Retreive Task from act_ru_variable

Dear Camunda Users

I have the following, very simple process diagram:
grafik

Within the task “Do Something 1” I defined two input/output parameters

The Service Task uses the following Java Class:
package ch.hslu.ba.responsibilityWithVariables;

public class responsibilityWithVariables implements JavaDelegate {
@Override
public void execute(DelegateExecution delegateExecution) throws Exception {

    ProcessEngine processEngine = ProcessEngines.getDefaultProcessEngine();
    RepositoryService repositoryService = processEngine.getRepositoryService();
    RuntimeService runtimeService = processEngine.getRuntimeService();
    BpmnModelInstance modelInstance = delegateExecution.getBpmnModelInstance();

    // Database configuration
    String user = "sa";
    String password = "sa";
    String url = "jdbc:h2:./camunda-db";
    String jdbcDriver = "org.h2.Driver";
    String sqlStatement = "SELECT * FROM ACT_RU_TASK";
    String sqlStatement1 = "SELECT * FROM ACT_RU_VARIABLE";

    try {
        Class.forName(jdbcDriver);

        Connection connection = DriverManager.getConnection(url, user, password);

        Statement statement1 = connection.createStatement();
        Statement statement2 = connection.createStatement();

        ResultSet resultSet1 = statement1.executeQuery(sqlStatement);
        ResultSet resultSet2 = statement2.executeQuery(sqlStatement1);

        while (resultSet1.next()){
            String name = resultSet1.getString("NAME_");
            String prozessInstanzId = resultSet1.getString("PROC_INST_ID_");
            String taskId = resultSet1.getString("EXECUTION_ID_");
            System.out.println("Aufgabenname: " + name);
            System.out.println("Prozessinstanz ID: " + prozessInstanzId);
            System.out.println("Aufgaben ID: " + taskId);
            System.out.println();

        }

        while (resultSet2.next()){
            String name = resultSet2.getString("NAME_");
            String id = resultSet2.getString("PROC_INST_ID_");
            String type = resultSet2.getString("TYPE_");
            String text = resultSet2.getString("TEXT_");
            System.out.println("Variablenname: " + name);
            System.out.println("Prozessinstanz ID:" + id);
            System.out.println("Datentyp: " + type);
            System.out.println("Wert: " + text);
            System.out.println();

        }
        statement1.close();
        statement2.close();
        connection.close();

    } catch (Exception e){
        e.printStackTrace();
    }
}

}

As a Result I Receive all active tasks and the variables.

I woud like to merge the variables to the tasks but as soon as I try to retreive the TASK_ID from the table act_ru_variables, there are only NULL values available. Is there a Solution to this problem?

Thanks a lot!