spring源码系列-1

<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
public ContextLoaderListener() {}
//带参构造
public ContextLoaderListener(WebApplicationContext context) {
super(context);
}

//会先加载和实例化父类，所以父类中的静态代码块先执行，然后再执行init，其实还是调用父类的initWebApplicationContext方法。
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.ge
4000
tServletContext());
}

//desdroy
@Override
public void contextDestroyed(ServletContextEvent event) {
closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
}

public class ContextLoader {

public static final String CONTEXT_ID_PARAM = "contextId";
public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation";
//用于指定webApplicationContext的默认类
public static final String CONTEXT_CLASS_PARAM = "contextClass";
public static final String CONTEXT_INITIALIZER_CLASSES_PARAM = "contextInitializerClasses";
public static final String GLOBAL_INITIALIZER_CLASSES_PARAM = "globalInitializerClasses";
public static final String LOCATOR_FACTORY_SELECTOR_PARAM = "locatorFactorySelector";
public static final String LOCATOR_FACTORY_KEY_PARAM = "parentContextKey";
private static final String INIT_PARAM_DELIMITERS = ",; \t\n";

//静态代码块将spring-web jar包中的ContextLoader.properties配置文件中的org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext加载到Properties作为默认策略，赋给变量defaultStrategies
private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
private static final Properties defaultStrategies;
static {
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
}
}

//Map from (thread context) ClassLoader to corresponding 'current' WebApplicationContext.
private static final Map<ClassLoader, WebApplicationContext> currentContextPerThread =
new ConcurrentHashMap<ClassLoader, WebApplicationContext>(1);

// The 'current' WebApplicationContext, if the ContextLoader class is deployed in the web app ClassLoader itself.
private static volatile WebApplicationContext currentContext;

// The root WebApplicationContext instance that this loader manages.
private WebApplicationContext context;

//Holds BeanFactoryReference when loading parent factory via ContextSingletonBeanFactoryLocator.
private BeanFactoryReference parentContextRef;

public ContextLoader() {
}
public ContextLoader(WebApplicationContext context) {
this.context = context;
}

//执行完静态代码块就执行这个方法，初始化web项目的上下文对象
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {

//如果从ServletContext里获取到org.springframework.web.context.WebApplicationContext.ROOT的话抛出异常（无法初始化上下文对象，请检查web.xml里是否配置了多余的ContextLoader*）
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}

Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();

try {
//在本地变量（context）保存上下文，确保上下文在ServletContext关闭情况下可用
//原文： Store context in local instance variable, to guarantee that it is available on ServletContext shutdown.
if (this.context == null) {
//创建web项目上下文对象
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
//初始化spring上下文信息（重要）
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 ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
catch (Error err) {
logger.error("Context initialization failed", err);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
throw err;
}
}

//要实例化的上下文对象类必须是ConfigurableWebApplicationContext接口的实现类，按照默认构造实例化该对象，默认类XmlWebApplicationContext也是该接口的实现类，可自行查看该接口的其它实现类。如果自定义的类不是该接口的实现类则会抛出异常：Custom context class [自定义class] is not of type [org.springframework.web.context.ConfigurableWebApplicationContext]
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
Class<?> contextClass = determineContextClass(sc);
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
}

//返回WebApplicationContext的实现类Class对象, 默认XmlWebApplicationContext或者用户自定义的类。web.xml中配置contextClass用于指定该类，如果没有配置则使用默认的类
protected Class<?> determineContextClass(ServletContext servletContext) {
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
else {
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
try {
return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}

@Deprecated
protected WebApplicationContext createWebApplicationContext(ServletContext sc, ApplicationContext parent) {
return createWebApplicationContext(sc);
}

//初始化spring上下文信息
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// 设置spring上下文对象的id，web.xml配置了则使用配置的id名，没有配置则使用org.springframework.web.context.WebApplicationContext：
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
//将ServletContext和contextConfigLocation初始化到spring上下文对象
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}

// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}

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

protected void customizeContext(ServletContext sc, ConfigurableWebApplicationContext wac) {
List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> initializerClasses =
determineContextInitializerClasses(sc);
if (initializerClasses.isEmpty()) {
// no ApplicationContextInitializers have been declared -> nothing to do
return;
}

ArrayList<ApplicationContextInitializer<ConfigurableApplicationContext>> initializerInstances =
new ArrayList<ApplicationContextInitializer<ConfigurableApplicationContext>>();

for (Class<ApplicationContextInitializer<ConfigurableApplicationContext>> initializerClass : initializerClasses) {
Class<?> initializerContextClass =
GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
if (initializerContextClass != null) {
Assert.isAssignable(initializerContextClass, wac.getClass(), String.format(
"Could not add context initializer [%s] since its generic parameter [%s] " +
"is not assignable from the type of application context used by this " +
"context loader [%s]: ", initializerClass.getName(), initializerContextClass.getName(),
wac.getClass().getName()));
}
initializerInstances.add(BeanUtils.instantiateClass(initializerClass));
}

AnnotationAwareOrderComparator.sort(initializerInstances);
for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : initializerInstances) {
initializer.initialize(wac);
}
}

protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>
determineContextInitializerClasses(ServletContext servletContext) {

List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes =
new ArrayList<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>();

String globalClassNames = servletContext.getInitParameter(GLOBAL_INITIALIZER_CLASSES_PARAM);
if (globalClassNames != null) {
for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
classes.add(loadInitializerClass(className));
}
}

String localClassNames = servletContext.getInitParameter(CONTEXT_INITIALIZER_CLASSES_PARAM);
if (localClassNames != null) {
for (String className : StringUtils.tokenizeToStringArray(localClassNames, INIT_PARAM_DELIMITERS)) {
classes.add(loadInitializerClass(className));
}
}

return classes;
}

@SuppressWarnings("unchecked")
private Class<ApplicationContextInitializer<ConfigurableApplicationContext>> loadInitializerClass(String className) {
try {
Class<?> clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
Assert.isAssignable(ApplicationContextInitializer.class, clazz);
return (Class<ApplicationContextInitializer<ConfigurableApplicationContext>>) clazz;
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException("Failed to load context initializer class [" + className + "]", ex);
}
}

protected ApplicationContext loadParentContext(ServletContext servletContext) {
ApplicationContext parentContext = null;
String locatorFactorySelector = servletContext.getInitParameter(LOCATOR_FACTORY_SELECTOR_PARAM);
String parentContextKey = servletContext.getInitParameter(LOCATOR_FACTORY_KEY_PARAM);

if (parentContextKey != null) {
// locatorFactorySelector may be null, indicating the default "classpath*:beanRefContext.xml"
BeanFactoryLocator locator = ContextSingletonBeanFactoryLocator.getInstance(locatorFactorySelector);
Log logger = LogFactory.getLog(ContextLoader.class);
if (logger.isDebugEnabled()) {
logger.debug("Getting parent context definition: using parent context key of '" +
parentContextKey + "' with BeanFactoryLocator");
}
this.parentContextRef = locator.useBeanFactory(parentContextKey);
parentContext = (ApplicationContext) this.parentContextRef.getFactory();
}

return parentContext;
}

public void closeWebApplicationContext(ServletContext servletContext) {
servletContext.log("Closing Spring root WebApplicationContext");
try {
if (this.context instanceof ConfigurableWebApplicationContext) {
((ConfigurableWebApplicationContext) this.context).close();
}
}
finally {
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = null;
}
else if (ccl != null) {
currentContextPerThread.remove(ccl);
}
servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
if (this.parentContextRef != null) {
this.parentContextRef.release();
}
}
}

public static WebApplicationContext getCurrentWebApplicationContext() {
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl != null) {
WebApplicationContext ccpt = currentContextPerThread.get(ccl);
if (ccpt != null) {
return ccpt;
}
}
return currentContext;
}

}