spring mvc DispatcherServlet详解之前传---FrameworkServlet

/**
* Interface to provide configuration for a web application. This is read-only while
* the application is running, but may be reloaded if the implementation supports this.
*
* <p>This interface adds a {@code getServletContext()} method to the generic
* ApplicationContext interface, and defines a well-known application attribute name
* that the root context must be bound to in the bootstrap process.
*
* <p>Like generic application contexts, web application contexts are hierarchical.
* There is a single root context per application, while each servlet in the application
* (including a dispatcher servlet in the MVC framework) has its own child context.
*
* <p>In addition to standard application context lifecycle capabilities,
* WebApplicationContext implementations need to detect {@link ServletContextAware}
* beans and invoke the {@code setServletContext} method accordingly.*/
public interface WebApplicationContext extends ApplicationContext {

<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath*:conf/applicationContext*.xml</param-value>
</context-param>

<servlet>
<servlet-name>mvcServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:conf/spring-dispatcher-servlet.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolverorg.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolverorg.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMappingorg.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapterorg.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolverorg.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslatororg.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolverorg.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

A web application can define any number of DispatcherServlets. Each servlet will operate in its own namespace, loading its own application context with mappings, handlers, etc. Only the root application context as loaded by ContextLoaderListener, if any, will be shared. As of Spring 3.1, DispatcherServlet may now be injected with a web application context, rather than creating its own internally. This is useful in Servlet 3.0+ environments, which support programmatic registration of servlet instances.

/**
* Called by Spring via {@link ApplicationContextAware} to inject the current
* application context. This method allows FrameworkServlets to be registered as
* Spring beans inside an existing {@link WebApplicationContext} rather than
* {@link #findWebApplicationContext() finding} a
* {@link org.springframework.web.context.ContextLoaderListener bootstrapped} context.
* <p>Primarily added to support use in embedded servlet containers.
* @since 4.0
*/
@Override
public void setApplicationContext(ApplicationContext applicationContext) {
if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {
this.webApplicationContext = (WebApplicationContext) applicationContext;
this.webApplicationContextInjected = true;
}
}

/**
* Map config parameters onto bean properties of this servlet, and
* invoke subclass initialization.
* @throws ServletException if bean properties are invalid (or required
* properties are missing), or if subclass initialization fails.
*/
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
} // Set bean properties from init parameters.
try {
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
throw ex;
} // Let subclasses do whatever initialization they like.
initServletBean(); if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}

/**
* Overridden method of {@link HttpServletBean}, invoked after any bean properties
* have been set. Creates this servlet's WebApplicationContext.
*/
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis(); try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
} if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}

/**
* Initialize and publish the WebApplicationContext for this servlet.
* <p>Delegates to {@link #createWebApplicationContext} for actual creation
* of the context. Can be overridden in subclasses.
* @return the WebApplicationContext instance
* @see #FrameworkServlet(WebApplicationContext)
* @see #setContextClass
* @see #setContextConfigLocation
*/
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null; if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
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 -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
} if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
} if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
} return wac;
}

WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext()); /**
* Find the root {@link WebApplicationContext} for this web app, typically
* loaded via {@link org.springframework.web.context.ContextLoaderListener}.
* <p>Will rethrow an exception that happened on root context startup,
* to differentiate between a failed context startup and no context at all.
* @param sc ServletContext to find the web application context for
* @return the root WebApplicationContext for this web app, or {@code null} if none
* @see org.springframework.web.context.WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
*/
public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
}
/**
* Find a custom {@link WebApplicationContext} for this web app.
* @param sc ServletContext to find the web application context for
* @param attrName the name of the ServletContext attribute to look for
* @return the desired WebApplicationContext for this web app, or {@code null} if none
*/
public static WebApplicationContext getWebApplicationContext(ServletContext sc, String attrName) {
Assert.notNull(sc, "ServletContext must not be null");
Object attr = sc.getAttribute(attrName);
if (attr == null) {
return null;
}
if (attr instanceof RuntimeException) {
throw (RuntimeException) attr;
}
if (attr instanceof Error) {
throw (Error) attr;
}
if (attr instanceof Exception) {
throw new IllegalStateException((Exception) attr);
}
if (!(attr instanceof WebApplicationContext)) {
throw new IllegalStateException("Context attribute is not of type WebApplicationContext: " + attr);
}
return (WebApplicationContext) attr;
}

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());
}
} wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener())); // 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(getServletContext(), getServletConfig());
} postProcessWebApplicationContext(wac);
applyInitializers(wac);
wac.refresh();
}

/**
* Retrieve a {@code WebApplicationContext} from the {@code ServletContext}
* attribute with the {@link #setContextAttribute configured name}. The
* {@code WebApplicationContext} must have already been loaded and stored in the
* {@code ServletContext} before this servlet gets initialized (or invoked).
* <p>Subclasses may override this method to provide a different
* {@code WebApplicationContext} retrieval strategy.
* @return the WebApplicationContext for this servlet, or {@code null} if not found
* @see #getContextAttribute()
*/
protected WebApplicationContext findWebApplicationContext() {
String attrName = getContextAttribute();
if (attrName == null) {
return null;
}
WebApplicationContext wac =
WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
}
return wac;
}

/**
* Instantiate the WebApplicationContext for this servlet, either a default
* {@link org.springframework.web.context.support.XmlWebApplicationContext}
* or a {@link #setContextClass custom context class}, if set.
* <p>This implementation expects custom contexts to implement the
* {@link org.springframework.web.context.ConfigurableWebApplicationContext}
* interface. Can be overridden in subclasses.
* <p>Do not forget to register this servlet instance as application listener on the
* created context (for triggering its {@link #onRefresh callback}, and to call
* {@link org.springframework.context.ConfigurableApplicationContext#refresh()}
* before returning the context instance.
* @param parent the parent ApplicationContext to use, or {@code null} if none
* @return the WebApplicationContext for this servlet
* @see org.springframework.web.context.support.XmlWebApplicationContext
*/
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Servlet with name '" + getServletName() +
"' will try to create custom WebApplicationContext context of class '" +
contextClass.getName() + "'" + ", using parent context [" + parent + "]");
}
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); wac.setEnvironment(getEnvironment());
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation()); configureAndRefreshWebApplicationContext(wac); return wac;
}

if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}

/**
* Return the ServletContext attribute name for this servlet's WebApplicationContext.
* <p>The default implementation returns
* {@code SERVLET_CONTEXT_PREFIX + servlet name}.
* @see #SERVLET_CONTEXT_PREFIX
* @see #getServletName
*/
public String getServletContextAttributeName() {
return SERVLET_CONTEXT_PREFIX + getServletName();
}

/**
* Prefix for the ServletContext attribute for the WebApplicationContext.
* The completion is the servlet name.
*/
public static final String SERVLET_CONTEXT_PREFIX = FrameworkServlet.class.getName() + ".CONTEXT.";

public abstract class FrameworkServlet
extends HttpServletBean
implements ApplicationContextAwareBase servlet for Spring's web framework. Provides integration with a Spring application context, in a JavaBean-based overall solution.
This class offers the following functionality: Manages a WebApplicationContext instance per servlet. The servlet's configuration is determined by beans in the servlet's namespace.
Publishes events on request processing, whether or not a request is successfully handled.
Subclasses must implement doService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) to handle requests. Because this extends HttpServletBean rather than HttpServlet directly, bean properties are automatically mapped onto it. Subclasses can override initFrameworkServlet() for custom initialization. Detects a "contextClass" parameter at the servlet init-param level, falling back to the default context class, XmlWebApplicationContext, if not found. Note that, with the default FrameworkServlet, a custom context class needs to implement the ConfigurableWebApplicationContext SPI. Accepts an optional "contextInitializerClasses" servlet init-param that specifies one or more ApplicationContextInitializer classes. The managed web application context will be delegated to these initializers, allowing for additional programmatic configuration, e.g. adding property sources or activating profiles against the context's environment. See also ContextLoader which supports a "contextInitializerClasses" context-param with identical semantics for the "root" web application context. Passes a "contextConfigLocation" servlet init-param to the context instance, parsing it into potentially multiple file paths which can be separated by any number of commas and spaces, like "test-servlet.xml, myServlet.xml". If not explicitly specified, the context implementation is supposed to build a default location from the namespace of the servlet. Note: In case of multiple config locations, later bean definitions will override ones defined in earlier loaded files, at least when using Spring's default ApplicationContext implementation. This can be leveraged to deliberately override certain bean definitions via an extra XML file. The default namespace is "'servlet-name'-servlet", e.g. "test-servlet" for a servlet-name "test" (leading to a "/WEB-INF/test-servlet.xml" default location with XmlWebApplicationContext). The namespace can also be set explicitly via the "namespace" servlet init-param. As of Spring 3.1, FrameworkServlet may now be injected with a web application context, rather than creating its own internally. This is useful in Servlet 3.0+ environments, which support programmatic registration of servlet instances. See FrameworkServlet(WebApplicationContext) Javadoc for details.