Java tutorial
/* * Copyright 2002-2018 the original author or 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 * * https://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 org.springframework.beans.factory.config; import org.springframework.beans.factory.FactoryBean; import org.springframework.beans.factory.FactoryBeanNotInitializedException; import org.springframework.lang.Nullable; /** * {@link FactoryBean} which returns a value which is the result of a static or instance * method invocation. For most use cases it is better to just use the container's * built-in factory method support for the same purpose, since that is smarter at * converting arguments. This factory bean is still useful though when you need to * call a method which doesn't return any value (for example, a static class method * to force some sort of initialization to happen). This use case is not supported * by factory methods, since a return value is needed to obtain the bean instance. * * <p>Note that as it is expected to be used mostly for accessing factory methods, * this factory by default operates in a <b>singleton</b> fashion. The first request * to {@link #getObject} by the owning bean factory will cause a method invocation, * whose return value will be cached for subsequent requests. An internal * {@link #setSingleton singleton} property may be set to "false", to cause this * factory to invoke the target method each time it is asked for an object. * * <p><b>NOTE: If your target method does not produce a result to expose, consider * {@link MethodInvokingBean} instead, which avoids the type determination and * lifecycle limitations that this {@link MethodInvokingFactoryBean} comes with.</b> * * <p>This invoker supports any kind of target method. A static method may be specified * by setting the {@link #setTargetMethod targetMethod} property to a String representing * the static method name, with {@link #setTargetClass targetClass} specifying the Class * that the static method is defined on. Alternatively, a target instance method may be * specified, by setting the {@link #setTargetObject targetObject} property as the target * object, and the {@link #setTargetMethod targetMethod} property as the name of the * method to call on that target object. Arguments for the method invocation may be * specified by setting the {@link #setArguments arguments} property. * * <p>This class depends on {@link #afterPropertiesSet()} being called once * all properties have been set, as per the InitializingBean contract. * * <p>An example (in an XML based bean factory definition) of a bean definition * which uses this class to call a static factory method: * * <pre class="code"> * <bean id="myObject" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> * <property name="staticMethod" value="com.whatever.MyClassFactory.getInstance"/> * </bean></pre> * * <p>An example of calling a static method then an instance method to get at a * Java system property. Somewhat verbose, but it works. * * <pre class="code"> * <bean id="sysProps" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> * <property name="targetClass" value="java.lang.System"/> * <property name="targetMethod" value="getProperties"/> * </bean> * * <bean id="javaVersion" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> * <property name="targetObject" ref="sysProps"/> * <property name="targetMethod" value="getProperty"/> * <property name="arguments" value="java.version"/> * </bean></pre> * * @author Colin Sampaleanu * @author Juergen Hoeller * @since 21.11.2003 * @see MethodInvokingBean * @see org.springframework.util.MethodInvoker */ public class MethodInvokingFactoryBean extends MethodInvokingBean implements FactoryBean<Object> { private boolean singleton = true; private boolean initialized = false; /** Method call result in the singleton case. */ @Nullable private Object singletonObject; /** * Set if a singleton should be created, or a new object on each * {@link #getObject()} request otherwise. Default is "true". */ public void setSingleton(boolean singleton) { this.singleton = singleton; } @Override public void afterPropertiesSet() throws Exception { prepare(); if (this.singleton) { this.initialized = true; this.singletonObject = invokeWithTargetException(); } } /** * Returns the same value each time if the singleton property is set * to "true", otherwise returns the value returned from invoking the * specified method on the fly. */ @Override @Nullable public Object getObject() throws Exception { if (this.singleton) { if (!this.initialized) { throw new FactoryBeanNotInitializedException(); } // Singleton: return shared object. return this.singletonObject; } else { // Prototype: new object on each call. return invokeWithTargetException(); } } /** * Return the type of object that this FactoryBean creates, * or {@code null} if not known in advance. */ @Override public Class<?> getObjectType() { if (!isPrepared()) { // Not fully initialized yet -> return null to indicate "not known yet". return null; } return getPreparedMethod().getReturnType(); } @Override public boolean isSingleton() { return this.singleton; } }