[笔记]spring容器源码分析（二）基于注解实现的

spring容器源码分析（基于注解方式）

1、 一些概念

• 定义Bean的注解：

@Component : 基本注解, 标识了一个受 Spring 管理的组件
@Repository : 标识持久层组件
@Service : 标识服务层(业务层)组件
@Controller : 标识表现层组件

Spring 能够从 classpath 下自动扫描, 实例化具有特定注解的组件。

2、初步

通过在applicationContext.xml中配置如下后，spring会自动扫描该路径下的所有bean。而如果Bean上面有相应的@Service,@Controller等注解，那么Spring的IOC容器将会帮我们实例对象，并设置属性。

<context:component-scan base-package="xxx.xxx.xxx.xxx">
		<context:include-filter type="annotation"
			expression="org.springframework.stereotype.Component" />
		<context:include-filter type="annotation"
			expression="org.springframework.stereotype.Repository" />
		<context:include-filter type="annotation"
			expression="org.springframework.stereotype.Service" />
</context:component-scan>

3、spring如何实现注解驱动的呢？

好难搞 今天事情有点多，放一个大佬的认知 点击前往 下次在更

---

放一张流程注入图：

从父类 AnnotationConfigApplicationContext中入手：

/**
     * Create a new AnnotationConfigApplicationContext, scanning for bean definitions
     * in the given packages and automatically refreshing the context.
     * @param basePackages the packages to check for annotated classes
     */
    public AnnotationConfigApplicationContext(String... basePackages) {
        this();
        scan(basePackages);//扫描包
        refresh();//调用AbstractApplicationContext中的refresh方法
    }

可以从scan()函数再进一步分析

/**
     * Perform a scan within the specified base packages.
     * @param basePackages the packages to check for annotated classes
     * @return number of beans registered
     */
    public int scan(String... basePackages) {
        int beanCountAtScanStart = this.registry.getBeanDefinitionCount();

        doScan(basePackages);//扫描

        // Register annotation config processors, if necessary.
        if (this.includeAnnotationConfig) {
            AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
        }

        return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
    }

很明显扫描的时候主要时进一步通过doScan()来实现的：

    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
        for (String basePackage : basePackages) {//遍历所有的包
            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);//查找候选组件
            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);//注册beandefinition
                }
            }
        }
        return beanDefinitions;
    }

doScan()函数中遍历了所有的包，在通过相应的包查找候选组件 ，具体实在findCandidateComponents():

/**
     * Scan the class path for candidate components.
     * @param basePackage the package to check for annotated classes
     * @return a corresponding Set of autodetected bean definitions
     */
    public Set<BeanDefinition> findCandidateComponents(String basePackage) {
        Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();
        try {
            String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
                    resolveBasePackage(basePackage) + "/" + this.resourcePattern;//补充路径
            Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
            boolean traceEnabled = logger.isTraceEnabled();
            boolean debugEnabled = logger.isDebugEnabled();
            for (Resource resource : resources) {//遍历Resource
                if (traceEnabled) {
                    logger.trace("Scanning " + resource);
                }
                if (resource.isReadable()) {
                    try {//通过asm获取class，暂且不研究asm
                        MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
                        if (isCandidateComponent(metadataReader)) {//判断是否为候选组件
                            ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                            sbd.setResource(resource);
                            sbd.setSource(resource);
                            if (isCandidateComponent(sbd)) {//判断是否为候选组件
                                if (debugEnabled) {
                                    logger.debug("Identified candidate component class: " + resource);
                                }
                                candidates.add(sbd);//添加候选组件
                            }
                            else {
                                if (debugEnabled) {
                                    logger.debug("Ignored because not a concrete top-level class: " + resource);
                                }
                            }
                        }
                        else {
                            if (traceEnabled) {
                                logger.trace("Ignored because not matching any filter: " + resource);
                            }
                        }
                    }
                    catch (Throwable ex) {
                        throw new BeanDefinitionStoreException(
                                "Failed to read candidate component class: " + resource, ex);
                    }
                }
                else {
                    if (traceEnabled) {
                        logger.trace("Ignored because not readable: " + resource);
                    }
                }
            }
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
        }
        return candidates;
    }

在findCandidateComponents()中存在两个判断的条件

/**
     * Determine whether the given bean definition qualifies as candidate.
     * <p>The default implementation checks whether the class is concrete
     * (i.e. not abstract and not an interface). Can be overridden in subclasses.
     * @param beanDefinition the bean definition to check
     * @return whether the bean definition qualifies as a candidate component
     */
    protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
        return (beanDefinition.getMetadata().isConcrete() && beanDefinition.getMetadata().isIndependent());
    }

/**
     * Determine whether the given class does not match any exclude filter
     * and does match at least one include filter.
     * @param metadataReader the ASM ClassReader for the class
     * @return whether the class qualifies as a candidate component
     */
    protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
        for (TypeFilter tf : this.excludeFilters) {
            // 默认为空
            if (tf.match(metadataReader, this.metadataReaderFactory)) {
                return false;
            }
        }
        // 默认有(见registerDefaultFilters方法)
        for (TypeFilter tf : this.includeFilters) {
            if (tf.match(metadataReader, this.metadataReaderFactory)) {
                return isConditionMatch(metadataReader);
            }
        }
        return false;
    }

很自然的看到match()方法：

if (matchSelf(metadataReader)) {
    return true;
}

protected boolean matchSelf(MetadataReader metadataReader) {
    // 获取元注解
    AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
    // AnnortationMetadata(当前类的注解)（annotationSet ）
    return metadata.hasAnnotation(this.annotationType.getName()) ||
        // metaAnnotationMap(当前类的注解以及当前类的注解的派生注解)
        (this.considerMetaAnnotations && metadata.hasMetaAnnotation(this.annotationType.getName()));
}

而matchSelf()中结构如下：

	@Override
    protected boolean matchSelf(MetadataReader metadataReader) {
        AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
        return metadata.hasAnnotation(this.annotationType.getName()) ||
                (this.considerMetaAnnotations && metadata.hasMetaAnnotation(this.annotationType.getName()));
    }

查看hasAnnotation和 hasMetaAnnotation方法：

	@Override
    public boolean hasAnnotation(String annotationType) {
        return this.annotationSet.contains(annotationType);
    }

    @Override
    public boolean hasMetaAnnotation(String metaAnnotationType) {
        Collection<Set<String>> allMetaTypes = this.metaAnnotationMap.values();
        for (Set<String> metaTypes : allMetaTypes) {
            if (metaTypes.contains(metaAnnotationType)) {
                return true;
            }
        }
        return false;
    }

PS:

metadata.hasAnnotation：例如如果当前类上的注解为@Service,那么元注解的annotationSet属性则为Service，不包含默认过滤器中的@Component和@named条件之一，返回false。
metadata.hasMetaAnnotation：例如如果当前类上的注解为@Service，那么元注解的metaAnotationMap则有@Service和@Component（@Service是@Component的派生属性），包含默认过滤器的@Component条件,则为true。

以上内容是针对性学习了 不迷烟火大佬

另外放一个Spring的基础复习链接 传送