JAVA to SAP Integration - How to read Idocs and their numbers Delivered to SAP from a J2EE Application?

In the SAP marketplace they offer a Java library for processing IDocs with can be installed on top of JCo (https://websmp106.sap-ag.de/~form/sapnet?_SHORTKEY=01100035870000719346&). Make sure to download the version that works with your JCo Version (should be 3 for newly developed applications). Now follow these steps:

1.) Create a connection using SAP transaction sm59.
2.) Create an IDoc port using SAP transaction we21 (use destination name from step 1)
3.) Create a logical system using SAP transaction bd54, e.g. "MYJAVA"="My Java Programm"
4.) Create a "partner" relationship for your Java program using SAP transaction we20: Use the partner number from step 3 and the port from step 2.
5.) Use Java code similar to this:

JCoIDocServer server = JCoIDoc.getServer("MYSERVER");
server.setIDocHandlerFactory(new MyIDocHandlerFactory());
server.setTIDHandler(new MyTidHandler());

class MyIDocHandler implements JCoIDocHandler {
  public void handleRequest(JCoServerContext context, IDocDocumentList list) {
    IDocDocumentIterator iterator = list.iterator();
    while (iterator.hasNext()) {
      IDocDocument document = iterator.next();
      System.out.println(document.getMessageType());
      System.out.println(document.getIDocNumber());
      System.out.println(document.getSenderPartnerNumber());
      System.out.println(document.getIDocType());
      System.out.println(document.getIDocTypeExtension());
   
      try {
        IDocSegment root = document.getRootSegment();
        IDocSegment child;
        // one child node
        child = root.getFirstChild("TYPE1");
        System.out.println(child.getString("NAME"));
        // multiple child nodes
        IDocSegmentIterator segmentIterator = root.getChildrenIterator("TYPE2");
        while (segmentIterator.hasNext()) {
          child = segmentIterator.next();
          System.out.println(child.getString("NAME"));
        }
      } catch (IDocFieldNotFoundException exception) {
        // handle
      }
    }
  }
}

class MyIDocHandlerFactory implements JCoIDocHandlerFactory {
  private JCoIDocHandler handler = new MyIDocHandler();
  public JCoIDocHandler getIDocHandler(JCoIDocServerContext serverCtx) {
    return handler;
  }
}

static class MyTidHandler implements JCoServerTIDHandler {
  public boolean checkTID(JCoServerContext context, String tid) {
    // handle
    return true;
  }

  public void confirmTID(JCoServerContext context, String tid) {
    // handle
  }

  public void commit(JCoServerContext context, String tid)
  {
    // handle
  }

  public void rollback(JCoServerContext context, String tid) {
    // handle
  }
}


class MyIDocHandlerFactory implements JCoIDocHandlerFactory {
  private JCoIDocHandler handler = new MyIDocHandler();
  public JCoIDocHandler getIDocHandler(JCoIDocServerContext serverCtx) {
    return handler;
  }
}

static class MyTidHandler implements JCoServerTIDHandler {
  public boolean checkTID(JCoServerContext context, String tid) {
    // handle
    return true;
  }

  public void confirmTID(JCoServerContext context, String tid) {
    // handle
  }

  public void commit(JCoServerContext context, String tid)
  {
    // handle
  }

  public void rollback(JCoServerContext context, String tid) {
    // handle
  }
}