How to fill out POST HTML forms from my Java Application?

Question

Hi -
I am writing a little Java GUI program that will allow a user to fill out data from the GUI and then submit that data. When they submit the data (two text fields) I want to take the two text fields and submit them via the POST form method of a HTML document over the web.
Here is what I got so far:
host = new URL("http", "<my_address>", web port, "/query.html");
            InputStream in = host.openStream();
            BufferedInputStream bufIn = new BufferedInputStream(in);
            for (;;)
                int data = bufIn.read();
                // Check for end of file
                if (data == -1)
                    break;
                else
                    System.out.print ( (char) data);
            }What that code does is makes a URL, opens a stream, and reads the HTML source of the file at the specified URL. There is a form that submits data via the POST method, and I would like to know how to write data to specific forms and specific input types of that form.
Then, I'd like to be able to read the response I get after submitting the form.
Is this possible?
Thanks,

Answer 1

Here is how one of my e-books go about Posting
I tryied in one of my projects and it works ok
(Tricks of the Java Programming Gurus)
There's another reason you may want to manipulate a URLConnection object directly: You may want to post data to a URL, rather than just fetching a document. Web browsers do this with data from online forms, and your applets might use the same mechanism to return data to the server after giving the user a chance to supply information.
As of this writing, posting is only supported to HTTP URLs. This interface will likely be enhanced in the future-the HTTP protocol supports two ways of sending data to a URL ("post" and "put"), while FTP, for example, supports only one. Currently, the Java library sidesteps the issue, supporting just one method ("post"). Eventually, some mechanism will be needed to enable applets to exert more control over how URLConnection objects are used for output.
To prepare a URL for output, you first create the URL object just as you would if you were retrieving a document. Then, after gaining access to the URLConnection object, you indicate that you intend to use the connection for output using the setDoOutput method:
URL gather = new URL("http://www.foo.com/cgi-bin/gather.cgi");
URLConnection c = gather.openConnection();
c.setDoOutput(true); Once you finish the preparation, you can get the output stream for the connection, write your data to it, and you're done:
DataOutputStream out = new DataOutputStream(c.getOutputStream());
out.writeBytes("name=Bloggs%2C+Joe+David&favoritecolor=blue");
out.close();
//MY COMMENT
//This part can be improved using the URLEncoder
//******************************************************You might be wondering why the data in the example looks so ugly. That's a good question, and the answer has to do with the limitation mentioned previously: Using URL objects for output is only supported for the HTTP protocol. To be more accurate, version 1.0 of the Java library really only supports output-mode URL objects for posting forms data using HTTP.
For mostly historical reasons, HTTP forms data is returned to the server in an encoded format, where spaces are changed to plus signs (+), line delimiters to ampersands (&), and various other "special" characters are changed to three-letter escape sequences. The original data for the previous example, before encoding, was the following:
name=Bloggs, Joe David
favoritecolor=blue If you know enough about HTTP that you are curious about the details of what actually gets sent to the HTTP server, here's a transcript of what might be sent to www.foo.com if the example code listed previously were compiled into an application and executed:
POST /cgi-bin/gather.cgi HTTP/1.0
User-Agent: Java1.0
Referer: http://www.foo.com/cgi-bin/gather.cgi
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Content-type: application/x-www-form-urlencoded
Content-length: 43name=Bloggs%2C+Joe+David&favoritecolor=blue
Java takes care of building and sending all those protocol headers for you, including the Content-length header, which it calculates automatically. The reason you currently can send only forms data is that the Java library assumes that's all you will want to send. When you use an HTTP URL object for output, the Java library always labels the data you send as encoded form data.
Once you send the forms data, how do you read the resulting output from the server? The URLConnection class is designed so that you can use an instance for both output and input. It defaults to input-only, and if you turn on output mode without explicitly setting input mode as well, input mode is turned off. If you do both explicitly, however, you can both read and write using a URLConnection:
c.setDoOutput(true);
c.setDoInput(true); The only unfortunate thing is that, although URLConnection was designed to make such things possible, version 1.0 of the Java library doesn't support them properly. As of this writing, a bug in the library prevents you from using a single HTTP URLConnection for both input and output.
//MY COMMENTS
When you doing URL encoding
you should not encode it as one string becouse then it will encode the '=' signes and '&' signes also
you should encode all the field names and values seperatly and then join them using '&'s and '='s
Ex:-
public static void addField(StringBuffer sb,String name, String value){
   if (sb.length()>0){
      sb.append("&");
   sb.append(URLEncoder.encode(name,"UTF-8"));
   sb.append("=");
   sb.append(URLEncoder.encode(value,"UTF-8"));
}