使用URL实现和站点的交互

在日常项目应用中，经常需要向Web站点发送Get请求、Post请求，并从Web站点获取响应。例如我们可以通过以下代码来实现：

public   class   TestGetPost {

       /**

      * 向指定的URL发送Get方法的请求

      */

       public   static  String sendGet(String url,String param){

           String result =  "" ;

           BufferedReader in =  null ;

           String urlName = url +   "?"  +param;

              try  {

                URL realUrl =  new  URL(urlName);

                   //打开和URL之间的连接

                URLConnection conn = realUrl.openConnection();

                   //设置通用的请求属性

                conn.setRequestProperty(   "accept" ,  "*/*" );

                conn.setRequestProperty(   "connection" ,  "Keep-Alive"  );

                conn.setRequestProperty(   "user-agent" ,  "Mozilla/4.0 (compatible;MSIE 6.0;Windows NT 5.1;SV1)"   );

                   //建立实际的连接

                conn.connect();

                   //获取所有的响应头字段

                Map<String,List<String>> map = conn.getHeaderFields();

                   //遍历所有的响应头字段

                   for (String key:map.keySet()){

                     System.   out .println(key+   "--->" +map.get(key));

                }

                   //定义BufferedReader输入流来读取URL的响应

                in =  new  BufferedReader(   new  InputStreamReader(conn.getInputStream()));

                String line;

                   while ((line=in.readLine())!=   null ){

                     result +=  "\n" +line;

                }

           }  catch  (Exception e) {

                System.   out .println(   "发送GET请求出现异常"   + e);

                e.printStackTrace();

           }

              //使用finally块来关闭输入流

              finally {

                   try {

                        if (in!=   null ){

                           in.close();

                     }

                }   catch (IOException ex){

                     ex.printStackTrace();

                }

           }

              return  result;

     }

     

       /*

      * 向指定URL发送Post方法的请求

      */

     

       public   static  String sentPost(String url,String param){

           PrintWriter out =  null ;

           BufferedReader in =  null ;

           String result =  "" ;

              try  {

                URL realUrl =  new  URL(url);

                   //打开和URL之间的连接

                URLConnection conn = realUrl.openConnection();

                   //设置通用的请求属性

                conn.setRequestProperty(   "accept" ,  "*/*" );

                conn.setRequestProperty(   "connection" ,  "Keep-Alive"  );

                conn.setRequestProperty(   "user-agent" ,  "Mozilla/4.0 (compatible;MSIE 6.0;Windows NT 5.1;SV1)"   );

                   //发送Post请求必须设置如下两行

                conn.setDoInput(   true );

                conn.setDoOutput(   true );

                   //获取URLConnection对象对应的输出流

                out =  new  PrintWriter(conn.getOutputStream());

                   //发送请求参数

                out.print(param);

                   //flush 输出流的缓冲

                out.flush();

                   //定义BufferedReader输入流来读取URL的响应

                in =  new  BufferedReader(   new  InputStreamReader(conn.getInputStream()));

                String line;

                   while ((line=in.readLine())!=   null ){

                     result +=  "\n" +line;

                }

           }  catch  (Exception e) {

                System.   out .println(   "发送POST请求出现异常!"   +e);

                e.printStackTrace();

           }

           

              //使用finally块来关闭输入流，输出流

              finally {

                   try {

                        if (out!=   null ){

                           out.close();

                     }

                        if (in!=   null ){

                           in.close();

                     }

                }   catch (IOException ex){

                     ex.printStackTrace();

                }

           }

           

              return  result;

     }

     

       public   static   void  main(String []args){

              //发送Get请求

           String s = TestGetPost.sendGet(  "http://localhost:8080/aa/1.html" ,   null );

           System.   out .println(s);

           

              //发送Post请求

           String s1 = TestGetPost.sentPost(  "http://localhost:8080/aa/1.html" ,  "user=李刚&pass=abc"  );

           System.   out .println(s1);

     }

}

在上述代码中，在发送Get请求时只需要将请求参数放在URL字符串之后用“？”隔开，程序直接调用URLConnection对象的Connect方法即可。如果程序需要发送Post请求，则需要先设置doIn和doOut两个请求头字段值，然后再使用URLConnection对应的输出流来发送请求参数即可。