File Expression Language

The File Expression Language is an extension to the Simple language, adding file related capabilities. These capabilities are related to common use cases working with file path and names. The goal is to allow expressions to be used with the File and FTP components for setting dynamic file patterns for both consumer and producer.

Syntax

This language is an extension to the Simple language so the Simple syntax applies also. So the table below only lists the additional. By contrast to the Simple language, the File Language also supports the use of Constant expressions to enter a fixed filename, for example.

All the file tokens use the same expression name as the method on the java.io.File object. For example: file:absolute refers to the java.io.File.getAbsolute() method.

File Token Example

Relative Paths

We have a java.io.File handle for the file hello.txt in the following relative directory: .\filelanguage\test. And we configure our endpoint to use this starting directory .\filelanguage.

The file tokens returned are:

Absolute Paths

We have a java.io.File handle for the file hello.txt in the following absolute directory: \workspace\camel\camel-core\target\filelanguage\test. And we configure out endpoint to use the absolute starting directory: \workspace\camel\camel-core\target\filelanguage.

The file tokens return are:

Examples

You can enter a fixed Constant expression such as myfile.txt:

fileName="myfile.txt"

Lets assume we use the file consumer to read files and want to move the read files to backup folder with the current date as a sub folder. This can be achieved using an expression like:

fileName="backup/${date:now:yyyyMMdd}/${file:name.noext}.bak"

relative folder names are also supported so suppose the backup folder should be a sibling folder then you can append .. as:

fileName="../backup/${date:now:yyyyMMdd}/${file:name.noext}.bak"

As this is an extension to the Simple language we have access to all the goodies from this language also, so in this use case we want to use the in.header.type as a parameter in the dynamic expression:

fileName="../backup/${date:now:yyyyMMdd}/type-${in.header.type}/backup-of-${file:name.noext}.bak"

If you have a custom Date you want to use in the expression then Camel supports retrieving dates from the message header.

fileName="orders/order-${in.header.customerId}-${date:in.header.orderDate:yyyyMMdd}.xml"

And finally we can also use a bean expression to invoke a POJO class that generates some String output (or convertible to String) to be used:

fileName="uniquefile-${bean:myguidgenerator.generateid}.txt"

And of course all this can be combined in one expression where you can use the File Language, Simple and the Bean language in one combined expression. This is pretty powerful for those common file path patterns.

Using Spring's PropertyPlaceholderConfigurer with the File Component

In Camel you can use the File Language directly from the Simple language which makes a Content Based Router easier to do in Spring XML, where we can route based on file extensions as shown below:

<from uri="file://input/orders"/>
  <choice>
    <when>
      <simple>${file:ext} == 'txt'</simple>
      <to uri="bean:orderService?method=handleTextFiles"/>
    </when>
    <when>
      <simple>${file:ext} == 'xml'</simple>
      <to uri="bean:orderService?method=handleXmlFiles"/>
    </when>
    <otherwise>
      <to uri="bean:orderService?method=handleOtherFiles"/>
    </otherwise>
  </choice>

If you use the fileName option on the File endpoint to set a dynamic filename using the File Language then make sure you use the alternative syntax (available from Camel 2.5) to avoid clashing with Spring's PropertyPlaceholderConfigurer.

<bean id="propertyPlaceholder" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="location" value="classpath:bundle-context.cfg"/>
</bean>

<bean id="sampleRoute" class="SampleRoute">
  <property name="fromEndpoint" value="${fromEndpoint}"/>
  <property name="toEndpoint" value="${toEndpoint}"/>
</bean>

fromEndpoint=activemq:queue:test
toEndpoint=file://fileRoute/out?fileName=test-$simple{date:now:yyyyMMdd}.txt

Notice how we use the $simple{} syntax in the toEndpoint above. If you don't do this, they will clash and Spring will throw an exception:

org.springframework.beans.factory.BeanDefinitionStoreException:
Invalid bean definition with name 'sampleRoute' defined in class path resource [bundle-context.xml]:
Could not resolve placeholder 'date:now:yyyyMMdd'

Dependencies

The File language is part of camel-core.