001/* 002 * Copyright 2002-2018 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.beans.factory.config; 018 019import org.springframework.beans.factory.FactoryBean; 020import org.springframework.beans.factory.FactoryBeanNotInitializedException; 021import org.springframework.lang.Nullable; 022 023/** 024 * {@link FactoryBean} which returns a value which is the result of a static or instance 025 * method invocation. For most use cases it is better to just use the container's 026 * built-in factory method support for the same purpose, since that is smarter at 027 * converting arguments. This factory bean is still useful though when you need to 028 * call a method which doesn't return any value (for example, a static class method 029 * to force some sort of initialization to happen). This use case is not supported 030 * by factory methods, since a return value is needed to obtain the bean instance. 031 * 032 * <p>Note that as it is expected to be used mostly for accessing factory methods, 033 * this factory by default operates in a <b>singleton</b> fashion. The first request 034 * to {@link #getObject} by the owning bean factory will cause a method invocation, 035 * whose return value will be cached for subsequent requests. An internal 036 * {@link #setSingleton singleton} property may be set to "false", to cause this 037 * factory to invoke the target method each time it is asked for an object. 038 * 039 * <p><b>NOTE: If your target method does not produce a result to expose, consider 040 * {@link MethodInvokingBean} instead, which avoids the type determination and 041 * lifecycle limitations that this {@link MethodInvokingFactoryBean} comes with.</b> 042 * 043 * <p>This invoker supports any kind of target method. A static method may be specified 044 * by setting the {@link #setTargetMethod targetMethod} property to a String representing 045 * the static method name, with {@link #setTargetClass targetClass} specifying the Class 046 * that the static method is defined on. Alternatively, a target instance method may be 047 * specified, by setting the {@link #setTargetObject targetObject} property as the target 048 * object, and the {@link #setTargetMethod targetMethod} property as the name of the 049 * method to call on that target object. Arguments for the method invocation may be 050 * specified by setting the {@link #setArguments arguments} property. 051 * 052 * <p>This class depends on {@link #afterPropertiesSet()} being called once 053 * all properties have been set, as per the InitializingBean contract. 054 * 055 * <p>An example (in an XML based bean factory definition) of a bean definition 056 * which uses this class to call a static factory method: 057 * 058 * <pre class="code"> 059 * <bean id="myObject" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 060 * <property name="staticMethod" value="com.whatever.MyClassFactory.getInstance"/> 061 * </bean></pre> 062 * 063 * <p>An example of calling a static method then an instance method to get at a 064 * Java system property. Somewhat verbose, but it works. 065 * 066 * <pre class="code"> 067 * <bean id="sysProps" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 068 * <property name="targetClass" value="java.lang.System"/> 069 * <property name="targetMethod" value="getProperties"/> 070 * </bean> 071 * 072 * <bean id="javaVersion" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> 073 * <property name="targetObject" ref="sysProps"/> 074 * <property name="targetMethod" value="getProperty"/> 075 * <property name="arguments" value="java.version"/> 076 * </bean></pre> 077 * 078 * @author Colin Sampaleanu 079 * @author Juergen Hoeller 080 * @since 21.11.2003 081 * @see MethodInvokingBean 082 * @see org.springframework.util.MethodInvoker 083 */ 084public class MethodInvokingFactoryBean extends MethodInvokingBean implements FactoryBean<Object> { 085 086 private boolean singleton = true; 087 088 private boolean initialized = false; 089 090 /** Method call result in the singleton case. */ 091 @Nullable 092 private Object singletonObject; 093 094 095 /** 096 * Set if a singleton should be created, or a new object on each 097 * {@link #getObject()} request otherwise. Default is "true". 098 */ 099 public void setSingleton(boolean singleton) { 100 this.singleton = singleton; 101 } 102 103 @Override 104 public void afterPropertiesSet() throws Exception { 105 prepare(); 106 if (this.singleton) { 107 this.initialized = true; 108 this.singletonObject = invokeWithTargetException(); 109 } 110 } 111 112 113 /** 114 * Returns the same value each time if the singleton property is set 115 * to "true", otherwise returns the value returned from invoking the 116 * specified method on the fly. 117 */ 118 @Override 119 @Nullable 120 public Object getObject() throws Exception { 121 if (this.singleton) { 122 if (!this.initialized) { 123 throw new FactoryBeanNotInitializedException(); 124 } 125 // Singleton: return shared object. 126 return this.singletonObject; 127 } 128 else { 129 // Prototype: new object on each call. 130 return invokeWithTargetException(); 131 } 132 } 133 134 /** 135 * Return the type of object that this FactoryBean creates, 136 * or {@code null} if not known in advance. 137 */ 138 @Override 139 public Class<?> getObjectType() { 140 if (!isPrepared()) { 141 // Not fully initialized yet -> return null to indicate "not known yet". 142 return null; 143 } 144 return getPreparedMethod().getReturnType(); 145 } 146 147 @Override 148 public boolean isSingleton() { 149 return this.singleton; 150 } 151 152}