Spring源码学习笔记@Configuration
1概述
本文基于Spring Framework版本5.0.0(最新版本5.3.4,SringBoot最新版本2.4.2。(参考文档: https://docs.spring.io/spring-boot/docs/current/api/)
1.1Spring各个版本区别
GA:General Availability,正式发布的版本，官方推荐使用此版本。在国外都是用GA来说明release版本的。
PRE: 预览版,内部测试f版. 主要是给开发人员和测试人员测试和找BUG用的，不建议使用；
SNAPSHOT: 快照版，可以稳定使用，且仍在继续改进版本。
1.2 @Configuraion
1.2.1注解作用
Annotating a class with @Configuration indicates that its primary purpose is as a source of bean definitions. Furthermore, @Configuration classes let inter-bean dependencies be defined by calling other @Bean methods in the same class. The simplest possible @Configuration class reads as follows:
中文的解释就是:
@Configuration有两个作用:
- 表明其主要目的是作为Bean定义的来源。
- 此外，
@Configuration类允许通过调用@Bean同一类中的其他方法来定义Bean之间的依赖关系。
2代码示例
2.1pom文件配置
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
<!--2.spring对web的支持,依赖 spring-webmvc-->
<!--此时jar包会自动下载(spring-context、spring-web、spring-webmvc)-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${springframework.version}</version>
</dependency>
<!--2.2.spring dao层依赖(jdbc 和 tx)-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jdbc</artifactId>
<version>${springframework.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-tx</artifactId>
<version>${springframework.version}</version>
</dependency>
<!--2.3.spring test相关依赖-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
<version>${springframework.version}</version>
</dependency>
</dependencies>
2.2 定义普通的pojo类
2.3定义配置类
package com.kikop.config;
import com.kikop.model.MySchool;
import com.kikop.model.MyUser;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
/**
* @author kikop
* @version 1.0
* @project Name: myspringdemo
* @file Name: AppConfig
* @desc 可以实现基于Java的配置类加载Spring的应用上下文
* @date 2021/2/14
* @time 10:50
* @by IDE: IntelliJ IDEA
*/
// @Configuration:可理解为用spring的时候xml里面的<beans>标签,特别是Beans依赖是,确保被构造一次
//@Configuration
public class AppConfig_BeanDependency {
@Bean
public MySchool mySchool() {
MySchool mySchool = new MySchool();
mySchool.setName("hytc");
System.out.println(mySchool);
return mySchool;
}
@Bean
public MyUser myUser() {
// 这里测试 mySchool是否是单例Bean,实际是用了Spring的字节码增强代理技术。
MySchool mySchool = mySchool();
MyUser myUser = new MyUser();
myUser.setUserName("kikop");
return myUser;
}
}
2.4测试
private static void AppConfig_BeanDependencyTest() {
AnnotationConfigApplicationContext annotationConfigApplicationContext =
new AnnotationConfigApplicationContext();
annotationConfigApplicationContext.register(AppConfig_BeanDependency.class);
annotationConfigApplicationContext.refresh();
annotationConfigApplicationContext.close();
}
public static void main(String[] args) {
AppConfig_BeanDependencyTest();
}
2.5 输出
- @Configuration开启时:
use myschool default constructor!
com.kikop.model.MySchool@701fc37a
- @Configuration关闭时(注意:MySchool被构造了两遍):
use myschool default constructor!
com.kikop.model.MySchool@631330c
use myschool default constructor!
com.kikop.model.MySchool@42f93a98
3 @Configuration源码解读
3.1总结
Spring 容器在初始化刷新时,检查是否有@Configuration配置的注解类,如果有,则进行配置类的代理增强ConfigurationClassEnchancer(默认CGLIB)。
配置类中的methodBean方法由lite变为full。AppConfig的配置类转换成AppConfig@BySpringCGLIB,从而Spring中@Bean注解的Beam方法在调用时会被Enchancer动态代理拦截。具体代理时机在容器刷新:invokeBeanFactoryPostProcessors方法中。
一句话,它的本质是动态代理!
具体实现如下:
@Override
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();
// Prepare the bean factory for use in this context.
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);
/**
* Instantiate and invoke all registered BeanFactoryPostProcessor beans,
* respecting explicit order if given.
* <p>Must be called before singleton instantiation.
*/
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// org\springframework\context\annotation\ConfigurationClassPostProcessor.java
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
int factoryId = System.identityHashCode(beanFactory);
if (this.factoriesPostProcessed.contains(factoryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + beanFactory);
}
this.factoriesPostProcessed.add(factoryId);
if (!this.registriesPostProcessed.contains(factoryId)) {
// BeanDefinitionRegistryPostProcessor hook apparently not supported...
// Simply call processConfigurationClasses lazily at this point then.
processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
}
// 在这里进行配置类的增强
enhanceConfigurationClasses(beanFactory);
beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
}
if (configBeanDefs.isEmpty()) {
// nothing to enhance -> return immediately
return;
}
ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
AbstractBeanDefinition beanDef = entry.getValue();
// If a @Configuration class gets proxied, always proxy the target class
beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
try {
// Set enhanced subclass of the user-specified bean class
Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
if (configClass != null) {
Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
/**
* Creates a new CGLIB {@link Enhancer} instance.
*/
private Enhancer newEnhancer(Class<?> superclass, @Nullable ClassLoader classLoader) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(superclass);
enhancer.setInterfaces(new Class<?>[] {EnhancedConfiguration.class});
enhancer.setUseFactory(false);
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader));
enhancer.setCallbackFilter(CALLBACK_FILTER);
enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes());
return enhancer;
}
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