Spring 基于注解启动
主要有两个Class实现注解启动
- AnnotationConfigApplicationContext
- AnnotationConfigWebApplicationContext
我们以AnnotationConfigApplicationContext 为研究对象
AnnotationConfigApplicationContext.png
引入Spring 最小依赖
org.springframework spring-context${spring.version}
编写器启动代码
public static void main(String[] args) {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
applicationContext.register(BeanConfig.class);
applicationContext.refresh();
Date date = applicationContext.getBean("date",Date.class);
System.out.println(date);
}
AnnotationConfigApplicationContext 构造函数
public AnnotationConfigApplicationContext() {
//负责注册Class ，读取器
this.reader = new AnnotatedBeanDefinitionReader(this);
//负责扫描指定类路径下的Class，注册bean
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
AnnotatedBeanDefinitionReader 构造方法
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, getOrCreateEnvironment(registry));
}
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;
//初始化Conditionevaluator
this.conditionevaluator = new Conditionevaluator(registry, environment, null);
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
Conditionevaluator 这个对象干什么,点击进去
public Conditionevaluator(@Nullable BeanDefinitionRegistry registry,
@Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {
this.context = new ConditionContextImpl(registry, environment, resourceLoader);
}
//ConditionContextImpl 实现了ConditionContext接口，Conditionevaluator静态内部类
public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry,
@Nullable Environment environment, @Nullable ResourceLoader resourceLoader) {
this.registry = registry;
this.beanFactory = deduceBeanFactory(registry);
this.environment = (environment != null ? environment : deduceEnvironment(registry));
this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry));
this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory);
}
可以知道Conditionevaluator使用外部传参的方法初始化了Spring容器顶级对象
BeanFactory,Environment,ResourceLoader,ClassLoader。在将这些传给ConditionContextImpl为接下来的解析@Conditional注解做好准备
ClassPathBeanDefinitionScanner构造函数
public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) {
this(registry, true);
}
public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) {
this(registry, useDefaultFilters, getOrCreateEnvironment(registry));
}
public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
Environment environment) {
this(registry, useDefaultFilters, environment,
(registry instanceof ResourceLoader ? (ResourceLoader) registry : null));
}
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);
}
protected void registerDefaultFilters() {
this.includeFilters.add(new AnnotationTypeFilter(Component.class));
ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
}
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class) ClassUtils.forName("javax.inject.Named", cl)), false));
logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}
绕了地球几圈了，其实就是将Spring 顶级接口 Environment,ResourceLoader赋值，使用默认注解过滤器，首先将@Component加入List中，判断当前环境是否支持JSR-250，JSR-330，相应加入过滤器中。也就是这个扫描器默认只扫描@Component或者JSR-250，JSR-330的标记的Class。
applicationContext.register(BeanConfig.class)
public void register(Class... annotatedClasses) {
Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
this.reader.register(annotatedClasses); //调用 刚刚初始化读取器
}
|
============================AnnotatedBeanDefinitionReader 读取器代码======================================================================================================
public void register(Class... annotatedClasses) {
for (Class annotatedClass : annotatedClasses) {
registerBean(annotatedClass);
}
}
public void registerBean(Class annotatedClass) {
doRegisterBean(annotatedClass, null, null, null);
}
void doRegisterBean(Class annotatedClass, @Nullable Supplier instanceSupplier, @Nullable String name,
@Nullable Class[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
//根据Class的Annotated 得出元数据 Annotationmetadata
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
if (this.conditionevaluator.shouldSkip(abd.getmetadata())) { //如果 @Conditional条件不满足，不进行注册
return;
}
abd.setInstanceSupplier(instanceSupplier);
//解析Class是否有@Scope,解析@Scope注解返回Scopemetadata对象，没有直接返回空
Scopemetadata scopemetadata = this.scopemetadataResolver.resolveScopemetadata(abd);
abd.setScope(scopemetadata.getScopeName());
//判断注解上Value是否有值，有就使用这个作为BeanName，没有则取类名
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
//继续解析Annotationmetadata的@Lazy,@Primary，@DependsOn，@Role，@Description的注解，放入结果放入对象的属性中
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
//这个类只是BeanDefinition 包装类
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
//是否需要代理类，如果是则修改内部属性，重新生成BeanDefinition 对象
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopemetadata, definitionHolder, this.registry);
//调用DefaultListableBeanFactory.registerBeanDefinition的方法，做一些安全性校验再，将definitionHolder 放入register容器中
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}
这个方法就是将注册的Bean，解析Class上的注解，初始化注解数据，做相应处理，转化成BeanDefinition ,放入Spring 容器中保存起来。
我们看下BeanDefinition是怎么实现注册到Spring的容器中，主要由DefaultListableBeanFactory.registerBeanDefinition来实现
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
//对beanDefinition 进行校验判断MethodOverrides不能为空，必须拥有工厂方法
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
//这个方法是判断是否允许出现重名bean，并且是不同的定义bean，是否可以覆盖前者
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
//调用alreadyCreated.isEmpty()，alreadyCreated Set对象，保存已经创建beanName
//文档中表示created，跟这里注册应该不是同一个行为，这个要看到后面才知道什么意思
if (hasBeanCreationStarted()) {
synchronized (this.beanDefinitionMap) {//更新数据
this.beanDefinitionMap.put(beanName, beanDefinition);
List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set updatedSingletons = new linkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
//Spring beanDefinition 容器，一个Map转载
this.beanDefinitionMap.put(beanName, beanDefinition);
//保存beanName，主要用于记录每个bean注册顺序
this.beanDefinitionNames.add(beanName);
//删除单例，注册成一个普通bean
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
//更新Spring容器里beanName
resetBeanDefinition(beanName);
}
}
将beanDefinition注册到Spring容器中，并没有太多复杂的逻辑，只是做一些安全性的检查。
BeanDefinition
一个BeanDefinition描述了一个bean的实例，包括属性值，构造方法参数值和继承自它的类的更多信息。BeanDefinition仅仅是一个最简单的接口，主要功能是允许BeanFactoryPostProcessor 例如PropertyPlaceHolderConfigure 能够检索并修改属性值和别的bean的元数据（译注）
Spring 容器beanDefinition主要分为RootBeanDefinition,AnnotatedGenericBeanDefinition这两种
- RootBeanDefinition Spring Factory中的特定bean
- AnnotatedGenericBeanDefinition 用户自定义bean
Spring 启动流程总结
AnnotationConfigApplicationContext 初始化.png
这些BeanDefinition只是放入到Spirng 容器中，并没有进行任何初始化对象的操作，真正的IOC操作都在refresh(),这个方法有空再进行分析。
总结
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