v811_spc009/external/auto/value/userguide/extensions.md

Extensions

AutoValue can be extended to implement new features for classes annotated with @AutoValue.

Using extensions

Each extension is a class. If that class is on the processorpath when you compile your @AutoValue class, the extension can run.

Some extensions are triggered by their own annotations, which you add to your class; others may be triggered in other ways. Consult the extension's documentation for usage instructions.

Writing an extension

To add a feature, write a class that extends AutoValueExtension, and put that class on the processorpath along with AutoValueProcessor.

AutoValueExtension uses the ServiceLoader mechanism, which means:

• Your class must be public and have a public no-argument constructor.
• Its fully-qualified name must appear in a file called META-INF/services/com.google.auto.value.extension.AutoValueExtension in a JAR that is on the compiler's classpath or processorpath.

You can use AutoService to make implementing the ServiceLoader pattern easy.

Without extensions, AutoValue generates a subclass of the @AutoValue class. Extensions can work by generating a chain of subclasses, each of which alters behavior by overriding or implementing new methods.

TODO

• How to distribute extensions.
• List of known extensions.