在Java中用Socket类模拟HTTP协议

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Http客户端程序已集成在Java语言中，可以通过URLConnection类调用。遗憾的是，由于SUN没有公布Http客户程序的源码，它实现的细节仍是一个谜。本文根据HTTP协议规范，用Java.net.Socket类实现一个HTTP协议客户端程序。

HTTP协议
HTTP协议同其它TCP/IP协议集中的协议一样，是遵循客户/服务器模型工作的。客户端发往服务端的信息格式如下:
------------------------------
请求方法 URL HTTP协议的版本号
提交的元信息
**空行**
实体
------------------------------
请求方法是对这次连接工作的说明，目前HTTP协议已经发展到1.1版，它包括GET、HEAD、POST、DELETE、OPTIONS、TRACE、PUT七种。元信息是关于当前请求的信息。通过分析元信息，可以检查实体数据是否完整，接收过程是否出错，类型是否匹配等。元信息的引入使HTTP协议通信更加稳妥可靠。实体是请求的具体内容。将上述报文发往Web服务器，如果成功，应答格式如下:
--------------------------------
HTTP协议的版本号应答状态码应答状态码说明
接收的元信息
**空行**
实体
--------------------------------
以上报文发向客户端，并且接收成功，彼此间关闭连接，完成一次握手。下面用最常用的GET方法，来说明具体的报文应用
----------------------------------
GET http://www.youhost.com
HTTP/1.0
accept: www/source; text/html; image/gif; image/jpeg; */*
User_Agent: myAgent
**空行**
-----------------------------------
这个报文是向www.youhost.com主机请求一个缺省HTML文档。客户端HTTP协议版本号是1.0版，元信息包括可接收的文件格式，用户代理，每一段之间用回车换行符分隔，最后以一个空行结束。发向服务器后，如果执行过程正常，服务器返回以下代码:
------------------------------------
HTTP/1.1 200 OK
Date: Tue, 14 Sep 1999 02:19:57 GMT
Server: Apache/1.2.6
Connection: close
Content-Type: text/html
**空行**
<html><head>...</head><body>...</body></html>
------------------------------------
HTTP/1.1表示这个HTTP服务器是1.1版，200是服务器对客户请求的应答状态码，OK是对应答状态码的解释，之后是这个文档的元信息和文档正文。(相关应答状态码和元信息的解释请参阅Inetrnet标准草案:RFC2616)。

Http.java

import java.net.*;
import java.io.*;
import java.util.Properties;
import java.util.Enumeration;

public class Http {
    protected Socket client;
    protected BufferedOutputStream sender;
    protected BufferedInputStream receiver;
    protected ByteArrayInputStream byteStream;
    protected URL target;
    private int responseCode=-1;
    private String responseMessage="";
    private String serverVersion="";
    private Properties header = new Properties();
    public Http() { }
    public Http(String url) {
        GET(url) ;
    }

    /* GET方法根据URL，会请求文件、数据库查询结果、程序运行结果等多种内容 */
    public void GET(String url) {
        try {
            checkHTTP(url);
            openServer(target.getHost(),target.getPort() );
            String cmd = "GET "+ getURLFormat(target) +" HTTP/1.0/r/n"
            + getBaseHeads()+"/r/n";
            sendMessage(cmd);
            receiveMessage();
        } catch(ProtocolException p) {
            p.printStackTrace();
            return;
        } catch(UnknownHostException e) {
            e.printStackTrace();
            return;
        } catch(IOException i) {
            i.printStackTrace();
            return;
        }
    }

    /*
    * HEAD方法只请求URL的元信息，不包括URL本身。若怀疑本机和服务器上的
    * 文件相同，用这个方法检查最快捷有效。
    */
    public void HEAD(String url) {
        try {
            checkHTTP(url);
            openServer(target.getHost(),target.getPort() );
            String cmd = "HEAD "+getURLFormat(target)+" HTTP/1.0/r/n"
            +getBaseHeads()+"/r/n";
            sendMessage(cmd);
            receiveMessage();
        }catch(ProtocolException p) {
            p.printStackTrace();
            return;
        }catch(UnknownHostException e) {
            e.printStackTrace();
            return;
        }catch(IOException i) {
            i.printStackTrace();
            return;
        }
    }

    /*
    * POST方法是向服务器传送数据，以便服务器做出相应的处理。例如网页上常用的
    * 提交表格。
    */
    public void POST(String url,String content) {
        try {
            checkHTTP(url);
            openServer(target.getHost(),target.getPort() );
            String cmd = "POST "+ getURLFormat(target) +"HTTP/1.0/r/n"+getBaseHeads();
            cmd += "Content-type: application/x-www-form-urlencoded/r/n";
            cmd += "Content-length: " + content.length() + "/r/n/r/n";
            cmd += content+"/r/n";
            sendMessage(cmd);
            receiveMessage();
        }catch(ProtocolException p) {
            p.printStackTrace();
            return;
        }catch(UnknownHostException e) {
            e.printStackTrace();
            return;
        }catch(IOException i) {
            i.printStackTrace();
            return;
        }
    }

    protected void checkHTTP(String url) throws ProtocolException {
        try {
            URL target = new URL(url);
            if(target==null || !target.getProtocol().toUpperCase().equals("HTTP") )
           throw new ProtocolException("这不是HTTP协议");
            this.target = target;
        } catch(MalformedURLException m) {
            throw new ProtocolException("协议格式错误");
        }
    }

    /*
    * 与Web服务器连接。若找不到Web服务器，InetAddress会引发UnknownHostException
    * 异常。若Socket连接失败，会引发IOException异常。
    */
    protected void openServer(String host,int port) throws
        UnknownHostException,IOException {
            header.clear();
            responseMessage=""; responseCode=-1;
        try {
            if(client!=null) closeServer();
            if(byteStream != null) {
                byteStream.close(); byteStream=null;
            }
            InetAddress address = InetAddress.getByName(host);
            client = new Socket(address,port==-1?80:port);
            sender = new BufferedOutputStream(client.getOutputStream());
            receiver = new BufferedInputStream(client.getInputStream());
        }catch(UnknownHostException u) {
            throw u;
        }catch(IOException i) {
            throw i;
        }
    }

    /* 关闭与Web服务器的连接 */
    protected void closeServer() throws IOException {
        if(client==null) return;
        try {
            client.close(); sender.close(); receiver.close();
        } catch(IOException i) {
            throw i;
        }
        client=null; sender=null; receiver=null;
    }

    protected String getURLFormat(URL target) {
        String spec = "http://
+target.getHost();
        if(target.getPort()!=-1)
            spec+=":"+target.getPort();
        return spec+=target.getFile();
    }

    /* 向Web服务器传送数据 */
    protected void sendMessage(String data) throws IOException{
        sender.write(data.getBytes(),0,data.length());
        sender.flush();
    }

    /* 接收来自Web服务器的数据 */
    protected void receiveMessage() throws IOException{
        byte data[] = new byte[1024];
        int count=0;
        int word=-1;
        // 解析第一行
        while( (word=receiver.read())!=-1 ) {
            if(word=='/r'||word=='/n') {
                word=receiver.read();
                if(word=='/n') word=receiver.read();
                break;
            }
            if(count == data.length) data = addCapacity(data);
                data[count++]=(byte)word;
        }
        String message = new String(data,0,count);
        int mark = message.indexOf(32);
        serverVersion = message.substring(0,mark);
        while( mark<message.length() && message.charAt(mark+1)==32 ) mark++;
        responseCode = Integer.parseInt(message.substring(mark+1,mark+=4));
        responseMessage = message.substring(mark,message.length()).trim();

        // 应答状态码和处理请读者添加
        switch(responseCode) {
            case 400:
            throw new IOException("错误请求");
            case 404:
            throw new FileNotFoundException( getURLFormat(target) );
            case 503:
            throw new IOException("服务器不可用" );
        }
        if(word==-1) throw new ProtocolException("信息接收异常终止");
        int symbol=-1;
        count=0;
        // 解析元信息
        while( word!='/r' && word!='/n' && word>-1) {
            if(word=='/t') word=32;
            if(count==data.length) data = addCapacity(data);
            data[count++] = (byte)word;
            parseLine: {
                while( (symbol=receiver.read()) >-1 ) {
                    switch(symbol) {
                        case '/t':
                            symbol=32; break;
                        case '/r':
                        case '/n':
                            word = receiver.read();
                            if( symbol=='/r' && word=='/n') {
                                word=receiver.read();
                                if(word=='/r') word=receiver.read();
                            }
                            if( word=='/r' || word=='/n' || word>32) break parseLine;
                            symbol=32; break;
                    }
                    if(count==data.length) data = addCapacity(data);
                    data[count++] = (byte)symbol;
                }
                word=-1;
            }
            message = new String(data,0,count);
            mark = message.indexOf(':');
            String key = null;
            if(mark>0) key = message.substring(0,mark);
            mark++;
            while( mark<message.length() && message.charAt(mark)<=32 ) mark++;
            String value = message.substring(mark,message.length() );
            header.put(key,value);
            count=0;
        }
        // 获得正文数据
        while( (word=receiver.read())!=-1) {
            if(count == data.length) data = addCapacity(data);
            data[count++] = (byte)word;
        }
        if(count>0) byteStream = new ByteArrayInputStream(data,0,count);
        data=null;
        closeServer();
    }

    public String getResponseMessage() {
        return responseMessage;
    }

    public int getResponseCode() {
        return responseCode;
    }

    public String getServerVersion() {
        return serverVersion;
    }

    public InputStream getInputStream() {
        return byteStream;
    }

    public synchronized String getHeaderKey(int i) {
        if(i>=header.size()) return null;
        Enumeration enum = header.propertyNames();
        String key = null;
        for(int j=0; j<=i; j++)
            key = (String)enum.nextElement();
        return key;
    }

    public synchronized String getHeaderValue(int i) {
        if(i>=header.size()) return null;
        return header.getProperty(getHeaderKey(i));
    }

    public synchronized String getHeaderValue(String key) {
        return header.getProperty(key);
    }

    protected String getBaseHeads() {
        String inf = "User-Agent: myselfHttp/1.0/r/n"+
        "Accept: www/source; text/html; image/gif; */*/r/n";
        return inf;
    }

    private byte[] addCapacity(byte rece[]){
        byte temp[] = new byte[rece.length+1024];
        System.arraycopy(rece,0,temp,0,rece.length);
        return temp;
    }

    public static void main(String[] args)     {
        Http http=new Http();
        //http.GET("http://192.168.1.5
);
        int i;
        for (i=0; i<50000; i++) {
            http.GET("http://www.model-dl.com/modelinfo.asp?modelid=101);

            http.POST("http://www.model-dl.com/modelinfo.asp?modelid=101,"ratecontd=101&MM_insert=form1");
        }
    }
}