/*
* Copyright 2002-2017 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
*
* http://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;
/**
* {@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 */
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
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;
}
}