類比帶Servlet技術的HTTP伺服器的Java實現，servletjava

類比帶Servlet技術的HTTP伺服器的Java實現，servletjava

上一篇文章說道, Web發展初期, 使用者只能查看靜態頁面. 隨著Web發展,只能顯示靜態頁面的web顯然已經不能滿足福士的需求,所以出現了CGI和用Java編寫的Servlet程式.
Servlet可以根據使用者的請求動態產生html頁面,然後發給瀏覽器.

下面類比一下這個過程:

• HttpServer2類:伺服器類,負責啟動Http服務.
• Servlet介面: 定義Servlet服務介面.
• HelloServlet類:實現Servlet介面.使用者提交請求時,HttpServer2將請求發給HelloServlet處理.處理完後動態產生頁面返回給使用者.
• ServletRequest類: 封裝使用者的請求.交給HelloServlet處理.
• ServletResponse類: 封裝返回的響應.由HelloServlet返回.

HttpServer2類

伺服器類,負責啟動Http服務.

import java.io.*;import java.net.*;public class HttpServer2 {    private static final int port = 8088;    private ServerSocket serverSocket = null;    public HttpServer2() throws IOException {        serverSocket = new ServerSocket(port);        System.out.println("HTTPServer startup OK...");    }    public void work() throws IOException {        while (true) {            try {                Socket socket = serverSocket.accept();                ServletRequest request = new ServletRequest(                        socket.getInputStream());                ServletResponse response = new ServletResponse(                        socket.getOutputStream());                System.out.println("Receive request:\n" + request.getRequest());                String servletName = request.getServletName();        //動態產生servlet                Servlet servlet = (Servlet) Class.forName(servletName)                        .newInstance();    //調用servlet介面                servlet.init();                servlet.service(request, response);                servlet.destroy();                socket.close();            } catch (Exception e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }    public static void main(String[] args) throws IOException,            InterruptedException {        HttpServer2 httpServer = new HttpServer2();        httpServer.work();    }}

Servlet介面

定義Servlet服務介面.

public interface Servlet {    public void init();    public void service(ServletRequest req, ServletResponse res) throws Exception;    public void destroy();}

HelloServlet類

實現Servlet介面.使用者提交請求時,HttpServer2將請求發給HelloServlet處理.處理完後動態產生頁面返回給使用者.

public class HelloServlet implements Servlet {    @Override    public void init() {        // TODO Auto-generated method stub        System.out.println("servlet init ");    }    @Override    public void service(ServletRequest req, ServletResponse res)            throws Exception {        // TODO Auto-generated method stub        String contentType = req.getContentType();        String param = req.getParam();    //組裝HTTP回應標頭        String header = res.assembleResponseHeader(contentType);    //組裝HTTP響應本文        String body = res.assembleResponseBody(param);    //返迴響應        res.write(header + body);    }    @Override    public void destroy() {        // TODO Auto-generated method stub        System.out.println("servlet destroy ");    }}

ServletRequest類

封裝使用者的請求.交給HelloServlet處理.

import java.io.IOException;import java.io.InputStream;public class ServletRequest {    private String request;    private InputStream socketIn;    private String URI;    private String contentType;    private String param;    public ServletRequest(InputStream socketIn) throws IOException {        // TODO Auto-generated constructor stub        this.socketIn = socketIn;        this.request = _getRequest();        this.URI = _getURI();        this.contentType = _getContentType();        this.param = _getParam();    }    public String getRequest() {        return request;    }    public String getURI() {        return URI;    }    public String getContentType() {        return contentType;    }    public String getParam() {        return param;    }    private String _getRequest() throws IOException {        int size = socketIn.available();        byte[] requestBuff = new byte[size];        socketIn.read(requestBuff);        return new String(requestBuff);    }    //獲得要調用servlet的類名    public String getServletName(){        return URI.substring(URI.indexOf("/") + 1, URI.indexOf("?"));    }    private String _getURI() {        String firstLine = request.substring(0, request.indexOf("\r\n"));        String[] parts = firstLine.split(" ");        return parts[1];    }    private String _getContentType() {        /* 決定HTTP響應本文的類型 */        return "html";    }//獲得請求參數    private String _getParam() {        String paramString = URI.substring(URI.indexOf("?") + 1);        String[] paramPairs = paramString.split("=");        return paramPairs[1];    }}

ServletResponse類

封裝返回的響應.由HelloServlet返回.

import java.io.IOException;import java.io.OutputStream;public class ServletResponse {    private OutputStream outputStream;    public ServletResponse(OutputStream outputStream) {        // TODO Auto-generated constructor stub        this.outputStream = outputStream;    }    public String assembleResponseHeader(String contentType) {        /* 建立HTTP響應結果 */        // HTTP響應的第一行        String responseFirstLine = "HTTP/1.1 200 OK\r\n";        // HTTP回應標頭        String responseHeader = "Content-Type:" + contentType + "\r\n\r\n";        return responseFirstLine + responseHeader;    }    public String assembleResponseBody(String param) {        String content = "<body><h1>Hello:" + param + "</h1></body>";        String title = "<head><title>HelloWorld</title></head>";        String body = "<html>" + title + content + "</html>";        return body;    }    public void write(String res) throws IOException {        outputStream.write(res.getBytes());    }}

測試

在chrome瀏覽器輸入http://localhost:8088/HelloServlet?username=tom.
即使用者請求的參數是tom,要調用HelloServlet. (在實際的servlet實現中,是用一個web.xm設定檔實現URI到servlet的映射.)

servlet解析出來後組裝成html返回給瀏覽器.顯示為Hello:tom