Spring核心接口之InitializingBean

一、InitializingBean接口说明
InitializingBean接口为bean提供了属性初始化后的处理方法，它只包括afterPropertiesSet方法，凡是继承该接口的类，在bean的属性初始化后都会执行该方法。

package org.springframework.beans.factory; 


/** 

 * Interface to be implemented by beans that need to react once all their 

 * properties have been set by a BeanFactory: for example, to perform custom 

 * initialization, or merely to check that all mandatory properties have been set. 

 * 

 * <p>An alternative to implementing InitializingBean is specifying a custom 

 * init-method, for example in an XML bean definition. 

 * For a list of all bean lifecycle methods, see the BeanFactory javadocs. 

 * 

 * @author Rod Johnson 

 * @see BeanNameAware 

 * @see BeanFactoryAware 

 * @see BeanFactory 

 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName 

 * @see org.springframework.context.ApplicationContextAware 

 */ 

public interface InitializingBean { 


 /** 

 * Invoked by a BeanFactory after it has set all bean properties supplied 

 * (and satisfied BeanFactoryAware and ApplicationContextAware). 

 * <p>This method allows the bean instance to perform initialization only 

 * possible when all bean properties have been set and to throw an 

 * exception in the event of misconfiguration. 

 * @throws Exception in the event of misconfiguration (such 

 * as failure to set an essential property) or if initialization fails. 

 */ 

 void afterPropertiesSet() throws Exception; 


}

从方法名afterPropertiesSet也可以清楚的理解该方法是在属性设置后才调用的。

二、源码分析接口应用
通过查看spring的加载bean的源码类(AbstractAutowireCapableBeanFactory)可以看到

protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd) 

 throws Throwable { 

//判断该bean是否实现了实现了InitializingBean接口，如果实现了InitializingBean接口，则调用bean的afterPropertiesSet方法 

 boolean isInitializingBean = (bean instanceof InitializingBean); 

 if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) { 

 if (logger.isDebugEnabled()) { 

 logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'"); 

 } 

 if (System.getSecurityManager() != null) { 

 try { 

 AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { 

 public Object run() throws Exception { 

 //调用afterPropertiesSet 

 ((InitializingBean) bean).afterPropertiesSet(); 

 return null; 

 } 

 }, getAccessControlContext()); 

 } 

 catch (PrivilegedActionException pae) { 

 throw pae.getException(); 

 } 

 } 

 else { 

 //调用afterPropertiesSet 

 ((InitializingBean) bean).afterPropertiesSet(); 

 } 

 } 


 if (mbd != null) { //判断是否指定了init-method方法，如果指定了init-method方法，则再调用制定的init-method 

 String initMethodName = mbd.getInitMethodName(); 

 if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) && 

 !mbd.isExternallyManagedInitMethod(initMethodName)) { 

 //反射调用init-method方法 

 invokeCustomInitMethod(beanName, bean, mbd); 

 } 

 } 

 }

分析代码可以了解：
1：spring为bean提供了两种初始化bean的方式，实现InitializingBean接口，实现afterPropertiesSet方法，或者在配置文件中同过init-method指定，两种方式可以同时使用
2：实现InitializingBean接口是直接调用afterPropertiesSet方法，比通过反射调用init-method指定的方法效率相对来说要高点。但是init-method方式消除了对spring的依赖
3：如果调用afterPropertiesSet方法时出错，则不调用init-method指定的方法。

三、接口应用
InitializingBean接口在spring框架中本身就很多应用，这就不多说了。我们在实际应用中如何使用该接口呢？

1、使用InitializingBean接口处理一个配置文件：

import java.io.File; 

 import java.io.FileInputStream; 

 import java.util.Properties; 


 import org.springframework.beans.factory.InitializingBean; 


 public class ConfigBean implements InitializingBean{ 


 //微信公众号配置文件 

 private String configFile; 


 private String appid; 


 private String appsecret; 


 public String getConfigFile() { 

 return configFile; 

 } 


 public void setConfigFile(String configFile) { 

 this.configFile = configFile; 

 } 


 public void afterPropertiesSet() throws Exception { 

 if(configFile!=null){ 

 File cf = new File(configFile); 

 if(cf.exists()){ 

 Properties pro = new Properties(); 

 pro.load(new FileInputStream(cf)); 

 appid = pro.getProperty("wechat.appid"); 

 appsecret = pro.getProperty("wechat.appsecret"); 

 } 

 } 

 System.out.println(appid); 

 System.out.println(appsecret); 

 } 

 }

2、配置
spring配置文件：
<bean id="configBean" class="com.ConfigBean">
<property name="configFile" value="d:/wechat.properties"></property>
</bean>
wechat.properties配置文件
wechat.appid=wxappid
wechat.appsecret=wxappsecret
3、测试

public static void main(String[] args) throws Exception { 

 String config = Test.class.getPackage().getName().replace('.', '/') + "/bean.xml"; 

 ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(config); 

 context.start(); 

 }

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