How to know the Post parameters of a form?

Question

Hello
I am developing an application where, I have to login to web site, etc. I am newbie in this kind of development. I can access the web page, retreive the page. So, GET part is working fine. I have problem with Post. I am using JDK 1.6 with apache's HttpClient 3.1 for communicating through the web site. After setting parameters in NameValuePair[], when i run execuseMethod(postMethod), it throws the following exception :
i]Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: host parameter is null
I think, I may be going wrong in providing proper headers, parameters, etc. Can anyone help me know:
1. How can I know what parameters, I need to pass in the POST method. Along with form attributes, their may be any hidden values to be passed. How can I find out that.
2. Their is a submit button, how do i deal with that - tell the post method to click it ?
3. Same with headers. Which attributes needs to be set of headers and what values?
I saw some files on net, where prg'er are adding few other parameters that are hidden - but not all hidden parameters!
Any help is appreciative. Please it would be nice if you can help me out. I am new in this type of development. I have spend 2 days looking out for this problem, but couldn't find any help yet. Please any help at the earliest is benificial.
Thanks
Terry

Answer 1

Ok. To check the host before executing the post methd, I gave :
        HttpConnectionManager connectMgr = client.getHttpConnectionManager();  // ************
        HostConfiguration hc = client.getHostConfiguration();                                 // *************
        if (connectMgr.getConnection(hc).isOpen() == true)                                  // EXCEPTION - hc contents r null
            System.out.println("Connection is OPEN");
        else {
            System.out.println("Connection is ******************* NOT OPEN *************** ");
        method.setRequestBody(data);
        int statusCode = 0;
        try {
            statusCode = client.executeMethod(hc, method);
            System.out.println("Register Send: " + method.getStatusLine().toString());
        }catch (HttpException e) {
            method.releaseConnection();
            System.out.println("HTTP EXception : " + e.getMessage());
        }catch (IOException ie) {
            method.releaseConnection();
            System.out.println("Error Exe Method - Post. Status Code = " + statusCode);
            ie.printStackTrace();
        }HttpConnectionManager has hostname, portNo, httpconnectin isopen -> false
HostConfiguration has host, port, localAddress all null
Due to the null value the exception is thrown. What do I do now? Infact, in my GEt also, I tried the same thing, their also host is null of HostConfiguration, but it works well, as it doesn't have to send anything.I have no clue to move ahead.Also, what must be the content length?
Thanks