SpringBoot扩展篇：@Scope和@Lazy源码解析

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已于 2025-02-05 21:04:51 修改 · 991 阅读

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#spring boot #后端 #java

于 2025-02-05 20:48:17 首次发布

SpringBoot扩展篇：@Scope和@Lazy源码解析

1. 研究主题及Demo

A class

@Component
public class A {
   
   

    @Lazy
    @Autowired
    public B b;

    public B getB() {
   
   
        return b;
    }
}

B class

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
@Component
public class B {
   
   
}

测试类

@SpringBootApplication
public class WebApplication{
   
   
    public static void main(String[] args) {
   
   
        ConfigurableApplicationContext run = SpringApplication.run(WebApplication.class, args);
        A a = run.getBean(A.class);
        System.out.println(a.b);
        System.out.println(a.b);
        System.out.println(a.b);
    }
}

研究问题1：为什么打印三次b对象的地址值不一样，从源码角度分析Spring是如何实现的？

在这里插入图片描述

研究问题2：为什么会debug看到的是代理对象，而打印出来的不是代理对象？

2. 注册BeanDefinition

在Spring对@Component扫描的时候，会调用ClassPathBeanDefinitionScanner#doScan生成beandefinition对象，可参考：
SpringBoot 源码解析5：ConfigurationClassPostProcessor整体流程和@ComponentScan源码分析

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
   
   
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
		for (String basePackage : basePackages) {
   
   
			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
			for (BeanDefinition candidate : candidates) {
   
   
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				if (candidate instanceof AbstractBeanDefinition) {
   
   
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}
				if (candidate instanceof AnnotatedBeanDefinition) {
   
   
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
				if (checkCandidate(beanName, candidate)) {
   
   
					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
					definitionHolder =
							AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
					beanDefinitions.add(definitionHolder);
					registerBeanDefinition(definitionHolder, this.registry);
				}
			}
		}
		return beanDefinitions;