org.wamblee.general.ThreadSpecificProxyFactory Maven / Gradle / Ivy
/*
* Copyright 2005-2010 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.wamblee.general;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
/**
*
* Thread-specific proxy is used to create implementations of interfaces that
* delegate to a thread-specific implementation of the service.
*
*
*
* It can be used for instance to create a contextual reference to an entity
* manager that delegates to a thread-specific instance.
*
*
*
* The {@link #set(Object)} method sets the current service instance for the
* current thread. The {@link #get()} method gets the current service instance
* for the current thread. The {@link #getProxy()} method gets a proxy that will
* delegate at runtime to the thread-specific instance. The result from this
* method can be passed at construction of an object that will be used by
* multiple threads.
*
*
*
* This class is mostly used by infrastructure code (utilities) and test tools.
*
*
*
* Care has been taken so that the invocation handler is serializable. However,
* it is only serializable within one virtual machine. It cannot be used in a
* distributed context where it can be sent to another JVM.
*
*
*
* This class currently does not do any cleanup. So it should not be used in production code
* but only in test utilities.
*
*
* @param T
* Interface to proxy.
* @author Erik Brakkee
*
*/
public class ThreadSpecificProxyFactory {
/**
* Optional callback invoked to create the thread-specific object when there
* is no object yet associated with the current thread.
*
* @author Erik Brakkee
*
*/
public static interface CreationCallback {
/**
* Creates the object.
*
* @return Object.
*/
T create();
}
private ThreadLocal svc;
private Class clazz;
private T proxy;
/**
* Constructs the factory.
*
* @param aClass
* Interface class of the service to proxy.
*/
public ThreadSpecificProxyFactory(Class aClass) {
this(aClass, null);
}
/**
* Constructs the factory with a callback to create thread-specific objects
* automatically.
*
* @param aClass
* Interface class of the service to proxy.
* @param aCallback
* Callback to create the object if it does not exist. When null,
* then no initialization is done.
*/
public ThreadSpecificProxyFactory(Class aClass,
final CreationCallback aCallback) {
if (!aClass.isInterface()) {
throw new IllegalArgumentException("Class " + aClass.getName() +
" is not an interface");
}
svc = new ThreadLocal() {
@Override
protected T initialValue() {
if (aCallback != null) {
return aCallback.create();
}
return null;
}
};
clazz = aClass;
proxy = createProxy();
}
/**
* Sets the thread-specific service.
*
* @param aService
* Service, use null value to reset.
*/
public void set(T aService) {
svc.set(aService);
}
/**
* Gets the current thread-specific service. To get a contextual reference
* that can be used by any thread but delegates to a thread-specific
* instance, use {@link #getProxy()}.
*
* @return Service.
*/
public T get() {
return svc.get();
}
/**
* Gets the proxy that delegates to the thread-specific instance set by
* {@link #set(Object)}
*
* @return Proxy.
*/
public T getProxy() {
return proxy;
}
private T createProxy() {
InvocationHandler handler = new ThreadSpecificInvocationHandler(svc,
clazz);
Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
new Class[] { clazz });
T proxyObj;
try {
proxyObj = (T) proxyClass.getConstructor(
new Class[] { InvocationHandler.class }).newInstance(
new Object[] { handler });
return proxyObj;
} catch (Exception e) {
throw new RuntimeException("Could not create proxy for " +
clazz.getName(), e);
}
}
}