Spring核心接口之InitializingBean

1、InitializingBean接口說明

InitializingBean接口爲bean提供了屬性初始化後的處理方法，它只包括afterPropertiesSet方法，凡是繼承該接口的類，在bean的屬性初始化後都會執行該方法。

 

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;

 

}

 

從方法名afterPropertiesSet也能夠清楚的理解該方法是在屬性設置後才調用的。

 

2、源碼分析接口應用

經過查看spring的加載bean的源碼類(AbstractAutowireCapableBeanFactory)能夠看到

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

throws Throwable {

//判斷該bean是否實現了實現了InitializingBean接口，若是實現了InitializingBean接口，則調用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 {

//調用afterPropertiesSet

((InitializingBean) bean).afterPropertiesSet();

return null;

}

}, getAccessControlContext());

}

catch (PrivilegedActionException pae) {

throw pae.getException();

}

}

else {

//調用afterPropertiesSet

((InitializingBean) bean).afterPropertiesSet();

}

}

 

if (mbd != null) { //判斷是否指定了init-method方法，若是指定了init-method方法，則再調用制定的init-method

String initMethodName = mbd.getInitMethodName();

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

!mbd.isExternallyManagedInitMethod(initMethodName)) {

//反射調用init-method方法

invokeCustomInitMethod(beanName, bean, mbd);

}

}

}

分析代碼能夠了解：

1：spring爲bean提供了兩種初始化bean的方式，實現InitializingBean接口，實現afterPropertiesSet方法，或者在配置文件中同過init-method指定，兩種方式能夠同時使用

2：實現InitializingBean接口是直接調用afterPropertiesSet方法，比經過反射調用init-method指定的方法效率相對來講要高點。可是init-method方式消除了對spring的依賴

3：若是調用afterPropertiesSet方法時出錯，則不調用init-method指定的方法。

 

3、接口應用

   InitializingBean接口在spring框架中自己就不少應用，這就很少說了。咱們在實際應用中如何使用該接口呢？

 

一、使用InitializingBean接口處理一個配置文件：

import java.io.File;

import java.io.FileInputStream;

import java.util.Properties;

 

import org.springframework.beans.factory.InitializingBean;

 

public class ConfigBean implements InitializingBean{

 

//微信公衆號配置文件

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);

}

}

二、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

三、測試

     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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