Filter

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

How can a component avoid receiving uninteresting messages?

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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 1 options, which are listed below.

Name Description Default Type

expression

Required Expression to determine if the message should be filtered or not. If the expression returns an empty value or false then the message is filtered (dropped), otherwise the message is continued being routed.

ExpressionDefinition

statusPropertyName

Name of exchange property to use for storing the status of the filtering. Setting this allows to know if the filter predicate evaluated as true or false.

String

description

Sets the description of this node.

DescriptionDefinition

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.

from("direct:a")
    .filter(simple("${header.foo} == 'bar'"))
        .to("direct:bar")
    .end()
    .to("direct:b")

And in XML:

<route>
    <from uri="direct:a"/>
    <filter>
        <simple>${header.foo} == 'bar'</simple>
        <to uri="direct:bar"/>
    </filter>
    <to uri="direct:b"/>
</route>

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

from("direct:start").
        filter().xpath("/person[@name='James']").
        to("mock:result");

And in XML:

<route>
    <from uri="direct:start"/>
    <filter>
        <xpath>/person[@name='James']</xpath>
        <to uri="mock:result"/>
    </filter>
</route>

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

from("direct:start")
    .filter().method(MyBean.class, "isGoldCustomer")
      .to("mock:gold")
    .end()
    .to("mock:all");
}

And then 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");
    }

}

And in XML we can call the bean in `<method> where we can specify the FQN classname of the bean as shown:

<route>
    <from uri="direct:start"/>
    <filter>
        <method type="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
    </filter>
    <to uri="mock:all"/>
</route>

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:

from("direct:start")
    .filter().method(MyBean.class, "isGoldCustomer").statusPropertyName("gold")
      .to("mock:gold")
    .end()
    .to("mock:all");
}

And in XML:

<route>
    <from uri="direct:start"/>
    <filter statusPropertyName="gold">
        <method type="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
    </filter>
    <to uri="mock:all"/>
</route>

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:

<route>
    <from uri="direct:start"/>
    <filter>
        <method type="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
    </filter>
    <to uri="mock:all"/>
</route>

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 continue routing for messages that was filtered. To do this, you can use the Stop EIP as shown:

<route>
    <from uri="direct:start"/>
    <filter>
        <method type="com.foo.MyBean" method="isGoldCustomer"/>
        <to uri="mock:gold"/>
        <stop/>
    </filter>
    <to uri="mock:all"/>
</route>
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