Introduce AOP testing utilities

This commit introduces support in the spring-test module for obtaining a
reference to the underlying target object hidden behind one or more
proxies.

Specifically this commit introduces AopTestUtils with two methods:

 - getTargetObject(Object)

 - getUltimateTargetObject(Object)

Issue: SPR-13005

spring-test/src/main/java/org/springframework/test/util/AopTestUtils.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2002-2015 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.springframework.test.util;
+
+import org.springframework.aop.framework.Advised;
+import org.springframework.aop.support.AopUtils;
+
+/**
+ * {@code AopTestUtils} is a collection of AOP-related utility methods for
+ * use in unit and integration testing scenarios.
+ *
+ * <p>For Spring's core AOP utilities, see
+ * {@link org.springframework.aop.support.AopUtils AopUtils} and
+ * {@link org.springframework.aop.framework.AopProxyUtils AopProxyUtils}.
+ *
+ * @author Sam Brannen
+ * @since 4.2
+ * @see org.springframework.aop.support.AopUtils
+ * @see org.springframework.aop.framework.AopProxyUtils
+ */
+public class AopTestUtils {
+
+	/**
+	 * Get the <em>target</em> object of the supplied {@code candidate} object.
+	 * <p>If the supplied {@code candidate} is a Spring
+	 * {@linkplain AopUtils#isAopProxy proxy}, the target of the proxy will
+	 * be returned; otherwise, the {@code candidate} will be returned
+	 * <em>as is</em>.
+	 *
+	 * @param candidate the instance to check (potentially a Spring AOP proxy)
+	 * @return the target object or the {@code candidate}; never {@code null}
+	 * @throws IllegalStateException if an error occurs while unwrapping a proxy
+	 * @see Advised#getTargetSource()
+	 * @see #getUltimateTargetObject
+	 */
+	@SuppressWarnings("unchecked")
+	public static <T> T getTargetObject(Object candidate) {
+		try {
+			if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
+				return (T) ((Advised) candidate).getTargetSource().getTarget();
+			}
+		}
+		catch (Exception e) {
+			throw new IllegalStateException("Failed to unwrap proxied object.", e);
+		}
+
+		// else
+		return (T) candidate;
+	}
+
+	/**
+	 * Get the ultimate <em>target</em> object of the supplied {@code candidate}
+	 * object, unwrapping not only a top-level proxy but also any number of
+	 * nested proxies.
+	 * <p>If the supplied {@code candidate} is a Spring
+	 * {@linkplain AopUtils#isAopProxy proxy}, the ultimate target of all
+	 * nested proxies will be returned; otherwise, the {@code candidate}
+	 * will be returned <em>as is</em>.
+	 *
+	 * @param candidate the instance to check (potentially a Spring AOP proxy)
+	 * @return the ultimate target object or the {@code candidate}; never
+	 * {@code null}
+	 * @throws IllegalStateException if an error occurs while unwrapping a proxy
+	 * @see Advised#getTargetSource()
+	 * @see org.springframework.aop.framework.AopProxyUtils#ultimateTargetClass
+	 */
+	@SuppressWarnings("unchecked")
+	public static <T> T getUltimateTargetObject(Object candidate) {
+		try {
+			if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {
+				return (T) getUltimateTargetObject(((Advised) candidate).getTargetSource().getTarget());
+			}
+		}
+		catch (Exception e) {
+			throw new IllegalStateException("Failed to unwrap proxied object.", e);
+		}
+
+		// else
+		return (T) candidate;
+	}
+
+}

spring-test/src/test/java/org/springframework/test/util/AopTestUtilsTests.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2002-2015 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.springframework.test.util;
+
+import org.junit.Test;
+
+import org.springframework.aop.framework.ProxyFactory;
+import org.springframework.aop.support.AopUtils;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+import static org.springframework.test.util.AopTestUtils.*;
+
+/**
+ * Unit tests for {@link AopTestUtils}.
+ *
+ * @author Sam Brannen
+ * @since 4.2
+ */
+public class AopTestUtilsTests {
+
+	private final FooImpl foo = new FooImpl();
+
+
+	@Test
+	public void getTargetObjectForNonProxiedObject() {
+		Foo target = getTargetObject(foo);
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getTargetObjectWrappedInSingleJdkDynamicProxy() {
+		Foo target = getTargetObject(jdkProxy(foo));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getTargetObjectWrappedInSingleCglibProxy() {
+		Foo target = getTargetObject(cglibProxy(foo));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getTargetObjectWrappedInDoubleJdkDynamicProxy() {
+		Foo target = getTargetObject(jdkProxy(jdkProxy(foo)));
+		assertNotSame(foo, target);
+	}
+
+	@Test
+	public void getTargetObjectWrappedInDoubleCglibProxy() {
+		Foo target = getTargetObject(cglibProxy(cglibProxy(foo)));
+		assertNotSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectForNonProxiedObject() {
+		Foo target = getUltimateTargetObject(foo);
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInSingleJdkDynamicProxy() {
+		Foo target = getUltimateTargetObject(jdkProxy(foo));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInSingleCglibProxy() {
+		Foo target = getUltimateTargetObject(cglibProxy(foo));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInDoubleJdkDynamicProxy() {
+		Foo target = getUltimateTargetObject(jdkProxy(jdkProxy(foo)));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInDoubleCglibProxy() {
+		Foo target = getUltimateTargetObject(cglibProxy(cglibProxy(foo)));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInCglibProxyWrappedInJdkDynamicProxy() {
+		Foo target = getUltimateTargetObject(jdkProxy(cglibProxy(foo)));
+		assertSame(foo, target);
+	}
+
+	@Test
+	public void getUltimateTargetObjectWrappedInCglibProxyWrappedInDoubleJdkDynamicProxy() {
+		Foo target = getUltimateTargetObject(jdkProxy(jdkProxy(cglibProxy(foo))));
+		assertSame(foo, target);
+	}
+
+	private Foo jdkProxy(Foo foo) {
+		ProxyFactory pf = new ProxyFactory();
+		pf.setTarget(foo);
+		pf.addInterface(Foo.class);
+		Foo proxy = (Foo) pf.getProxy();
+		assertTrue("Proxy is a JDK dynamic proxy", AopUtils.isJdkDynamicProxy(proxy));
+		assertThat(proxy, instanceOf(Foo.class));
+		return proxy;
+	}
+
+	private Foo cglibProxy(Foo foo) {
+		ProxyFactory pf = new ProxyFactory();
+		pf.setTarget(foo);
+		pf.setProxyTargetClass(true);
+		Foo proxy = (Foo) pf.getProxy();
+		assertTrue("Proxy is a CGLIB proxy", AopUtils.isCglibProxy(proxy));
+		assertThat(proxy, instanceOf(FooImpl.class));
+		return proxy;
+	}
+
+
+	static interface Foo {
+	}
+
+	static class FooImpl implements Foo {
+	}
+
+}