【spring源码】spring web 启动与关闭

web.xml中有这么一段声明

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/applicationContext.xml</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

ContextLoaderListener类是启动的开始点，观察

ContextLoaderListener类的实现，如下：

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
    public ContextLoaderListener() {
    }

    public ContextLoaderListener(WebApplicationContext context) {
        super(context);
    }

    public void contextInitialized(ServletContextEvent event) {
        this.initWebApplicationContext(event.getServletContext());
    }

    public void contextDestroyed(ServletContextEvent event) {
        this.closeWebApplicationContext(event.getServletContext());
        ContextCleanupListener.cleanupAttributes(event.getServletContext());
    }
}

利用ServletContextListener接口监听到启动事件，调用 ContextLoader.initWebApplicationContext方法完成启动

过程在 ContextLoader.initWebApplicationContext事件中，如下：

try {
                if (this.context == null) {
                    this.context = this.createWebApplicationContext(servletContext);
                }

                if (this.context instanceof ConfigurableWebApplicationContext) {
                    ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context;
                    if (!cwac.isActive()) {
                        if (cwac.getParent() == null) {
                            ApplicationContext parent = this.loadParentContext(servletContext);    //跟踪出来此块为空，即父容器默认空
                            cwac.setParent(parent);
                        }

                        this.configureAndRefreshWebApplicationContext(cwac, servletContext);
                    }
                }

                servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
                ClassLoader ccl = Thread.currentThread().getContextClassLoader();
                if (ccl == ContextLoader.class.getClassLoader()) {
                    currentContext = this.context;
                } else if (ccl != null) {
                    currentContextPerThread.put(ccl, this.context);
                }

                if (logger.isDebugEnabled()) {
                    logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
                }

                if (logger.isInfoEnabled()) {
                    long elapsedTime = System.currentTimeMillis() - startTime;
                    logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
                }

                return this.context;
            } catch (RuntimeException var8) {
                logger.error("Context initialization failed", var8);
                servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var8);
                throw var8;
            } catch (Error var9) {
                logger.error("Context initialization failed", var9);
                servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var9);
                throw var9;
            }

重点方法有两个

1：createWebApplicationContext

        通过反射，构造一个ConfigurableWebApplicationContext类的实例，即WebApplicationContext类实例

2：configureAndRefreshWebApplicationContext

        源码如下：

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {

        wac.setServletContext(sc);
        configLocationParam = sc.getInitParameter("contextConfigLocation");
        if (configLocationParam != null) {
            wac.setConfigLocation(configLocationParam);
        }

        ConfigurableEnvironment env = wac.getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            ((ConfigurableWebEnvironment)env).initPropertySources(sc, (ServletConfig)null);
        }

        this.customizeContext(sc, wac);
        wac.refresh();

 将第一步创建的ConfigurableWebApplicationContext，以及环境上下文ServletContext传入进来

 获取xml的配置文件，即ioc的application.xml配置文件，以及初始化容器属性参数

 重点在ConfigurableWebApplicationContext的refresh()方法

实现如下：

代码在AbstractApplicationContext类中，

public void refresh() throws BeansException, IllegalStateException {
        Object var1 = this.startupShutdownMonitor;
        synchronized(this.startupShutdownMonitor) {
            this.prepareRefresh(); //准备初始化
            
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();  //该方法调用了beanFactory的创建，DefaultListableBeanFactory beanFactory = this.createBeanFactory(),
            即实例化的是DefaultListableBeanFactory类，该方法源码在后面
            以及定义了XmlBeanDefinitionReader，该XmlBeanDefinitionReader获取（application.xml）即spring web的配置文件，

            this.prepareBeanFactory(beanFactory);//通过上下文初始化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();
            }

        }
    }

次方法是同步的，避免重复刷新，每个步骤都放在单独的方法内，流程清晰，是值得学习的地方。这里面有个重要的方法是finishBeanFactoryInitialization(beanFactory);，里面的内容是Spring如何实例化bean，并注入依赖的，这个内容下一节讲，本节只说明Spring是如何加载class文件的。

首先就是prepareRefresh()方法。

protected void prepareRefresh() {  
    this.startupDate = System.currentTimeMillis();  
  
    synchronized (this.activeMonitor) {  
        this.active = true;  
    }  
  
    if (logger.isInfoEnabled()) {  
        logger.info("Refreshing " + this);  
    }  
  
    // Initialize any placeholder property sources in the context environment  
    initPropertySources();  
  
    // Validate that all properties marked as required are resolvable  
    // see ConfigurablePropertyResolver#setRequiredProperties  
    getEnvironment().validateRequiredProperties();  
}  

此方法做一些准备工作，如记录开始时间，输出日志，initPropertySources();和getEnvironment().validateRequiredProperties();一般没干什么事。

接下来就是初始化BeanFactory，是整个refresh()方法的核心，其中完成了配置文件的加载、解析、注册

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();  

看看它里面都做了些什么？

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

首先refreshBeanFactory()：

 

protected final void refreshBeanFactory() throws BeansException {  
    if (hasBeanFactory()) {  
        destroyBeans();  
        closeBeanFactory();  
    }  
    try {  
        DefaultListableBeanFactory beanFactory = createBeanFactory();  
        beanFactory.setSerializationId(getId());  
        customizeBeanFactory(beanFactory);  
        loadBeanDefinitions(beanFactory);  
        synchronized (this.beanFactoryMonitor) {  
            this.beanFactory = beanFactory;  
        }  
    }  
    catch (IOException ex) {  
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);  
    }  
}  

我们看到会创建一个DefaultListableBeanFactory实例

DefaultListableBeanFactory beanFactory = createBeanFactory();

再设置一个ID

beanFactory.setSerializationId(getId());

然后设置一些自定义参数：

customizeBeanFactory(beanFactory);

这里面最重要的就是loadBeanDefinitions(beanFactory);方法了。

@Override  
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {  
    // Create a new XmlBeanDefinitionReader for the given BeanFactory.  
    XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);  
  
    // Configure the bean definition reader with this context's  
    // resource loading environment.  
    beanDefinitionReader.setEnvironment(this.getEnvironment());  
    beanDefinitionReader.setResourceLoader(this);  
    beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));  
  
    // Allow a subclass to provide custom initialization of the reader,  
    // then proceed with actually loading the bean definitions.  
    initBeanDefinitionReader(beanDefinitionReader);  
    loadBeanDefinitions(beanDefinitionReader);  
}  

 此方法会通过XmlBeanDefinitionReader加载bean定义。具体的实现方法是在org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions方法中定义的。这里设计了层层调用，有好多重载方法，主要就是加载Spring所有的配置文件(可能会有多个)，以备后面解析，注册之用。我一路追踪到org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(Element root)

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

这里创建了一个BeanDefinitionParserDelegate示例，解析XML的过程就是委托它完成的，我们不关心它是怎样解析XML的，我们只关心是怎么加载类的，所以就要看parseBeanDefinitions(root, this.delegate)方法了。

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

我们看到最终解析XML元素的是delegate.parseCustomElement(ele)方法，最终会走到一下方法.

public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {  
    String namespaceUri = getNamespaceURI(ele);  
    NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);  
    if (handler == null) {  
        error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);  
        return null;  
    }  
    return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));  
}  

 

这里会根据不同的XML节点，会委托NamespaceHandlerSupport找出合适的BeanDefinitionParser，如果我们配置了

 

<context:component-scan  
    base-package="com.geeekr.service,com.geeekr.dao" />  

那么对应BeanDefinitionParser就是org.springframework.context.annotation.ComponentScanBeanDefinitionParser，来看看它的parse方法。

@Override  
public BeanDefinition parse(Element element, ParserContext parserContext) {  
    String[] basePackages = StringUtils.tokenizeToStringArray(element.getAttribute(BASE_PACKAGE_ATTRIBUTE),  
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);  
  
    // Actually scan for bean definitions and register them.  
    ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);  
    Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);  
    registerComponents(parserContext.getReaderContext(), beanDefinitions, element);  
  
    return null;  
}  

不难看出这里定义了一个ClassPathBeanDefinitionScanner，通过它去扫描包中的类文件，注意：这里是类文件而不是类，因为现在这些类还没有被加载，只是ClassLoader能找到这些class的路径而已。到目前为止，感觉真想距离我们越来越近了。顺着继续往下摸。进入doSacn方法里，映入眼帘的又是一大坨代码，但是我们只关心观点的部分。

 

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {  
    Assert.notEmpty(basePackages, "At least one base package must be specified");  
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();  
    for (String basePackage : basePackages) {  
        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) {  
                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);  
                registerBeanDefinition(definitionHolder, this.registry);  
            }  
        }  
    }  
    return beanDefinitions;  
}  

一眼就能看出是通过

Set<BeanDefinition> candidates = findCandidateComponents(basePackage);  

有时候不得不佩服这些外国人起名字的功力，把扫描出来的类叫做candidates(候选人)；真是不服不行啊，这种名字真的很容易理解有不有？哈哈，貌似扯远了。继续往下看。这里只列出方法的主题部分。

public Set<BeanDefinition> findCandidateComponents(String basePackage) {  
    Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();  
    try {  
        String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +  
                resolveBasePackage(basePackage) + "/" + this.resourcePattern;  
        Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);  
        boolean traceEnabled = logger.isTraceEnabled();  
        boolean debugEnabled = logger.isDebugEnabled();  
        for (Resource resource : resources) {  
            if (traceEnabled) {  
                logger.trace("Scanning " + resource);  
            }  
            if (resource.isReadable()) {  
                try {  
                    MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);  
                    if (isCandidateComponent(metadataReader)) {  
                        ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);  
                        sbd.setResource(resource);  
                        sbd.setSource(resource);  
 

先看这两句：

String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + "/" + this.resourcePattern;  

假设我们配置的需要扫描的包名为com.geeekr.service，那么packageSearchPath的值就是classpath*:com.geeekr.service/**/*.class，意思就是com.geeekr.service包(包括子包)下所有class文件；如果配置的是*，那么packageSearchPath的值就是classpath*:*/**/*.class。这里的表达式是Spring自己定义的。Spring会根据这种表达式找出相关的class文件。

Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);  

这一句就把相关class文件加载出来了，那我们就要看看，Spring究竟是如何把class文件找到的了。首先看看resourcePatternResolver的定义:

private ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();  

 

进入getResources方法

@Override  
public Resource[] getResources(String locationPattern) throws IOException {  
    Assert.notNull(locationPattern, "Location pattern must not be null");  
    if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {  
        // a class path resource (multiple resources for same name possible)  
        if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {  
            // a class path resource pattern  
            return findPathMatchingResources(locationPattern);  
        }  
        else {  
            // all class path resources with the given name  
            return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));  
        }  
    }  
    else {  
        // Only look for a pattern after a prefix here  
        // (to not get fooled by a pattern symbol in a strange prefix).  
        int prefixEnd = locationPattern.indexOf(":") + 1;  
        if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {  
            // a file pattern  
            return findPathMatchingResources(locationPattern);  
        }  
        else {  
            // a single resource with the given name  
            return new Resource[] {getResourceLoader().getResource(locationPattern)};  
        }  
    }  
}  

这里会先判断表达式是否以classpath*:开头。前面我们看到Spring已经给我们添加了这个头，这里当然符合条件了。接着会进入findPathMatchingResources方法。在这里又把**/*.class去掉了，然后在调用getResources方法，然后在进入findAllClassPathResources方法。这里的参数只剩下包名了例如com/geeekr/service/。

 

protected Resource[] findAllClassPathResources(String location) throws IOException {  
    String path = location;  
    if (path.startsWith("/")) {  
        path = path.substring(1);  
    }  
    ClassLoader cl = getClassLoader();  
    Enumeration<URL> resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));  
    Set<Resource> result = new LinkedHashSet<Resource>(16);  
    while (resourceUrls.hasMoreElements()) {  
        URL url = resourceUrls.nextElement();  
        result.add(convertClassLoaderURL(url));  
    }  
    return result.toArray(new Resource[result.size()]);  
}  

真相大白了，Spring也是用的ClassLoader加载的class文件。一路追踪，原始的ClassLoader是Thread.currentThread().getContextClassLoader();。到此为止，就拿到class文件了。
Spring会将class信息封装成BeanDefinition，然后再放进DefaultListableBeanFactory的beanDefinitionMap中。

拿到了class文件后，就要看看Spring是如何装配bean的了，下一节，继续看。