有关HttpURLConnection充当代理转发Session丢失的问题

我同事最近使用甲方的专题制图的服务，在请求图片的过程中总是出现问题，最后发现原来是我们的代理（实际上是HttpURLConnection）类在转发的过程中把Session丢失，导致请求图片不成功。搞得他也蛮郁闷，甲方也很小气，不让看代码调试。

知道问题出在Session上，于是我在网上搜了一下解决方案，自己也测试了一下，解决思路如下：

1、第一次上传数据的时候，记录下SessionID(以便下次请求图片使用，而不至于session丢失s)。

2、第二次请求图片的时候，将上次记录的SessionId再传过去。

代码如下（测试代码有些粗糙）：

//----------------第一次上传数据

   URL  request=new URL("http://126.33.8.251:7001/zjTMap/tTSymbolServlet?tag=config&symbolID=10&dField=%25E5%2588%25B6%25E5%259B%25BE%25E5%258C%25BA%25E5%259F%259F&cFields=%25E7%25AC%25AC%25E4%25B8%2580%25E4%25BA%25A7%25E4%25B8%259A;&rFields=%25E5%25AE%2581%25E6%25B3%25A2%25E5%25B8%2582,%25E6%259D%25AD%25E5%25B7%259E%25E5%25B8%2582&years=&dataset=%255B%257B'%25E7%25AC%25AC%25E4%25B8%2580%25E4%25BA%25A7%25E4%25B8%259A':208.41,'%25E5%2588%25B6%25E5%259B%25BE%25E5%258C%25BA%25E5%259F%259F':'%25E6%259D%25AD%25E5%25B7%259E%25E5%25B8%2582'%257D,%257B'%25E7%25AC%25AC%25E4%25B8%2580%25E4%25BA%25A7%25E4%25B8%259A':219.13,'%25E5%2588%25B6%25E5%259B%25BE%25E5%258C%25BA%25E5%259F%259F':'%25E5%25AE%2581%25E6%25B3%25A2%25E5%25B8%2582'%257D%255D&maxSize=100&minSize=16&width=80&height=80&serviceURL=%25E6%25B5%2599%25E6%25B1%259F%25E6%2594%25BF%25E5%258C%25BA/1test");
		   HttpURLConnection conn=(HttpURLConnection)request.openConnection();
		   conn.setRequestMethod("GET" );
		   conn.setDoOutput(true );
		   conn.connect();
		   //
		   String session_value = conn.getHeaderField("Set-Cookie" );
		   String[] sessionId = session_value.split(";");
		   System.out.println(sessionId[0]);		 

//----------------------第二次请求图片

 URL url =  new  URL( "http://126.33.8.251:7001/zjTMap/tTSymbolServlet?tag=image&symbolID=10&region=%25E5%25AE%2581%25E6%25B3%25A2%25E5%25B8%2582&cFields=%25E7%25AC%25AC%25E4%25B8%2580%25E4%25BA%25A7%25E4%25B8%259A;&unit=%25E6%2597%25A0&width=80&height=80&bLabel=1");
		   HttpURLConnection conn2 = (HttpURLConnection)url.openConnection();
		   conn2.setRequestMethod("GET" );
		   conn2.setDoOutput(true );
		   //第二次运行的时候，把上次读取的session的值设置上
		   conn2.setRequestProperty( "Cookie", sessionId[0]);
		   OutputStream fos= conn2.getOutputStream();
		   IOUtil.copy(conn2.getInputStream(), new FileOutputStream("c:\\test.png"));

 代码执行完毕，跑到C盘看看，test.png打开完好。