模拟带Servlet技术的HTTP服务器的Java实现

上一篇文章说道, Web发展初期, 用户只能查看静态页面. 随着Web发展,只能显示静态页面的web显然已经不能满足大众的需求,所以出现了CGI和用Java编写的Servlet程序.
Servlet可以根据用户的请求动态的生成html页面,然后发给浏览器.

下面模拟一下这个过程:

• HttpServer2类:服务器类,负责启动Http服务.
• Servlet接口: 定义Servlet服务接口.
• HelloServlet类:实现Servlet接口.用户提交请求时,HttpServer2将请求发给HelloServlet处理.处理完后动态生成页面返回给用户.
• ServletRequest类: 封装用户的请求.交给HelloServlet处理.
• ServletResponse类: 封装返回的响应.由HelloServlet返回.

HttpServer2类

服务器类,负责启动Http服务.

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();    ​    ​//动态生成servlet                Servlet servlet = (Servlet) Class.forName(servletName)                        .newInstance();    ​//调用servlet接口                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接口

定义Servlet服务接口.

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

HelloServlet类

实现Servlet接口.用户提交请求时,HttpServer2将请求发给HelloServlet处理.处理完后动态生成页面返回给用户.

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();    ​//组装HTTP响应头        String header = res.assembleResponseHeader(contentType);    ​//组装HTTP响应正文        String body = res.assembleResponseBody(param);    ​//返回响应        res.write(header + body);    }    @Override    public void destroy() {        // TODO Auto-generated method stub        System.out.println("servlet destroy ");    }}

ServletRequest类

封装用户的请求.交给HelloServlet处理.

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);    }    ​//获得要调用servlet的类名    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() {        /* 决定HTTP响应正文的类型 */        return "html";    }//获得请求参数    private String _getParam() {        String paramString = URI.substring(URI.indexOf("?") + 1);        String[] paramPairs = paramString.split("=");        return paramPairs[1];    }}

ServletResponse类

封装返回的响应.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) {        /* 创建HTTP响应结果 */        // HTTP响应的第一行        String responseFirstLine = "HTTP/1.1 200 OK\r\n";        // HTTP响应头        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());    }}

测试

在chrome浏览器输入http://localhost:8088/HelloServlet?username=tom.
即用户请求的参数是tom,要调用HelloServlet. (在实际的servlet实现中,是用一个web.xm配置文件实现URI到servlet的映射.)

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servlet解析出来后组装成html返回给浏览器.显示为Hello:tom