com.diffplug.common.base

Class DurianPlugins

java.lang.Object

com.diffplug.common.base.DurianPlugins

public class DurianPlugins
extends Object

A programmatic and pluggable implementation of public static final.

To write code that requires an instance of IPlugin, you write something like this:

IPlugin instance = DurianPlugins.get(IPlugin.class, defaultImplementation);

Once someone has requested a class from DurianPlugins, whatever instance was returned will continue to be returned for every future call. This has the same behavior as if you declared a public static final IPlugin.

Before the value has been requested, it can be set programmatically using register(java.lang.Class<T>, T), or by setting a system property. This allows setting global behaviors appropriate for diverse environments.

This eternal instance for a given class is determined in this order:

1. the first call to register(java.lang.Class<T>, T)
2. if a system property named durian.plugins.{pluginClass.getCanonicalName()} is set to the fully-qualified name (Class.getName()) of an implementation class with a no-argument constructor, then an instance of that class will be instantiated and used as the plugin implementation
3. the defaultImplementation that was specified in the first call to get()

This class was inspired by RxJava’s RxJavaPlugins. Many thanks to them!

Field Summary

Fields

Modifier and Type	Field and Description
static String	PROPERTY_PREFIX Prefix to system property keys for specifying plugin classes.

Method Summary

Modifier and Type	Method and Description
static <T> T	get(Class<T> pluginClass, T defaultImpl) Returns an instance of pluginClass which is guaranteed to be identical throughout the runtime existence of this library.
static <T> void	register(Class<T> pluginClass, T pluginImpl) Registers an implementation as a global override of any injected or default implementations.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

PROPERTY_PREFIX

public static final String PROPERTY_PREFIX

Prefix to system property keys for specifying plugin classes.

See Also:

Constant Field Values

Method Detail

register

public static <T> void register(Class<T> pluginClass,
                                T pluginImpl)
                         throws IllegalStateException

Registers an implementation as a global override of any injected or default implementations.

Parameters:

pluginClass - The interface which is being registered.

pluginImpl - The implementation of that interface which is being registered.

Throws:

IllegalStateException - If called more than once or if a value has already been requested.

get

public static <T> T get(Class<T> pluginClass,
                        T defaultImpl)

Returns an instance of pluginClass which is guaranteed to be identical throughout the runtime existence of this library. The returned instance is determined by:

1. the first call to register(java.lang.Class<T>, T)
2. if a system property named durian.plugins.{pluginClass.getCanonicalName()} is set to the fully-qualified name (Class.getName()) of an implementation class with a no-argument constructor, then an instance of that class will be instantiated and used as the plugin implementation
3. the defaultImplementation that was specified in the first call to get()

Parameters:

pluginClass - The interface which is being requested.

defaultImpl - A default implementation of that interface.

Returns:

An instance of pluginClass, which is guaranteed to be returned for every future request for pluginClass.