1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.eventbus; 18 19 import com.google.common.base.Preconditions; 20 import java.lang.reflect.InvocationTargetException; 21 import java.lang.reflect.Method; 22 23 /** 24 * Wraps a single-argument 'handler' method on a specific object. 25 * 26 * <p>This class only verifies the suitability of the method and event type if 27 * something fails. Callers are expected to verify their uses of this class. 28 * 29 * <p>Two EventHandlers are equivalent when they refer to the same method on the 30 * same object (not class). This property is used to ensure that no handler 31 * method is registered more than once. 32 * 33 * @author Cliff Biffle 34 */ 35 class EventHandler { 36 37 /** Object sporting the handler method. */ 38 private final Object target; 39 /** Handler method. */ 40 private final Method method; 41 42 /** 43 * Creates a new EventHandler to wrap {@code method} on @{code target}. 44 * 45 * @param target object to which the method applies. 46 * @param method handler method. 47 */ EventHandler(Object target, Method method)48 EventHandler(Object target, Method method) { 49 Preconditions.checkNotNull(target, 50 "EventHandler target cannot be null."); 51 Preconditions.checkNotNull(method, "EventHandler method cannot be null."); 52 53 this.target = target; 54 this.method = method; 55 method.setAccessible(true); 56 } 57 58 /** 59 * Invokes the wrapped handler method to handle {@code event}. 60 * 61 * @param event event to handle 62 * @throws InvocationTargetException if the wrapped method throws any 63 * {@link Throwable} that is not an {@link Error} ({@code Error}s are 64 * propagated as-is). 65 */ handleEvent(Object event)66 public void handleEvent(Object event) throws InvocationTargetException { 67 try { 68 method.invoke(target, new Object[] { event }); 69 } catch (IllegalArgumentException e) { 70 throw new Error("Method rejected target/argument: " + event, e); 71 } catch (IllegalAccessException e) { 72 throw new Error("Method became inaccessible: " + event, e); 73 } catch (InvocationTargetException e) { 74 if (e.getCause() instanceof Error) { 75 throw (Error) e.getCause(); 76 } 77 throw e; 78 } 79 } 80 toString()81 @Override public String toString() { 82 return "[wrapper " + method + "]"; 83 } 84 hashCode()85 @Override public int hashCode() { 86 final int PRIME = 31; 87 return (PRIME + method.hashCode()) * PRIME + target.hashCode(); 88 } 89 equals(Object obj)90 @Override public boolean equals(Object obj) { 91 if(this == obj) { 92 return true; 93 } 94 95 if(obj == null) { 96 return false; 97 } 98 99 if(getClass() != obj.getClass()) { 100 return false; 101 } 102 103 final EventHandler other = (EventHandler) obj; 104 105 return method.equals(other.method) && target == other.target; 106 } 107 108 } 109