User Guide
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Using Custom Properties with Expression Language

You can use NiFi Expression Language to reference FlowFile attributes, compare them to other values, and manipulate their values when you are creating and configuring dataflows.

In addition to using FlowFile attributes, system properties, and environment properties within Express Language, you can also define custom properties for Expression Language use. Defining custom properties gives you more flexibility in handling and processing dataflows. You can also create custom properties for connection, server, and service properties, for easier dataflow configuration.

To create custom properties for use with Expression Language, identify one or more sets of key/value pairs, and give them to your system administrator.

NiFi properties have resolution precedence of which you should be aware when creating custom properties:

  • Processor-specific attributes

  • FlowFile properties

  • FlowFile attributes

  • From variable registry:

    • User defined properties (custom properties)

    • System properties

    • Operating System environment variables

When you are creating custom properties, ensure that each custom property contains a distinct property value, so that it is not overridden by existing environment properties, system properties, or FlowFile attributes. Once you have added the new custom properties, ensure that you have updated the field in the file, with the custom properties location.

For more information on Expression Language, see the Expression Lanuaguage Guide. For information on how to define custom properties, see the System Administrator's Guide.