Spring Open Sourse Research(ContextLoaderListener Parts)

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Spring Web Servlet 工作

Spring 源码分析(ContextLoaderListener Parts)
ContextLoaderListener .java

java 代码

public class ContextLoaderListener implements ServletContextListener {
private ContextLoader contextLoader;
/**
* Initialize the root web application context.
*/
public void contextInitialized(ServletContextEvent event) {
this.contextLoader = createContextLoader();
this.contextLoader.initWebApplicationContext(event.getServletContext());
}
/**
* Create the ContextLoader to use. Can be overridden in subclasses.
* @return the new ContextLoader
*/
protected ContextLoader createContextLoader() {
return new ContextLoader();
}
/**
* Return the ContextLoader used by this listener.
* @return the current ContextLoader
*/
public ContextLoader getContextLoader() {
return this.contextLoader;
}
/**
* Close the root web application context.
*/
public void contextDestroyed(ServletContextEvent event) {
if (this.contextLoader != null) {
this.contextLoader.closeWebApplicationContext(event.getServletContext());
}
}
}

2ContectLoader.java
//初始化工作,调用默认策略DEFAULT_STRATEGIES_PATH

java 代码

static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
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());
}
}

调用默认策略DEFAULT_STRATEGIES_PATH
Spring在web环境下会默认初始化XmlWebApplicationContext这个

defaultStrategies:

java 代码

# Default WebApplicationContext implementation class for ContextLoader.
# Used as fallback when no explicit context implementation has been specified as context-param.
# Not meant to be customized by application developers.
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
this.contextLoader.initWebApplicationContext(event.getServletContext());

初始化工作

java 代码

/**
* Initialize Spring's web application context for the given servlet context,
* according to the "contextClass" and "contextConfigLocation" context-params.
* @param servletContext current servlet context
* @return the new WebApplicationContext
* @throws IllegalStateException if there is already a root application context present
* @throws BeansException if the context failed to initialize
* @see #CONTEXT_CLASS_PARAM
* @see #CONFIG_LOCATION_PARAM
*/
public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
throws IllegalStateException, BeansException {
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!");
}
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
// Determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
this.context = createWebApplicationContext(servletContext, parent);
servletContext.setAttribute(
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, 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;
}
}

initWebApplicationContext()调用了createWebApplicationContext()

java 代码

/**
* Instantiate the root WebApplicationContext for this loader, either the
* default context class or a custom context class if specified.
* This implementation expects custom contexts to implement
* ConfigurableWebApplicationContext. Can be overridden in subclasses.
* @param servletContext current servlet context
* @param parent the parent ApplicationContext to use, or null if none
* @return the root WebApplicationContext
* @throws BeansException if the context couldn't be initialized
* @see ConfigurableWebApplicationContext
*/
protected WebApplicationContext createWebApplicationContext(
ServletContext servletContext, ApplicationContext parent) throws BeansException {
//取得代用的从Context Class ,WebApplicationContext default
Class contextClass = determineContextClass(servletContext);
//判断contextClass是否是ConfigurableWebApplicationContext的子类，如果不是，throws ApplicationContextException
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
//初始化这个类
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setParent(parent);
wac.setServletContext(servletContext);
String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocation != null) {
wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation,
ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
wac.refresh();
return wac;
}

java 代码

/**
* Return the WebApplicationContext implementation class to use, either the
* default XmlWebApplicationContext or a custom context class if specified.
* @param servletContext current servlet context
* @return the WebApplicationContext implementation class to use
* @throws ApplicationContextException if the context class couldn't be loaded
* @see #CONTEXT_CLASS_PARAM
* @see org.springframework.web.context.support.XmlWebApplicationContext
*/
protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException {
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName);
}
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);
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}

Notice: public static final String CONTEXT_CLASS_PARAM = "contextClass";

BeanUtils.java

java 代码

public static Object instantiateClass(Constructor ctor, Object[] args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
if (!Modifier.isPublic(ctor.getModifiers()) ||
!Modifier.isPublic(ctor.getDeclaringClass().getModifiers())) {
ctor.setAccessible(true);
}
return ctor.newInstance(args);
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor.getDeclaringClass(),
"Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor.getDeclaringClass(),
"Has the class definition changed? Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor.getDeclaringClass(),
"Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor.getDeclaringClass(),
"Constructor threw exception", ex.getTargetException());
}
}

ConfigurableWebApplicationContext.java

java 代码

public interface ConfigurableWebApplicationContext extends WebApplicationContext, ConfigurableApplicationContext {
//context para value分隔符
String CONFIG_LOCATION_DELIMITERS = ",; \t\n";
void setServletContext(ServletContext servletContext);
void setServletConfig(ServletConfig servletConfig);
ServletConfig getServletConfig();
void setNamespace(String namespace);
String getNamespace();
void setConfigLocations(String[] configLocations);
String[] getConfigLocations();
}

In a word, ContextLoaderListener invoke ContextLoader，and ContextLoader delegate and create ConfigurableWebApplicationContext
ConfigurableWebApplicationContext is an object including web servlet context,servletconfig,and contextConfigLocation.
Is is significant as follows

servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
context is an object of ConfigurableWebApplicationContext;

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2007-08-25 09:21
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