上一篇文章說道, Web發展初期, 使用者只能檢視靜態頁面. 隨著Web發展,只能顯示靜態頁面的web顯然已經不能滿足大眾的需求,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的生成html頁面,然後發給瀏覽器.

下面模擬一下這個過程:

• 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.處理完後動態生成頁面返回給使用者.
• 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();
    ​
    ​//動態生成servlet
                Servlet servlet = (Servlet) Class.forName(servletName)
                        .newInstance();

    ​//呼叫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.處理完後動態生成頁面返回給使用者.

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響應頭
        String header = res.assembleResponseHeader(contentType);
    ​//組裝HTTP響應正文
        String body = res.assembleResponseBody(param);
    ​//返回響應
        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);
    }
    ​//獲得要呼叫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響應正文的型別 */
        return "html";
    }

//獲得請求引數
    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響應頭
        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.
即使用者請求的引數是tom,要呼叫HelloServlet. (在實際的servlet實現中,是用一個web.xm配置檔案實現URI到servlet的對映.)

​

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