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List Files Using the File Connector

Use the List operation to list the files and folders in the path pointed to by the directoryPath parameter. The List operation returns an array of messages in which:

  • Each message holds the file’s content in its payload.

  • The file’s attributes section carries the file’s metadata (such as name, creation time, and size).

  • The payload is empty if the element is a folder.

The List operation requires the directoryPath parameter, which represents the relative path of the directory to list, unless you specify the full path of the directory. The path is relative to the working directory value defined in the configuration referenced by the config-ref parameter. If no configuration is referenced, the working directory defaults to the value of the user.home system property. If the system property is not set, the connector fails to initialize.

For an example of setting a configuration, see File Connection Settings.

Next is an example of a List operation that references a file configuration and thus uses a relative path:

<file:list config-ref="File_Config" directoryPath="relativePath" />

As mentioned earlier, this returns an array of messages. In Anypoint Studio, DataSense displays the metadata for the operation’s output:

list output

The List operation lists both directories and files, but for files it also returns a lazy stream of the file’s contents in the payload, which can then be directly consumed by other operations. This means that you do not need to perform a Read operation after a List operation to access the file’s content. See Read Files Returned by List for an example.

Read Files Returned by List

The following example lists all files and folders in directoryPath and, in a foreach loop:

<file:list config-ref="File_Config" directoryPath="relativePath" />

        <when expression="#[not]">
            <logger message="Found file #[attributes.path] whose content is: #[payload]" />
            <flow-ref name="process-directory" />

The foreach loop determines whether each element is a file or folder with a choice component. If the element is a file, then a Logger outputs its path and contents. If the element is a directory, it is sent to another flow for processing.

There is no Read operation inside the foreach loop because, as mentioned earlier, the List operation already returns the file’s content in the payload, (but in a lazy manner), so there is no need to worry about performance or overhead when the stream is not consumed in the end.

List Files and Folders Within Subfolders

To list files or folders within any subfolders of the directoryPath, such as a recursive list, you can set the recursive parameter to true.

<file:list config-ref="File_Config" directoryPath="relativePath" recursive="true" />

Filter Files by Matching Criteria

You can use the <file:matcher> element to filter files based on the matching criteria you use for accepting or rejecting a file. Here is an example of file matching rules you can use:

Example: File Matcher
  maxSize="1024" />

All of the attributes above are optional and are ignored if not provided. They all relate to each other under an AND operator.

Top-level, Reusable Matcher

A file matcher can be a reusable element (a named top-level element) as shown in the following example:

For example:

<file:matcher name="smallFileMatcher" maxSize="100" />

<flow name="smallFiles">
  <file:list path="~/smallfiles" matcher="smallFileMatcher" />

Inner Element, Non-Reusable Matcher

A matcher can be an inner element that is proprietary to a particular component (non-reusable) as shown in the following example:

<flow name="smallFiles">
	<file:list path="~/smallfiles">
        <file:matcher maxSize="100" />

Time Between Size Checks Parameter

If you want to read the file contents returned by the List operation, but you are not sure if the file is still being written to, you can use the TimeBetweenSizeChecks parameter, which works with the TimeBetweenSizeCheckUnit parameter. Combined, these two parameters perform two size checks:

  • One when the flow reaches a point where the stream is about to be consumed. The time check is not done in the List operation because List returns a lazy stream pointing to the file’s content, so it makes sense to do the size check only when the stream is about to be consumed.

  • Another check is performed after the wait time set by the TimeBetweenSizeChecks and TimeBetweenSizeCheckUnit parameters

If both size checks return the same file size, then the stream is consumed successfully. If the two size checks return different file sizes, then the file is still being written to, so the stream is not consumed and the operation fails with an error.

Repeatable Streams

The List operation makes use of the repeatable streams functionality introduced in Mule 4. The operation returns a list of messages, where each message represents a file in the list and holds a stream to the file. A stream is repeatable by default.

For more information, refer to Streaming in Mule 4.

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