com.google.common.eventbus.EventSubscriber.java Source code

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Here is the source code for com.google.common.eventbus.EventSubscriber.java

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/*
 * Copyright (C) 2007 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.eventbus;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Preconditions;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import javax.annotation.Nullable;

/**
 * Wraps a single-argument subscriber method on a specific object.
 *
 * <p>This class only verifies the suitability of the method and event type if
 * something fails.  Callers are expected to verify their uses of this class.
 *
 * <p>Two EventSubscribers are equivalent when they refer to the same method on the
 * same object (not class).   This property is used to ensure that no subscriber
 * method is registered more than once.
 *
 * @author Cliff Biffle
 */
class EventSubscriber {

    /** Object sporting the subscriber method. */
    private final Object target;
    /** Subscriber method. */
    private final Method method;

    /**
     * Creates a new EventSubscriber to wrap {@code method} on @{code target}.
     *
     * @param target  object to which the method applies.
     * @param method  subscriber method.
     */
    EventSubscriber(Object target, Method method) {
        Preconditions.checkNotNull(target, "EventSubscriber target cannot be null.");
        Preconditions.checkNotNull(method, "EventSubscriber method cannot be null.");

        this.target = target;
        this.method = method;
        method.setAccessible(true);
    }

    /**
     * Invokes the wrapped subscriber method to handle {@code event}.
     *
     * @param event  event to handle
     * @throws InvocationTargetException  if the wrapped method throws any
     *     {@link Throwable} that is not an {@link Error} ({@code Error} instances are
     *     propagated as-is).
     */
    public void handleEvent(Object event) throws InvocationTargetException {
        checkNotNull(event);
        try {
            method.invoke(target, new Object[] { event });
        } catch (IllegalArgumentException e) {
            throw new Error("Method rejected target/argument: " + event, e);
        } catch (IllegalAccessException e) {
            throw new Error("Method became inaccessible: " + event, e);
        } catch (InvocationTargetException e) {
            if (e.getCause() instanceof Error) {
                throw (Error) e.getCause();
            }
            throw e;
        }
    }

    @Override
    public String toString() {
        return "[wrapper " + method + "]";
    }

    @Override
    public int hashCode() {
        final int PRIME = 31;
        return (PRIME + method.hashCode()) * PRIME + System.identityHashCode(target);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if (obj instanceof EventSubscriber) {
            EventSubscriber that = (EventSubscriber) obj;
            // Use == so that different equal instances will still receive events.
            // We only guard against the case that the same object is registered
            // multiple times
            return target == that.target && method.equals(that.method);
        }
        return false;
    }

    public Object getSubscriber() {
        return target;
    }

    public Method getMethod() {
        return method;
    }
}