读取输入后无法写入输出

Question

我正在编写一个连接到servlet的程序,感谢a HttpURLConnection但是我在查看url时卡住了

public void connect (String method) throws Exception {

server = (HttpURLConnection) url.openConnection ();
server.setDoInput (true);
server.setDoOutput (true);
server.setUseCaches (false);
server.setRequestMethod (method);
server.setRequestProperty ("Content-Type", "application / xml");

server.connect ();

/*if (server.getResponseCode () == 200)
{
System.out.println ("Connection OK at the url:" + url);
System.out.println ("------------------------------------------- ------- ");
}
else
System.out.println ("Connection failed"); 

}*/

我收到了错误:

java.net.ProtocolException:读取输入后无法写入输出.

如果我用注释中的代码检查网址,但不幸的是它完美地工作,我需要检查网址,所以我认为问题来自getResponseCode方法,但我不知道如何解决它

非常感谢你

Answer 1

HTTP协议基于请求 - 响应模式:您首先发送请求,服务器响应.一旦服务器响应,您就无法发送更多内容,这是没有意义的.(在知道你要发送什么内容之前,服务器怎么能给你一个响应代码？)

所以当你打电话时server.getResponseCode(),你有效地告诉服务器你的请求已经完成并且它可以处理它.如果要发送更多数据,则必须启动新请求.

查看您的代码,您想要检查连接本身是否成功,但是没有必要:如果连接不成功,Exception则抛出一个server.connect().但是连接尝试的结果与HTTP响应代码不同,HTTP响应代码总是在服务器处理完所有输入之后.

Answer 2

我认为例外不是由于printing url.在读取响应之后,应该尝试编写一些代码来设置请​​求体.

如果您在获取HttpURLConnection.getOutputStream()后尝试获取,则会发生此异常HttpURLConnection.getInputStream()

这是sun.net.www.protocol.http.HttpURLConnection.getOutputStream的实现:

public synchronized OutputStream getOutputStream() throws IOException {

     try {
         if (!doOutput) {
             throw new ProtocolException("cannot write to a URLConnection"
                            + " if doOutput=false - call setDoOutput(true)");
         }

         if (method.equals("GET")) {
             method = "POST"; // Backward compatibility
         }
         if (!"POST".equals(method) && !"PUT".equals(method) &&
             "http".equals(url.getProtocol())) {
             throw new ProtocolException("HTTP method " + method +
                                         " doesn't support output");
         }

         // if there's already an input stream open, throw an exception
         if (inputStream != null) {
             throw new ProtocolException("Cannot write output after reading 
                input.");
         }

         if (!checkReuseConnection())
             connect();

         /* REMIND: This exists to fix the HttpsURLConnection subclass.
          * Hotjava needs to run on JDK.FCS.  Do proper fix in subclass
          * for . and remove this.
          */

         if (streaming() && strOutputStream == null) {
             writeRequests();
         }
         ps = (PrintStream)http.getOutputStream();
         if (streaming()) {
             if (strOutputStream == null) {
                 if (fixedContentLength != -) {
                     strOutputStream = 
                        new StreamingOutputStream (ps, fixedContentLength);
                 } else if (chunkLength != -) {
                     strOutputStream = new StreamingOutputStream(
                         new ChunkedOutputStream (ps, chunkLength), -);
                 }
             }
             return strOutputStream;
         } else {
             if (poster == null) {
                 poster = new PosterOutputStream();
             }
             return poster;
         }
     } catch (RuntimeException e) {
         disconnectInternal();
         throw e;
     } catch (IOException e) {
         disconnectInternal();
         throw e;
     }
 }