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本篇内容主要讲解“Spring初始化Bean的使用方法”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Spring初始化Bean的使用方法”吧!
if (instanceWrapper == null) {
//上一篇bean的加载后部分主要分析了bean的创建,此步骤完成之后bean已经创建完成,但属性还没有赋值,Spring
//解决循环依赖的关键步骤就在此步骤完成之后,bean已创建但还没有属性赋值,如下图
instanceWrapper = createBeanInstance(beanName, mbd, args);
}如下图,以最简单的AB循环依赖为例,A中有属性类B,B中又有属性类A,那么初始化beanA的过程如下图.
//上图中addSingletonFactory逻辑,只有是单例的,允许循环依赖且该bean正在创建中(创建时会记录该属性,创建完成会移除该属性),
//只有三个条件都满足才会addSingletonFactory
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences
&& isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
//为避免后期循环依赖,可以在bean初始化后属性赋值之前将创建实例的ObjectFactory加入工厂
addSingletonFactory(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
return getEarlyBeanReference(beanName, mbd, bean);
}
});
}protected void addSingletonFactory(String beanName, ObjectFactory singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
synchronized (this.singletonObjects) {
if (!this.singletonObjects.containsKey(beanName)) {
//放入map中
this.singletonFactories.put(beanName, singletonFactory);
//目的是检测循环引用,移除
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
}//我们熟知的AOP就是在这里将advice动态织如bean中,若没有则直接返回bean
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
if (exposedObject == null) {
return exposedObject;
}
}
}
}
return exposedObject;
}protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
BeanWrapper instanceWrapper = null;
if (instanceWrapper == null) {
//1.创建bean,但还没有属性赋值
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//2.条件满足的话讲ObjectFactory放入map中,为了解决循环依赖
addSingletonFactory(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
return getEarlyBeanReference(beanName, mbd, bean);
}
});
Object exposedObject = bean;
try {
//3.属性赋值
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
//4.调用一系列初始化方法
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
}
return exposedObject;
}//之前已经分析了步骤1创建bean和步骤2添加ObjectFactory，现在来分析属性赋值populateBean。
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
//读取配置文件,解析标签之后,此处的pvs已经有值了,就是配置文件中配置的lwh sayHello
PropertyValues pvs = mbd.getPropertyValues();
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
//根据名称自动注入
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
//根据类型自动注入
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
//属性赋值
applyPropertyValues(beanName, mbd, bw, pvs);
}protected void autowireByName(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
//寻找bw中需要依赖注入的属性,若是配置文件中配置了person属性,则此处查出来的propertyNames为空
//因为配置文件中配置了name为person的bean,此处查找出来的propertyNames封装的就是person,若是将配置文
//件中autowire改为byType程序也可以正常运行;若将配置的person的id改为其他的,则byName不能正常运行,而
//byType可以正常运行
String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
for (String propertyName : propertyNames) {
if (containsBean(propertyName)) {
//递归初始化相关的bean,此处为person
Object bean = getBean(propertyName);
//加到pvs属性中
pvs.add(propertyName, bean);
registerDependentBean(propertyName, beanName);
}
}
}protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
MutablePropertyValues mpvs = null;
List<PropertyValue> original;
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
if (mpvs.isConverted()) {
try {
bw.setPropertyValues(mpvs);
return;
}
}
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
String propertyName = pv.getName();
Object originalValue = pv.getValue();
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if (convertible && originalValue instanceof TypedStringValue &&
!((TypedStringValue) originalValue).isDynamic() &&
!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}
else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}
try {
//赋值核心代码,此步骤完成之后,bean中的属性就被赋值了
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
}
}//分析完了属性赋值populateBean方法,然后分析一系列初始化方法
//属性赋值
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
//调用初始化方法
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
//1.激活Aware方法
invokeAwareMethods(beanName, bean);
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//2.执行BeanPostProcessor的before方法
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//3.激活用户定义的初始化方法,包括接口InitializingBean中的初始化方法和用户配置的init-method
invokeInitMethods(beanName, wrappedBean, mbd);
}
if (mbd == null || !mbd.isSynthetic()) {
//4.执行BeanPostProcessor的after方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}步骤1：激活Aware方法
private void invokeAwareMethods(final String beanName, final Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
}
if (bean instanceof BeanFactoryAware) {
//附录1中的类实现了BeanFactoryAware接口,因此会调用该方法,输出注入容器BeanFactroy
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}步骤2：执行BeanPostProcessor的before方法
ConfigurableBeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));
//BeanFactory要手动注册BeanPostProcessor,而ApplicationContext会手动检测
bf.addBeanPostProcessor(new MyTestBean());
bf.getBean("myTestBean", MyTestBean.class);public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName){
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
//调用这边会输出我是MyTestBean的postProcessBeforeInitialization方法
result = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}步骤3：激活用户的初始化方法
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd){
boolean isInitializingBean = (bean instanceof InitializingBean);
//删去了部分代码
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
//调用InitializingBean接口中定义的初始化方法
((InitializingBean) bean).afterPropertiesSet();
}
if (mbd != null) {
//配置文件init-method中配置的初始化方法
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
//底层使用反射调用初始化方法
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}步骤4：执行BeanPostProcessor的after方法
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName){
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessAfterInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}附录 1、根据名称注入例子
public class MyTestBean implements BeanFactoryAware, BeanPostProcessor, InitializingBean,
DestructionAwareBeanPostProcessor{
private BeanFactory beanFactory;
private Person person;
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
private String testStr = "xbx";
public String getTestStr() {
return testStr;
}
public void setTestStr(String testStr) {
this.testStr = testStr;
}
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
System.out.println("注入容器BeanFactory");
this.beanFactory = beanFactory;
}
public void init(){
System.out.println("我是MyTestBean的初始化方法");
}
public void destroy(){
System.out.println("我是MyTestBean的销毁方法");
}
public Object postProcessBeforeInitialization(Object bean, String beanName){
System.out.println("我是MyTestBean的postProcessBeforeInitialization方法");
return null;
}
public Object postProcessAfterInitialization(Object bean, String beanName){
System.out.println("我是MyTestBean的postProcessAfterInitialization方法");
return null;
}
public void afterPropertiesSet() throws Exception {
System.out.println("我是MyTestBean的自定义的初始化方法");
}
public void postProcessBeforeDestruction(Object bean, String beanName){
System.out.println("我是MyTestBean的自定义的销毁方法");
}
}//配置文件中只配置了testStr属性，并没有配置person属性 <bean id="myTestBean" class="com.lwh.spring.bean.MyTestBean" autowire="byName" init-method="init" destroy-method="destroy"> <property name="testStr" value="lwh sayHello"/> </bean> <bean id="person" class="com.lwh.spring.bean.Person"/>
到此，相信大家对“Spring初始化Bean的使用方法”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！
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