org.springframework.aop.support.DelegatingIntroductionInterceptor.java Source code

Introduction

Here is the source code for org.springframework.aop.support.DelegatingIntroductionInterceptor.java

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/*
 * Copyright 2002-2017 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
 *
 *      https://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.aop.support;

import org.aopalliance.intercept.MethodInvocation;

import org.springframework.aop.DynamicIntroductionAdvice;
import org.springframework.aop.IntroductionInterceptor;
import org.springframework.aop.ProxyMethodInvocation;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Convenient implementation of the
 * {@link org.springframework.aop.IntroductionInterceptor} interface.
 *
 * <p>Subclasses merely need to extend this class and implement the interfaces
 * to be introduced themselves. In this case the delegate is the subclass
 * instance itself. Alternatively a separate delegate may implement the
 * interface, and be set via the delegate bean property.
 *
 * <p>Delegates or subclasses may implement any number of interfaces.
 * All interfaces except IntroductionInterceptor are picked up from
 * the subclass or delegate by default.
 *
 * <p>The {@code suppressInterface} method can be used to suppress interfaces
 * implemented by the delegate but which should not be introduced to the owning
 * AOP proxy.
 *
 * <p>An instance of this class is serializable if the delegate is.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 16.11.2003
 * @see #suppressInterface
 * @see DelegatePerTargetObjectIntroductionInterceptor
 */
@SuppressWarnings("serial")
public class DelegatingIntroductionInterceptor extends IntroductionInfoSupport implements IntroductionInterceptor {

    /**
     * Object that actually implements the interfaces.
     * May be "this" if a subclass implements the introduced interfaces.
     */
    @Nullable
    private Object delegate;

    /**
     * Construct a new DelegatingIntroductionInterceptor, providing
     * a delegate that implements the interfaces to be introduced.
     * @param delegate the delegate that implements the introduced interfaces
     */
    public DelegatingIntroductionInterceptor(Object delegate) {
        init(delegate);
    }

    /**
     * Construct a new DelegatingIntroductionInterceptor.
     * The delegate will be the subclass, which must implement
     * additional interfaces.
     */
    protected DelegatingIntroductionInterceptor() {
        init(this);
    }

    /**
     * Both constructors use this init method, as it is impossible to pass
     * a "this" reference from one constructor to another.
     * @param delegate the delegate object
     */
    private void init(Object delegate) {
        Assert.notNull(delegate, "Delegate must not be null");
        this.delegate = delegate;
        implementInterfacesOnObject(delegate);

        // We don't want to expose the control interface
        suppressInterface(IntroductionInterceptor.class);
        suppressInterface(DynamicIntroductionAdvice.class);
    }

    /**
     * Subclasses may need to override this if they want to perform custom
     * behaviour in around advice. However, subclasses should invoke this
     * method, which handles introduced interfaces and forwarding to the target.
     */
    @Override
    @Nullable
    public Object invoke(MethodInvocation mi) throws Throwable {
        if (isMethodOnIntroducedInterface(mi)) {
            // Using the following method rather than direct reflection, we
            // get correct handling of InvocationTargetException
            // if the introduced method throws an exception.
            Object retVal = AopUtils.invokeJoinpointUsingReflection(this.delegate, mi.getMethod(),
                    mi.getArguments());

            // Massage return value if possible: if the delegate returned itself,
            // we really want to return the proxy.
            if (retVal == this.delegate && mi instanceof ProxyMethodInvocation) {
                Object proxy = ((ProxyMethodInvocation) mi).getProxy();
                if (mi.getMethod().getReturnType().isInstance(proxy)) {
                    retVal = proxy;
                }
            }
            return retVal;
        }

        return doProceed(mi);
    }

    /**
     * Proceed with the supplied {@link org.aopalliance.intercept.MethodInterceptor}.
     * Subclasses can override this method to intercept method invocations on the
     * target object which is useful when an introduction needs to monitor the object
     * that it is introduced into. This method is <strong>never</strong> called for
     * {@link MethodInvocation MethodInvocations} on the introduced interfaces.
     */
    protected Object doProceed(MethodInvocation mi) throws Throwable {
        // If we get here, just pass the invocation on.
        return mi.proceed();
    }

}