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();

}