Spring源码解析（一）
文章目录
由于当前更多是使用Spring注解进行开发，所以从Spirng的注解容器AnnotationConfigApplicationContext开始分析。
public static void main(String[] args) {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringSourceApplication.class);
Object userDao = applicationContext.getBean("userDao");
System.out.println(userDao);
}
从上面代码可以看容器实例化后就直接从容器获取Bean了，所以可以判断在容器实例化的时候已经完成了Bean的创建，所以我们直接看AnnotationConfigApplicationContext的构造方法。
1.AnnotationConfigApplicationContext 的构造方法–this()分析
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
this();
register(annotatedClasses);
refresh();
}
由于AnnotationConfigApplicationContext继承了GenericApplicationContext，所以会先执行GenericApplicationContext的构造
public GenericApplicationContext() {
this.beanFactory = new DefaultListableBeanFactory();
}
在GenericApplicationContext的构造方法中，实例化了Bean工厂，并作为AnnotationConfigApplicationContext的属性存在。
接下来看AnnotationConfigApplicationContext的this方法
public AnnotationConfigApplicationContext() {
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
在this方法中分别实例化了AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner，先进入AnnotatedBeanDefinitionReader
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
Assert.notNull(environment, "Environment must not be null");
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
ConditionEvaluator是用来处理@Condition注解的，后面分析到@Condition再看，接下来进入AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
上面代码是将Spring内置的Bean定义（internalConfigurationAnnotationProcessor、internalEventListenerFactory、internalAutowiredAnnotationProcessor、internalRequiredAnnotationProcessor、internalCommonAnnotationProcessor、internalEventListenerProcessor）注册到Bean注册中心。
打断点可以看到在执行前bean定义个数为0：
执行后个数为6个：
接下来进入ClassPathBeanDefinitionScanner：
public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
Environment environment, @Nullable ResourceLoader resourceLoader) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
this.registry = registry;
if (useDefaultFilters) {
registerDefaultFilters();
}
setEnvironment(environment);
setResourceLoader(resourceLoader);
}
进入registerDefaultFilters，通过下图看到这段代码为ClassPathBeanDefinitionScanner（Bean扫描组件）添加过滤器，只扫描加了@Component和@ManagedBean注解的类。
总结下this方法做的事情，将spring内置Bean的Bean定义放入到BeanFactory，为BeanScanner添加过滤器，接下来分析register
2.AnnotationConfigApplicationContext 的构造方法–register()分析
public void register(Class<?>... annotatedClasses) {
for (Class<?> annotatedClass : annotatedClasses) {
registerBean(annotatedClass);
}
}
annotatedClasses是我们实例化AnnotationConfigApplicationContext的时候传入的class，一般是我们的主配置类，类型于xml形式的configuration文件。
进入registerBean:
1.实例化Bean定义AnnotatedGenericBeanDefinition
2.判断该实体是否有@Condition注解，并进行处理
3.注册Bean定义
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
abd.setInstanceSupplier(instanceSupplier);
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
abd.setScope(scopeMetadata.getScopeName());
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
if (qualifiers != null) {
for (Class<? extends Annotation> qualifier : qualifiers) {
if (Primary.class == qualifier) {
abd.setPrimary(true);
}
else if (Lazy.class == qualifier) {
abd.setLazyInit(true);
}
else {
abd.addQualifier(new AutowireCandidateQualifier(qualifier));
}
}
}
for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
customizer.customize(abd);
}
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
通过断点可以发现在执行完Register后加入了参数类Bean定义到BeanFactory
