---
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title: Migrating Exception Strategies to Mule Error Handlers
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content_type: documentation
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---
---
product: Mule Runtime
version: 4.3
---

# Migrating Exception Strategies to Mule Error Handlers

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

The following examples will guide you through the migration of the different exception strategies of
Mule 3 considering the new error handling components in Mule 4.

> [!IMPORTANT] The examples do not cover the migration of expressions used within the `when`
> attribute. See [Migrating MEL to DataWeave](https://docs.mulesoft.com/mule-runtime/4.3/migration-mel) for guidance with migrating
> expressions, and see [Working With Throwables](https://docs.mulesoft.com/java-module/latest/java-throwable) to use the
> Java module to analyze exceptions.

## Catch Exception Strategy

A Catch Exception Strategy is equivalent to an Error Handler with a single `on-error-continue`
component that accepts all errors, which is the default configuration:

Mule 3 Example

```xml
<flow name="catch">
  <!-- flow logic -->
  <catch-exception-strategy>
    <!-- error handling logic -->
  </catch-exception-strategy>
</flow>
```

Mule 4 Example

```xml
<flow name="catch">
  <!-- flow logic -->
  <error-handler>
    <on-error-continue>
      <!-- error handling logic -->
    </on-error-continue>
  </error-handler>
</flow>
```

## Rollback Exception Strategy

A simple (no redelivery) rollback exception strategy is equivalent to an error handler with a single
`on-error-propagate` component that accepts all errors, which is the default configuration:

Mule 3 Example

```xml
<flow name="rollback">
  <!-- flow logic -->
  <rollback-exception-strategy>
    <!-- error handling logic -->
  </rollback-exception-strategy>
</flow>
```

Mule 4 Example

```xml
<flow name="rollback">
  <!-- flow logic -->
  <error-handler>
    <on-error-propagate>
      <!-- error handling logic -->
    </on-error-propagate>
  </error-handler>
</flow>
```

## With Redelivery

- `idempotent-redelivery-policy` gets renamed to `redelivery-policy`

- `org.mule.runtime.core.api.exception.MessageRedeliveredException` has been replaced by the
  `REDELIVERY_EXHAUSTED` error type.

- `dead-letter-queue` is removed. Any outbound operation performed to publish to a DLQ must be done
  as part of the handling of the `REDELIVERY_EXHAUSTED` error, for example:

  Mule 3 Example

  ```xml
  <idempotent-redelivery-policy maxRedeliveryCount="${maxRedeliveryAttempts}">
      <dead-letter-queue>
          <http:request ... />
      </dead-letter-queue>
  </idempotent-redelivery-policy>
  ```

  Mule 4 Example

  ```xml
  <redelivery-policy maxRedeliveryCount="${maxRedeliveryAttempts}"/>

  ...

  <error-handler>
      <on-error-propagate type="REDELIVERY_EXHAUSTED">
          <http:request ... />
      </on-error-propagate>
  </error-handler>
  ```

- `maxRedelivery` in `rollback-exception-strategy` is not supported anymore. A `<redelivery-policy>`
  element with `maxRedelivery` must be created inside the `message-source`.

## Choice Exception Strategy

A Choice exception strategy with inner catch/rollback exception strategies is equivalent to an error
handler with on-error components continue/propagate according to the exception strategy kind, as
explained above:

Mule 3 Example

```xml
<flow name="choice">
  <!-- flow logic -->
  <choice-exception-strategy>
      <rollback-exception-strategy when="#[some_expression_here]">
          <!-- error handling logic -->
      </rollback-exception-strategy>
      <catch-exception-strategy/>
    </choice-exception-strategy>
</flow>
```

Mule 4 Example

```xml
<flow name="choice">
  <!-- flow logic -->
  <error-handler>
    <on-error-propagate when="#[some_expression_here]">
      <!-- error handling logic -->
    </on-error-propagate>
    <on-error-continue/>
  </error-handler>
</flow>
```

## Reference Exception Strategy

Considering that the referenced exception strategy has already been migrated according to the above
guidelines, migrating the actual reference is just adding a reference `error-handler`.

Mule 3 Example

```xml
<flow name="reference">
  <!-- flow logic -->
  <exception-strategy ref="referencedHandler"/>
</flow>
```

Mule 4 Example

```xml
<flow name="reference">
  <!-- flow logic -->
  <error-handler ref="referencedHandler"/>
</flow>
```

## See Also

[Error Handlers](https://docs.mulesoft.com/mule-runtime/4.3/error-handling)

[Blog: A Look into Error Handling in Mule 4 Beta](https://blogs.mulesoft.com/dev-guides/how-to-tutorials/how-to-error-handling-mule-4-beta/)