📄 用socket类实现http协议客户端应用.htm
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<DIV align=center><B><FONT size=3> 用Socket类实现HTTP协议客户端应用
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color=#333300>用Socket类实现HTTP协议客户端应用<BR><BR> <BR>梁颖健 <BR>liangyingjian@21cn.com <BR><BR>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<BR>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<BR>协议规范，用Java.net.Socket类实现一个HTTP协议客户端程序。<BR><BR>1.Socket类:<BR>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<BR>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<BR>I/O流，实现协议间的信息交换。<BR><BR>2 . HTTP协议<BR>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<BR>户端发往服务端的信息格式如下:<BR>------------------------------<BR>请求方法 URL HTTP协议的版本号<BR>提交的元信息<BR>**空行**<BR>实体<BR>------------------------------<BR>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、<BR>HEAD、POST、DELETE、OPTIONS、TRACE、PUT七种。元信息是关于当前请求的信息。通<BR>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<BR>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。<BR>将上述报文发往Web服务器，如果成功，应答格式如下:<BR>--------------------------------<BR>HTTP协议的版本号 应答状态码 应答状态码说明<BR>接收的元信息<BR>**空行**<BR>实体<BR>--------------------------------<BR>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。<BR>下面用最常用的GET方法，来说明具体的报文应用<BR>----------------------------------<BR>GET http://www.youhost.com HTTP/1.0<BR>accept: www/source; text/html; image/gif; image/jpeg; */*<BR>User_Agent: myAgent<BR>**空行**<BR>-----------------------------------<BR>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<BR>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<BR>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:<BR>------------------------------------<BR>HTTP/1.1 200 OK<BR>Date: Tue, 14 Sep 1999 02:19:57 GMT<BR>Server: Apache/1.2.6<BR>Connection: close<BR>Content-Type: text/html<BR>**空行**<BR><html><head>...</head><body>...</body></html><BR>------------------------------------<BR>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<BR>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<BR>信息的解释请参阅Inetrnet标准草案:RFC2616)。<BR><BR>3. HTTP客户端程序:<BR><BR>import java.net.*;<BR>import java.io.*;<BR>import java.util.Properties;<BR>import java.util.Enumeration;<BR>public class Http {<BR>protected Socket client;<BR>protected BufferedOutputStream sender;<BR>protected BufferedInputStream receiver;<BR>protected ByteArrayInputStream byteStream;<BR>protected URL target;<BR>private int responseCode=-1;<BR>private String responseMessage="";<BR>private String serverVersion="";<BR>private Properties header = new Properties();<BR>public Http() { }<BR>public Http(String url) {<BR>GET(url) ;<BR>}<BR>/* 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 */<BR>public void GET(String url) {<BR>try {<BR>checkHTTP(url);<BR>openServer(target.getHost(),target.getPort() );<BR>String cmd = "GET "+ getURLFormat(target) +" HTTP/1.0\r\n"<BR>+ getBaseHeads()+"\r\n";<BR>sendMessage(cmd);<BR>receiveMessage();<BR>}catch(ProtocolException p) {<BR>p.printStackTrace();<BR>return;<BR>}catch(UnknownHostException e) {<BR>e.printStackTrace();<BR>return;<BR>}catch(IOException i)<BR><BR>i.printStackTrace();<BR>return;<BR>}<BR>}<BR><BR>/*<BR>* 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<BR>* 文件相同，用这个方法检查最快捷有效。<BR>*/<BR>public void HEAD(String url) {<BR>try {<BR>checkHTTP(url);<BR>openServer(target.getHost(),target.getPort() );<BR>String cmd = "HEAD "+getURLFormat(target)+" HTTP/1.0\r\n"<BR>+getBaseHeads()+"\r\n";<BR>sendMessage(cmd);<BR>receiveMessage();<BR>}catch(ProtocolException p) {<BR>p.printStackTrace();<BR>return;<BR>}catch(UnknownHostException e) {<BR>e.printStackTrace();<BR>return;<BR>}catch(IOException i)<BR><BR>i.printStackTrace();<BR>return;<BR>}<BR>}<BR>/*<BR>* 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<BR>* 提交表格。<BR>*/<BR>public void POST(String url,String content) {<BR>try {<BR>checkHTTP(url);<BR>openServer(target.getHost(),target.getPort() );<BR>String cmd = "POST "+ getURLFormat(target) +"<BR>HTTP/1.0\r\n"+getBaseHeads();<BR>cmd += "Content-type: application/x-www-form-urlencoded\r\n";<BR>cmd += "Content-length: " + content.length() + "\r\n\r\n";<BR>cmd += content+"\r\n";<BR>sendMessage(cmd);<BR>receiveMessage();<BR>}catch(ProtocolException p) {<BR>p.printStackTrace();<BR>return;<BR>}catch(UnknownHostException e) {<BR>e.printStackTrace();<BR>return;<BR>}catch(IOException i)<BR><BR>i.printStackTrace();<BR>return;<BR>}<BR><BR>}<BR>protected void checkHTTP(String url) throws ProtocolException {<BR>try {<BR>URL target = new URL(url);<BR>if(target==null || !target.getProtocol().toUpperCase().equals("HTTP") )<BR>throw new ProtocolException("这不是HTTP协议");<BR>this.target = target;<BR>}catch(MalformedURLException m) {<BR>throw new ProtocolException("协议格式错误");<BR>}<BR>}<BR>/*<BR>* 与Web服务器连接。若找不到Web服务器，InetAddress会引发UnknownHostException<BR>* 异常。若Socket连接失败，会引发IOException异常。<BR>*/<BR>protected void openServer(String host,int port) throws<BR>UnknownHostException,IOException {<BR>header.clear();<BR>responseMessage=""; responseCode=-1;<BR>try {<BR>if(client!=null) closeServer();<BR>if(byteStream != null) {<BR>byteStream.close(); byteStream=null;<BR>}<BR>InetAddress address = InetAddress.getByName(host);<BR>client = new Socket(address,port==-1?80:port);<BR>sender = new BufferedOutputStream(client.getOutputStream());<BR>receiver = new BufferedInputStream(client.getInputStream());<BR>}catch(UnknownHostException u) {<BR>throw u;<BR>}catch(IOException i) {<BR>throw i;<BR>}<BR>}<BR>/* 关闭与Web服务器的连接 */<BR>protected void closeServer() throws IOException {<BR>if(client==null) return;<BR>try {<BR>client.close(); sender.close(); receiver.close();<BR>}catch(IOException i) {<BR>throw i;<BR>}<BR>client=null; sender=null; receiver=null;<BR>}<BR>protected String getURLFormat(URL target) {<BR>String spec = "http://"+target.getHost();<BR>if(target.getPort()!=-1)<BR>spec+=":"+target.getPort();<BR>return spec+=target.getFile();<BR>}<BR><BR>/* 向Web服务器传送数据 */<BR>protected void sendMessage(String data) throws IOException{<BR>sender.write(data.getBytes(),0,data.length());<BR>sender.flush();<BR>}<BR>/* 接收来自Web服务器的数据 */<BR>protected void receiveMessage() throws IOException{<BR>byte data[] = new byte[1024];<BR>int count=0;<BR>int word=-1;<BR>// 解析第一行<BR>while( (word=receiver.read())!=-1 ) {<BR>if(word=='\r'||word=='\n') {<BR>word=receiver.read();<BR>if(word=='\n') word=receiver.read();<BR>break;<BR>}<BR>if(count == data.length) data = addCapacity(data);<BR>data[count++]=(byte)word;<BR>}<BR>String message = new String(data,0,count);<BR>int mark = message.indexOf(32);<BR>serverVersion = message.substring(0,mark);<BR>while( mark<message.length() && message.charAt(mark+1)==32 ) mark++;<BR>responseCode = Integer.parseInt(message.substring(mark+1,mark+=4));<BR>responseMessage = message.substring(mark,message.length()).trim();<BR><BR>// 应答状态码和处理请读者添加<BR>switch(responseCode) {<BR>case 400:<BR>throw new IOException("错误请求");<BR>case 404:<BR>throw new FileNotFoundException( getURLFormat(target) );<BR>case 503:<BR>throw new IOException("服务器不可用" );<BR>}<BR>if(word==-1) throw new ProtocolException("信息接收异常终止");<BR>int symbol=-1;<BR>count=0;<BR>// 解析元信息<BR>while( word!='\r' && word!='\n' && word>-1) {<BR>if(word=='\t') word=32;<BR>if(count==data.length) data = addCapacity(data);<BR>data[count++] = (byte)word;<BR>parseLine: {<BR>while( (symbol=receiver.read()) >-1 ) {<BR>switch(symbol) {<BR>case '\t':<BR>symbol=32; break;<BR>case '\r':<BR>case '\n':<BR>word = receiver.read();<BR>if( symbol=='\r' && word=='\n') {<BR>word=receiver.read();<BR>if(word=='\r') word=receiver.read();<BR>}<BR>if( word=='\r' || word=='\n' || word>32) break parseLine;<BR>symbol=32; break;<BR>}<BR>if(count==data.length) data = addCapacity(data);<BR>data[count++] = (byte)symbol;<BR>}<BR>word=-1;<BR>}<BR>message = new String(data,0,count);<BR>mark = message.indexOf(':');<BR>String key = null;<BR>if(mark>0) key = message.substring(0,mark);<BR>mark++;<BR>while( mark<message.length() && message.charAt(mark)<=32 ) mark++;<BR>String value = message.substring(mark,message.length() );<BR>header.put(key,value);<BR>count=0;<BR>}<BR>// 获得正文数据<BR>while( (word=receiver.read())!=-1) {<BR>if(count == data.length) data = addCapacity(data);<BR>data[count++] = (byte)word;<BR>}<BR>if(count>0) byteStream = new ByteArrayInputStream(data,0,count);<BR>data=null;<BR>closeServer();<BR>}<BR>public String getResponseMessage() {<BR>return responseMessage;<BR>}<BR>public int getResponseCode() {<BR>return responseCode;<BR>}<BR>public String getServerVersion() {<BR>return serverVersion;<BR>}<BR>public InputStream getInputStream() {<BR>return byteStream;<BR>}<BR>public synchronized String getHeaderKey(int i) {<BR>if(i>=header.size()) return null;<BR>Enumeration enum = header.propertyNames();<BR>String key = null;<BR>for(int j=0; j<=i; j++)<BR>key = (String)enum.nextElement();<BR>return key;<BR>}<BR>public synchronized String getHeaderValue(int i) {<BR>if(i>=header.size()) return null;<BR>return header.getProperty(getHeaderKey(i));<BR>}<BR>public synchronized String getHeaderValue(String key) {<BR>return header.getProperty(key);<BR>}<BR>protected String getBaseHeads() {<BR>String inf = "User-Agent: myselfHttp/1.0\r\n"+<BR>"Accept: www/source; text/html; image/gif; */*\r\n";<BR>return inf;<BR>}<BR>private byte[] addCapacity(byte rece[]){<BR>byte temp[] = new byte[rece.length+1024];<BR>System.arraycopy(rece,0,temp,0,rece.length);<BR>return temp;<BR>}<BR>}<BR><BR>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。<BR> <BR></FONT></TD></TR>
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