Chapter 16. The File Language

Abstract

The file language is an extension to the simple language, not an independent language in its own right. But the file language extension can only be used in conjunction with File or FTP endpoints.

16.1. When to Use the File Language

Overview

The file language is an extension to the simple language which is not always available. You can use it under the following circumstances:
Note
The escape character, \, is not available in the file language.

In a File or FTP consumer endpoint

There are several URI options that you can set on a File or FTP consumer endpoint, which take a file language expression as their value. For example, in a File consumer endpoint URI you can set the fileName, move, preMove, moveFailed, and sortBy options using a file expression.
In a File consumer endpoint, the fileName option acts as a filter, determining which file will actually be read from the starting directory. If a plain text string is specified (for example, fileName=report.txt), the File consumer reads the same file each time it is updated. You can make this option more dynamic, however, by specifying a simple expression. For example, you could use a counter bean to select a different file each time the File consumer polls the starting directory, as follows:
file://target/filelanguage/bean/?fileName=${bean:counter.next}.txt&delete=true
Where the ${bean:counter.next} expression invokes the next() method on the bean registered under the ID, counter.
The move option is used to move files to a backup location after then have been read by a File consumer endpoint. For example, the following endpoint moves files to a backup directory, after they have been processed:
file://target/filelanguage/?move=backup/${date:now:yyyyMMdd}/${file:name.noext}.bak&recursive=false
Where the ${file:name.noext}.bak expression modifies the original file name, replacing the file extension with .bak.
You can use the sortBy option to specify the order in which file should be processed. For example, to process files according to the alphabetical order of their file name, you could use the following File consumer endpoint:
file://target/filelanguage/?sortBy=file:name
To process file according to the order in which they were last modified, you could use the following File consumer endpoint:
file://target/filelanguage/?sortBy=file:modified
You can reverse the order by adding the reverse: prefix—for example:
file://target/filelanguage/?sortBy=reverse:file:modified

On exchanges created by a File or FTP consumer

When an exchange originates from a File or FTP consumer endpoint, it is possible to apply file language expressions to the exchange throughout the route (as long as the original message headers are not erased). For example, you could define a content-based router, which routes messages according to their file extension, as follows:
<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>