Spring核心接口之InitializingBean

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;
}

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);
}
}
}

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);
}
}

<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

public static void main(String[] args) throws Exception {
         String config = Test.class.getPackage().getName().replace('.', '/') + "/bean.xml";
           ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(config);
           context.start();
        }