The wItem parameter that you have in the handlers is a reference to the curren Work Item and not to the previous one.
What you have to do is to return a Map<String,Object> in WorkItemA (just like you are doing), then map the results of that Work Item as process variables, and then map those variables (just the one you will need) as input parameters of WorkItemB. In WorkItemB you can get those values using wItem.getParameter(...).
My question is similar. In my executeWorkItem, I have
Map<String,Object> results = new HashMap<String,Object>();
results.put("Start_Date", "1999 01 01");
results.put("End_Date", "2000 01 01");
Chapter 14 of the User Guide says:
In Eclipse, there is a "Result Mapping" attribute associated with the service task. Do I create an association between the results variable and the process variable by using the "Result Mapping" attribute? The association seems to go in backwards. In other words, the Parameter (work item) and Variable (process) only go in one way, so I can't put the work item result into the process variable. I can only put the process variable into a work item result, which is the opposite of what I need to do. What am I doing wrong? Thanks.