Intermediate Events in jBPM – Complete Guide with Examples

 Intermediate Events in jBPM are BPMN elements that occur between the start and end of a workflow.

They allow you to pause, wait, send signals, catch messages, trigger timers, handle errors, and create real-life, production-ready business workflows.

In jBPM, Intermediate Events work through the BPMN2 engine and behave exactly as defined in the BPMN specification — but with jBPM-specific execution semantics such as Event Nodes, Node Instances, Signals, WorkItem interruptions, boundary events, and process instance correlation.

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⭐ What Are Intermediate Events?

Intermediate Events in jBPM can:

✔ Catch something (wait)
✔ Throw something (send/trigger)

They appear in the process flow, attached to an activity, or placed in the sequence path.

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Types of Intermediate Events in jBPM

Below is the full list — with examples, XML snippets, and usage.

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1️⃣ Timer Intermediate Event (Catch)

Used to delay or schedule actions inside a process.

📌 Examples:

• Wait for 2 days before sending a reminder

• Check SLA expiration

• Daily scheduled checks (cron)

XML Example

<intermediateCatchEvent id="Wait2Days">
  <timerEventDefinition>
    <timeDuration>P2D</timeDuration>
  </timerEventDefinition>
</intermediateCatchEvent>

Business Central

You configure delay using:
Duration, Cycle, or Date (ISO-8601).

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2️⃣ Message Intermediate Catch Event

Used when jBPM must wait for an external system to send a message.

In jBPM, messages are correlated using:

• MessageRef

• CorrelationKey (optional)

📌 Use cases:

• Wait for payment confirmation

• Wait for verification from an external microservice

• Wait for a file to be uploaded

Example

<intermediateCatchEvent id="WaitForMsg">
  <messageEventDefinition messageRef="MsgPaymentDone"/>
</intermediateCatchEvent>

You then trigger it using:

ksession.signalEvent("MsgPaymentDone", payload, processInstanceId);

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3️⃣ Message Intermediate Throw Event

Used to send messages to other processes.

📌 Example

• Trigger a downstream workflow

• Notify another jBPM process instance

• Send asynchronous event to microservices via custom handlers

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4️⃣ Signal Intermediate Events (Throw & Catch)

A signal is a broadcast event.
All active processes listening for the signal will respond.

📌 Examples:

• "PaymentCompleted"

• "DocumentUploaded"

• "FraudDetected"

Catching Signal

<intermediateCatchEvent id="SignalWait">
  <signalEventDefinition signalRef="PaymentCompleted"/>
</intermediateCatchEvent>

Throwing Signal

<intermediateThrowEvent id="SendSignal">
  <signalEventDefinition signalRef="PaymentCompleted"/>
</intermediateThrowEvent>

Triggering from Java

ksession.signalEvent("PaymentCompleted", data);

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5️⃣ Error Intermediate Event (Catch)

Used to capture errors thrown inside a task.

In jBPM, you can attach these to nodes:

• Service Tasks

• Script Tasks

• WorkItemHandlers

📌 Example:
An API call fails → throw error → catch error → move to fallback path.

Process XML

<intermediateCatchEvent id="CatchError">
  <errorEventDefinition errorRef="API_ERROR"/>
</intermediateCatchEvent>

Throwing from Java

throw new WorkItemHandlerException("API_ERROR", "API failed!");

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6️⃣ Escalation Intermediate Events (Throw & Catch)

Escalations are non-fatal alerts.

Use cases:
✔ SLA warning
✔ Supervisor notification
✔ Business exception that should not kill the process

Example Throw

<intermediateThrowEvent id="EscalateSLA">
  <escalationEventDefinition escalationRef="SLA_WARNING"/>
</intermediateThrowEvent>

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7️⃣ Compensation Intermediate Events

Used to roll back previous actions.

📌 Real-world examples:

• Refund a payment

• Reverse stock allocation

• Undo reservation

jBPM compensation works through compensation handlers attached to activities.

XML

<intermediateThrowEvent id="TriggerCompensation">
  <compensateEventDefinition activityRef="BookHotel"/>
</intermediateThrowEvent>

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8️⃣ Conditional Intermediate Event

Triggered when a condition becomes true at runtime.

📌 Example:
If approvalAmount > 50000, trigger a different path.

XML

<intermediateCatchEvent id="CondEvent">
  <conditionalEventDefinition>
    <condition xsi:type="tFormalExpression">
      #{approvalAmount > 50000}
    </condition>
  </conditionalEventDefinition>
</intermediateCatchEvent>

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Comparison Table

Event Type	Catch	Throw	Typical Usage
Timer	✔	✖	Wait for time or schedule
Message	✔	✔	System-to-system communication
Signal	✔	✔	Broadcast to all processes
Error	✔	✖	Exception handling
Escalation	✔	✔	Business warnings
Compensation	✔	✔	Undo/rollback
Conditional	✔	✖	Trigger when condition matches

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Real-World Example: Insurance Claim Process

Scenario Flow:

1. Claim submitted

2. Timer waits for 24 hours pending documents

3. External system sends verification message

4. If mismatch → Error event → move to manual review

5. If SLA at risk → Escalation event

6. If fraud detected → Signal event triggers audit process

7. If claim rejected → Compensation refunds customer

8. Final settlement task executes

This shows how intermediate events support real-world business logic.

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Best Practices for jBPM Intermediate Events

✔ Use message events for microservices communication
✔ Use signal events only when many processes must react
✔ Prefer error events over gateways for exceptions
✔ Use timers for reminders, SLAs, and delay logic
✔ Use conditional events for dynamic state changes
✔ Avoid mixing message, signal, and error handling in a single complex path
✔ Keep compensation actions simple and idempotent

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