I define several process variable in process
I found that if variable type is String value, the persistance in table jbpm_variableinstance is OK , I can read their value from the way as below codes.
if variable type is other types, such as Boolean/List, the result is always null.

Boolean type is in table jbpm_variableinstance is S type, same as String type variable, having T/F value.
While List type is B type in table, having null value.

Whats the problem? And how to save this kind of process varible.
Thanks a lot.

ProcessInstance pi = jbpmContext.getProcessInstance(new Long("xxxx"));
String originator = (String)pi.getContextInstance().getVariable("originator");
BooleanisDelegated = (Boolean)pi.getContextInstance().getVariable("isDelegated");
List delegators = (List)pi.getContextInstance().getVariable("delegators");