MIME Type and Encoding

DevKit is compatible only with Studio 6 and Mule 3. To build Mule 4 connectors, see the Mule SDK documentation.

In Mule 3.7 and newer, you can define the MIME type and encoding of a given return object from @Processor. See the Annotation Reference for more information on annotations.

While DevKit has the @Mime annotation, that element fetches that information at compile time, it’s not useful when the connector implements proxy or wrapping to a filesystem type of API.

Runtime Support

This feature lets you customize a return type. The following example shows how to trigger this feature:


Anypoint Studio Support

If the @Processor is annotated with @UserDefinedMetaData (which is not mandatory when using TransformingValue). That attribute helps Studio users change the metadata of the given processor in later usages if needed.

When enabled, an end user of Studio sees the Metadata tab in Studio that enables the user to change information for Metadata propagation as shown below.

Code example:

import org.mule.api.annotations.display.UserDefinedMetaData;
@Connector(name = "file-chooser", friendlyName="File Chooser")
public class FileChooserConnector {
    ConnectorConnectionStrategy connectionStrategy;
    @Processor(friendlyName="Open File as InputStream")
    public TransformingValue<InputStream,DataType<InputStream>> openFileAsIS(

Metadata tab:


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