Java-如何为GET和POST打开一个HttpURLConnection

Question

The request is to GET content from url and handle the content(different every time) properly, then POST the answer back to the same url. I encounter "Can't reset method: already connected" when I try to setRequestMethod("POST") after GET method executed. My code as below

public class MyClass {

    /**
     * @param args
     */

    public MyClass() {};

    public void process() {
        String url = "http://www.somesite.com/";
        String strPage = null;
        int n = 0;

        try{
            URL urlObj = new URL(url);
            HttpURLConnection urlConnection =
                    (HttpURLConnection)urlObj.openConnection();
            InputStream in = urlConnection.getInputStream();

            BufferedReader reader = new BufferedReader(new InputStreamReader(in));

            String strWhole = null;
            while(null != (strPage = reader.readLine())){
                strWhole += strPage;
            }

            //handle content here and calculate result
            ... ...
            //send result below

            urlConnection.setRequestMethod("POST");
            urlConnection.setDoOutput(true);
            String urlParameters = "aa=bb&cc=dd&ee=ff";

            DataOutputStream wr = new DataOutputStream(urlConnection.getOutputStream());
            wr.writeBytes(urlParameters);
            wr.flush();
            wr.close();             

            InputStream in1 = urlConnection.getInputStream();

            BufferedReader reader1 = new BufferedReader(new InputStreamReader(in));


            while(null != (strPage = reader1.readLine())){
                System.out.println(strPage);
            }

            reader1.close();            
        }
        catch(Exception e){
            String exception = e.getMessage();
            System.out.println(exception);
            if (reader != null) {
                reader.close();
            }

            if (reader1 != null) {
                reader1.close();
            }
        }

        return;

    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyClass dp = new MyClass();
        dp.process();

    }

}

Answer 1

It is impossible to reuse HttpURLConnection instance. But documentation says that under the hood, Java reuses connections for you:

The JDK supports both HTTP/1.1 and HTTP/1.0 persistent connections.

When the application finishes reading the response body or when the application calls close() on the InputStream returned by URLConnection.getInputStream() , the JDK's HTTP protocol handler will try to clean up the connection and if successful, put the connection into a connection cache for reuse by future HTTP requests.

The support for HTTP keep-Alive is done transparently.

Therefore, there is no need to reuse connections manually.

Answer 2

You must set all parameters first. Here's a code i use in my application:

     HttpURLConnection connection = (HttpURLConnection)new URL(url).openConnection();
     connection.setDoOutput(true);
     connection.setDoInput(true);
     connection.setInstanceFollowRedirects(false);
     connection.setRequestMethod("POST"); 
     connection.setRequestProperty("app_token", "my token"); // optional header you can set with your own data
     connection.setRequestProperty("charset", "utf-8");
     connection.setRequestProperty("Content-Length", String.valueOf(urlParameters.getBytes().length));
     connection.setUseCaches (false);
     DataOutputStream wr = new DataOutputStream(connection.getOutputStream ());
     wr.writeBytes(urlParameters);
     wr.flush();
     wr.close();
     connection.disconnect();
     InputStream is = connection.getInputStream();
     byte[] b = readWithoutSize(is);
     is.close();

The readWithoutSize is:

   public static byte[] readWithoutSize(InputStream is) throws IOException
   {
      ByteArrayOutputStream baos = new ByteArrayOutputStream(4096);
      byte[] buf = new byte[512];
      int leu;
      while ((leu = is.read(buf)) != -1)
         baos.write(buf,0,leu);
      return baos.toByteArray();
   }