flowable/flowable-engine · error · ELException

error.value.set.rvalue

Error message

error.value.set.rvalue

What it means

AstRightValue represents non-assignable (rvalue) expression nodes in the embedded JUEL/odysseus EL parser. Its setValue is always final and always throws ELException because an rvalue can never be an assignment target. Flowable throws it when a script or expression tries to write a value into something that is not a variable.

Solutions

1. Write to an actual variable instead: use delegateTask.setVariable / runtimeService.setVariable, or a left-value expression like a bare variable or property path.
2. If the target is a bean property, expose a setter and use the property path '${myBean.text}' as the lvalue rather than a method call or computed expression.
3. Verify the parsed expression root: check isLeftValue() on the node or use AST introspection before calling setValue.

Example fix

// before
expression.setValue(bindings, context, "newValue"); // ${order.total} -> ELException
// after
runtimeService.setVariable(execution.getId(), "orderTotal", "newValue");

if (valueExpression.isReadOnly(context)) { throw new IllegalArgumentException("Expression is not assignable: " + valueExpression.getExpressionString()); }

boolean isAssignable(ValueExpression ve, ELContext ctx) { return ve != null && !ve.isReadOnly(ctx); }

try { ve.setValue(ctx, value); } catch (ELException e) { log.error("Cannot assign to rvalue expression {}: {}", ve.getExpressionString(), e.getMessage()); }

When it happens

Trigger: Calling ELContext/ExpressionNode setValue (or a ValueExpression.setValue) whose AST root is a right-value node, e.g. setting into a method result, literal, or operator expression like '${a + b}' or '${myBean.getText()}' inside an expression assignment (e.g. flowable:expression used as write target, or delegating expression code calling setValue on the ValueExpression).

Common situations: BPMN process models where an expression is used on the left side of an assignment; misreading `${...}` expressions as settable properties; trying to mutate read-only bean properties via expression in a task listener or service task field injection.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Cannot set value of '', it's readonly!
• error.value.set.rvalue
• error.method.invalid
• error.value.set.rvalue
• Error while evaluating expression

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/2f7b055c98d5a035. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-engine-common/src/main/java/org/flowable/common/engine/impl/de/odysseus/el/tree/impl/ast/AstRightValue.java:58

	@Override
	public final Class<?> getType(Bindings bindings, ELContext context) {
		return null;
	}

	/**
	 * non-lvalues are always readonly, so answer <code>true</code>
	 */
	@Override
	public final boolean isReadOnly(Bindings bindings, ELContext context) {
		return true;
	}

	/**
	 * non-lvalues are always readonly, so throw an exception
	 */
	@Override
	public final void setValue(Bindings bindings, ELContext context, Object value) {
		throw new ELException(LocalMessages.get("error.value.set.rvalue", getStructuralId(bindings)));
	}

	@Override
	public final MethodInfo getMethodInfo(Bindings bindings, ELContext context, Class<?> returnType, Class<?>[] paramTypes) {
		return null;
	}

	@Override
	public final Object invoke(Bindings bindings, ELContext context, Class<?> returnType, Class<?>[] paramTypes, Object[] paramValues) {
		throw new ELException(LocalMessages.get("error.method.invalid", getStructuralId(bindings)));
	}

	@Override
	public final boolean isLeftValue() {
		return false;
	}
	
	@Override

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