1 /** 2 * Copyright (C) 2010 Google Inc. 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.inject.spi; 18 19 import com.google.inject.Binding; 20 import com.google.inject.Provider; 21 22 /** 23 * A Provider that is part of an extension which supports a custom 24 * BindingTargetVisitor. 25 * <p> 26 * When an extension binds a provider instance, the provider can implement this 27 * interface to allow users using the 28 * {@link Binding#acceptTargetVisitor(BindingTargetVisitor)} method to visit a 29 * custom visitor designed for that extension. A typical implementation within 30 * the extension would look like 31 * <pre> 32 * <V, B> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) { 33 * if(visitor instanceof MyCustomExtensionVisitor) { 34 * return ((MyCustomExtensionVisitor<B, V>)visitor).visitCustomExtension(customProperties, binding); 35 * } else { 36 * return visitor.visit(binding); 37 * } 38 * }</pre> 39 * 'MyCustomExtensionVisitor' in the example above would be an interface the 40 * extension provides that users can implement in order to be notified of custom 41 * extension information. These visitor interfaces must extend from 42 * BindingTargetVisitor. 43 * 44 * @since 3.0 45 * @author sameb@google.com (Sam Berlin) 46 */ 47 public interface ProviderWithExtensionVisitor<T> extends Provider<T> { 48 49 /** 50 * Instructs the extension determine if the visitor is an instance of a custom 51 * extension visitor, and if so, visit it using that method. If the visitor is 52 * not an instance of the custom extension visitor, this method <b>MUST</b> 53 * call visitor.visit(binding). 54 * <p> 55 * Due to issues with generics, the type parameters of this method do not 56 * relate to the type of the provider. In practice, the 'B' type will always 57 * be a supertype of 'T'. 58 */ acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding)59 <B, V> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, 60 ProviderInstanceBinding<? extends B> binding); 61 } 62