一、InitializingBean介面說明
InitializingBean介面為bean提供了屬性初始化後的處理方法,它只包括afterPropertiesSet方法,凡是繼承該介面的類,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也可以清楚的理解該方法是在屬性設定後才呼叫的。
二、原始碼分析介面應用
通過檢視spring的載入bean的原始碼類(AbstractAutowireCapableBeanFactory)可以看到
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介面,如果實現了InitializingBean介面,則呼叫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 {
//呼叫afterPropertiesSet
((InitializingBean) bean).afterPropertiesSet();
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
//呼叫afterPropertiesSet
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null) { //判斷是否指定了init-method方法,如果指定了init-method方法,則再呼叫制定的init-method
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
//反射呼叫init-method方法
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
分析程式碼可以瞭解:
1:spring為bean提供了兩種初始化bean的方式,實現InitializingBean介面,實現afterPropertiesSet方法,或者在配置檔案中同過init-method指定,兩種方式可以同時使用
2:實現InitializingBean介面是直接呼叫afterPropertiesSet方法,比通過反射呼叫init-method指定的方法效率相對來說要高點。但是init-method方式消除了對spring的依賴
3:如果呼叫afterPropertiesSet方法時出錯,則不呼叫init-method指定的方法。
三、介面應用
InitializingBean介面在spring框架中本身就很多應用,這就不多說了。我們在實際應用中如何使用該介面呢?
1、使用InitializingBean介面處理一個配置檔案:
import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;
import org.springframework.beans.factory.InitializingBean;
public class ConfigBean implements InitializingBean{
//微信公眾號配置檔案
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配置檔案:
<bean id="configBean" class="com.ConfigBean">
<property name="configFile" value="d:/wechat.properties"></property>
</bean>
wechat.properties配置檔案
wechat.appid=wxappid
wechat.appsecret=wxappsecret
3、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();
}