I used a back-end bean like this.

public String strUser = "user";
 public String getStrUser() {
 return strUser;
 }
 public void setStrUser(String strUser) {
 this.strUser = strUser;
 }

I used a Expression Language to this Processdefinition.xml as follows.

<process-definition xmlns="urn:jbpm.org:jpdl-3.2" name="loanProcess">
 <start-state name="start-state1">
 <task name="StartTask"></task>
 <transition to="task-node1"></transition>
 </start-state>
 <event type="task-create">
 <action class="com.sample.action.AssignUsr"></action>
 </event>
 <task-node name="task-node1">
 <task name="task1"> <assignment expression="user(#{obj[strUser]})"></assignment>
 </task>
 <transition to="End"></transition>
 </task-node>
 <end-state name="End"></end-state>

I set the back-end bean object to contextInstance in the following way in the JUnit

processInstance.getContextInstance().setVariable("obj", obj);

Got a stack trace like this

14:28:27,401 [main] DEBUG ExpressionAssignmentHandler : resolving first term 'user(#{obj[strUser]})'
Exception in thread "main" org.jbpm.graph.def.DelegationException: couldn't resolve assignment expression 'user(#{obj[strUser]})'
 at org.jbpm.taskmgmt.exe.TaskMgmtInstance.performAssignment(TaskMgmtInstance.java:216)
 at org.jbpm.taskmgmt.exe.TaskInstance.assign(TaskInstance.java:204)
 at org.jbpm.taskmgmt.exe.TaskMgmtInstance.createTaskInstance(TaskMgmtInstance.java:154)
 at org.jbpm.graph.node.TaskNode.execute(TaskNode.java:168)
 at org.jbpm.graph.def.Node.enter(Node.java:319)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.hibernate.proxy.pojo.cglib.CGLIBLazyInitializer.invoke(CGLIBLazyInitializer.java:157)
 at org.jbpm.graph.def.Node$$EnhancerByCGLIB$$89d40aac.enter(<generated>)
 at org.jbpm.graph.def.Transition.take(Transition.java:151)
 at org.jbpm.graph.def.Node.leave(Node.java:394)
 at org.jbpm.graph.node.StartState.leave(StartState.java:70)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.hibernate.proxy.pojo.cglib.CGLIBLazyInitializer.invoke(CGLIBLazyInitializer.java:157)
 at org.jbpm.graph.def.Node$$EnhancerByCGLIB$$89d40aac.leave(<generated>)
 at org.jbpm.graph.exe.Token.signal(Token.java:195)
 at org.jbpm.graph.exe.Token.signal(Token.java:140)
 at org.jbpm.graph.exe.ProcessInstance.signal(ProcessInstance.java:271)
 at com.cts.client.TestClient.main(TestClient.java:30)
Caused by: org.jbpm.identity.assignment.ExpressionAssignmentException: couldn't resolve assignment expression 'user(#{obj[strUser]})'
 at org.jbpm.identity.assignment.ExpressionAssignmentHandler.assign(ExpressionAssignmentHandler.java:97)
 at org.jbpm.taskmgmt.exe.TaskMgmtInstance.performAssignmentDelegation(TaskMgmtInstance.java:228)
 at org.jbpm.taskmgmt.exe.TaskMgmtInstance.performAssignment(TaskMgmtInstance.java:201)
 ... 23 more
Caused by: org.jbpm.identity.assignment.ExpressionAssignmentException: user '#{obj[strUser]}' couldn't be fetched from the user db
 at org.jbpm.identity.assignment.ExpressionAssignmentHandler.getUserByName(ExpressionAssignmentHandler.java:209)
 at org.jbpm.identity.assignment.ExpressionAssignmentHandler.resolveFirstTerm(ExpressionAssignmentHandler.java:147)
 at org.jbpm.identity.assignment.ExpressionAssignmentHandler.assign(ExpressionAssignmentHandler.java:75)
 ... 25 more

Am i doing something wrong!!!!
Is there any way to do the following i.e. to access certain variable from a back-end bean using Expression...

NB:- My jpbm is not integrated with Seam and I used to assign the task to that user whichever I wish to set in my back-end bean
Thanks
Soumya