How to avoid sending some or all message headers?

When I send a message to a Camel endpoint such as the Mail component, then the mail include some message headers I do not want. How can I avoid this?

Use removeHeaders in the route

This is a gotcha more people encounter. However it’s very easy to solve. To remove all headers use a wildcard expression:

from(...).removeHeaders("*").to("smtp://....")

Similarly to remove all headers except some of your own (myheader1 and myheader2) use a wildcard with a vararg:

from(...).removeHeaders("*", "myheader1", "myheader2").to("smtp://....")

To do (a similar thing) in XML DSL you simply do:

<route>
  <from uri="..."/>
  <removeHeaders pattern="*" excludePattern="header1|header2"/>
  <to uri="smtp://..."/>
</route>

At present, the excludePattern only supports one header name (which can be include wild cards or regular expressions). We tackle this limitation with CAMEL-6445.

Again to remove only Camel headers but no other transport headers:

from(...).removeHeaders("Camel*").to("smtp://....")

To do this in XML DSL you simply do:

<route>
  <from uri="..."/>
  <removeHeaders pattern="Camel*"/>
  <to uri="smtp://..."/>
</route>

There is also a removeHeader in the DSL to remove a single header. But it does not support patterns, so you can only remove a single header by its name.

Use HeaderFilterStrategy

An alternative is that some of the Camel Components supports configuring a custom header filter strategy. This allows you to implement the org.apache.camel.spi.HeaderFilterStrategy interface, where one can filter unwanted headers from the communication while not removing them from the Exchange. Though it’s often easier to use the removeHeaders in the Camel route as shown above.

Camel core offers a default filter strategy implementation, the DefaultHeaderFilterStrategy class, to which one can provide a regular expression pattern or a set of header names to be filtered out.

<bean class="org.apache.camel.impl.DefaultHeaderFilterStrategy" id="myFilter">
    <property name="outFilter">
        <set>
            <value>unwantedHeaderName</value>
        </set>
    </property>
</bean>
...
<setHeader name="allowedHeaderName"><constant>some metadata</constant></setHeader>
<setHeader name="unwantedHeaderName"><constant>some private data</constant></setHeader>
<to id="publish" uri="activemq:queue:destinationName?headerFilterStrategy=#myFilter"/>
<log message="${header.unwantedHeaderName}"/>

The destination queue would receive a JMS message with the allowedHeaderName as JMS property. If the queue messages are consumed by a Camel route, then the exchange will have the allowedHeaderName as a header. The log would print "some private data" since the header has only been filtered out from the producer endpoint, but not removed from the Exchange.

Selecting the accepted headers

The more steps a route has, more headers tend to be present in the exchange. When the number of headers is large, undetermined, or one can’t know in advance which headers must be filtered out, it is desirable not to deliver by default the headers to the destination endpoint.

In this case, one can filter out everything and selectively send only certain headers to the destination endpoint. The DefaultHeaderFilterStrategy behavior can be reversed so only certain headers are accepted through the filterOnMatch property.

<bean class="org.apache.camel.impl.DefaultHeaderFilterStrategy" id="myFilter">
    <property name="filterOnMatch" value="false" />
    ...
</bean>
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