port = 8080; try { //伺服器套接字對象 serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1")); } catch (IOException e) { e.printStackTrace(); System.exit(1); } // 迴圈等待請求 while (true) { Socket socket = null; InputStream input = null; OutputStream output = null; try { //等待連接,連接成功後,返回一個Socket對象 socket = serverSocket.accept(); input = socket.getInputStream(); output = socket.getOutputStream(); // 創建Request對象並解析 Request request = new Request(input); request.parse(); // 檢查是否是關閉服務命令 if (request.getUri().equals(SHUTDOWN_COMMAND)) { break; } // 創建 Response 對象 Response response = new Response(output); response.setRequest(request); if (request.getUri().startsWith("/servlet/")) { //請求uri以/servlet/開頭,表示servlet請求 ServletProcessor1 processor = new ServletProcessor1(); processor.process(request, response); } else { //靜態資源請求 StaticResourceProcessor processor = new StaticResourceProcessor(); processor.process(request, response); } // 關閉 socket socket.close(); } catch (Exception e) { e.printStackTrace(); System.exit(1); } } } }
常量類:
package ex02.pyrmont; import java.io.File; public class Constants { public static final String WEB_ROOT = System.getProperty("user.dir") + File.separator + "webroot"; public static final String WEB_SERVLET_ROOT = System.getProperty("user.dir") + File.separator + "target" + File.separator + "classes"; }
Request:
package ex02.pyrmont; import java.io.InputStream; import java.io.IOException; import java.io.BufferedReader; import java.io.UnsupportedEncodingException; import java.util.Enumeration; import java.util.Locale; import java.util.Map; import javax.servlet.RequestDispatcher; import javax.servlet.ServletInputStream; import javax.servlet.ServletRequest; public class Request implements ServletRequest { private InputStream input; private String uri; public Request(InputStream input) { this.input = input; } public String getUri() { return uri; } /** * * requestString形式如下: * GET /index.html HTTP/1.1 * Host: localhost:8080 * Connection: keep-alive * Cache-Control: max-age=0 * ... * 該函數目的就是為了獲取/index.html字元串 */ private String parseUri(String requestString) { int index1, index2; index1 = requestString.indexOf(' '); if (index1 != -1) { index2 = requestString.indexOf(' ', index1 + 1); if (index2 > index1) return requestString.substring(index1 + 1, index2); } return null; } //從InputStream中讀取request信息,並從request中獲取uri值 public void parse() { // Read a set of characters from the socket StringBuffer request = new StringBuffer(2048); int i; byte[] buffer = new byte[2048]; try { i = input.read(buffer); } catch (IOException e) { e.printStackTrace(); i = -1; } for (int j = 0; j < i; j++) { request.append((char) buffer[j]); } System.out.print(request.toString()); uri = parseUri(request.toString()); } /* implementation of the ServletRequest */ public Object getAttribute(String attribute) { return null; } public Enumeration<?> getAttributeNames() { return null; } public String getRealPath(String path) { return null; } public RequestDispatcher getRequestDispatcher(String path) { return null; } public boolean isSecure() { return false; } public String getCharacterEncoding() { return null; } public int getContentLength() { return 0; } public String getContentType() { return null; } public ServletInputStream getInputStream() throws IOException { return null; } public Locale getLocale() { return null; } public Enumeration<?> getLocales() { return null; } public String getParameter(String name) { return null; } public Map<?, ?> getParameterMap() { return null; } public Enumeration<?> getParameterNames() { return null; } public String[] getParameterValues(String parameter) { return null; } public String getProtocol() { return null; } public BufferedReader getReader() throws IOException { return null; } public String getRemoteAddr() { return null; } public String getRemoteHost() { return null; } public String getScheme() { return null; } public String getServerName() { return null; } public int getServerPort() { return 0; } public void removeAttribute(String attribute) { } public void setAttribute(String key, Object value) { } public void setCharacterEncoding(String encoding) throws UnsupportedEncodingException { } }View Code
Response:
package ex02.pyrmont; import java.io.OutputStream; import java.io.IOException; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.File; import java.io.PrintWriter; import java.util.Locale; import javax.servlet.ServletResponse; import javax.servlet.ServletOutputStream; public class Response implements ServletResponse { private static final int BUFFER_SIZE = 1024; Request request; OutputStream output; PrintWriter writer; public Response(OutputStream output) { this.output = output; } public void setRequest(Request request) { this.request = request; } //將web文件寫入到OutputStream位元組流中 public void sendStaticResource() throws IOException { byte[] bytes = new byte[BUFFER_SIZE]; FileInputStream fis = null; try { /* request.getUri has been replaced by request.getRequestURI */ File file = new File(Constants.WEB_ROOT, request.getUri()); fis = new FileInputStream(file); /* * HTTP Response = Status-Line(( general-header | response-header | * entity-header ) CRLF) CRLF [ message-body ] Status-Line = * HTTP-Version SP Status-Code SP Reason-Phrase CRLF */ int ch = fis.read(bytes, 0, BUFFER_SIZE); while (ch != -1) { output.write(bytes, 0, ch); ch = fis.read(bytes, 0, BUFFER_SIZE); } } catch (FileNotFoundException e) { String errorMessage = "HTTP/1.1 404 File Not Found\r\n" + "Content-Type: text/html\r\n" + "Content-Length: 23\r\n" + "\r\n" + "<h1>File Not Found</h1>"; output.write(errorMessage.getBytes()); } finally { if (fis != null) fis.close(); } } /** implementation of ServletResponse */ public void flushBuffer() throws IOException { } public int getBufferSize() { return 0; } public String getCharacterEncoding() { return null; } public Locale getLocale() { return null; } public ServletOutputStream getOutputStream() throws IOException { return null; } public PrintWriter getWriter() throws IOException { // autoflush is true, println() will flush, // but print() will not. writer = new PrintWriter(output, true); return writer; } public boolean isCommitted() { return false; } public void reset() { } public void resetBuffer() { } public void setBufferSize(int size) { } public void setContentLength(int length) { } public void setContentType(String type) { } public void setLocale(Locale locale) { } }View Code
靜態資源請求處理:
package ex02.pyrmont; import java.io.IOException; public class StaticResourceProcessor { public void process(Request request, Response response) { try { response.sendStaticResource(); } catch (IOException e) { e.printStackTrace(); } } }
Servlet請求處理:
package ex02.pyrmont.first; import java.net.URL; import java.net.URLClassLoader; import java.net.URLStreamHandler; import java.io.IOException; import javax.servlet.Servlet; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import ex02.pyrmont.Constants; import ex02.pyrmont.Request; import ex02.pyrmont.Response; public class ServletProcessor1 { public void process(Request request, Response response) { String uri = request.getUri(); String servletName = uri.substring(uri.lastIndexOf("/") + 1); //類載入器,用於從指定JAR文件或目錄載入類 URLClassLoader loader = null; try { URLStreamHandler streamHandler = null; //創建類載入器 loader = new URLClassLoader(new URL[]{new URL(null, "file:" + Constants.WEB_SERVLET_ROOT, streamHandler)}); } catch (IOException e) { System.out.println(e.toString()); } Class<?> myClass = null; try { //載入對應的servlet類 myClass = loader.loadClass(servletName); } catch (ClassNotFoundException e) { System.out.println(e.toString()); } Servlet servlet = null; try { //生產servlet實例 servlet = (Servlet) myClass.newInstance(); //執行ervlet的service方法 servlet.service((ServletRequest) request,(ServletResponse) response); } catch (Exception e) { System.out.println(e.toString()); } catch (Throwable e) { System.out.println(e.toString()); } } }
Servlet類:
import javax.servlet.*; import java.io.IOException; import java.io.PrintWriter; public class PrimitiveServlet implements Servlet { public void init(ServletConfig config) throws ServletException { System.out.println("init"); } public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { System.out.println("from service"); PrintWriter out = response.getWriter(); out.println("Hello. Roses are red."); out.print("Violets are blue."); } public void destroy() { System.out.println("destroy"); } public String getServletInfo() { return null; } public ServletConfig getServletConfig() { return null; } }
結果測試:
靜態資源請求:
servlet請求(因為只是第一個字元串被刷新到瀏覽器,所以你不能看到第二個字元串Violets are blue。我們將在後續完善該容器):
改進
前面實現的Servlet容器有一個嚴重的問題,用戶在servlet里可以直接將ServletRequest、ServletResponse向下轉 型為Request和Response類型,並直接調用其內部的public方法,這是一個不好的設計,改進方法是給Request、Response 增加外觀類,這樣,用戶只能訪問外觀類里定義的public方法。
Request外觀類
package ex02.pyrmont.second; import java.io.IOException; import java.io.BufferedReader; import java.io.UnsupportedEncodingException; import java.util.Enumeration; import java.util.Locale; import java.util.Map; import javax.servlet.RequestDispatcher; import javax.servlet.ServletInputStream; import javax.servlet.ServletRequest; import ex02.pyrmont.Request; public class RequestFacade implements ServletRequest { private ServletRequest request = null; public RequestFacade(Request request) { this.request = request; } /* implementation of the ServletRequest */ public Object getAttribute(String attribute) { return request.getAttribute(attribute); } public Enumeration<?> getAttributeNames() { return request.getAttributeNames(); } @SuppressWarnings("deprecation") public String getRealPath(String path) { return request.getRealPath(path); } public RequestDispatcher getRequestDispatcher(String path) { return request.getRequestDispatcher(path); } public boolean isSecure() { return request.isSecure(); } public String getCharacterEncoding() { return request.getCharacterEncoding(); } public int getContentLength() { return request.getContentLength(); } public String getContentType() { return request.getContentType(); } public ServletInputStream getInputStream() throws IOException { return request.getInputStream(); } public Locale getLocale() { return request.getLocale(); } public Enumeration<?> getLocales() { return request.getLocales(); } public String getParameter(String name) { return request.getParameter(name); } public Map<?, ?> getParameterMap() { return request.getParameterMap(); } public Enumeration<?> getParameterNames() { return request.getParameterNames(); } public String[] getParameterValues(String parameter) { return request.getParameterValues(parameter); } public String getProtocol() { return request.getProtocol(); } public BufferedReader getReader() throws IOException { return request.getReader(); } public String getRemoteAddr() { return request.getRemoteAddr(); } public String getRemoteHost() { return request.getRemoteHost(); } public String getScheme() { return request.getScheme(); } public String getServerName() { return request.getServerName(); } public int getServerPort() { return request.getServerPort(); } public void removeAttribute(String attribute) { request.removeAttribute(attribute); } public void setAttribute(String key, Object value) { request.setAttribute(key, value); } public void setCharacterEncoding(String encoding) throws UnsupportedEncodingException { request.setCharacterEncoding(encoding); } }View Code
Response外觀類
package ex02.pyrmont.second; import java.io.IOException; import java.io.PrintWriter; import java.util.Locale; import javax.servlet.ServletResponse; import javax.servlet.ServletOutputStream; import ex02.pyrmont.Response; public class ResponseFacade implements ServletResponse { private ServletResponse response; public ResponseFacade(Response response) { this.response = response; } public void flushBuffer() throws IOException { response.flushBuffer(); } public int getBufferSize() { return response.getBufferSize(); } public String getCharacterEncoding() { return response.getCharacterEncoding(); } public Locale getLocale() { return response.getLocale(); } public ServletOutputStream getOutputStream() throws IOException { return response.getOutputStream(); } public PrintWriter getWriter() throws IOException { return response.getWriter(); } public boolean isCommitted() { return response.isCommitted(); } public void reset() { response.reset(); } public void resetBuffer() { response.resetBuffer(); } public void setBufferSize(int size) { response.setBufferSize(size); } public void setContentLength(int length) { response.setContentLength(length); } public void setContentType(String type) { response.setContentType(type); } public void setLocale(Locale locale) { response.setLocale(locale); } }View Code
處理Servlet請求類:
package ex02.pyrmont.second; import java.net.URL; import java.net.URLClassLoader; import java.net.URLStreamHandler; import java.io.IOException; import javax.servlet.Servlet; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import ex02.pyrmont.Constants; import ex02.pyrmont.Request; import ex02.pyrmont.Response; public class ServletProcessor2 { public void process(Request request, Response response) { String uri = request.getUri(); String servletName = uri.substring(uri.lastIndexOf("/") + 1); // 類載入器,用於從指定JAR文件或目錄載入類 URLClassLoader loader = null; try { URLStreamHandler streamHandler = null; // 創建類載入器 loader = new URLClassLoader(new URL[] { new URL(null, "file:" + Constants.WEB_SERVLET_ROOT, streamHandler) }); } catch (IOException e) { System.out.println(e.toString()); } Class<?> myClass = null; try { // 載入對應的servlet類 myClass = loader.loadClass(servletName); } catch (ClassNotFoundException e) { System.out.println(e.toString()); } Servlet servlet = null; //給request、response增加外觀類,安全性考慮,防止用戶在servlet里直接將ServletRequest、ServletResponse向下轉型為Request和Response類型, //並直接調用其內部的public方法,因為RequestFacade、ResponseFacade里不會有parse、sendStaticResource等方法; RequestFacade requestFacade = new RequestFacade(request); ResponseFacade responseFacade = new ResponseFacade(response); try { servlet = (Servlet) myClass.newInstance(); servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade); } catch (Exception e) { System.out.println(e.toString()); } catch (Throwable e) { System.out.println(e.toString()); } } }View Code
其它代碼與前面實現的Servlet容器基本一致。
驗證程式,分別請求靜態資源和Servlet,發現結果與前面實現的容器一致;
參考資料:《深入剖析Tomcat》