Spring IOC 容器源码阅读笔记

最新推荐文章于 2022-08-27 18:27:54 发布

原创最新推荐文章于 2022-08-27 18:27:54 发布 · 357 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#spring #源码 #ioc #阅读 #笔记

spring 专栏收录该内容

5 篇文章

订阅专栏

本文详细记录了阅读Spring IOC容器源码的过程，从ClassPathXmlApplicationContext构造器开始，逐步剖析refresh()方法、bean工厂的刷新、bean定义的加载与注册，特别是解析bean定义的过程，展示了Spring如何管理bean的生命周期。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

参考的文章

Spring IOC容器源代码解析，作者带着看了一遍源码，边看边讲，非常nice。

正文

我对于Spring IOC（控制反转）的理解，是将对象的管理（控制）权从以前的程序员手中“反转”到了Spring IOC容器手中。
Spring IOC容器的定义接口（最基本的IOC容器）：BeanFactory，这个借口为具体的IOC容器的实现做了最基本的功能规定。

public interface BeanFactory {
    String FACTORY_BEAN_PREFIX = "&";

    Object getBean(String var1) throws BeansException;

    <T> T getBean(String var1, Class<T> var2) throws BeansException;

    <T> T getBean(Class<T> var1) throws BeansException;

    Object getBean(String var1, Object... var2) throws BeansException;

    <T> T getBean(Class<T> var1, Object... var2) throws BeansException;

    boolean containsBean(String var1);

    boolean isSingleton(String var1) throws NoSuchBeanDefinitionException;

    boolean isPrototype(String var1) throws NoSuchBeanDefinitionException;

    boolean isTypeMatch(String var1, ResolvableType var2) throws NoSuchBeanDefinitionException;

    boolean isTypeMatch(String var1, Class<?> var2) throws NoSuchBeanDefinitionException;

    Class<?> getType(String var1) throws NoSuchBeanDefinitionException;

    String[] getAliases(String var1);
}

围绕着BeanFactory，pring对于IOC容器有许多种实现（XmlBeanFactory，XmlWebApplicationContext.java，ClassPathXmlApplicationContext.java FileSystemXmlApplicationContext.java）。
我是以ClassPathXmlApplicationContext.java为例去看的源码。

ClassPathXmlApplicationContext构造器代码

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
        super(parent);
        this.setConfigLocations(configLocations);
        if(refresh) {
            this.refresh();
        }

    }

主要是调用了refresh()方法。bean的初始化逻辑是在这里完成的。

refresh()方法（refresh方法是在AbstractApplicationContext里的）

public void refresh() throws BeansException, IllegalStateException {
        Object var1 = this.startupShutdownMonitor;
        synchronized(this.startupShutdownMonitor) {
            this.prepareRefresh();
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
            this.prepareBeanFactory(beanFactory);

            try {
                this.postProcessBeanFactory(beanFactory);
                this.invokeBeanFactoryPostProcessors(beanFactory);
                this.registerBeanPostProcessors(beanFactory);
                this.initMessageSource();
                this.initApplicationEventMulticaster();
                this.onRefresh();
                this.registerListeners();
                this.finishBeanFactoryInitialization(beanFactory);
                this.finishRefresh();
            } catch (BeansException var9) {
                if(this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
                }
                this.destroyBeans();
                this.cancelRefresh(var9);
                throw var9;
            } finally {
                this.resetCommonCaches();
            }

        }
    }

这里重要的是ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();，获取一个新的beanFactory

obtainFreshBeanFactory()

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        this.refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        if(this.logger.isDebugEnabled()) {
            this.logger.debug("Bean factory for " + this.getDisplayName() + ": " + beanFactory);
        }

        return beanFactory;
    }

this.refreshBeanFactory();刷新beanFactory，如果已经建立了那么应该销毁重建。该方法是一个abstract方法，通过调试发现调用的是AbstractRefreshableApplicationContext中实现的refreshBeanFactory方法

refreshBeanFactory()

protected final void refreshBeanFactory() throws BeansException {
        if(this.hasBeanFactory()) {
            this.destroyBeans();
            this.closeBeanFactory();
        }

        try {
            DefaultListableBeanFactory beanFactory = this.createBeanFactory();
            beanFactory.setSerializationId(this.getId());
            this.customizeBeanFactory(beanFactory);
            this.loadBeanDefinitions(beanFactory);
            Object var2 = this.beanFactoryMonitor;
            synchronized(this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        } catch (IOException var5) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var5);
        }
    }

实现了如果已经建立了beanFactory，那么就销毁并关闭，重新建立。这里的this.loadBeanDefinitions(beanFactory);需要讲一下，它去加载那些bean的定义。
在AbstractXmlApplicationContext中定义了对资源的读取过程，默认由XmlBeanDefinitionReader来读取：

loadBeanDefinitions()

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = this.getConfigResources();
        if(configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }

        String[] configLocations = this.getConfigLocations();
        if(configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }

    }

doLoadBeanDefinitions()

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
        try {
            Document doc = this.doLoadDocument(inputSource, resource);
            return this.registerBeanDefinitions(doc, resource);
...
}

registerBeanDefinitions()

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = this.createBeanDefinitionDocumentReader();
        int countBefore = this.getRegistry().getBeanDefinitionCount();
        documentReader.registerBeanDefinitions(doc, this.createReaderContext(resource));
        return this.getRegistry().getBeanDefinitionCount() - countBefore;
    }

主要作用的还是documentReader.registerBeanDefinitions()方法。经过调试，发现调用的是DefaultBeanDefinitionDocumentReader中的registerBeanDefinitions()。
又经过调试发现是documentReader.registerBeanDefinitions()中的doRegisterBeanDefinitions()。实现的。

doRegisterBeanDefinitions

protected void doRegisterBeanDefinitions(Element root) {
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = this.createDelegate(this.getReaderContext(), root, parent);
        if(this.delegate.isDefaultNamespace(root)) {
            String profileSpec = root.getAttribute("profile");
            if(StringUtils.hasText(profileSpec)) {
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, ",; ");
                if(!this.getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                    if(this.logger.isInfoEnabled()) {
                        this.logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec + "] not matching: " + this.getReaderContext().getResource());
                    }

                    return;
                }
            }
        }

        this.preProcessXml(root);
        this.parseBeanDefinitions(root, this.delegate);
        this.postProcessXml(root);
        this.delegate = parent;
    }

实际上的解析工作都是交给delegate代理完成的。

parseBeanDefinitions()

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)) {
                        this.parseDefaultElement(ele, delegate);
                    } else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        } else {
            delegate.parseCustomElement(root);
        }

    }

该方法是遍历所有的子节点，然后分为默认的命名空间（import，alias，bean，beans）和自定义的命名空间（dubbo，shiro等等）。

parseDefaultElement()

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);
        } else if(delegate.nodeNameEquals(ele, "beans")) {
            this.doRegisterBeanDefinitions(ele);
        }

    }

根据不同的nodeName做不同处理。

processBeanDefinition

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if(bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

            try {
                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));
        }

    }

这里执行了delegate.parseBeanDefinitionElement()完成了对bean定义的解析，返回的BeanDefinitionHolder交给BeanDefinitionReaderUtils.registerBeanDefinition()，完成对一个bean的定义。

先说parseBeanDefinitionElement()

parseBeanDefinitionElement()

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(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) {
            this.checkNameUniqueness(beanName, aliases, ele);
        }

        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 {
                        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);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        } else {
            return null;
        }
    }

parseBeanDefinitionElement()方法具体完成。

parseBeanDefinitionElement()

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");
            }
    //创建一个AbstractBeanDefinition并设置好'类名'和'parent'
            AbstractBeanDefinition bd = this.createBeanDefinition(className, parent);
    //解析了Element的属性并设置到beanDefinition中去
            this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
    //设置启动参数
            this.parseMetaElements(ele, bd);
    //设置被期望重写
            this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
    //设置被替换的方法              
            this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            this.parseConstructorArgElements(ele, bd);
            this.parsePropertyElements(ele, bd);
            this.parseQualifierElements(ele, bd);
            bd.setResource(this.readerContext.getResource());
            bd.setSource(this.extractSource(ele));
    //这里，是为了防止并发问题？？？？？Spring在后面还用到了类似的手法
            AbstractBeanDefinition var7 = bd;
            return var7;
        } 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;
    }

经过parseBeanDefinitionElement完成了beanDefinition的各种设置，再说registerBeanDefinition，把设置完成的beanDefinition注册到IOC容器中

registerBeanDefinition()

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[] var4 = aliases;
            int var5 = aliases.length;

            for(int var6 = 0; var6 < var5; ++var6) {
                String alias = var4[var6];
                registry.registerAlias(beanName, alias);
            }
        }

    }

主要有通过传来的参数注册器.registerBeanDefinition()，再就是注册别名。这里只看registerBeanDefinition()方法。

registerBeanDefinition()这里用的是DefaultListableBeanFactory，PS：XmlBeanFactory是继承的DefaultListableBeanFactory。

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 var9) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
            }
        }

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

            if(oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                if(this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else if(!beanDefinition.equals(oldBeanDefinition)) {
                if(this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else if(this.logger.isDebugEnabled()) {
                this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
            }

            this.beanDefinitionMap.put(beanName, beanDefinition);
        } else {
            if(this.hasBeanCreationStarted()) {
                Map var4 = this.beanDefinitionMap;
                synchronized(this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition);
    //这种new一个新对象，处理完后，将需要修改的引用指向new的新对象，可以降低并发的影响，也就是避免多线程操作同一对象喽。

                    List<String> updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if(this.manualSingletonNames.contains(beanName)) {
                        Set<String> updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            } else {
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                this.manualSingletonNames.remove(beanName);
            }

            this.frozenBeanDefinitionNames = null;
        }

        if(oldBeanDefinition != null || this.containsSingleton(beanName)) {
            this.resetBeanDefinition(beanName);
        }

    }

可以看到最后IOC容器是基于private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap(256);对象的，所有定义好的bean都是在这个线程安全的hashmap中存取的，而且Spring用到了大量的以空间换取“避免多个线程操作同一个对象”这种方法。