1 /** 2 * Copyright (C) 2008 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; 18 19 import com.google.inject.spi.BindingScopingVisitor; 20 import com.google.inject.spi.BindingTargetVisitor; 21 import com.google.inject.spi.Element; 22 23 /** 24 * A mapping from a key (type and optional annotation) to the strategy for getting instances of the 25 * type. This interface is part of the introspection API and is intended primarily for use by 26 * tools. 27 * 28 * <p>Bindings are created in several ways: 29 * <ul> 30 * <li>Explicitly in a module, via {@code bind()} and {@code bindConstant()} 31 * statements: 32 * <pre> 33 * bind(Service.class).annotatedWith(Red.class).to(ServiceImpl.class); 34 * bindConstant().annotatedWith(ServerHost.class).to(args[0]);</pre></li> 35 * <li>Implicitly by the Injector by following a type's {@link ImplementedBy 36 * pointer} {@link ProvidedBy annotations} or by using its {@link Inject annotated} or 37 * default constructor.</li> 38 * <li>By converting a bound instance to a different type.</li> 39 * <li>For {@link Provider providers}, by delegating to the binding for the provided type.</li> 40 * </ul> 41 * 42 * 43 * <p>They exist on both modules and on injectors, and their behaviour is different for each: 44 * <ul> 45 * <li><strong>Module bindings</strong> are incomplete and cannot be used to provide instances. 46 * This is because the applicable scopes and interceptors may not be known until an injector 47 * is created. From a tool's perspective, module bindings are like the injector's source 48 * code. They can be inspected or rewritten, but this analysis must be done statically.</li> 49 * <li><strong>Injector bindings</strong> are complete and valid and can be used to provide 50 * instances. From a tools' perspective, injector bindings are like reflection for an 51 * injector. They have full runtime information, including the complete graph of injections 52 * necessary to satisfy a binding.</li> 53 * </ul> 54 * 55 * @param <T> the bound type. The injected is always assignable to this type. 56 * 57 * @author crazybob@google.com (Bob Lee) 58 * @author jessewilson@google.com (Jesse Wilson) 59 */ 60 public interface Binding<T> extends Element { 61 62 /** 63 * Returns the key for this binding. 64 */ getKey()65 Key<T> getKey(); 66 67 /** 68 * Returns the scoped provider guice uses to fulfill requests for this 69 * binding. 70 * 71 * @throws UnsupportedOperationException when invoked on a {@link Binding} 72 * created via {@link com.google.inject.spi.Elements#getElements}. This 73 * method is only supported on {@link Binding}s returned from an injector. 74 */ getProvider()75 Provider<T> getProvider(); 76 77 /** 78 * Accepts a target visitor. Invokes the visitor method specific to this binding's target. 79 * 80 * @param visitor to call back on 81 * @since 2.0 82 */ acceptTargetVisitor(BindingTargetVisitor<? super T, V> visitor)83 <V> V acceptTargetVisitor(BindingTargetVisitor<? super T, V> visitor); 84 85 /** 86 * Accepts a scoping visitor. Invokes the visitor method specific to this binding's scoping. 87 * 88 * @param visitor to call back on 89 * @since 2.0 90 */ acceptScopingVisitor(BindingScopingVisitor<V> visitor)91 <V> V acceptScopingVisitor(BindingScopingVisitor<V> visitor); 92 } 93