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context.getprocessengineconfiguration() is null in evaluating expression

I have a helper method to evaluate expressions in an execution:

public Object evaluateExpression(DelegateExecution execution, String expr) {
   Expression expression = expressionManager.createExpression(expr);
   return expression.getValue(execution);
}
‍‍‍‍‍‍

but in calling this method, the expression.getValue() method throws NullPointerException (only in evaluating expressions by this method):

java.lang.NullPointerException at org.activiti.engine.impl.el.JuelExpression.getValue(JuelExpression.java:45)
‍‍‍

It shows that Context.getProcessEngineConfiguration() is null:

public Object getValue(VariableScope variableScope) {
    ELContext elContext = Context.getProcessEngineConfiguration().getExpressionManager().getElContext(variableScope);
    try {
      ExpressionGetInvocation invocation = new ExpressionGetInvocation(valueExpression, elContext);
      Context.getProcessEngineConfiguration()
        .getDelegateInterceptor()
        .handleInvocation(invocation);
      return invocation.getInvocationResult();      
    } catch (PropertyNotFoundException pnfe) {
      throw new ActivitiException("Unknown property used in expression: " + expressionText, pnfe);
    } catch (MethodNotFoundException mnfe) {
      throw new ActivitiException("Unknown method used in expression: " + expressionText, mnfe);
    } catch(ELException ele) {
      throw new ActivitiException("Error while evaluating expression: " + expressionText, ele);
    } catch (Exception e) {
      throw new ActivitiException("Error while evaluating expression: " + expressionText, e);
    }
  }
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

I'm not sure what is wrong! I'm using version 5.17.0.

Thanks in advance for any help you are able to provide.

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Comments

In addition, the expressionManager is injected with Spring. but if i use:
<java>
ExpressionManager expressionManager = Context.getProcessEngineConfiguration() .getExpressionManager();
</java>
the Context.getProcessEngineConfiguration() is null and it throws NullPointerException.

jbarrez

When are you executing this? The nullpointer should not happen when you call that code during an API call, and a valid CommandContext is created.

No api call is involved and no Command Context is created; because in my use-case, i need to evaluate some expressions manually. This issue is resolved by creating a custom command:

<java>
public class EvauluateExpressionCmd implements Command<Object>, Serializable {

private static final long serialVersionUID = 1L;

private Expression expression;
private VariableScope variableScope;

public EvauluateExpressionCmd(Expression expression, VariableScope variableScope) {
this.expression = expression;
this.variableScope = variableScope;
}

@Override
public Object execute(CommandContext commandContext) {
return expression.getValue(variableScope);
}
}
</java>
And execute it with ManagementService:
<java>
public Object getValue(String expr, DelegateExecution execution) {
Expression expression = expressionManager.createExpression(getEvaluableExpression(expr));
EvauluateExpressionCmd command = new EvauluateExpressionCmd(expression, execution);
return managementService.executeCommand(command);
}
</java>

But i can't figure out, when exactly we need to create custom commands??

trademak

When you need to run logic against an Activiti entity like the ExecutionEntity you always need a custom command, because it will need to be able to lookup Context values and be able to run a query against the Activiti entities.

Best regards,