Spring 启动时context加载源码分析 |

1月 11, 2018 | Nix.Huang

测试源码下载test-annotation.zip
有如下的代码

@Component
public class HelloWorldService {

	@Value("${name:World}")
	private String name;

	public String getHelloMessage() {
		return "Hello " + this.name;
	}

}

@Configuration
public class BootStrap {
	@Bean
	public static HelloWorldService helloService() {
		return new HelloWorldService();
	}

	public static void main(String[] args) {
		InstantiationStrategy instantiationStrategy = new SimpleInstantiationStrategy();
		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
		beanFactory.setInstantiationStrategy(instantiationStrategy);
		
		AnnotationConfigApplicationContext applicationContext = 
				new AnnotationConfigApplicationContext(beanFactory);
		applicationContext.register(BootStrap.class);
		applicationContext.refresh();

		HelloWorldService service = applicationContext.getBean(HelloWorldService.class);
		System.out.println(service.getHelloMessage());
		applicationContext.close();
	}
}

@Component

public class HelloWorldService {

@Value("${name:World}")

private String name;

public String getHelloMessage() {

return "Hello " + this.name;

}

@Configuration

public class BootStrap {

@Bean

public static HelloWorldService helloService() {

return new HelloWorldService();

}

public static void main(String[] args) {

InstantiationStrategy instantiationStrategy = new SimpleInstantiationStrategy();

DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

beanFactory.setInstantiationStrategy(instantiationStrategy);

AnnotationConfigApplicationContext applicationContext =

new AnnotationConfigApplicationContext(beanFactory);

applicationContext.register(BootStrap.class);

applicationContext.refresh();

HelloWorldService service = applicationContext.getBean(HelloWorldService.class);

System.out.println(service.getHelloMessage());

applicationContext.close();

}

HelloWorldService.getHelloMessage方法简单的返回name的值， BootStrap.main方法中使用AnnotationConfigApplicationContext 构造一个上下文对象，为了演示的方便，显示的声明了DefaultListableBeanFactory和InstantiationStrategy实例。通过applicationContext.getBean()获取bean的引用，并调用 service.getHelloMessage() 方法。
上下文的加载主要发生在applicationContext.register方法和applicationContext.refresh方法中，
applicationContext.register方法的作用是为参数（使用@Configuration注解的class）生成BeanDefinition 对象并调用DefaultListableBeanFactory.registerBeanDefinition将BeanDefinition注册到DefaultListableBeanFactory中。
applicationContext.refresh()的功能要更多，主要功能一的是调用PostProcessor为@Configuration类中的@Bean标注的方法生成对应的BeanDefinition对象，并注册到DefaultListableBeanFactory中，
功能二是遍历DefaultListableBeanFactory中BeanDefinition，产生真正的对象。

本文由javacoder.cn整理，转载注明出处

为@Configuration类中@Bean标注的方法生成BeanDefinition对象详细过程如下
步骤1、找到合适的BeanDefinitionRegistryPostProcessor处理器

org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors() {
	...
	//获取适用的BeanDefinitionRegistryPostProcessor bean名称
	String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
	...
	//根据beanName获取PostProcessor， 处理@Configuration标注类的beanName为
	//org.springframework.context.annotation.internalConfigurationAnnotationProcessor 
	//实现为org.springframework.context.annotation.ConfigurationClassPostProcessor
	ConfigurationClassPostProcessor postProcessor =beanFactory.getBean(postProcessorNames[0], BeanDefinitionRegistryPostProcessor.class)
}

org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors() {

...

//获取适用的BeanDefinitionRegistryPostProcessor bean名称

String[] postProcessorNames =

beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

...

//根据beanName获取PostProcessor，处理@Configuration标注类的beanName为

//org.springframework.context.annotation.internalConfigurationAnnotationProcessor

//实现为org.springframework.context.annotation.ConfigurationClassPostProcessor

ConfigurationClassPostProcessor postProcessor =beanFactory.getBean(postProcessorNames[0], BeanDefinitionRegistryPostProcessor.class)

}

步骤2、为@Configuration产生ConfigurationClass对象
//使用ConfigurationClassParser解析@Configuration标注的类,
//每一个@Configuration标注的类产生一个ConfigurationClass对象，
//ConfigurationClass.getBeanMethods()能获得该类中所有使用@Bean标注的方法，
//@Bean标注的方法使用BeanMethod对象表示

org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
	ConfigurationClassParser parser = new ConfigurationClassParser(
				this.metadataReaderFactory, this.problemReporter, this.environment,
				this.resourceLoader, this.componentScanBeanNameGenerator, registry);
	parser.parse(configCandidates);
	parser.validate();
	this.reader.loadBeanDefinitions(parser.getConfigurationClasses());
}

org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(BeanDefinitionRegistry registry) {

ConfigurationClassParser parser = new ConfigurationClassParser(

this.metadataReaderFactory, this.problemReporter, this.environment,

this.resourceLoader, this.componentScanBeanNameGenerator, registry);

parser.parse(configCandidates);

parser.validate();

this.reader.loadBeanDefinitions(parser.getConfigurationClasses());

}

步骤3、@Bean标注的方法产生BeanDefinition并注入到DefaultListableBeanFactory中

org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
	ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass);
	beanDef.setBeanClassName(configClass.getMetadata().getClassName());
	beanDef.setFactoryMethodName(metadata.getMethodName());
	//registry 是DefaultListableBeanFactory的实例
	this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}

org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {

ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass);

beanDef.setBeanClassName(configClass.getMetadata().getClassName());

beanDef.setFactoryMethodName(metadata.getMethodName());

//registry 是DefaultListableBeanFactory的实例

this.registry.registerBeanDefinition(beanName, beanDefToRegister);

}

此过程的调用栈：

根据BeanDefinition生成实例过程的调用栈：

Posted in: spring practise

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Spring 启动时context加载源码分析

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