用Socket类实现HTTP协议客户端应用-

1、用Socket类实现HTTP协议客户端应用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J.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J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

2、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。

3、下面用最常用的GET方法,来说明具体的报文应用-GET HTTP/1.0accept: www/source; text/html; image/gif; image/jpeg; */*User_Agent: myAgent*空行*-这个报文是向主机请求一个缺省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/1.2.6Conn

4、ection: closeContent-Type: text/html*空行*.-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 .*;import java.io.*;import java.util.Properties;import java.util.Enumeration;public class Http protected Socket client;prote

5、cted 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

6、 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/1.0rn+ getBaseHeads(+rn;sendMessage(cmd;receiveMessage(;catch(ProtocolException p p.printStackTrace(;return;c

7、atch(UnknownHostException e e.printStackTrace(;return;catch(IOException ii.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/1.0r

8、n+getBaseHeads(+rn;sendMessage(cmd;receiveMessage(;catch(ProtocolException p p.printStackTrace(;return;catch(UnknownHostException e e.printStackTrace(;return;catch(IOException ii.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 c

9、heckHTTP(url;openServer(target.getHost(,target.getPort( ;String cmd = POST + getURLFormat(target +HTTP/1.0rn+getBaseHeads(;cmd += Content-type: application/x-www-form-urlencodedrn;cmd += Content-length: + content.length( + rnrn;cmd += content+rn;sendMessage(cmd;receiveMessage(;catch(ProtocolExceptio

10、n p p.printStackTrace(;return;catch(UnknownHostException e e.printStackTrace(;return;catch(IOException ii.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 Protoco

11、lException(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.clea

12、r(;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 Buffere

13、dInputStream(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=

14、null;protected String getURLFormat(URL target String spec = http:/+target.getHost(;if(target.getPort(!=-1spec+=:+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

15、务器的数据*/protected void receiveMessage( throws IOExceptionbyte data = new byte1024;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;datacount+=(byteword;String message

16、= new String(data,0,count;int mark = message.indexOf(32;serverVersion = message.substring(0,mark; while( 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 IOEx

17、ception(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;

18、datacount+ = (byteword; 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 | word32 break parseLine; symbol=32; break; if(count=data.l

19、ength data = addCapacity(data; datacount+ = (bytesymbol; word=-1; message = new String(data,0,count; mark = message.indexOf(:; String key = null; if(mark0 key = message.substring(0,mark; mark+; while( mark0 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 InputStrea