文章目录
- 简介
- 应用场景
- 代码示例
- 运行示例
简介
这篇文章主要介绍了Spring中InitializingBean的使用详细解析，InitializingBean是Spring提供的拓展性接口，提供了属性初始化后的处理方法,它只有一个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。
spring容器中Bean的生命周期内所有可扩展的点的调用顺序| 扩展接口 | 实现接口 |
|---|---|
| ApplicationContextlnitializer | initialize |
| AbstractApplicationContext | refreshe |
| BeanDefinitionRegistryPostProcessor | postProcessBeanDefinitionRegistry |
| BeanDefinitionRegistryPostProcessor | postProcessBeanFactory |
| BeanFactoryPostProcessor | postProcessBeanFactory |
| instantiationAwareBeanPostProcessor | postProcessBeforelnstantiation |
| SmartlnstantiationAwareBeanPostProcessor | determineCandidateConstructors |
| MergedBeanDefinitionPostProcessor | postProcessMergedBeanDefinition |
| InstantiationAwareBeanPostProcessor | postProcessAfterlnstantiation |
| SmartInstantiationAwareBeanPostProcessor | getEarlyBeanReference |
| BeanFactoryAware | postProcessPropertyValues |
| ApplicationContextAwareProcessor | invokeAwarelnterfaces |
| BeanNameAware | setBeanName |
| InstantiationAwareBeanPostProcessor | postProcessBeforelnstantiation| |
| BeanNameAware | setBeanName |
| @PostConstruct | |
| InitializingBean | afterPropertiesSet |
| FactoryBean | getobject |
| SmartlnitializingSingleton | afterSingletonslnstantiated |
| CommandLineRunner | run |
| DisposableBean | destroy |
/**
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//执行BeanPostProcessor接口实现类的postProcessBeforeInitialization方法
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//如果bean实现了InitializingBean或者自定义了initMethod，
//会在这里执行InitializingBean#afterPropertiesSet和initMethod方法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
//执行BeanPostProcessor接口实现类的postProcessAfterInitialization方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
protected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd)
throws Throwable {
//判断bean是否实现了InitializingBean
boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.hasAnyExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isTraceEnabled()) {
logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
((InitializingBean) bean).afterPropertiesSet();
return null;
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
//如果实现了InitializingBean，真接调用afterPropertiesSet()，
((InitializingBean) bean).afterPropertiesSet();
}
}
if (mbd != null && bean.getClass() != NullBean.class) {
//获取bean自定义的init-method方法
String initMethodName = mbd.getInitMethodName();
if (StringUtils.hasLength(initMethodName) &&
!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.hasAnyExternallyManagedInitMethod(initMethodName)) {
//如果自定义了init-method方法，在这里开始执行；
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}
看完源码部分，我们可以很清楚地知道InitializingBean#afterPropertiesSet方法和init-method是什么时候用什么方式来调用的（ 通过反射调用init-method），且InitializingBean#afterPropertiesSet方法的执行时机要稍早于init-method。另外，如果调用afterPropertiesSet方法时出错，则不调用init-method指定的方法
应用场景
这个扩展点是比较有用的一个扩展点，可以用于
- 修改默认设置的属性
- 添加补充额外的属性值
- 或者针对关键属性做校验
- spring MVC内容有一个经典的实现场景，RequestMappingHandlerMapping完成URL与controller的映射工作
public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMapping implements InitializingBean {
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}
protected void initHandlerMethods() {
//循环所有的bean
for (String beanName : getCandidateBeanNames()) {
//如果bean名字不是以scopedTarget.开头
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
processCandidateBean(beanName);
}
}
//日志输出
handlerMethodsInitialized(getHandlerMethods());
}
protected void processCandidateBean(String beanName) {
Class<?> beanType = null;
try {
beanType = obtainApplicationContext().getType(beanName);
}
catch (Throwable ex) {
if (logger.isTraceEnabled()) {
logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
}
}
//他们是否是Handler(类上标注@Controller注解或者@RequestMapping注解)
if (beanType != null && isHandler(beanType)) {
//获取这个类上所有标注@RequestMapping的方法信息，以RequestMappingInfo形式把他们储存到MappingRegistry中
detectHandlerMethods(beanName);
}
}
代码示例
完成一个rsa对象的初始化，方便该类方法调用使用
@Slf4j
@Configuration
public class ExtendInitializingBean implements InitializingBean {
private RSA rsa;
@Override
public void afterPropertiesSet() {
String priv = "MIICdQIBADANBgkqhkiG9w0BAQEFAASCAl8wggJbAgEAAoGBAJzDhvCJBIIuZzNu\n" +
"+dHWY5inSAN6d/yqWOTl/5rWofT2+m59qjKoFuJ9kkuYUCkIpoEtLhu5PfOAdR9R\n" +
"bsVnfXThgwOQFHx1/v4URXwOBrBHRYhPy8fApJSfdBWgKMs9GZ5WbDWVkPm7xhvJ\n" +
"t716Wtx/leCjvq87jWVg8oo83uKtAgMBAAECgYAW77bNInG3QxHUy9kf03XpY8Rc\n" +
"xJeiBMyShSJjuyFMMFy45jMM9rIOe8qiu+DdTXI14UXnRtsNHHpGgEmBoYrl4IZ9\n" +
"Wgbxn0fkrcHaw4F8GoAapyqAgNkyU3kAf8of6G+ZeMulcZtbb7NXVkwTaRHOkzBg\n" +
"2a44HCSQ2n/fHPxfwwJBANFhUKWMOV3SqEN7RjsxWNAk8P25xHzIWq6KCyhOx5Vm\n" +
"KLIttnYUiA3UA3q5RJK8Hqh0a2JGcg8O9HawOuMWAAsCQQC/qxNG08pX8dm5mh5B\n" +
"9d/Wc09U9V7Xni9gqqS5adjxChm97t5h8k3wRxTqDWHCJyZTkezy7pmZvaFWqwLO\n" +
"xkMnAkBLEbIBeNIEkoejkiovBNVL40LIJXeOKaNhmrq/W+dw6CzFHWCi21+gXZhV\n" +
"wuEUHwB68yqhFJLGVV1OxIaIbpXbAkBBY0WiRiKjuhiDHzbvXchNSu1nmIYQnSCg\n" +
"o9aqgpfGM6HwkAtB8v3v2PAjoQkWyXBj1ka14fx43J6sCI9ep3jFAkBDi3wnlIzc\n" +
"LpJxumw84P8f3pVJ1xKx9tchAh1W+hhcaq+/S+u3rIJcXfXWLojUp7yMyKjzy2lU\n" +
"PNC8Qke0R/qC";
String pub = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCcw4bwiQSCLmczbvnR1mOYp0gD\n" +
"enf8qljk5f+a1qH09vpufaoyqBbifZJLmFApCKaBLS4buT3zgHUfUW7FZ3104YMD\n" +
"kBR8df7+FEV8DgawR0WIT8vHwKSUn3QVoCjLPRmeVmw1lZD5u8Ybybe9elrcf5Xg\n" +
"o76vO41lYPKKPN7irQIDAQAB";
rsa = new RSA(priv, pub);
log.info("afterPropertiesSet--Extend--run");
}
private void init(){
log.info("init------run");
}
@Bean(initMethod = "init")
public ExtendInitializingBean execInit(){
return new ExtendInitializingBean();
}
}
运行示例
