Filter

The Message Filter from the EIP patterns allows you to filter messages.

How can a component avoid receiving uninteresting messages?

image

Use a special kind of Message Router, a Message Filter, to eliminate undesired messages from a channel based on a set of criteria.

The message filter implemented in Camel is similar to if (predicate) { block } in Java. The filter will include the message if the predicate evaluated to true .

EIP options

The Filter eip supports the following options which are listed below.

Name Description Default Type

note

The note for this node.

String

description

The description for this node.

String

disabled

Whether to disable this EIP from the route during build time. Once an EIP has been disabled then it cannot be enabled later at runtime.

false

Boolean

expression

Required The predicate expression to evaluate. Messages where the predicate returns false are filtered out and not routed further.

ExpressionDefinition

statusPropertyName

Name of an exchange property to store whether the filter predicate matched or not. The value is stored as a boolean.

String

outputs

Required

List

Exchange properties

The Filter eip has no exchange properties.

Example

The Camel Simple language is great to use with the Filter EIP when routing is based on the content of the message, such as checking message headers.

  • Java

  • XML

  • YAML 

from("direct:a")
    .filter(simple("${header.foo} == 'bar'"))
        .to("direct:bar")
    .end()
    .to("direct:b")
<route>
    <from uri="direct:a"/>
    <filter>
        <simple>${header.foo} == 'bar'</simple>
        <to uri="direct:bar"/>
    </filter>
    <to uri="direct:b"/>
</route>
- route:
    from:
      uri: direct:a
      steps:
        - filter:
            expression:
              simple:
                expression: "${header.foo} == 'bar'"
            steps:
              - to:
                  uri: direct:bar
        - to:
            uri: direct:b

You can use many languages as the predicate, such as XPath :

  • Java

  • XML

  • YAML 

from("direct:start").
        filter().xpath("/person[@name='James']").
        to("mock:result");
<route>
    <from uri="direct:start"/>
    <filter>
        <xpath>/person[@name='James']</xpath>
        <to uri="mock:result"/>
    </filter>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - filter:
            expression:
              xpath:
                expression: "/person[@name='James']"
            steps:
              - to:
                  uri: mock:result

Here is another example of calling a method on a bean to define the filter behavior:

  • Java

  • XML

  • YAML 

from("direct:start")
    .filter().method(MyBean.class, "isGoldCustomer")
      .to("mock:gold")
    .end()
    .to("mock:all");
<route>
    <from uri="direct:start"/>
    <filter>
        <method beanType="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
    </filter>
    <to uri="mock:all"/>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - filter:
            expression:
              method:
                method: isGoldCustomer
                beanType: com.foo.MyBean
            steps:
              - to:
                  uri: mock:gold
        - to:
            uri: mock:all

The bean can have a method that returns a boolean as the predicate: 

public static class MyBean {

    public boolean isGoldCustomer(@Header("level") String level) {
        return level.equals("gold");
    }

}

Filtering with status property

To know whether an Exchange was filtered or not, then you can choose to specify a name of a property to store on the exchange with the result (boolean), using statusPropertyName as shown below:

  • Java

  • XML

  • YAML 

from("direct:start")
    .filter().method(MyBean.class, "isGoldCustomer").statusPropertyName("gold")
      .to("mock:gold")
    .end()
    .to("mock:all");
<route>
    <from uri="direct:start"/>
    <filter statusPropertyName="gold">
        <method beanType="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
    </filter>
    <to uri="mock:all"/>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - filter:
            statusPropertyName: gold
            expression:
              method:
                method: isGoldCustomer
                beanType: com.foo.MyBean
            steps:
              - to:
                  uri: mock:gold
        - to:
            uri: mock:all

In the example above then Camel will store an exchange property with key gold with the result of the filtering, whether it was true or false .

Filtering and stopping

When using the Message Filter EIP, then it only applies to its children.

For example, in the previous example then for a message that is a gold customer will be routed to both mock:gold and mock:all (predicate is true). However, for a non-gold message (predicate is false) then the message will not be routed in the filter block, but will be routed to mock:all.

Sometimes you may want to stop routing for messages that were filtered. To do this, you can use the Stop EIP as shown:

  • Java

  • XML

  • YAML 

from("direct:start")
    .filter().method(MyBean.class, "isGoldCustomer").statusPropertyName("gold")
      .to("mock:gold")
      .stop()
    .end()
    .to("mock:all");
<route>
    <from uri="direct:start"/>
    <filter>
        <method beanType="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
        <stop/>
    </filter>
    <to uri="mock:all"/>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - filter:
            expression:
              method:
                method: isGoldCustomer
                beanType: com.foo.MyBean
            steps:
              - to:
                  uri: mock:gold
              - stop: {}
        - to:
            uri: mock:all