spring源码-bean之初始化-1

Posted 2020-12-29 小不点丶

　　一、spring的IOC控制反转：控制反转——Spring通过一种称作控制反转（IOC）的技术促进了松耦合。当应用了IOC，一个对象依赖的其它对象会通过被动的方式传递进来，而不是这个对象自己创建或者查找依赖对象。说白了就是原本需要手动去创建和管理的对象，现在交给容器了。在容器的基础上，实现对象的控制。这个方式也很好的减少了开发者在框架上面的时间，更多关注点在业务逻辑上面。

　　二、这表博客的主要目的是研究，bean容器的初始化，会在最基本的bean初始化作源码的解析和分析。如何存在不妥当的地方，还请指出！

　　三、BeanFactory是spring的核心，通过工厂的模式来创建和使用bean。

　　四、我们都知道spring的bean初始化，依赖xml文件来实现的，所以这里重点讲解XmlBeanFactory的初始化过程。可能有人会问为什么不是ApplicationContext，相对于ApplicationContext，XmlBeanFactory是基础的bean初始化过程，后续我会单独将ApplicationContext又做了哪些动作。

　　五、源码解读

　　1）创建xml配置文件spring-bean.xml（这里省略User,，重点不在这里）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="user" class="com.pinnet.customLabel.User"/>
</beans>

　　2）开始创建对象

package com.pinnet.bean;

import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;

public class Test {

    public static void main(String[] args) {
        //读取资源
        Resource resource = new ClassPathResource("spring-bean.xml");
        //初始化容器
        new XmlBeanFactory(resource);
    }
}

　　3）初始化XmlBeanFactory

private final XmlBeanDefinitionReader reader;

    public XmlBeanFactory(Resource resource) throws BeansException {
        this(resource, (BeanFactory)null);
    }

    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
        super(parentBeanFactory);
        //用XmlBeanDefinitionReader，来进行加载
        this.reader = new XmlBeanDefinitionReader(this);
        //解析资源
        this.reader.loadBeanDefinitions(resource);
    }

　　4）loadBeanDefinitions

public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        //包装成EncodedResource
        return this.loadBeanDefinitions(new EncodedResource(resource));
    }

    public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
        Assert.notNull(encodedResource, "EncodedResource must not be null");
        if (this.logger.isInfoEnabled()) {
            this.logger.info("Loading XML bean definitions from " + encodedResource.getResource());
        }

        Set<EncodedResource> currentResources = (Set)this.resourcesCurrentlyBeingLoaded.get();
        if (currentResources == null) {
            currentResources = new HashSet(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }

        if (!((Set)currentResources).add(encodedResource)) {
            throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        } else {
            int var6;
            try {
                //转换成InputStream流
                InputStream inputStream = encodedResource.getResource().getInputStream();

                try {
                    InputSource inputSource = new InputSource(inputStream);
                    if (encodedResource.getEncoding() != null) {
                        inputSource.setEncoding(encodedResource.getEncoding());
                    }
                    //进一步解析
                    var6 = this.doLoadBeanDefinitions(inputSource, encodedResource.getResource());
                } finally {
                    inputStream.close();
                }
            } catch (IOException var15) {
                throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), var15);
            } finally {
                ((Set)currentResources).remove(encodedResource);
                if (((Set)currentResources).isEmpty()) {
                    this.resourcesCurrentlyBeingLoaded.remove();
                }
            }
            return var6;
        }
    }

　　5）doLoadBeanDefinitions

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
        try {
            int validationMode = this.getValidationModeForResource(resource);
            //读取xml为doc
            Document doc = this.documentLoader.loadDocument(inputSource, this.getEntityResolver(), this.errorHandler, validationMode, this.isNamespaceAware());
            //注册BeanDefinition
            return this.registerBeanDefinitions(doc, resource);
        } catch (BeanDefinitionStoreException var5) {
            throw var5;
        } catch (SAXParseException var6) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var6.getLineNumber() + " in XML document from " + resource + " is invalid", var6);
        } catch (SAXException var7) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var7);
        } catch (ParserConfigurationException var8) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var8);
        } catch (IOException var9) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var9);
        } catch (Throwable var10) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var10);
        }
    }

　　6）registerBeanDefinitions

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        this.logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        BeanDefinitionParserDelegate delegate = this.createHelper(readerContext, root);
　　　　 //此方法用于提供子类处理之用
        this.preProcessXml(root);
        this.parseBeanDefinitions(root, delegate);
　　　　　//此方法用于提供子类处理之用
        this.postProcessXml(root);
    }

　　7）parseBeanDefinitions（这一部分就是解析过程了）

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)) {
　　　　　　　　　　　　　　//默认标签解析
                        this.parseDefaultElement(ele, delegate);
                    } else {
　　　　　　　　　　　　　　//自定义标签解析（这里后面讲，这个也是非常重要的拓展功能）　　　　　　　　
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        } else {
            delegate.parseCustomElement(root);
        }

    }

　　8）parseDefaultElement（默认标签解析，这里关注bean）

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, "import")) {
            this.importBeanDefinitionResource(ele);
        } else if (delegate.nodeNameEquals(ele, "alias")) {
            this.processAliasRegistration(ele);
        } else if (delegate.nodeNameEquals(ele, "bean")) {
            this.processBeanDefinition(ele, delegate);
        }
    }

　　9）processBeanDefinition

 protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //这里主要是解析过程
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                //这里注册bean到beanDefinitionMap，后面会看到
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name \'" + bdHolder.getBeanName() + "\'", ele, var5);
            }
            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

　　a、parseBeanDefinitionElement

　　public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
        return this.parseBeanDefinitionElement(ele, (BeanDefinition)null);
    }

    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        String id = ele.getAttribute("id");
        String nameAttr = ele.getAttribute("name");
        List<String> aliases = new ArrayList();
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; ");
            aliases.addAll((Collection)Arrays.asList(nameArr));
        }

        String beanName = id;
        if (!StringUtils.hasText(id) && !aliases.isEmpty()) {
            beanName = (String)aliases.remove(0);
            if (this.logger.isDebugEnabled()) {
                this.logger.debug("No XML \'id\' specified - using \'" + beanName + "\' as bean name and " + aliases + " as aliases");
            }
        }

        if (containingBean == null) {
            //检查id和别名是否重复
            this.checkNameUniqueness(beanName, aliases, ele);
        }

        //解析过程
        AbstractBeanDefinition beanDefinition = this.parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(beanDefinition, this.readerContext.getRegistry(), true);
                    } else {
                        //生成beanName
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && 
　　　　　　　　　　　　　　　　!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }
                    if (this.logger.isDebugEnabled()) {
                        this.logger.debug("Neither XML \'id\' nor \'name\' specified - using generated bean name [" + beanName + "]");
                    }
                } catch (Exception var9) {
                    this.error(var9.getMessage(), ele);
                    return null;
                }
            }
            String[] aliasesArray = StringUtils.toStringArray(aliases);
            //将别名和beanName放入BeanDefinitionHolder
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        } else {
            return null;
        }
    }

　　parseBeanDefinitionElement（进一步解析过程，可以自己查看源码，这里不讲解）

public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {
        this.parseState.push(new BeanEntry(beanName));
        String className = null;
        if (ele.hasAttribute("class")) {
            className = ele.getAttribute("class").trim();
        }
        try {
            String parent = null;
            if (ele.hasAttribute("parent")) {
                parent = ele.getAttribute("parent");
            }
            //创建GenericBeanDefinition
            AbstractBeanDefinition bd = this.createBeanDefinition(className, parent);
            //解析bean上面的默认元素
            this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
            //meta
            this.parseMetaElements(ele, bd);
            //lookup-method
            this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            //replaced-method
            this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            //constructor-arg
            this.parseConstructorArgElements(ele, bd);
            //property
            this.parsePropertyElements(ele, bd);
            //qualifier
            this.parseQualifierElements(ele, bd);
            bd.setResource(this.readerContext.getResource());
            bd.setSource(this.extractSource(ele));
            //所有解析过后的元素全部放在AbstractBeanDefinition里面
            AbstractBeanDefinition var8 = bd;
            return var8;
        } catch (ClassNotFoundException var13) {
            this.error("Bean class [" + className + "] not found", ele, var13);
        } catch (NoClassDefFoundError var14) {
            this.error("Class that bean class [" + className + "] depends on not found", ele, var14);
        } catch (Throwable var15) {
            this.error("Unexpected failure during bean definition parsing", ele, var15);
        } finally {
            this.parseState.pop();
        }
        return null;
    }

　　b、registerBeanDefinition（将AbstractBeanDefinition的相关数据放入beanDefinitionMap）

public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            String[] var7 = aliases;
            int var6 = aliases.length;

            for(int var5 = 0; var5 < var6; ++var5) {
                String aliase = var7[var5];
                registry.registerAlias(beanName, aliase);
            }
        }

    }

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) {
            try {
                ((AbstractBeanDefinition)beanDefinition).validate();
            } catch (BeanDefinitionValidationException var6) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var6);
            }
        }

        Map var3 = this.beanDefinitionMap;
        synchronized(this.beanDefinitionMap) {
            Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
            if (oldBeanDefinition != null) {
                if (!this.allowBeanDefinitionOverriding) {
                    throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean \'" + beanName + "\': There is already [" + oldBeanDefinition + "] bound.");
                }

                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean \'" + beanName + "\': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else {
                this.beanDefinitionNames.add(beanName);
                this.frozenBeanDefinitionNames = null;
            }
            //将beanName和beanDefinition形成键值对的形式，保存在Map中
            this.beanDefinitionMap.put(beanName, beanDefinition);
            this.resetBeanDefinition(beanName);
        }
    }

　　六、好了，这就是源码的实现过程，中间省略了很多的判定和实现过程。主要的流程，基本上就是这样。这里重点注意几个点，也是对流程的梳理

　　1）初始化XmlBeanFactory，需要注意XmlBeanDefinitionReader：这是整个解读过程的关键

　　2）然后就是字符集包装，然后形成流EncodedResource、inputSource

　　3）解析xml，基本上是通过spring的DefaultDocumentLoader实现的，通过对Document文档的解析来实现标签和元素的解析

　　4）判断是否是默认标签是通过xml的Namespace来实现的，默认Namespace的读取目录是通过DefaultNamespaceHandlerResolver来实现的，也就是读取spring.handlers和spring.schemas，后续会讲到这两个文件的作用

　　public boolean isDefaultNamespace(String namespaceUri) {
        return !StringUtils.hasLength(namespaceUri) || "http://www.springframework.org/schema/beans".equals(namespaceUri);
    }

　　protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
        return new DefaultNamespaceHandlerResolver(this.getResourceLoader().getClassLoader());
    }

　　spring.handlers

http\\://www.springframework.org/schema/p=org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler
http\\://www.springframework.org/schema/util=org.springframework.beans.factory.xml.UtilNamespaceHandler

　　spring.schemas

http\\://www.springframework.org/schema/beans/spring-beans-2.0.xsd=org/springframework/beans/factory/xml/spring-beans-2.0.xsd
http\\://www.springframework.org/schema/beans/spring-beans-2.5.xsd=org/springframework/beans/factory/xml/spring-beans-2.5.xsd
http\\://www.springframework.org/schema/beans/spring-beans-3.0.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd
http\\://www.springframework.org/schema/beans/spring-beans.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd
http\\://www.springframework.org/schema/tool/spring-tool-2.0.xsd=org/springframework/beans/factory/xml/spring-tool-2.0.xsd
http\\://www.springframework.org/schema/tool/spring-tool-2.5.xsd=org/springframework/beans/factory/xml/spring-tool-2.5.xsd
http\\://www.springframework.org/schema/tool/spring-tool-3.0.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd
http\\://www.springframework.org/schema/tool/spring-tool.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd
http\\://www.springframework.org/schema/util/spring-util-2.0.xsd=org/springframework/beans/factory/xml/spring-util-2.0.xsd
http\\://www.springframework.org/schema/util/spring-util-2.5.xsd=org/springframework/beans/factory/xml/spring-util-2.5.xsd
http\\://www.springframework.org/schema/util/spring-util-3.0.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd
http\\://www.springframework.org/schema/util/spring-util.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd

　　5）解析bean标签，是生产一个GenericBeanDefinition这个类是继承AbstractBeanDefinition生产BeanDefinition的过程其实就是讲标签里面的元素进行解析放入的过程

　　6）注册的过程是放在DefaultListableBeanFactory里面的beanDefinitionMap，是不是有点奇怪过程并没有DefaultListableBeanFactory。在源码的9）中使用了BeanDefinitionRegistry ，而这个BeanDefinitionRegistry 也是我们最开始使用的XmlBeanFactory，但是XmlBeanFactory，并没有太多的实现。看来一个结构：

　　其实最开始调用XmlBeanFactory的时候就已经使用了DefaultListableBeanFactory，值不够是继承关系而已。所以这里基本上所有的数据都在DefaultListableBeanFactory里面了

　　7）最后解析过程就到这里，主要数据全部在DefaultListableBeanFactory的beanDefinitionMap里面。

　　8）注意一点，别名的加载过程也很重要，这里不多介绍，多想法自己查看源码

　　七、容器的初始化基本上就是这样了，主要是梳理流程和spring在IOC的控制中做了什么。