Spring注解原理探索（四）

之 Spring处理注解的源码分析

管理注解bean定义的两个容器：

• AnnotationConfigApplicationContext
• AnnotationConfigWebApplicationContext

AnnotationConfigApplicationContext 的 Java doc 原语：

Standalone application context, accepting annotated classes as input.
... Alllows for registering classes one by one
using {@link #register(Class...)} as well as for classpath scanning using {@link #scan(String...)}.

这两个类是 直接依赖于注解 作为容器配置信息 的 IOC容器。

AnnotationConfigWebApplicationContext 是AnnotationConfigApplicationContext 的Web版本。
两者虽然实现方式略有差别，但处理注解的逻辑一样。
先扫描（scan(String...)）类路径（classpath），然后一一注册（register(Class<?>...)）。

简单点，以 AnnotationConfigApplicationContext 为例。

AnnotationConfigApplicationContext的源码：

package org.springframework.context.annotation;

public class AnnotationConfigApplicationContext extends GenericApplicationContext implements AnnotationConfigRegistry {
    // 读取器：读取注解的Bean，并注册到容器中。
    private final AnnotatedBeanDefinitionReader reader;
    // 扫描器：扫描类路径中注解的Bean，并注册到容器中。
    private final ClassPathBeanDefinitionScanner scanner;

    public AnnotationConfigApplicationContext() {
        // reader和scanner，功能类似，使用场景不同：annotatedClasses, basePakages.
        this.reader = new AnnotatedBeanDefinitionReader(this);
        this.scanner = new ClassPathBeanDefinitionScanner(this);
    }

    public AnnotationConfigApplicationContext(DefaultListableBeanFactory beanFactory) {
        super(beanFactory);
        this.reader = new AnnotatedBeanDefinitionReader(this);
        this.scanner = new ClassPathBeanDefinitionScanner(this);
    }

/*********************************
 *  1 区
 ***/
    public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
        this();
        register(annotatedClasses);
        refresh();
    }

    public AnnotationConfigApplicationContext(String... basePackages) {
        this();
        scan(basePackages);
        refresh();
    }
/*********************************/
    @Override
    public void setEnvironment(ConfigurableEnvironment environment) {
        super.setEnvironment(environment);
        this.reader.setEnvironment(environment);
        this.scanner.setEnvironment(environment);
    }

    public void setBeanNameGenerator(BeanNameGenerator beanNameGenerator) {
        this.reader.setBeanNameGenerator(beanNameGenerator);
        this.scanner.setBeanNameGenerator(beanNameGenerator);
        getBeanFactory().registerSingleton(
                AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, beanNameGenerator);
    }

    public void setScopeMetadataResolver(ScopeMetadataResolver scopeMetadataResolver) {
        this.reader.setScopeMetadataResolver(scopeMetadataResolver);
        this.scanner.setScopeMetadataResolver(scopeMetadataResolver);
    }

/***************************
 *  2 区
 ***/
    public void register(Class<?>... annotatedClasses) {
        Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
        this.reader.register(annotatedClasses);
    }

    public void scan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        this.scanner.scan(basePackages);
    }
/***************************/
    @Override
    protected void prepareRefresh() {
        this.scanner.clearCache();
        super.prepareRefresh();
    }
}

请注意：
AnnotationCnofigApplicationContext 类的源码中的 “1 区”：

AnnotationConfigApplicationContext的基本功能在构造函数中完成。

实例化reader 和scanner；然后调用 register(Class<?>... annotatedClasses) 或 scan(String... basePackages) 方法；最后刷新。

而 register(Class<?>... annotatedClasses) 方法调用reader.register(Class<?>... annotatedClasses)；

scan(String... basePackages) 方法调用scanner.scan(String... basePackages)。

AnnotatedBeanDefinitionReader 和 ClassPathBeanDefinitionScanner 功能类似，二者取其一。

AnnotationConfigApplicationContext 类的源码中的 “2 区”：

如下两个方法完成了Spring的扫描注册功能：
reader.register(Class<?>... annotatedClasses);
scanner.scan(String... basePackages);

reader.register(Class<?>... annotatedClasses) 的源码：

public void register(Class<?>... annotatedClasses) {
        for (Class<?> annotatedClass : annotatedClasses) {
            registerBean(annotatedClass);
        }
    }

public void registerBean(Class<?> annotatedClass) {
        registerBean(annotatedClass, null, (Class<? extends Annotation>[]) null);
    }


// 注解功能实现区
@SuppressWarnings("unchecked")
public void registerBean(Class<?> annotatedClass, String name, Class<? extends Annotation>... qualifiers) {
    AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
    if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
        return;
    }

    ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
    abd.setScope(scopeMetadata.getScopeName());
    String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        
    AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
    if (qualifiers != null) {
        for (Class<? extends Annotation> qualifier : qualifiers) {
            if (Primary.class == qualifier) {
                abd.setPrimary(true);
            } else if (Lazy.class == qualifier) {
                abd.setLazyInit(true);
            } else {
                abd.addQualifier(new AutowireCandidateQualifier(qualifier));
            }
        }
    }

    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
    definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
    BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}

scanner.scan(String... basePackages) 源码：

public int scan(String... basePackages) {
        int beanCountAtScanStart = this.registry.getBeanDefinitionCount();

        doScan(basePackages);    // 备注：重点关注此处

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

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


// 注解功能实现区
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Assert.notEmpty(basePackages, "At least one base package must be specified");
    /**
     * BeanDefinitionHoder: Holder for a BeanDefinition with name and aliases.
     * BeanDefinition: A BeanDefinition describes a bean instance,   
     *   which has property values, constructor argument values, and 
     *   further information supplied by concrete implementations.
     */
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
    for (String basePackage : basePackages) {  // 多个包路径
        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;
}

[待续]