Simulate user browser behaviour in java - forms

There are two major approaches:

• use a browser library. There you define all actions you want to do.
• parse the browser response manually and fill the forms by on low-level.

Browser library
Advantages:

• very powerful;
• manages well when the output of web server is changed; 

Disadvantages:

• heavy;
• slow

Free Java libraries:

• prowser - no info, please make a comment
• htmlunit - no info, please make a comment

Manual submitting
Advantages:

• very light for simple tasks; 
• no need of additional library and studying its API; 
• faster;

Disadvantages:

• catching form fields in not reliable. If someone wants to lay it, it easily could do it.
• when the output of the parsed page changes, it could break parsing;
• forget about compatibility with javascript this way;

I choose manual submitting because my tasks were quite simple.

A example code:

        HttpURLConnection connection = null;
        try {
            OutputStreamWriter wr = null;
            BufferedReader rd  = null;

            URL serverUrl = new URL( serverAddress );

            log.info( "trying to connect to " + serverUrl.toURI() );
            
            connection = (HttpURLConnection)serverUrl.openConnection();
            connection.setRequestMethod( "POST" );
            connection.setDoOutput( true );
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // needed for sumbitting forms data
            connection.setInstanceFollowRedirects( followRedirects );

        ....

        StringBuilder pageSubmitBody = new StringBuilder();

        pageSubmitBody.append("auth_token=").append( authToken );

        pageSubmitBody.append("&utf8=").append( ala_bala );

        ....

            connection.connect();

            wr = new OutputStreamWriter(connection.getOutputStream());
            wr.write( pageSubmitBody.toString() );
            wr.flush();

etc.