Are you sure you should be writing Java? 
The class PostMethod cannot be found. You either need to import the class with an import configuration on the service or use the fully-qualified classname.
In my humble opinion, you are headed down the wrong path in trying to do an HTTP post using Java code within IS. There are two reasons for this statement: 1) IS can perform HTTP posts just fine and provides services to do so–you are reinventing the wheel; 2) you are apparently new to Java as this error is a very, very basic problem. I would advise strongly against continuing down this path.
#webMethods#Integration-Server-and-ESB#Flow-and-Java-services