Chapter 16. The File Language

The file language is an extension to the simple language which is not always available. You can use it under the following circumstances:

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

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>

File variables can be used whenever a route starts with a File or FTP consumer endpoint, which implies that the underlying message body is of java.io.File type. The file variables enable you to access various parts of the file pathname, almost as if you were invoking the methods of the java.io.File class (in fact, the file language extracts the information it needs from message headers that have been set by the File or FTP endpoint).

Some of file variables return paths that are defined relative to a starting directory, which is just the directory that is specified in the File or FTP endpoint. For example, the following File consumer endpoint has the starting directory, ./filetransfer (a relative path):

file:filetransfer

The following FTP consumer endpoint has the starting directory, ./ftptransfer (a relative path):

ftp://myhost:2100/ftptransfer

In general, the file variables are named after corresponding methods on the java.io.File class. For example, the file:absolute variable gives the value that would be returned by the java.io.File.getAbsolute() method.

Table 16.1, “Variables for the File Language” shows all of the variable supported by the file language.

Consider a File consumer endpoint, where the starting directory is specified as a relative pathname. For example, the following File endpoint has the starting directory, ./filelanguage:

file://filelanguage

Now, while scanning the filelanguage directory, suppose that the endpoint has just consumed the following file:

./filelanguage/test/hello.txt

And, finally, assume that the filelanguage directory itself has the following absolute location:

/workspace/camel/camel-core/target/filelanguage

Given the preceding scenario, the file language variables return the following values, when applied to the current exchange:

Consider a File consumer endpoint, where the starting directory is specified as an absolute pathname. For example, the following File endpoint has the starting directory, /workspace/camel/camel-core/target/filelanguage:

file:///workspace/camel/camel-core/target/filelanguage

Now, while scanning the filelanguage directory, suppose that the endpoint has just consumed the following file:

./filelanguage/test/hello.txt

Given the preceding scenario, the file language variables return the following values, when applied to the current exchange: