| 用Socket类实现HTTP协议客户端应用 |
| 梁颖健 liangyingjian@21cn.com 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。1.Socket类:了解TCP/IP协议集通信的读者知道，协议间的通信是通过Socket完成的。在Java.net包中，Socket类就是对Socket的具体实现。它通过连接到主机后，返回一个I/O流，实现协议间的信息交换。2 . 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/1.0accept: 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 OKDate: Tue, 14 Sep 1999 02:19:57 GMTServer: Apache/1.2.6Connection: closeContent-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)。3. HTTP客户端程序: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) throwsUnknownHostException,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;}}注: 程序中只实现GET、HEAD、POST三种方法。其他几种因不常使用，暂且忽略。 |
