标签:容器 Spring bean Bean 源码 registry 注册 new
Spring中共有两种bean,一种为普通bean,另一种则为工厂bean:
BeanFactory 用于管理Bean的一个工厂,所有的Bean都是由BeanFactory(也就是IOC容器)来进行管理的
FactoryBean 是一个能生产或者修饰对象生成的工厂Bean,它的实现与设计模式中的工厂模式和修饰器模式类似,省去xml配置工厂模式出现的。通过FactoryBean创建一个代理类来增强目标类。
二、bean的创建
我们继续看AbstractApplicationContext.refresh方法
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
5、invokeBeanFactoryPostProcessors(beanFactory)
遍历所有实现BeanFactoryPostProcessor接口的实现类
// 调用beanFactory的后置处理器 BeanDefinitionRegistryPostProcessor
// 用户可以实现BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry 注册bean
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
// 用户实现了BeanFactoryPostProcessor 但没有实现BeanDefinitionRegistryPostProcessor
regularPostProcessors.add(postProcessor);
}
}
解析注解完成bean的注册,前面只是注册了XML中的bean而没有注册被注解标注的bean
// 会调用ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry 解析注解,注册bean
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
我们需要知道哪些注解标识的就是bean交给spring管理。
1、@Configuration+@Bean
用@Configuration注释类表明其主要目的是作为bean定义的源,@Configuration类允许通过调用同一类中的其他@Bean方法来定义bean之间的依赖关系。
@Configuration
public class AppConfig {
@Bean
public MyService myService() {
return new MyService();
}
@Bean
public UserService userService(){
return new UserService(myService());
}
}
配置了@Configuration ,打印结果显示 UserService 依赖的对象myService和从容器中获取的对象 myService;
没有配置@Configuration,UserService依赖的对象myService 不是从容器中获取的,只是一个普通的对象。
因为@Configuration修饰的AppConfig是一个cglib的代理对象,所以@Configuration 保证了配置类的内部方法之间依赖调用时都从容器中获取bean
2、@ComponentScan+@Component, @Repository,@Service, @Controller
这个用的比较多就不一一介绍了。
3、@Import
在下面例子中MyImportBeanDefinitionRegistrar:
如果实现了ImportSelector接口,实例化会并调用其selectImports方法,可以根据这个方法来规定bean只能根据类型来装配
如果实现了DeferredImportSelector,实例化并且调用其selectImports方法,会晚于前面一个的调用,
如果实现了ImportBeanDefinitionRegistrar接口,实例化并且调用其registerBeanDefinitions方法,可以修改注册bean的信息。
如果都没实现就只会实例化类
@Configuration
@Import(value = MyImportBeanDefinitionRegistrar.class)
public class AppConfig {
@Bean
public User user(){
return new User();
}
}
在@MapperScan注解中就使用了@import,所以可以扫描解析mapper文件
4、@Conditional
MyConditional会实现Condition接口中的matches方法,满足什么条件才能装配bean
@Configuration
public class AppConfig {
@Bean
@Conditional(value = MyConditional.class)
public User user(){
return new User();
}
}
在回到invokeBeanDefinitionRegistryPostProcessors方法中,可以看到会调用实现BeanFactoryPostProcessor接口的postProcessBeanDefinitionRegistry方法。我们重点看ConfigurationClassPostProcessor解析注解的后置处理器。
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {
// ConfigurationClassPostProcessor
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessBeanDefinitionRegistry(registry);
}
}
进入ConfigurationClassPostProcessor.processConfigBeanDefinitions去扫描注解并注册bean。
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
do {
// 解析配置类 @ComponentScan (bean注册到容器) @Import @ImportResource @Bean(后面三个不会注册到bean容器)
parser.parse(candidates);
parser.validate();
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
// 注册bean到容器
// 注册实现了ImportSelector的bean
// 方法bean注册到容器
// @ImportResource("spring.xml") 配置的bean注册到容器
// 实现ImportBeanDefinitionRegistrar的bean 注册到容器
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
candidates.clear();
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
BeanDefinition bd = registry.getBeanDefinition(candidateName);
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
candidateNames = newCandidateNames;
}
}
while (!candidates.isEmpty());
首先会扫描并解析@Configuration注解,parser.parse(candidates)
//在这个parse方法中,所有DeferredImportSelector实现类都会被放入集合deferredImportSelectors中,
// 它们的selectImports方法不会被执行,而其他ImportSelector实现类的selectImports都会被执行
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
里面会调用doProcessConfigurationClass(configClass, sourceClass)
这里处理将@Component修饰的bean注册到容器
// 处理@ComponentScan 将@Component修饰的bean注册到容器
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
// @ComponentScan扫描bean,返回@Component修饰的BeanDefinitionHolder 集合,并且
// 会将bean注册到容器
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
处理@Import注解的,如果是实现ImportSelector接口的类不会在此时注册到bean中,而在最开始的processConfigBeanDefinitions调用this.reader.loadBeanDefinitions(configClasses)注册
// 处理@Import implements ImportSelector 并不会将bean注册到容器
processImports(configClass, sourceClass, getImports(sourceClass), true);
那么现在为止所有的bean的信息都注册到DefaultListableBeanFactory的map集合中去了
标签:容器,Spring,bean,Bean,源码,registry,注册,new 来源: https://blog.csdn.net/qq_38682952/article/details/104656128
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