spring源码解析--上

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首先是配置类

package com.lusai.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("com.lusai.service")
public class SpringConfig {

}

然后是IndexService

package com.lusai.service;

import org.springframework.stereotype.Service;

@Service
public class IndexService {

    public void hello(){
        System.out.println("IndexService");
    }

}

然后是测试

public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(SpringConfig.class);//从这里开始看
        IndexService indexService = (IndexService) applicationContext.getBean("indexService");
        indexService.hello();
    }

看结果

可以看到,IndexService 已经交给spring管理了,我们就开始学习源码吧

/**
 * 这个构造方法需要传入一个配置类

 * 然后会把这个被注解了的类通过注解读取器读取,继而解析
 * Create a new AnnotationConfigApplicationContext, deriving bean definitions
 * from the given annotated classes and automatically refreshing the context.
 * @param annotatedClasses one or more annotated classes,
 * e.g. {@link Configuration @Configuration} classes
 */
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
   //annotatedClasses --->  配置类的class对象
   //这里由于他有父类，故而会先调用父类的构造方法，然后才会调用自己的构造方法
   //在自己构造方法中初始一个读取器和扫描器
   this();//进这里看
   register(annotatedClasses);
   refresh();
}

继续看this()

/**
     * 初始化一个bean的读取器和扫描器
     * 何谓读取器和扫描器参考上面的属性注释
     * 默认构造函数，如果直接调用这个默认构造方法，需要在稍后通过调用其register()
     * 去注册配置类（javaconfig），并调用refresh()方法刷新容器，
     * 触发容器对注解Bean的载入、解析和注册过程
     * Create a new AnnotationConfigApplicationContext that needs to be populated
     * through {@link #register} calls and then manually {@linkplain #refresh refreshed}.
     */
    public AnnotationConfigApplicationContext() {
        /**
         * 父类的构造方法
         * 创建一个读取注解的Bean定义读取器
         * 什么是BeanDefinition
         */
        this.reader = new AnnotatedBeanDefinitionReader(this);
        //可以用来扫描包或者类，继而转换成BeanDefinition
        //但是实际上我们扫描包工作不是scanner这个对象来完成的
        //是spring自己new的一个ClassPathBeanDefinitionScanner
        //这里的scanner仅仅是为了程序员能够在外部调用AnnotationConfigApplicationContext对象的scan方法
        this.scanner = new ClassPathBeanDefinitionScanner(this);
    }

我们看一下this.reader

/**
     * 这个类顾名思义是一个reader，一个读取器
     * 读取什么呢？还是顾名思义:AnnotatedBeanDefinition意思是读取一个被加了注解的BeanDefinition
     * 这个类在构造方法中实例化的
     */
    private final AnnotatedBeanDefinitionReader reader;

我们再看一下AnnotatedBeanDefinitionReader 的定义

可以看出有个BeanDefinitionRegistry,看这个名字应该是BeanDefinition的注册器,那么BeanDefinition是什么呢,看一下

/**
 * BeanDefinition描述了一个bean实例
 * A BeanDefinition describes a bean instance, which has property values,
 * constructor argument values, and further information supplied by
 * concrete implementations.
 *
 * <p>This is just a minimal interface: The main intention is to allow a
 * {@link BeanFactoryPostProcessor} such as {@link PropertyPlaceholderConfigurer}
 * to introspect and modify property values and other bean metadata.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 19.03.2004
 * @see ConfigurableListableBeanFactory#getBeanDefinition
 * @see org.springframework.beans.factory.support.RootBeanDefinition
 * @see org.springframework.beans.factory.support.ChildBeanDefinition
 */
public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {

    /**
     * 单例作用域的作用域标识符：“singleton”。
     * Scope identifier for the standard singleton scope: "singleton".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;

    /**
     * 非单例作用域的作用域标识符：“prototype”。
     * Scope identifier for the standard prototype scope: "prototype".
     * <p>Note that extended bean factories might support further scopes.
     * @see #setScope
     */
    String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;

    /**
     * 还没搞懂 权限的值
     * Role hint indicating that a {@code BeanDefinition} is a major part
     * of the application. Typically corresponds to a user-defined bean.
     */
    int ROLE_APPLICATION = 0;

    /**
     * Role hint indicating that a {@code BeanDefinition} is a supporting
     * part of some larger configuration, typically an outer
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     * {@code SUPPORT} beans are considered important enough to be aware
     * of when looking more closely at a particular
     * {@link org.springframework.beans.factory.parsing.ComponentDefinition},
     * but not when looking at the overall configuration of an application.
     */
    int ROLE_SUPPORT = 1;

    /**
     * Role hint indicating that a {@code BeanDefinition} is providing an
     * entirely background role and has no relevance to the end-user. This hint is
     * used when registering beans that are completely part of the internal workings
     * of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
     * 就是我这Bean是Spring自己的，和你用户没有一毛钱关系
     */
    int ROLE_INFRASTRUCTURE = 2;

    // Modifiable attributes

    /**
     * 设置父BeanDefinition的名字
     * Set the name of the parent definition of this bean definition, if any.
     */
    void setParentName(@Nullable String parentName);

    /**
     * 获得父BeanDefinition的名字
     * Return the name of the parent definition of this bean definition, if any.
     */
    @Nullable
    String getParentName();

    /**
     * 指定此BeanDefinition的bean类名
     * Specify the bean class name of this bean definition.
     * <p>The class name can be modified during bean factory post-processing,
     * typically replacing the original class name with a parsed variant of it.
     * @see #setParentName
     * @see #setFactoryBeanName
     * @see #setFactoryMethodName
     */
    void setBeanClassName(@Nullable String beanClassName);

    /**
     * 获取此BeanDefinition的bean类名
     * Return the current bean class name of this bean definition.
     * <p>Note that this does not have to be the actual class name used at runtime, in
     * case of a child definition overriding/inheriting the class name from its parent.
     * Also, this may just be the class that a factory method is called on, or it may
     * even be empty in case of a factory bean reference that a method is called on.
     * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
     * rather only use it for parsing purposes at the individual bean definition level.
     * @see #getParentName()
     * @see #getFactoryBeanName()
     * @see #getFactoryMethodName()
     */
    @Nullable
    String getBeanClassName();

    /**
     *设置此BeanDefinition的scope的类型
     * Override the target scope of this bean, specifying a new scope name.
     * @see #SCOPE_SINGLETON
     * @see #SCOPE_PROTOTYPE
     */
    void setScope(@Nullable String scope);

    /**
     * 获取此BeanDefinition的scope的类型
     * Return the name of the current target scope for this bean,
     * or {@code null} if not known yet.
     */
    @Nullable
    String getScope();

    /**
     * 设置懒加载
     * Set whether this bean should be lazily initialized.
     * <p>If {@code false}, the bean will get instantiated on startup by bean
     * factories that perform eager initialization of singletons.
     */
    void setLazyInit(boolean lazyInit);

    /**
     * 获取是否懒加载
     * Return whether this bean should be lazily initialized, i.e. not
     * eagerly instantiated on startup. Only applicable to a singleton bean.
     */
    boolean isLazyInit();

    /**
     * 设置dependsOn,将首先初始化这些bean
     * Set the names of the beans that this bean depends on being initialized.
     * The bean factory will guarantee that these beans get initialized first.
     */
    void setDependsOn(@Nullable String... dependsOn);

    /**
     * 获取被dependsOn的beans的名字
     * Return the bean names that this bean depends on.
     */
    @Nullable
    String[] getDependsOn();

    /**
     * 设置是否参与自动装配的候选,与autowire-candidate有关
     * Set whether this bean is a candidate for getting autowired into some other bean.
     * <p>Note that this flag is designed to only affect type-based autowiring.
     * It does not affect explicit references by name, which will get resolved even
     * if the specified bean is not marked as an autowire candidate. As a consequence,
     * autowiring by name will nevertheless inject a bean if the name matches.
     */
    void setAutowireCandidate(boolean autowireCandidate);

    /**
     * 获取是否参与自动装配的候选
     * Return whether this bean is a candidate for getting autowired into some other bean.
     */
    boolean isAutowireCandidate();

    /**
     * 设置@Primay注解
     * Set whether this bean is a primary autowire candidate.
     * <p>If this value is {@code true} for exactly one bean among multiple
     * matching candidates, it will serve as a tie-breaker.
     */
    void setPrimary(boolean primary);

    /**
     * 获取该bean是否被@Primay注解
     * Return whether this bean is a primary autowire candidate.
     */
    boolean isPrimary();

    /**
     * Specify the factory bean to use, if any.
     * This the name of the bean to call the specified factory method on.
     * @see #setFactoryMethodName
     */
    void setFactoryBeanName(@Nullable String factoryBeanName);

    /**
     * Return the factory bean name, if any.
     */
    @Nullable
    String getFactoryBeanName();

    /**
     * 与bean标签的factory-method有关
     * Specify a factory method, if any. This method will be invoked with
     * constructor arguments, or with no arguments if none are specified.
     * The method will be invoked on the specified factory bean, if any,
     * or otherwise as a static method on the local bean class.
     * @see #setFactoryBeanName
     * @see #setBeanClassName
     */
    void setFactoryMethodName(@Nullable String factoryMethodName);

    /**
     * Return a factory method, if any.
     */
    @Nullable
    String getFactoryMethodName();

    /**
     * 存放构造方法的参数和顺序等 constructor-arg标签的index和name等属性
     * Return the constructor argument values for this bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the ConstructorArgumentValues object (never {@code null})
     */
    ConstructorArgumentValues getConstructorArgumentValues();

    /**
     * 判断构造方法有没有参数值
     * Return if there are constructor argument values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasConstructorArgumentValues() {
        return !getConstructorArgumentValues().isEmpty();
    }

    /**
     * bean标签的property属性
     * Return the property values to be applied to a new instance of the bean.
     * <p>The returned instance can be modified during bean factory post-processing.
     * @return the MutablePropertyValues object (never {@code null})
     */
    MutablePropertyValues getPropertyValues();

    /**
     * Return if there are property values values defined for this bean.
     * @since 5.0.2
     */
    default boolean hasPropertyValues() {
        return !getPropertyValues().isEmpty();
    }

    /**
     * Set the name of the initializer method.
     * @since 5.1
     */
    void setInitMethodName(@Nullable String initMethodName);

    /**
     * Return the name of the initializer method.
     * @since 5.1
     */
    @Nullable
    String getInitMethodName();

    /**
     * Set the name of the destroy method.
     * @since 5.1
     */
    void setDestroyMethodName(@Nullable String destroyMethodName);

    /**
     * Return the name of the destroy method.
     * @since 5.1
     */
    @Nullable
    String getDestroyMethodName();

    /**
     * Set the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @since 5.1
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    void setRole(int role);

    /**
     * Get the role hint for this {@code BeanDefinition}. The role hint
     * provides the frameworks as well as tools with an indication of
     * the role and importance of a particular {@code BeanDefinition}.
     * @see #ROLE_APPLICATION
     * @see #ROLE_SUPPORT
     * @see #ROLE_INFRASTRUCTURE
     */
    int getRole();

    /**
     *  @Description注解,描述,无太大意义
     * Set a human-readable description of this bean definition.
     * @since 5.1
     */
    void setDescription(@Nullable String description);

    /**
     * Return a human-readable description of this bean definition.
     */
    @Nullable
    String getDescription();

    // Read-only attributes

    /**
     * Return whether this a <b>Singleton</b>, with a single, shared instance
     * returned on all calls.
     * @see #SCOPE_SINGLETON
     */
    boolean isSingleton();

    /**
     * Return whether this a <b>Prototype</b>, with an independent instance
     * returned for each call.
     * @since 3.0
     * @see #SCOPE_PROTOTYPE
     */
    boolean isPrototype();

    /**
     * 判断是否是抽象类,为什么可以是抽象类
     * Return whether this bean is "abstract", that is, not meant to be instantiated.
     */
    boolean isAbstract();

    /**
     * 对文件的描述
     * Return a description of the resource that this bean definition
     * came from (for the purpose of showing context in case of errors).
     */
    @Nullable
    String getResourceDescription();

    /**
     * Return the originating BeanDefinition, or {@code null} if none.
     * Allows for retrieving the decorated bean definition, if any.
     * <p>Note that this method returns the immediate originator. Iterate through the
     * originator chain to find the original BeanDefinition as defined by the user.
     */
    @Nullable
    BeanDefinition getOriginatingBeanDefinition();

}

BeanDefinition描述了一个bean实例,可以理解为:我们定义的对象交给spring管理以后会变成一个个BeanDefinition

好了,看看下一个

//可以用来扫描包或者类，继而转换成BeanDefinition
        //但是实际上我们扫描包工作不是scanner这个对象来完成的
        //是spring自己new的一个ClassPathBeanDefinitionScanner
        //这里的scanner仅仅是为了程序员能够在外部调用AnnotationConfigApplicationContext对象的scan方法
        this.scanner = new ClassPathBeanDefinitionScanner(this);

这里的scanner 我们也不深究,姑且认为是一个扫描器

继续看构造方法

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
        //annotatedClasses --->  配置类的class对象
        //这里由于他有父类，故而会先调用父类的构造方法，然后才会调用自己的构造方法
        //在自己构造方法中初始一个读取器和扫描器
        this();
        register(annotatedClasses);//进这里看
        refresh();
    }

看register方法

/**
     * 注册单个bean给容器
     * 比如有新加的类可以用这个方法
     * 但是注册注册之后需要手动调用refresh方法去触发容器解析注解
     *
     * 有两个意思
     * 他可以注册一个配置类
     * 他还可以单独注册一个bean
     * Register one or more annotated classes to be processed.
     * <p>Note that {@link #refresh()} must be called in order for the context
     * to fully process the new classes.
     * @param annotatedClasses one or more annotated classes,
     * e.g. {@link Configuration @Configuration} classes
     * @see #scan(String...)
     * @see #refresh()
     */
    public void register(Class<?>... annotatedClasses) {
        Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
        this.reader.register(annotatedClasses);//被注解的类
    }

我们把配置类的扫描注释掉看下

@Configuration
//@ComponentScan("com.lusai.service")
public class SpringConfig {

}

运行测试类,看下结果

扫描不到报错,我们改成如下形式再试一下

public static void main(String[] args) {
        //AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(SpringConfig.class);
        AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(IndexService.class);
        IndexService indexService = (IndexService) applicationContext.getBean("indexService");
        indexService.hello();
    }

看结果

ok,可以看出register方法有两个意思:1.他可以注册一个配置类2.他还可以单独注册一个bean

好了,继续点进去看源码

/**
     * Register one or more annotated classes to be processed.
     * <p>Calls to {@code register} are idempotent; adding the same
     * annotated class more than once has no additional effect.
     * @param annotatedClasses one or more annotated classes,
     * e.g. {@link Configuration @Configuration} classes
     */
    public void register(Class<?>... annotatedClasses) {
        for (Class<?> annotatedClass : annotatedClasses) {
            registerBean(annotatedClass);
        }
    }

继续看registerBean

/**
     * Register a bean from the given bean class, deriving its metadata from
     * class-declared annotations.
     * @param annotatedClass the class of the bean
     */
    public void registerBean(Class<?> annotatedClass) {
        doRegisterBean(annotatedClass, null, null, null);
    }

继续看doRegisterBean

/**
     * Register a bean from the given bean class, deriving its metadata from
     * class-declared annotations.
     * @param annotatedClass the class of the bean
     * @param instanceSupplier a callback for creating an instance of the bean
     * (may be {@code null})
     * @param name an explicit name for the bean
     * @param qualifiers specific qualifier annotations to consider, if any,
     * in addition to qualifiers at the bean class level
     * @param definitionCustomizers one or more callbacks for customizing the
     * factory's {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
     * @since 5.0
     */
    <T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
            @Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {

        /**
         * 根据指定的bean创建一个AnnotatedGenericBeanDefinition
         * 这个AnnotatedGenericBeanDefinition可以理解为一个数据结构
         * AnnotatedGenericBeanDefinition包含了类的其他信息,比如一些元信息
         * scope，lazy等等.
         * 此时因为传入的注解,所以new AnnotatedGenericBeanDefinition
         */
        AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
        /**
         * 判断这个类是否需要跳过解析
         * 通过代码可以知道spring判断是否跳过解析，主要判断类有没有加注解
         */
        if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
            return;
        }

        abd.setInstanceSupplier(instanceSupplier);
        /**
         * 得到类的作用域 singleton
         */
        ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
        /**
         * 把类的作用域添加到数据结构结构中
         */
        abd.setScope(scopeMetadata.getScopeName());
        /**
         * 生成类的名字通过beanNameGenerator
         */
        String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        /**
         * 处理类当中的通用注解
         * 分析源码可以知道他主要处理
         * Lazy DependsOn Primary Role等等注解
         * 处理完成之后processCommonDefinitionAnnotations中依然是把他添加到数据结构当中
         */
        AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
        if (qualifiers != null) {//qualifiers总是为null
            for (Class<? extends Annotation> qualifier : qualifiers) {
                //如果配置了@Primary注解，如果加了则作为首选
                if (Primary.class == qualifier) {
                    abd.setPrimary(true);
                }
                //懒加载，前面加过
                else if (Lazy.class == qualifier) {
                    abd.setLazyInit(true);
                }
                else {
                    //如果使用了除@Primary和@Lazy以外的其他注解，则为该Bean添加一个根据名字自动装配的限定符
                    //这里难以理解，后面会详细介绍
                    abd.addQualifier(new AutowireCandidateQualifier(qualifier));
                }
            }
        }
        //自定义注解
        for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
            customizer.customize(abd);
        }

        /**
         * 这个BeanDefinitionHolder也是一个数据结构,这个对象放入了BeanDefinition和beanName,可以理解为一个map
         */
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
        /**
         * ScopedProxyMode 这个知识点比较复杂，需要结合web去理解
         * 可以暂时放一下，等说道springmvc的时候再说
         * 或者看情况现在说也是一样的
         */
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
        /**
         * 把上述的这个数据结构注册给registry
         * registy就是AnnotatonConfigApplicationContext
         * AnnotatonConfigApplicationContext在初始化的時候通過調用父類的構造方法
         * 實例化了一个DefaultListableBeanFactory
         * *registerBeanDefinition里面就是把definitionHolder这个数据结构包含的信息注册到
         * DefaultListableBeanFactory这个工厂
         */
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
    }

看下这行的源码

AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);

继续

public static void processCommonDefinitionAnnotations(AnnotatedBeanDefinition abd) {
        processCommonDefinitionAnnotations(abd, abd.getMetadata());
    }

继续

/**
     * 检查常用的注解
     * @param abd
     * @param metadata
     */
    static void processCommonDefinitionAnnotations(AnnotatedBeanDefinition abd, AnnotatedTypeMetadata metadata) {
        //检查Lazy注解,如果有将它放入AnnotatedBeanDefinition
        AnnotationAttributes lazy = attributesFor(metadata, Lazy.class);
        if (lazy != null) {
            abd.setLazyInit(lazy.getBoolean("value"));
        }
        else if (abd.getMetadata() != metadata) {
            lazy = attributesFor(abd.getMetadata(), Lazy.class);
            if (lazy != null) {
                abd.setLazyInit(lazy.getBoolean("value"));
            }
        }
        //检查Primary注解,如果有将它放入AnnotatedBeanDefinition
        if (metadata.isAnnotated(Primary.class.getName())) {
            abd.setPrimary(true);
        }
        //检查DependsOn注解,如果有将它放入AnnotatedBeanDefinition
        AnnotationAttributes dependsOn = attributesFor(metadata, DependsOn.class);
        if (dependsOn != null) {
            abd.setDependsOn(dependsOn.getStringArray("value"));
        }
        //检查Role注解,如果有将它放入AnnotatedBeanDefinition
        AnnotationAttributes role = attributesFor(metadata, Role.class);
        if (role != null) {
            abd.setRole(role.getNumber("value").intValue());
        }
        //检查Description注解,如果有将它放入AnnotatedBeanDefinition
        AnnotationAttributes description = attributesFor(metadata, Description.class);
        if (description != null) {
            abd.setDescription(description.getString("value"));
        }
    }

分析源码可以知道他主要处理Lazy DependsOn Primary Role等等注解
处理完成之后是把他添加到AnnotatedGenericBeanDefinition数据结构当中

继续看下面

BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);

看下BeanDefinitionHolder 的定义

这个BeanDefinitionHolder也是一个对象,这个对象放入了BeanDefinition和beanName

好了,我们看最后一行关键代码:

BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);

点进去

public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();//获取beanName
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());//关键代码

        //别名,先不看
        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

看那行关键代码

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        //DefaultListableBeanFactory
        this.beanFactory.registerBeanDefinition(beanName, beanDefinition);
    }

这里的this.beanFactory是DefaultListableBeanFactory,这个是默认的bean工厂

再点进去看

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {//验证
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
        if (existingDefinition != null) {
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
            }
            else if (existingDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (logger.isInfoEnabled()) {
                    logger.info("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            existingDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else if (!beanDefinition.equals(existingDefinition)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Overriding bean definition for bean '" + beanName +
                            "' with a different definition: replacing [" + existingDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (logger.isTraceEnabled()) {
                    logger.trace("Overriding bean definition for bean '" + beanName +
                            "' with an equivalent definition: replacing [" + existingDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        else {
            if (hasBeanCreationStarted()) {
                // Cannot modify startup-time collection elements anymore (for stable iteration)
                synchronized (this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    removeManualSingletonName(beanName);
                }
            }
            else {//关键代码
                // Still in startup registration phase
                //这里的beanDefinitionMap是一个map,存放beanName,beanDefinition
                this.beanDefinitionMap.put(beanName, beanDefinition);
                //这里的beanDefinitionNames是一个list,存放beanName
                this.beanDefinitionNames.add(beanName);
                removeManualSingletonName(beanName);
            }
            this.frozenBeanDefinitionNames = null;
        }

        if (existingDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

看我注释的地方,那里就是关键代码

这里的this.beanDefinitionMap看一下

/** Map of bean definition objects, keyed by bean name. */
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);

这里我们debug一下

可以看到除了indexService之外很多内置的bean,那么这些类是什么时候注册的,都有什么用呢?我们后面再研究

我们register看完了,现在看refresh方法

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
        //annotatedClasses --->  配置类的class对象
        //这里由于他有父类，故而会先调用父类的构造方法，然后才会调用自己的构造方法
        //在自己构造方法中初始一个读取器和扫描器
        this();
        register(annotatedClasses);
        refresh();//进这里看
    }

点进去

@Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            ////准备工作包括设置启动时间，是否激活标识位，
            // 初始化属性源(property source)配置
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            //返回一个factory 为什么需要返回一个工厂
            //因为要对工厂进行初始化
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            //准备工厂
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.

                //这个方法在当前版本的spring是没用任何代码的
                //可能spring期待在后面的版本中去扩展吧
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //在spring的环境中去执行已经被注册的 factory processors
                //设置执行自定义的ProcessBeanFactory 和spring内部自己定义的
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                //注册beanPostProcessor
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                //初始化应用事件广播器
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

看看下面这行

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

点进去

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();
        return getBeanFactory();
    }

继续看getBeanFactory()方法

@Override
    public final ConfigurableListableBeanFactory getBeanFactory() {
        return this.beanFactory;
    }

这里的this.beanFactory就是上文提到的DefaultListableBeanFactory

    private final DefaultListableBeanFactory beanFactory;

好,下面我们看这行

prepareBeanFactory(beanFactory);

点进去

/**
 *
 * 配置其标准的特征，比如上下文的加载器ClassLoader和post-processors回调
 * Configure the factory's standard context characteristics,
 * such as the context's ClassLoader and post-processors.
 * @param beanFactory the BeanFactory to configure
 * 此处的beanFactory参数等于DefaultListableFactory
 */
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
   // Tell the internal bean factory to use the context's class loader etc.
   beanFactory.setBeanClassLoader(getClassLoader());
   //bean表达式解释器，后面说  能够获取bean当中的属性在前台页面
   beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
   //对象与string类型的转换   <property red="dao">
   beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

   // Configure the bean factory with context callbacks.
   //添加一个后置管理器
   //ApplicationContextAwareProcessor
   // 能够在bean中获得到各种*Aware（*Aware都有其作用）
   beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));//核心代码

   beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
   beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
   beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
   beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
   beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

   // BeanFactory interface not registered as resolvable type in a plain factory.
   // MessageSource registered (and found for autowiring) as a bean.
   beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
   beanFactory.registerResolvableDependency(ResourceLoader.class, this);
   beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
   beanFactory.registerResolvableDependency(ApplicationContext.class, this);

   // Register early post-processor for detecting inner beans as ApplicationListeners.
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

   // Detect a LoadTimeWeaver and prepare for weaving, if found.
   if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      // Set a temporary ClassLoader for type matching.
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
   }

   //意思是如果自定义的Bean中没有名为"systemProperties"和"systemEnvironment"的Bean，
   // 则注册两个Bena，Key为"systemProperties"和"systemEnvironment"，Value为Map，
   // 这两个Bean就是一些系统配置和系统环境信息
   // Register default environment beans.
   if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
   }
   if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
   }
   if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
      beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
   }
}

我们看一下核心的那行代码

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));//核心代码

打断点

@Override
    public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
        Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
        // Remove from old position, if any
        this.beanPostProcessors.remove(beanPostProcessor);
        // Track whether it is instantiation/destruction aware
        if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
            this.hasInstantiationAwareBeanPostProcessors = true;
        }
        if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
            this.hasDestructionAwareBeanPostProcessors = true;
        }
        // Add to end of list
        this.beanPostProcessors.add(beanPostProcessor);//核心代码
    }

我们看一下this.beanPostProcessors是什么

/** BeanPostProcessors to apply in createBean. */ private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();

BeanPostProcessor就是传说中的后置处理器,通过实现BeanPostProcessor接口，程序员就可插手bean实例化的过程

我们试一下

@Service
public class IndexService {

    public IndexService(){
        System.out.println("IndexService  构造方法");
    }

    @PostConstruct
    public void init(){
        System.out.println("IndexService  init方法");
    }

    public void hello(){
        System.out.println("IndexService");
    }

}

配置类

@Configuration
@ComponentScan("com.lusai")
public class SpringConfig {

}

实现BeanPostProcessor接口的类

@Component
public class TestBeanPostProcessor implements BeanPostProcessor {

    /**
     * 在bean初始化之前执行
     */
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("indexService")){
            System.out.println("indexService  postProcessBeforeInitialization");
        }
        //这里也可以产生代理对象 Proxy.newProxyInstance()
        return bean;
    }

    /**
     * 初始化之后
     */
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("indexService")){
            System.out.println("indexService  postProcessAfterInitialization");
        }
        return bean;
    }
}

测试类

public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(SpringConfig.class);
        //AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(IndexService.class);
        IndexService indexService = (IndexService) applicationContext.getBean("indexService");
        indexService.hello();
    }

看下结果

插手成功

好了,我们继续这行代码

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));//核心代码

我们看下此处的ApplicationContextAwareProcessor,这个类实现了BeanPostProcessor 接口,重写了postProcessBeforeInitialization方法

class ApplicationContextAwareProcessor implements BeanPostProcessor {

    @Override
    @Nullable
    public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
        AccessControlContext acc = null;

        if (System.getSecurityManager() != null &&
                (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                        bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                        bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
            acc = this.applicationContext.getBeanFactory().getAccessControlContext();
        }

        if (acc != null) {
            AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                invokeAwareInterfaces(bean);
                return null;
            }, acc);
        }
        else {
            invokeAwareInterfaces(bean);//看这行
        }

        return bean;
    }

}

看下那行代码

private void invokeAwareInterfaces(Object bean) {
   if (bean instanceof Aware) {
      if (bean instanceof EnvironmentAware) {//EnvironmentAware用于获取配置文件
         //比如this.applicationContext.getEnvironment().getProperty("url")
         //ConfigurableEnvironment environment = this.applicationContext.getEnvironment();
         ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
      }
      if (bean instanceof EmbeddedValueResolverAware) {
         ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
      }
      if (bean instanceof ResourceLoaderAware) {
         ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
      }
      if (bean instanceof ApplicationEventPublisherAware) {
         ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
      }
      if (bean instanceof MessageSourceAware) {
         ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
      }
      if (bean instanceof ApplicationContextAware) {//实现ApplicationContextAware接口,可以在spring管理的单例bean中中使用原型依赖bean
         ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
      }
   }
}

我们测试一下ApplicationContextAware接口

@Service
public class IndexService implements ApplicationContextAware {

    private ApplicationContext applicationContext;
    public IndexService(){
        System.out.println("IndexService  构造方法");
    }

    @PostConstruct
    public void init(){
        System.out.println("IndexService  init方法");
    }

    public void hello(){
        System.out.println("IndexService");
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext=applicationContext;
        System.out.println(applicationContext);
    }
}

运行测试类,看下结果

好了,我们继续看源码

　　　　　　　　//目前是空方法,留给后续扩展
                postProcessBeanFactory(beanFactory);

                //完成扫描和解析(类--->beanDefinition)         beanDefinitionMap
                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

第一个是空方法,看第二行

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
   //先看下getBeanFactoryPostProcessors方法
   PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

   // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
   // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
   if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
      beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
      beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
   }
}

先看下getBeanFactoryPostProcessors方法

public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
        return this.beanFactoryPostProcessors;
    }

这里的this.beanFactoryPostProcessors就是BeanFactoryPostProcessor的集合,如下

private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = new ArrayList<>();

那么BeanFactoryPostProcessor是什么?有什么用呢?

BeanFactoryPostProcessor是spring的扩展点之一
 * 实现该接口，可以在spring的bean创建之前修改bean的定义属性。
 * spring允许BeanFactoryPostProcessor在容器实例化任何其它bean之前读取配置元数据，
 * 并可以根据需要进行修改，例如可以把bean的scope从singleton改为prototype，也可以把property的值给修改掉。
 * 可以同时配置多个BeanFactoryPostProcessor，并通过设置'order'属性来控制各个BeanFactoryPostProcessor的执行次序。
 * BeanFactoryPostProcessor是在spring容器加载了bean的定义文件之后，在bean实例化之前执行的

来测试一下这个功能

@Component
public class TestBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        BeanDefinition indexService = beanFactory.getBeanDefinition("indexService");
        String scope = indexService.getScope();
        System.out.println(scope);
        indexService.setScope("prototype");
        System.out.println(scope);
    }
}

这篇就先到这里吧