package org.wamblee.general;
import java.lang.reflect.InvocationHandler;
-import java.lang.reflect.InvocationTargetException;
-import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
/**
+ * <p>
* Thread-specific proxy is used to create implementations of interfaces that
* delegate to a thread-specific implementation of the service.
+ * </p>
*
- * It is used for instance to pass a transaction scoped entity manager around.
+ * <p>
+ * It can be used for instance to create a contextual reference to an entity
+ * manager that delegates to a thread-specific instance.
+ * </p>
*
- * 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.
+ * <p>
+ * 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.
+ * </p>
*
- * This class is mostly used by other test tools.
+ * <p>
+ * This class is mostly used by infrastructure code (utilities) and test tools.
+ * </p>
+ *
+ * <p>
+ * 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.
+ * </p>
*
* @param T
* Interface to proxy.
*
*/
public class ThreadSpecificProxyFactory<T> {
- private class ThreadSpecificInvocationHandler implements InvocationHandler {
- @Override
- public Object invoke(Object aProxy, Method aMethod, Object[] aArgs)
- throws Throwable {
- try {
- return aMethod.invoke(svc.get(), aArgs);
- } catch (InvocationTargetException e) {
- throw e.getCause();
- }
- }
+ /**
+ * 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<T> {
+ /**
+ * Creates the object.
+ *
+ * @return Object.
+ */
+ T create();
}
- private ThreadLocal<T> svc = new ThreadLocal<T>();
+ private ThreadLocal<T> svc;
private Class clazz;
+ private T proxy;
/**
* Constructs the factory.
* Interface class of the service to proxy.
*/
public ThreadSpecificProxyFactory(Class<T> 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<T> aClass,
+ final CreationCallback<T> aCallback) {
if (!aClass.isInterface()) {
throw new IllegalArgumentException("Class " + aClass.getName() +
" is not an interface");
}
+ svc = new ThreadLocal<T>() {
+ @Override
+ protected T initialValue() {
+ if (aCallback != null) {
+ return aCallback.create();
+ }
+ return null;
+ }
+ };
clazz = aClass;
+ proxy = createProxy();
+
}
/**
public void set(T aService) {
svc.set(aService);
}
-
+
/**
- * Gets the current thread-specific service.
- * @return Service.
+ * 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() {
+ public T get() {
return svc.get();
}
* @return Proxy.
*/
public T getProxy() {
- InvocationHandler handler = new ThreadSpecificInvocationHandler();
+ return proxy;
+ }
+
+ private T createProxy() {
+ InvocationHandler handler = new ThreadSpecificInvocationHandler(svc,
+ clazz);
Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
new Class[] { clazz });
- T proxy;
+ T proxyObj;
try {
- proxy = (T) proxyClass.getConstructor(
+ proxyObj = (T) proxyClass.getConstructor(
new Class[] { InvocationHandler.class }).newInstance(
new Object[] { handler });
- return proxy;
+ return proxyObj;
} catch (Exception e) {
throw new RuntimeException("Could not create proxy for " +
clazz.getName(), e);
git://wamblee.org / utils / blobdiff