2. spring中IOC的实现源码篇【analyze spring framework source】

2B青年欢乐多啊，最近研究spring源码，做点笔记，欢迎继续补充, 持续更新

接上一篇 1. Introduce how to import the Spring Framework sourcecode into an eclipse project

一. 结构

spring中bean管理设计到下面3个包

core 相当于一个工具类，bean包是对IOC的实现包，context是在bean的基础扩展功能

IOC的实现原理简介

简单实现

package org.benson;

import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.core.io.ClassPathResource;

public class Test4DebugSpringIOC {
    ConfigurableListableBeanFactory beanFactory = new DefaultListableBeanFactory();//manage bean factory
    ClassPathResource resource = new ClassPathResource(
            "applicationContext.xml");//resource
    XmlBeanDefinitionReader xmlReader=new XmlBeanDefinitionReader((BeanDefinitionRegistry)beanFactory); //register
    
    public Test4DebugSpringIOC() {
        // TODO load and registered BeanDefinition
        xmlReader.loadBeanDefinitions(resource);
    }
    public static void main(String[] args) {
        Test4DebugSpringIOC test4DebugSpring= new Test4DebugSpringIOC();
        Test4DebugSpringBean test4DebugSpringBean = (Test4DebugSpringBean) test4DebugSpring.beanFactory
                .getBean("testAlias");
        test4DebugSpringBean.SayHolle();
    }
}

 1，找到bean的定义文件（Resource）

      如此处classPathResource，用于找到文件位置

 2，把定义文件解析成BeanDefinition对象并进行注册，在XmlBeanDefinitionReader中

            int validationMode = getValidationModeForResource(resource);//Validation xml file  . XmlBeanDefinitionReader doLoadBeanDefinitions
            Document doc = this.documentLoader.loadDocument(
                    inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());//parse to doc . through documentLoader(DefaultDocumentLoader)
            return registerBeanDefinitions(doc, resource);

一个普通bean的解析step 

 i 调用DefaultDocumentLoader把XML解析成DOC并进行XSD，DTD等格式验证.

 DefaultDocumentLoader调用了SAX的DocumentBuilderFactory.newInstance()，把XML文件解析成一个org.w3c.dom.Document对象(标准的DOM解析方式)，当然也设置XML验证的validationMode，namespace

    /**
     * Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
     * XML parser.
     */
    public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
            ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {

        DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
        if (logger.isDebugEnabled()) {
            logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
        }
        DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
        return builder.parse(inputSource);
    }

ii DefaultBeanDefinitionDocumentReader读取document中的所有Element. 

registerBeanDefinitions(doc, resource)中调用BeanDefinitionDocumentReader的registerBeanDefinitions方法获根节点

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
		this.readerContext = readerContext;

		logger.debug("Loading bean definitions");
		Element root = doc.getDocumentElement();

		doRegisterBeanDefinitions(root);
	}

得到XML的根节点,调用doRegisterBeanDefinitions

    /**
     * Register each bean definition within the given root {@code <beans/>} element.
     * @throws IllegalStateException if {@code <beans profile="..."} attribute is present
     * and Environment property has not been set
     * @see #setEnvironment
     */
    protected void doRegisterBeanDefinitions(Element root) {
..//profile

        // any nested <beans> elements will cause recursion in this method. In
        // order to propagate and preserve <beans> default-* attributes correctly,
        // keep track of the current (parent) delegate, which may be null. Create
        // the new (child) delegate with a reference to the parent for fallback purposes,
        // then ultimately reset this.delegate back to its original (parent) reference.
        // this behavior emulates a stack of delegates without actually necessitating one.
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createHelper(readerContext, root, parent);

        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);
        postProcessXml(root);

        this.delegate = parent;
    }

然后从获得根结点的所有子节点，进行循环

    /**
     * Parse the elements at the root level in the document:
     * "import", "alias", "bean".
     * @param root the DOM root element of the document
     */
    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        if (delegate.isDefaultNamespace(root)) {
            NodeList nl = root.getChildNodes();
            for (int i = 0; i < nl.getLength(); i++) {
                Node node = nl.item(i);
                if (node instanceof Element) {
                    Element ele = (Element) node;
                    if (delegate.isDefaultNamespace(ele)) {
                        parseDefaultElement(ele, delegate);//parse defalut element
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

 此处isDefaultNamespace方法是获取namespace为http://www.springframework.org/schema/beans的node，目前对应schema定义的包括"bean" "alis" "beans" "import" ,处理方法为parseDefaultElement(ele, delegate)，如果发现是bean标签则调用processBeanDefinition方法

    /**
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); //parse to object of BeanDefinitionHolder
        if (bdHolder != null) {//if it is not exit. parse it from xml
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

iii 调用BeanDefinitionParserDelegate对象完成doc中Element->BeanDefinitionHolder的转换

    /**
     * Parses the supplied <code>&lt;bean&gt;</code> element. May return <code>null</code>
     * if there were errors during parse. Errors are reported to the
     * {@link org.springframework.beans.factory.parsing.ProblemReporter}.
     */
    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        String id = ele.getAttribute(ID_ATTRIBUTE);
        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
... ... //vacation
        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
....

return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        }

先获得别名，这里叫nameAttr先转成数组，然后通过BeanDefinitionHolder把它和beanName，beandefine绑定在一起

/**
     * Parse the bean definition itself, without regard to name or aliases. May return
     * <code>null</code> if problems occurred during the parsing of the bean definition.
     */
    public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {

        this.parseState.push(new BeanEntry(beanName));

        String className = null;
        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
        }

        try {
            String parent = null;
            if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
                parent = ele.getAttribute(PARENT_ATTRIBUTE);
            }
            AbstractBeanDefinition bd = createBeanDefinition(className, parent);

            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));

            parseMetaElements(ele, bd);
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

            parseConstructorArgElements(ele, bd);
            parsePropertyElements(ele, bd);
            parseQualifierElements(ele, bd);

            bd.setResource(this.readerContext.getResource());
            bd.setSource(extractSource(ele));

            return bd;
        }

全部当成属性设置到了AbstractBeanDefinition 的对象中，具体可以看AbstractBeanDefinition 类

最后返回BeanDefinitionHolder；BeanDefinitionHolder是由beanname+aliasArray+beandefinition组成的一个对象

IV 然后回到ii的最后调用BeanDefinitionReaderUtils.registerBeanDefinition注册beandefine对象，并调BeanDefinitionRegistry接口进行注册，如DefaultListableBeanFactory

完成转换后，BeanDefinitionReaderUtils.registerBeanDefinition 调用到 BeanDefinitionRegistry接口实现类的registerBeanDefinition方法把对象放入bean的工厂容器中

     * Register the given bean definition with the given bean factory.
     * @param definitionHolder the bean definition including name and aliases
     * @param registry the bean factory to register with
     * @throws BeanDefinitionStoreException if registration failed
     */
    public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

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

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

 在DefaultListableBeanFactory的实现也很简单了，直接用map添加下就OK了

    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {
....//Validation

            this.beanDefinitionMap.put(beanName, beanDefinition);//add it to beanDefinitionMap
        }

        resetBeanDefinition(beanName); //reset all exist
    }

 3，查找，通过getbean获得bean，用ConfigurableListableBeanFactory，如DefaultListableBeanFactory

这部分功能主要在abstractbeanfactory中完成，如果是singleton（即spring的default）

i   transformedBeanName(name) ，得到SimpleAliasRegistry 的 map 属性 aliasMap，转换为beanname（别名功能）

ii  Object sharedInstance = getSingleton(beanName); 尝试从DefaultSingletonBeanRegistry的MAP singletonObjects中拿出bean (singleton功能)

iii  bean = getObjectForBeanInstance(sharedInstance, name, beanName, null) 处理factorybean部分，附 Spring FactoryBean源码浅析

iv final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); 从bean注册的信息中找到bean 对应的 BeanDefinition

v return createBean(beanName, mbd, args); 创建新的bean，通过BeanDefinition的描述信息来，并填充到DefaultSingletonBeanRegistry的singletonObjects中

beanfactory的主要代码，加上了些注释

    /**
     * Return an instance, which may be shared or independent, of the specified bean.
     * @param name the name of the bean to retrieve
     * @param requiredType the required type of the bean to retrieve
     * @param args arguments to use if creating a prototype using explicit arguments to a
     * static factory method. It is invalid to use a non-null args value in any other case.
     * @param typeCheckOnly whether the instance is obtained for a type check,
     * not for actual use
     * @return an instance of the bean
     * @throws BeansException if the bean could not be created
     */
    @SuppressWarnings("unchecked")
    protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {
        final String beanName = transformedBeanName(name); //get true name from attribute aliasMap of SimpleAliasRegistry
        Object bean;
        // Eagerly check singleton cache for manually registered singletons.
        Object sharedInstance = getSingleton(beanName); //get instance object from the attribute singletonObjects of DefaultSingletonBeanRegistry
        if (sharedInstance != null && args == null) {
            if (logger.isDebugEnabled()) {
                if (isSingletonCurrentlyInCreation(beanName)) {
                    logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                            "' that is not fully initialized yet - a consequence of a circular reference");
                }
                else {
                    logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
                }
            }
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); // it is for that class witch is implement interface factorybean
        }

        else {
            // Fail if we're already creating this bean instance:
            // We're assumably within a circular reference.
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // Not found -> check parent.
                String nameToLookup = originalBeanName(name);
                if (args != null) {
                    // Delegation to parent with explicit args.
                    return (T) parentBeanFactory.getBean(nameToLookup, args);
                }
                else {
                    // No args -> delegate to standard getBean method.
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }
            }

            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);//get BeanDefinition from registered information
            checkMergedBeanDefinition(mbd, beanName, args);

            // Guarantee initialization of beans that the current bean depends on.
            String[] dependsOn = mbd.getDependsOn();
            if (dependsOn != null) {
                for (String dependsOnBean : dependsOn) {
                    getBean(dependsOnBean);
                    registerDependentBean(dependsOnBean, beanName);
                }
            }

            // Create bean instance.
            if (mbd.isSingleton()) {
                sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                    //create new instance and put in attribute map singletonObjects of DefaultSingletonBeanRegistry
                    public Object getObject() throws BeansException {
                        try {
                            return createBean(beanName, mbd, args);
                        }
                        catch (BeansException ex) {
                            // Explicitly remove instance from singleton cache: It might have been put there
                            // eagerly by the creation process, to allow for circular reference resolution.
                            // Also remove any beans that received a temporary reference to the bean.
                            destroySingleton(beanName);
                            throw ex;
                        }
                    }
                });
                bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
            }

            else if (mbd.isPrototype()) {
                // It's a prototype -> create a new instance.
                Object prototypeInstance = null;
                try {
                    beforePrototypeCreation(beanName);
                    prototypeInstance = createBean(beanName, mbd, args);
                }
                finally {
                    afterPrototypeCreation(beanName);
                }
                bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
            }

            else {
                String scopeName = mbd.getScope();
                final Scope scope = this.scopes.get(scopeName);
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
                }
                try {
                    Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                        public Object getObject() throws BeansException {
                            beforePrototypeCreation(beanName);
                            try {
                                return createBean(beanName, mbd, args);
                            }
                            finally {
                                afterPrototypeCreation(beanName);
                            }
                        }
                    });
                    bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                }
                catch (IllegalStateException ex) {
                    throw new BeanCreationException(beanName,
                            "Scope '" + scopeName + "' is not active for the current thread; " +
                            "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                            ex);
                }
            }
        }

        // Check if required type matches the type of the actual bean instance.
        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {
                return getTypeConverter().convertIfNecessary(bean, requiredType);
            }
            catch (TypeMismatchException ex) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Failed to convert bean '" + name + "' to required type [" +
                            ClassUtils.getQualifiedName(requiredType) + "]", ex);
                }
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        }
        return (T) bean;
    }

附 bean中的主要结构

主要类，下列类从上往下继承

SimpleAliasRegistry 用于维护一个 aliasMap，维护别名功能

DefaultSingletonBeanRegistry map 维护 singletonObjects，维护工厂单例，一个工厂一个单例，非N个工厂一个单例

FactoryBeanRegistrySupport，

AbstractBeanFactory ，factorybean的主要实现类，其doGetBean,getBean是主要获得bean的入口 ，维护一个mergedBeanDefinitions

AbstractAutowireCapableBeanFactory,configureableBeanFactory的主要实现类,  createBean根据beandefine的信息创建相应的值

DefaultListableBeanFactory ConfigurableListableBeanFactory和BeanDefinitionRegistry接口的主要实现类，维护beanDefiniti信息

主要接口关系如下

Parse XML主要用到的几个相关类

* @see DocumentLoader
* @see DefaultDocumentLoader

TODO 对SAX几个工厂属性进行设置，schema等，调用SAX对XML转换成了DOC对象

* @see BeanDefinitionDocumentReader  
* @see DefaultBeanDefinitionDocumentReader

提供registerBeanDefinitions，和setEnvironment方法，用于DOC到beandefine的注册功能，遍历了doc的所有node，调用 BeanDefinitionParserDelegate解析node,并调用BeanDefinitionReaderUtils对解析的beandefine到beandefine注册类的注册

* @BeanDefinitionParserDelegate

主要解析类，各种属性，对beandefine对象属性的设置都是在此类完成

bean中ConfigurableListableBeanFactory接口继承了bean中的基本接口，DefaultListableBeanFactory是其唯一实现类，也是预留接口供扩展

接口因为可以多继承，所以用来表示系统的结构最合适不过，而JAVA中类单继承的，一般只是用来实现设计，侧重实现功能，因为类层次肯定是一条线。