File Expression Language
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From Camel 2.2: the file language is now merged with Simple language which means you can use all the file syntax directly within the simple language. |
The File Expression Language is an extension to the Simple language, adding file related capabilities. These capabilities is are related to common use cases working with file path and names. The goal is to allow expression expressions to be used with the File component and FTP components for setting dynamic file patterns for both the file consumer and file producer.
Syntax
This language is an extension to the 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 uses use the same expression name as the method on the java.io.File
object, for instance . For example: file:absolute
refers to the java.io.File.getAbsolute()
method.
All options returns a String object.
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Expression
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Description
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Note: not all expressions are supported by the current Exchange. For example, the FTP component supports some of the options, whereas the File component supports all of them. |
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refers to the file parent
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refers to the file path
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refers to the absolute file
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refers to the canonical path
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data:command:pattern
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for date formatting using the java.text.SimepleDataFormat
patterns. Supported commands are: now for current timestamp, file for the last modified timestamp of the file.
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bean:bean expression
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invoking a bean expression using the Bean language.
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simple:simple expression
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to invoke the simple expression, however simple: can be omitted as this language extends the simple language
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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:
Expression | Returns |
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file:absolute |
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file:absolute.path |
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file:ext |
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file:name |
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file:name.ext |
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file:name.noext |
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file:onlyname |
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file:onlyname.noext |
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file:parent |
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file:path |
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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:
Expression | Returns |
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file:absolute |
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file:absolute.path |
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file:ext |
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file:name |
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file:name.ext |
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file:name.noext |
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file:onlyname |
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file:onlyname.noext |
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file:parent |
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file:path |
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Examples
You can enter a fixed Constant expression such as myfile.txt
:
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fileName="myfile.txt"
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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 subfoldersub folder. This can be archived achieved using an expression like:
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fileName expression="backup/${date:now:yyyyMMdd}/${file:name.noext}.bak" |
relative folder names is are also supported so suppose the backup folder should be a sibling folder then you can append append ..
as:
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fileName expression="../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 the in.header.type
as a parameter in the dynamic expression:
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fileName expression="../backup/${date:now:yyyyMMdd}/type-${in.header.type}/backup-of-${file:name.noext}.bak" |
If you have a custom Date
you want to use in the expression then Camel supports retrieving dates from the message header.
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fileName="orders/order-${in.header.customerId}-${date:in.header.orderDate:yyyyMMdd}.xml" |
And finally we can also use a bean expression to invoke a POJO class that generates some some String
output (or convertible to String
) to be used:
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fileName expression="uniquefile-${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:
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<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>
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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
.
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<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>
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fromEndpoint=activemq:queue:test
toEndpoint=file://fileRoute/out?fileName=test-$simple{date:now:yyyyMMdd}.txt
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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:
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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'
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Dependencies
The File language is part of camel-core
.