spring ioc 源码解析（一）

我不是女神ヾ 2022-09-21 04:55 312阅读 0赞

#### spring ioc 原理 ####

#### 一、本地执行加载bean ####

BeanFactory bf = new XmlBeanFactory(new ClassPathResource("biz-service-base.xml"));
    ITestInfoService testInfoService = (ITestInfoService) bf.getBean("testService");

常见Resource实现类：

* @see WritableResource
     * @see ContextResource
     * @see FileSystemResource
     * @see ClassPathResource
     * @see UrlResource
     * @see ByteArrayResource
     * @see InputStreamResource

#### 二、spring 加载bean步骤 ####

1.构建Resource，指定加载文件的路径和加载文件的classLoder

public ClassPathResource(String path) {
            this(path, (ClassLoader) null);
        }
    
        /** * Create a new ClassPathResource for ClassLoader usage. * A leading slash will be removed, as the ClassLoader * resource access methods will not accept it. * @param path the absolute path within the classpath * @param classLoader the class loader to load the resource with, * or {@code null} for the thread context class loader * @see ClassLoader#getResourceAsStream(String) */
        public ClassPathResource(String path, ClassLoader classLoader) {
            Assert.notNull(path, "Path must not be null");
            String pathToUse = StringUtils.cleanPath(path);
            if (pathToUse.startsWith("/")) {
                pathToUse = pathToUse.substring(1);
            }
            this.path = pathToUse;
            this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
        }

2.利用XmlBeanFactory(Resource resource)构造器调用该类中持有的XmlBeanDefinitionReader类的loadBeanDefinitions(resource)方法加载xml资源

public XmlBeanFactory(Resource resource) throws BeansException {
            this(resource, null);
        }
    
        /** * Create a new XmlBeanFactory with the given input stream, * which must be parsable using DOM. * @param resource XML resource to load bean definitions from * @param parentBeanFactory parent bean factory * @throws BeansException in case of loading or parsing errors */
        public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
            super(parentBeanFactory);
            this.reader.loadBeanDefinitions(resource);
        }

3.XmlBeanDefinitionReader的loadBeanDefinitions方法中，首先利用resourcesCurrentlyBeingLoaded判断该xml文件是否正在加载中和是否存在循环引用，再调用doLoadBeanDefinitions(inputSource, encodedResource.getResource())进行bean继续加载

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
            Assert.notNull(encodedResource, "EncodedResource must not be null");
            if (logger.isInfoEnabled()) {
                logger.info("Loading XML bean definitions from " + encodedResource.getResource());
            }
    
            Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
            if (currentResources == null) {
                currentResources = new HashSet<EncodedResource>(4);
                this.resourcesCurrentlyBeingLoaded.set(currentResources);
            }
            if (!currentResources.add(encodedResource)) {
                throw new BeanDefinitionStoreException(
                        "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
            }
            try {
                InputStream inputStream = encodedResource.getResource().getInputStream();
                try {
                    InputSource inputSource = new InputSource(inputStream);
                    if (encodedResource.getEncoding() != null) {
                        inputSource.setEncoding(encodedResource.getEncoding());
                    }
                    return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
                }
                finally {
                    inputStream.close();
                }
            }
            catch (IOException ex) {
                throw new BeanDefinitionStoreException(
                        "IOException parsing XML document from " + encodedResource.getResource(), ex);
            }
            finally {
                currentResources.remove(encodedResource);
                if (currentResources.isEmpty()) {
                    this.resourcesCurrentlyBeingLoaded.remove();
                }
            }
        }

4.XmlBeanDefinitionReader的doLoadBeanDefinitions方法中，第一步获取xml解析模式（DTD OR XSD）, 第二步调用DocumentLoader中的loadDocument()方法获取xml文档,第三步调用XmlBeanDefinitionReader的registerBeanDefinitions()方法注册bean资源。

/** * Actually load bean definitions from the specified XML file. * @param inputSource the SAX InputSource to read from * @param resource the resource descriptor for the XML file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */
        protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
                throws BeanDefinitionStoreException {
            try {
                int validationMode = getValidationModeForResource(resource);
                Document doc = this.documentLoader.loadDocument(
                        inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
                return registerBeanDefinitions(doc, resource);
            }
            catch (BeanDefinitionStoreException ex) {
                throw ex;
            }
            catch (SAXParseException ex) {
                throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                        "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
            }
            catch (SAXException ex) {
                throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                        "XML document from " + resource + " is invalid", ex);
            }
            catch (ParserConfigurationException ex) {
                throw new BeanDefinitionStoreException(resource.getDescription(),
                        "Parser configuration exception parsing XML from " + resource, ex);
            }
            catch (IOException ex) {
                throw new BeanDefinitionStoreException(resource.getDescription(),
                        "IOException parsing XML document from " + resource, ex);
            }
            catch (Throwable ex) {
                throw new BeanDefinitionStoreException(resource.getDescription(),
                        "Unexpected exception parsing XML document from " + resource, ex);
            }
        }

5.XmlBeanDefinitionReader的registerBeanDefinitions方法中，利用DefaultBeanDefinitionDocumentReader调用registerBeanDefinitions(doc, createReaderContext(resource))进行bean加载注册，最后传递个doRegisterBeanDefinitions(root)方法进行最终加载.

protected void doRegisterBeanDefinitions(Element root) {
            String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
            if (StringUtils.hasText(profileSpec)) {
                Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                        profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
                if (!this.environment.acceptsProfiles(specifiedProfiles)) {
                    return;
                }
            }
    
            // 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(this.readerContext, root, parent);
    
            preProcessXml(root);
            parseBeanDefinitions(root, this.delegate);
            postProcessXml(root);
    
            this.delegate = parent;
        }

6.parseBeanDefinitions(root, this.delegate);对xml进行真正解析

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);
                        }
                        else {
                            delegate.parseCustomElement(ele);
                        }
                    }
                }
            }
            else {
                delegate.parseCustomElement(root);
            }
        }

7.parseDefaultElement(ele, delegate);解析spring默认标签<beans>、<bean>、<import>、<alias>。

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
            if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
                importBeanDefinitionResource(ele);
            }
            else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
                processAliasRegistration(ele);
            }
            else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
                processBeanDefinition(ele, delegate);
            }
            else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
                // recurse
                doRegisterBeanDefinitions(ele);
            }
        }

8.processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) 解析bean标签的所有属性在BeanDefinitionHolder中,然后通过BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());注册刚刚获取的bdHolder.

/** * 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);
            if (bdHolder != null) {
                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));
            }
        }

9.上面BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);对bean节点所有属性，并通过反射创建bean class

public static AbstractBeanDefinition createBeanDefinition(
                String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException {
    
            GenericBeanDefinition bd = new GenericBeanDefinition();
            bd.setParentName(parentName);
            if (className != null) {
                if (classLoader != null) {
                    bd.setBeanClass(ClassUtils.forName(className, classLoader));
                }
                else {
                    bd.setBeanClassName(className);
                }
            }
            return bd;
        }

10.BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());真正利用Map<beanName, beanDefinition>保存单例bean的缓存。key 为beanName ,value为BeanDefinition对象

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 ex) {
                    throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                            "Validation of bean definition failed", ex);
                }
            }
    
            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.");
                    }
                    else {
                        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;
                }
                this.beanDefinitionMap.put(beanName, beanDefinition);
            }
    
            resetBeanDefinition(beanName);
        }

11.执行过程

14:30:59.155 [main] DEBUG o.s.core.env.StandardEnvironment - Initializing new StandardEnvironment
    14:30:59.171 [main] DEBUG o.s.core.env.StandardEnvironment - Adding [systemProperties] PropertySource with lowest search precedence
    14:30:59.179 [main] DEBUG o.s.core.env.StandardEnvironment - Adding [systemEnvironment] PropertySource with lowest search precedence
    14:30:59.184 [main] DEBUG o.s.core.env.StandardEnvironment - Initialized StandardEnvironment with PropertySources [systemProperties,systemEnvironment]
    14:30:59.197 [main] INFO  o.s.b.f.xml.XmlBeanDefinitionReader - Loading XML bean definitions from class path resource [biz-service-base.xml]
    14:30:59.393 [main] DEBUG o.s.b.f.xml.DefaultDocumentLoader - Using JAXP provider [com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl]
    14:30:59.640 [main] DEBUG o.s.b.f.xml.PluggableSchemaResolver - Loading schema mappings from [META-INF/spring.schemas]
    14:30:59.663 [main] DEBUG o.s.b.f.xml.PluggableSchemaResolver - Loaded schema mappings: {
       http://mybatis.org/schema/mybatis-spring-1.2.xsd=org/mybatis/spring/config/mybatis-spring-1.2.xsd, http://www.springframework.org/schema/jee/spring-jee-3.2.xsd=org/springframework/ejb/config/spring-jee-3.2.xsd, http://www.springframework.org/schema/util/spring-util.xsd=org/springframework/beans/factory/xml/spring-util-3.2.xsd, http://www.springframework.org/schema/task/spring-task.xsd=org/springframework/scheduling/config/spring-task-3.2.xsd, http://www.springframework.org/schema/beans/spring-beans-3.1.xsd=org/springframework/beans/factory/xml/spring-beans-3.1.xsd, http://www.springframework.org/schema/cache/spring-cache.xsd=org/springframework/cache/config/spring-cache-3.2.xsd, http://www.springframework.org/schema/aop/spring-aop-3.0.xsd=org/springframework/aop/config/spring-aop-3.0.xsd, http://www.springframework.org/schema/task/spring-task-3.1.xsd=org/springframework/scheduling/config/spring-task-3.1.xsd, http://www.springframework.org/schema/aop/spring-aop-2.0.xsd=org/springframework/aop/config/spring-aop-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/beans/spring-beans.xsd=org/springframework/beans/factory/xml/spring-beans-3.2.xsd, http://www.springframework.org/schema/jee/spring-jee-2.5.xsd=org/springframework/ejb/config/spring-jee-2.5.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd=org/springframework/jdbc/config/spring-jdbc-3.1.xsd, http://www.springframework.org/schema/tool/spring-tool-3.1.xsd=org/springframework/beans/factory/xml/spring-tool-3.1.xsd, http://www.springframework.org/schema/jee/spring-jee-3.1.xsd=org/springframework/ejb/config/spring-jee-3.1.xsd, http://www.springframework.org/schema/aop/spring-aop.xsd=org/springframework/aop/config/spring-aop-3.2.xsd, http://www.springframework.org/schema/tx/spring-tx-3.2.xsd=org/springframework/transaction/config/spring-tx-3.2.xsd, http://www.springframework.org/schema/context/spring-context-3.2.xsd=org/springframework/context/config/spring-context-3.2.xsd, 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/util/spring-util-3.2.xsd=org/springframework/beans/factory/xml/spring-util-3.2.xsd, http://www.springframework.org/schema/lang/spring-lang-3.2.xsd=org/springframework/scripting/config/spring-lang-3.2.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/cache/spring-cache-3.2.xsd=org/springframework/cache/config/spring-cache-3.2.xsd, http://www.springframework.org/schema/task/spring-task-3.0.xsd=org/springframework/scheduling/config/spring-task-3.0.xsd, http://mybatis.org/schema/mybatis-spring.xsd=org/mybatis/spring/config/mybatis-spring-1.2.xsd, http://www.springframework.org/schema/tx/spring-tx-2.5.xsd=org/springframework/transaction/config/spring-tx-2.5.xsd, http://www.springframework.org/schema/context/spring-context-2.5.xsd=org/springframework/context/config/spring-context-2.5.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc-3.0.xsd=org/springframework/jdbc/config/spring-jdbc-3.0.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/tx/spring-tx.xsd=org/springframework/transaction/config/spring-tx-3.2.xsd, http://www.springframework.org/schema/lang/spring-lang.xsd=org/springframework/scripting/config/spring-lang-3.2.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/util/spring-util-2.5.xsd=org/springframework/beans/factory/xml/spring-util-2.5.xsd, http://www.springframework.org/schema/lang/spring-lang-2.5.xsd=org/springframework/scripting/config/spring-lang-2.5.xsd, http://www.springframework.org/schema/aop/spring-aop-3.2.xsd=org/springframework/aop/config/spring-aop-3.2.xsd, http://www.springframework.org/schema/jee/spring-jee-3.0.xsd=org/springframework/ejb/config/spring-jee-3.0.xsd, http://www.springframework.org/schema/tx/spring-tx-3.1.xsd=org/springframework/transaction/config/spring-tx-3.1.xsd, http://www.springframework.org/schema/jee/spring-jee-2.0.xsd=org/springframework/ejb/config/spring-jee-2.0.xsd, http://www.springframework.org/schema/context/spring-context-3.1.xsd=org/springframework/context/config/spring-context-3.1.xsd, http://www.springframework.org/schema/util/spring-util-3.1.xsd=org/springframework/beans/factory/xml/spring-util-3.1.xsd, http://www.springframework.org/schema/lang/spring-lang-3.1.xsd=org/springframework/scripting/config/spring-lang-3.1.xsd, http://www.springframework.org/schema/cache/spring-cache-3.1.xsd=org/springframework/cache/config/spring-cache-3.1.xsd, http://www.springframework.org/schema/context/spring-context.xsd=org/springframework/context/config/spring-context-3.2.xsd, http://www.springframework.org/schema/jee/spring-jee.xsd=org/springframework/ejb/config/spring-jee-3.2.xsd, http://www.springframework.org/schema/aop/spring-aop-2.5.xsd=org/springframework/aop/config/spring-aop-2.5.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc.xsd=org/springframework/jdbc/config/spring-jdbc-3.2.xsd, http://www.springframework.org/schema/beans/spring-beans-3.2.xsd=org/springframework/beans/factory/xml/spring-beans-3.2.xsd, http://www.springframework.org/schema/tx/spring-tx-2.0.xsd=org/springframework/transaction/config/spring-tx-2.0.xsd, http://www.springframework.org/schema/aop/spring-aop-3.1.xsd=org/springframework/aop/config/spring-aop-3.1.xsd, http://www.springframework.org/schema/task/spring-task-3.2.xsd=org/springframework/scheduling/config/spring-task-3.2.xsd, http://www.springframework.org/schema/tx/spring-tx-3.0.xsd=org/springframework/transaction/config/spring-tx-3.0.xsd, http://www.springframework.org/schema/context/spring-context-3.0.xsd=org/springframework/context/config/spring-context-3.0.xsd, http://www.springframework.org/schema/tool/spring-tool.xsd=org/springframework/beans/factory/xml/spring-tool-3.2.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/lang/spring-lang-3.0.xsd=org/springframework/scripting/config/spring-lang-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/lang/spring-lang-2.0.xsd=org/springframework/scripting/config/spring-lang-2.0.xsd, http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsd=org/springframework/jdbc/config/spring-jdbc-3.2.xsd, http://www.springframework.org/schema/tool/spring-tool-3.2.xsd=org/springframework/beans/factory/xml/spring-tool-3.2.xsd, http://www.springframework.org/schema/beans/spring-beans-2.5.xsd=org/springframework/beans/factory/xml/spring-beans-2.5.xsd}
    14:30:59.666 [main] DEBUG o.s.b.f.xml.PluggableSchemaResolver - Found XML schema [http://www.springframework.org/schema/beans/spring-beans-3.2.xsd] in classpath: org/springframework/beans/factory/xml/spring-beans-3.2.xsd
    14:30:59.815 [main] DEBUG o.s.b.f.x.DefaultBeanDefinitionDocumentReader - Loading bean definitions
    14:34:54.381 [main] DEBUG o.s.beans.factory.xml.XmlBeanFactory - Creating shared instance of singleton bean 'testService'
    14:34:54.383 [main] DEBUG o.s.beans.factory.xml.XmlBeanFactory - Creating instance of bean 'testService'
    14:34:54.423 [main] DEBUG o.s.beans.factory.xml.XmlBeanFactory - Eagerly caching bean 'testService' to allow for resolving potential circular references
    14:34:54.484 [main] DEBUG o.s.beans.factory.xml.XmlBeanFactory - Finished creating instance of bean 'testService'