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[utils] / support / general / src / main / java / org / wamblee / general / ThreadSpecificProxyFactory.java

diff --git a/support/general/src/main/java/org/wamblee/general/ThreadSpecificProxyFactory.java b/support/general/src/main/java/org/wamblee/general/ThreadSpecificProxyFactory.java
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+/*
+ * 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.InvocationTargetException;
+import java.lang.reflect.Method;
+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 is used for instance to pass a transaction scoped entity manager around.
+ * 
+ * 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 other test tools. 
+ * 
+ * @param T
+ *            Interface to proxy.
+ * @author Erik Brakkee
+ * 
+ */
+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();
+            }
+        }
+    }
+
+    private ThreadLocal<T> svc = new ThreadLocal<T>();
+    private Class clazz;
+
+    /**
+     * Constructs the factory.
+     * 
+     * @param aClass
+     *            Interface class of the service to proxy.
+     */
+    public ThreadSpecificProxyFactory(Class<T> aClass) {
+        if (!aClass.isInterface()) {
+            throw new IllegalArgumentException("Class " + aClass.getName() +
+                " is not an interface");
+        }
+        clazz = aClass;
+    }
+
+    /**
+     * 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. 
+     * @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() {
+        InvocationHandler handler = new ThreadSpecificInvocationHandler();
+        Class proxyClass = Proxy.getProxyClass(clazz.getClassLoader(),
+            new Class[] { clazz });
+        T proxy;
+        try {
+            proxy = (T) proxyClass.getConstructor(
+                new Class[] { InvocationHandler.class }).newInstance(
+                new Object[] { handler });
+            return proxy;
+        } catch (Exception e) {
+            throw new RuntimeException("Could not create proxy for " +
+                clazz.getName(), e);
+        }
+    }
+}