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Until Successful Scope

The until-successful scope processes messages through the processors within its scope until the operation succeeds. Until-successful’s processing occurs asynchronously from the main flow. After passing a message into the until-successful scope, the main flow immediately regains control of the thread.

Until-successful repeatedly retries to process a message which is attempting to complete an activity such as:

  • dispatching to outbound endpoints, for example, when calling a remote web service that may have availability issues

  • executing a component method, for example, when executing on a Spring bean that may depend on unreliable resources

  • executing a subflow

<until-successful objectStore-ref="objectStore" maxRetries="5" secondsBetweenRetries="60" doc:name="Until Successful">
    <http:outbound-endpoint exchange-pattern="request-response" host="localhost" port="8081" method="POST" doc:name="HTTP"/>
</until-successful>

Success and Failure

As this scope continues to processes messages until successful, it is important to understand the definition of successful in context of Mule message processing.

FAILURE

A message processor within the until-successful scope throws an exception.

SUCCESS

A message processor within the until-successful scope does not return a message (i.e. is a one-way endpoint)

conditional

Where you have configured a failure expression (see below), Mule evaluates the return message against the expression to dynamically determine if the action has failed or succeeded.

FAILURE

A message processor within the until-successful scope contains an exception payload.

SUCCESS

A message processor within the until-successful scope does not contain an exception payload.

Configuring failureExpression

The following illustrates how to configure the failureExpression on an until-successful scope:

<until-successful objectStore-ref="objectStore"
                  failureExpression="#[header:INBOUND:http.status != 202]"
                  maxRetries="6"
                  secondsBetweenRetries="600">
    <http:outbound-endpoint address="http://acme.com/api/flakey"
                            exchange-pattern="request-response"
                            method="POST" />
</until-successful>

Configuring a Dead Letter Queue

To manage messages which have exhausted the number of maxRetries within the until-successful scope, you can define a DLQ (dead letter queue) endpoint to which Mule can send such messages. Refer to the code sample below for an example configuration.

<until-successful objectStore-ref="objectStore"
                  deadLetterQueue-ref="dlqChannel"
                  maxRetries="3"
                  secondsBetweenRetries="10">
...
</until-successful>

Until-Successful and Object Store

This message processor needs an ListableObjectStore instance in order to persist messages pending (re)processing. There are several implementations available in Mule, including the following:

  • DefaultInMemoryObjectStore: default in-memory store

  • DefaultPersistentObjectStore: default persistent store

  • FileObjectStore: file-based store

  • QueuePersistenceObjectStore: global queue store

  • SimpleMemoryObjectStore: in-memory store

See Mule Object Stores for further information about object stores in Mule. The following code sample illustrates how to configure an in-memory store:

<spring:bean id="objectStore" class="org.mule.util.store.SimpleMemoryObjectStore" />

See Also