spring源码阅读(1)--Bean解析流程

Bean解析核心流程

• BeanDefinition
• 默认标签解析
• 自定义标签解析

DefaultBeanDefinitionDocumentReader.java 

　　/**
     * 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)) {
                        // 默认标签解析
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        // 自定义标签解析
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

• SPI机制在加载自定义标签中的应用

DefaultNamespaceHandlerResolver.java

    /**
　　　* 
     * Locate the {@link NamespaceHandler} for the supplied namespace URI
     * from the configured mappings.
     * @param namespaceUri the relevant namespace URI
     * @return the located {@link NamespaceHandler}, or {@code null} if none found
     */
    @Override
    @Nullable
    public NamespaceHandler resolve(String namespaceUri) {
        //获取spring中所有jar包里面的 "META-INF/spring.handlers"文件，并且建立映射关系
        Map<String, Object> handlerMappings = getHandlerMappings();
        //根据namespaceUri：http://www.springframework.org/schema/context，获取到这个命名空间的处理类
        Object handlerOrClassName = handlerMappings.get(namespaceUri);
        if (handlerOrClassName == null) {
            return null;
        }
        else if (handlerOrClassName instanceof NamespaceHandler) {
            return (NamespaceHandler) handlerOrClassName;
        }
        else {
            String className = (String) handlerOrClassName;
            try {
                Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
                if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
                    throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
                            "] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
                }
                NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);

                //调用处理类的init方法，在init方法中完成标签元素解析类的注册
                namespaceHandler.init();
                handlerMappings.put(namespaceUri, namespaceHandler);
                return namespaceHandler;
            }
            catch (ClassNotFoundException ex) {
                throw new FatalBeanException("Could not find NamespaceHandler class [" + className +
                        "] for namespace [" + namespaceUri + "]", ex);
            }
            catch (LinkageError err) {
                throw new FatalBeanException("Unresolvable class definition for NamespaceHandler class [" +
                        className + "] for namespace [" + namespaceUri + "]", err);
            }
        }
    }

 

• conponent-scan原理

ComponentScanBeanDefinitionParser.java

    @Override
    @Nullable
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        //获取basePackage属性
        String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
        basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
        //可以用逗号分开
        String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);

        //创建注解扫描器
        // Actually scan for bean definitions and register them.
        ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
        //扫描并把扫描的类封装成beanDefinition对象  核心方法，重要程度 5
        Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
        registerComponents(parserContext.getReaderContext(), beanDefinitions, element);

        return null;
    }

 

ClassPathBeanDefinitionScanner.java

　　/**
　　　* 扫描并把扫描的类封装成beanDefinition对象  核心方法，重要程度 5*
     * Perform a scan within the specified base packages,
     * returning the registered bean definitions.
     * <p>This method does <i>not</i> register an annotation config processor
     * but rather leaves this up to the caller.
     * @param basePackages the packages to check for annotated classes
     * @return set of beans registered if any for tooling registration purposes (never {@code null})
     */
    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
        for (String basePackage : basePackages) {
            //扫描到有注解的类并封装成BeanDefinition对象
            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
            for (BeanDefinition candidate : candidates) {
                ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
                candidate.setScope(scopeMetadata.getScopeName());
                String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
                if (candidate instanceof AbstractBeanDefinition) {
                    //支持了@Lazy @DependOn注解
                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
                }
                if (candidate instanceof AnnotatedBeanDefinition) {
                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
                }
                if (checkCandidate(beanName, candidate)) {
                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                    definitionHolder =
                            AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                    beanDefinitions.add(definitionHolder);
                    //BeanDefinition注册
                    registerBeanDefinition(definitionHolder, this.registry);
                }
            }
        }
        return beanDefinitions;
    }

策略模式

模板设计模式

委托设计模式(专人专事)

工厂模式

流程图

对于实践的指导意义

延申项

java BIO体系总结