The ForwardingWrapperTester.java Java example source code
/*
* Copyright (C) 2012 The Guava 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 com.google.common.testing;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.fail;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import com.google.common.base.Throwables;
import com.google.common.collect.Lists;
import com.google.common.reflect.AbstractInvocationHandler;
import com.google.common.reflect.Reflection;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Tester to ensure forwarding wrapper works by delegating calls to the corresponding method
* with the same parameters forwarded and return value forwarded back or exception propagated as is.
*
* <p>For example: {@code
* new ForwardingWrapperTester().testForwarding(Foo.class, new Function<Foo, Foo>() {
* public Foo apply(Foo foo) {
* return new ForwardingFoo(foo);
* }
* });}</pre>
*
* @author Ben Yu
* @since 14.0
*/
@Beta
@GwtIncompatible
public final class ForwardingWrapperTester {
private boolean testsEquals = false;
/**
* Asks for {@link Object#equals} and {@link Object#hashCode} to be tested.
* That is, forwarding wrappers of equal instances should be equal.
*/
public ForwardingWrapperTester includingEquals() {
this.testsEquals = true;
return this;
}
/**
* Tests that the forwarding wrapper returned by {@code wrapperFunction} properly forwards
* method calls with parameters passed as is, return value returned as is, and exceptions
* propagated as is.
*/
public <T> void testForwarding(
Class<T> interfaceType, Function wrapperFunction) {
checkNotNull(wrapperFunction);
checkArgument(interfaceType.isInterface(), "%s isn't an interface", interfaceType);
Method[] methods = getMostConcreteMethods(interfaceType);
AccessibleObject.setAccessible(methods, true);
for (Method method : methods) {
// Under java 8, interfaces can have default methods that aren't abstract.
// No need to verify them.
// Can't check isDefault() for JDK 7 compatibility.
if (!Modifier.isAbstract(method.getModifiers())) {
continue;
}
// The interface could be package-private or private.
// filter out equals/hashCode/toString
if (method.getName().equals("equals")
&& method.getParameterTypes().length == 1
&& method.getParameterTypes()[0] == Object.class) {
continue;
}
if (method.getName().equals("hashCode")
&& method.getParameterTypes().length == 0) {
continue;
}
if (method.getName().equals("toString")
&& method.getParameterTypes().length == 0) {
continue;
}
testSuccessfulForwarding(interfaceType, method, wrapperFunction);
testExceptionPropagation(interfaceType, method, wrapperFunction);
}
if (testsEquals) {
testEquals(interfaceType, wrapperFunction);
}
testToString(interfaceType, wrapperFunction);
}
/** Returns the most concrete public methods from {@code type}. */
private static Method[] getMostConcreteMethods(Class<?> type) {
Method[] methods = type.getMethods();
for (int i = 0; i < methods.length; i++) {
try {
methods[i] = type.getMethod(methods[i].getName(), methods[i].getParameterTypes());
} catch (Exception e) {
throw Throwables.propagate(e);
}
}
return methods;
}
private static <T> void testSuccessfulForwarding(
Class<T> interfaceType, Method method, Function wrapperFunction) {
new InteractionTester<T>(interfaceType, method).testInteraction(wrapperFunction);
}
private static <T> void testExceptionPropagation(
Class<T> interfaceType, Method method, Function wrapperFunction) {
final RuntimeException exception = new RuntimeException();
T proxy = Reflection.newProxy(interfaceType, new AbstractInvocationHandler() {
@Override protected Object handleInvocation(Object p, Method m, Object[] args)
throws Throwable {
throw exception;
}
});
T wrapper = wrapperFunction.apply(proxy);
try {
method.invoke(wrapper, getParameterValues(method));
fail(method + " failed to throw exception as is.");
} catch (InvocationTargetException e) {
if (exception != e.getCause()) {
throw new RuntimeException(e);
}
} catch (IllegalAccessException e) {
throw new AssertionError(e);
}
}
private static <T> void testEquals(
Class<T> interfaceType, Function wrapperFunction) {
FreshValueGenerator generator = new FreshValueGenerator();
T instance = generator.newFreshProxy(interfaceType);
new EqualsTester()
.addEqualityGroup(wrapperFunction.apply(instance), wrapperFunction.apply(instance))
.addEqualityGroup(wrapperFunction.apply(generator.newFreshProxy(interfaceType)))
// TODO: add an overload to EqualsTester to print custom error message?
.testEquals();
}
private static <T> void testToString(
Class<T> interfaceType, Function wrapperFunction) {
T proxy = new FreshValueGenerator().newFreshProxy(interfaceType);
assertEquals("toString() isn't properly forwarded",
proxy.toString(), wrapperFunction.apply(proxy).toString());
}
private static Object[] getParameterValues(Method method) {
FreshValueGenerator paramValues = new FreshValueGenerator();
final List<Object> passedArgs = Lists.newArrayList();
for (Class<?> paramType : method.getParameterTypes()) {
passedArgs.add(paramValues.generateFresh(paramType));
}
return passedArgs.toArray();
}
/** Tests a single interaction against a method. */
private static final class InteractionTester<T> extends AbstractInvocationHandler {
private final Class<T> interfaceType;
private final Method method;
private final Object[] passedArgs;
private final Object returnValue;
private final AtomicInteger called = new AtomicInteger();
InteractionTester(Class<T> interfaceType, Method method) {
this.interfaceType = interfaceType;
this.method = method;
this.passedArgs = getParameterValues(method);
this.returnValue = new FreshValueGenerator().generateFresh(method.getReturnType());
}
@Override protected Object handleInvocation(Object p, Method calledMethod, Object[] args)
throws Throwable {
assertEquals(method, calledMethod);
assertEquals(method + " invoked more than once.", 0, called.get());
for (int i = 0; i < passedArgs.length; i++) {
assertEquals("Parameter #" + i + " of " + method + " not forwarded",
passedArgs[i], args[i]);
}
called.getAndIncrement();
return returnValue;
}
void testInteraction(Function<? super T, ? extends T> wrapperFunction) {
T proxy = Reflection.newProxy(interfaceType, this);
T wrapper = wrapperFunction.apply(proxy);
boolean isPossibleChainingCall = interfaceType.isAssignableFrom(method.getReturnType());
try {
Object actualReturnValue = method.invoke(wrapper, passedArgs);
// If we think this might be a 'chaining' call then we allow the return value to either
// be the wrapper or the returnValue.
if (!isPossibleChainingCall || wrapper != actualReturnValue) {
assertEquals("Return value of " + method + " not forwarded", returnValue,
actualReturnValue);
}
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
} catch (InvocationTargetException e) {
throw Throwables.propagate(e.getCause());
}
assertEquals("Failed to forward to " + method, 1, called.get());
}
@Override public String toString() {
return "dummy " + interfaceType.getSimpleName();
}
}
}
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