Spring MVC之HandlerMap 初始化
DispatcherServlet请求处理请求的过程中，会发现getHandler实际上是调用AbstractUrlHandlerMapping.getHandlerInternal()。 通过对该段代码进行走读后发现，是通过handlermap.get(urlPath)获取匹配的handler的，那么该handlerMap是在什么时候进行初始化的呢？
通过DefaultAnnotationHandlerMapping的继承关系可以去分析初始化的过程。
通过继承关系可以知道DefaultAnnotationHandlerMapping实现了ApplicationContextAware接口，这个接口的主要功能就是在Application初始化完成后会条用该接扩的setApplicationContext()方法。
AbstractDetectingUrlHandlerMapping是HandlerMapping初始化的关键入口，在初始化方法中首先调用父类的初始化方法，然后查找处理器。这个抽象类使用了模板方法模式，将具体的determineUrlsForHanlder方法延迟到子类中实现。
/**
* Abstract implementation of the {@link org.springframework.web.servlet.HandlerMapping}
* interface, detecting URL mappings for handler beans through introspection of all
* defined beans in the application context.
*
* @author Juergen Hoeller
* @since 2.5
* @see #determineUrlsForHandler
*/
public abstract class AbstractDetectingUrlHandlerMapping extends AbstractUrlHandlerMapping {
private boolean detectHandlersInAncestorContexts = false;
/**
* Set whether to detect handler beans in ancestor ApplicationContexts.
* <p>Default is "false": Only handler beans in the current ApplicationContext
* will be detected, i.e. only in the context that this HandlerMapping itself
* is defined in (typically the current DispatcherServlet's context).
* <p>Switch this flag on to detect handler beans in ancestor contexts
* (typically the Spring root WebApplicationContext) as well.
*/
public void setDetectHandlersInAncestorContexts(boolean detectHandlersInAncestorContexts) {
this.detectHandlersInAncestorContexts = detectHandlersInAncestorContexts;
}
/**
*在ApplicatonObjectSupport的setApplicationContext()方法中调用该方法
* Calls the {@link #detectHandlers()} method in addition to the
* superclass's initialization.
*/
@Override
public void initApplicationContext() throws ApplicationContextException {
// 调用父类的initApplicationContext()方法
super.initApplicationContext();
//查找Handler
detectHandlers();
}
/**
* 注册所有能够从应用上下文中找到的handler
* Register all handlers found in the current ApplicationContext.
* <p>The actual URL determination for a handler is up to the concrete
* {@link #determineUrlsForHandler(String)} implementation. A bean for
* which no such URLs could be determined is simply not considered a handler.
* @throws org.springframework.beans.BeansException if the handler couldn't be registered
* @see #determineUrlsForHandler(String)
*/
protected void detectHandlers() throws BeansException {
if (logger.isDebugEnabled()) {
logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
}
// 从上下文中获取所有的beanNames
String[] beanNames = (this.detectHandlersInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
// 遍历所有BeanNames
for (String beanName : beanNames) {
//调用子类实现方法，判定这个bean 处理的url
String[] urls = determineUrlsForHandler(beanName);
// 如果这个bean可以处理url则将调用父类的registerHandler方法完成 url和handler映射关系的注册
if (!ObjectUtils.isEmpty(urls)) {
// URL paths found: Let's consider it a handler.
registerHandler(urls, beanName);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
}
}
}
}
/**
* Determine the URLs for the given handler bean.
* @param beanName the name of the candidate bean
* @return the URLs determined for the bean,
* or <code>null</code> or an empty array if none
*/
protected abstract String[] determineUrlsForHandler(String beanName);
}
DefaultAnnotationHandlerMapping继承了AbstractDetectingUrlHandlerMapping,实现了父类的抽象方法，首先查找这个类是否有RequestMapping的注解以及这个Bean中所有方法是否有这个注解
public class DefaultAnnotationHandlerMapping extends AbstractDetectingUrlHandlerMapping {
static final String USE_DEFAULT_SUFFIX_PATTERN = DefaultAnnotationHandlerMapping.class.getName() + ".useDefaultSuffixPattern";
private boolean useDefaultSuffixPattern = true;
private final Map<Class<?>, RequestMapping> cachedMappings = new HashMap<Class<?>, RequestMapping>();
/**
* Set whether to register paths using the default suffix pattern as well:
* i.e. whether "/users" should be registered as "/users.*" and "/users/" too.
* <p>Default is "true". Turn this convention off if you intend to interpret
* your <code>@RequestMapping</code> paths strictly.
* <p>Note that paths which include a ".xxx" suffix or end with "/" already will not be
* transformed using the default suffix pattern in any case.
*/
public void setUseDefaultSuffixPattern(boolean useDefaultSuffixPattern) {
this.useDefaultSuffixPattern = useDefaultSuffixPattern;
}
/**
* Checks for presence of the {@link org.springframework.web.bind.annotation.RequestMapping}
* annotation on the handler class and on any of its methods.
*/
@Override
protected String[] determineUrlsForHandler(String beanName) {
ApplicationContext context = getApplicationContext();
Class<?> handlerType = context.getType(beanName);
RequestMapping mapping = context.findAnnotationOnBean(beanName, RequestMapping.class);
if (mapping != null) {
// @RequestMapping found at type level
this.cachedMappings.put(handlerType, mapping);
Set<String> urls = new LinkedHashSet<String>();
String[] typeLevelPatterns = mapping.value();
if (typeLevelPatterns.length > 0) {
// @RequestMapping specifies paths at type level
String[] methodLevelPatterns = determineUrlsForHandlerMethods(handlerType, true);
for (String typeLevelPattern : typeLevelPatterns) {
if (!typeLevelPattern.startsWith("/")) {
typeLevelPattern = "/" + typeLevelPattern;
}
boolean hasEmptyMethodLevelMappings = false;
for (String methodLevelPattern : methodLevelPatterns) {
if (methodLevelPattern == null) {
hasEmptyMethodLevelMappings = true;
}
else {
String combinedPattern = getPathMatcher().combine(typeLevelPattern, methodLevelPattern);
addUrlsForPath(urls, combinedPattern);
}
}
if (hasEmptyMethodLevelMappings ||
org.springframework.web.servlet.mvc.Controller.class.isAssignableFrom(handlerType)) {
addUrlsForPath(urls, typeLevelPattern);
}
}
return StringUtils.toStringArray(urls);
}
else {
// actual paths specified by @RequestMapping at method level
return determineUrlsForHandlerMethods(handlerType, false);
}
}
else if (AnnotationUtils.findAnnotation(handlerType, Controller.class) != null) {
// @RequestMapping to be introspected at method level
return determineUrlsForHandlerMethods(handlerType, false);
}
else {
return null;
}
}
/**
* Derive URL mappings from the handler's method-level mappings.
* @param handlerType the handler type to introspect
* @param hasTypeLevelMapping whether the method-level mappings are nested
* within a type-level mapping
* @return the array of mapped URLs
*/
protected String[] determineUrlsForHandlerMethods(Class<?> handlerType, final boolean hasTypeLevelMapping) {
//在该类中返回值一直是null
String[] subclassResult = determineUrlsForHandlerMethods(handlerType);
if (subclassResult != null) {
return subclassResult;
}
// 创建一个set,之所以使用set就是set中不会有重复数据
final Set<String> urls = new LinkedHashSet<String>();
Set<Class<?>> handlerTypes = new LinkedHashSet<Class<?>>();
//添加类以及所有接口
handlerTypes.add(handlerType);
handlerTypes.addAll(Arrays.asList(handlerType.getInterfaces()));
// 遍历handlerTypes
for (Class<?> currentHandlerType : handlerTypes) {
// 反射处理
ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
public void doWith(Method method) {
// 获取所有该方法上的RequestMapping注解
RequestMapping mapping = AnnotationUtils.findAnnotation(method, RequestMapping.class);
// 如果存在RequestMapping注解
if (mapping != null) {
// 获取注解 value属性值
String[] mappedPatterns = mapping.value();
// 如果value的值不为空
if (mappedPatterns.length > 0) {
// 遍历mappedPatterns
for (String mappedPattern : mappedPatterns) {
//如果hasTypeLevelMapping=false,同时mappedPattern不是以"/"开头则在其前面加上"/"
if (!hasTypeLevelMapping && !mappedPattern.startsWith("/")) {
mappedPattern = "/" + mappedPattern;
}
//将url添加在set中
addUrlsForPath(urls, mappedPattern);
}
}
else if (hasTypeLevelMapping) {
// empty method-level RequestMapping
urls.add(null);
}
}
}
}, ReflectionUtils.USER_DECLARED_METHODS);
}
return StringUtils.toStringArray(urls);
}
/**
* Derive URL mappings from the handler's method-level mappings.
* @param handlerType the handler type to introspect
* @return the array of mapped URLs
*/
protected String[] determineUrlsForHandlerMethods(Class<?> handlerType) {
return null;
}
/**
* Add URLs and/or URL patterns for the given path.
* @param urls the Set of URLs for the current bean
* @param path the currently introspected path
*/
protected void addUrlsForPath(Set<String> urls, String path) {
urls.add(path);
if (this.useDefaultSuffixPattern && path.indexOf('.') == -1 && !path.endsWith("/")) {
urls.add(path + ".*");
urls.add(path + "/");
}
}
/**
* Validate the given annotated handler against the current request.
* @see #validateMapping
*/
@Override
protected void validateHandler(Object handler, HttpServletRequest request) throws Exception {
RequestMapping mapping = this.cachedMappings.get(handler.getClass());
if (mapping == null) {
mapping = AnnotationUtils.findAnnotation(handler.getClass(), RequestMapping.class);
}
if (mapping != null) {
validateMapping(mapping, request);
}
request.setAttribute(USE_DEFAULT_SUFFIX_PATTERN, this.useDefaultSuffixPattern);
}
/**
* Validate the given type-level mapping metadata against the current request,
* checking HTTP request method and parameter conditions.
* @param mapping the mapping metadata to validate
* @param request current HTTP request
* @throws Exception if validation failed
*/
protected void validateMapping(RequestMapping mapping, HttpServletRequest request) throws Exception {
RequestMethod[] mappedMethods = mapping.method();
if (!ServletAnnotationMappingUtils.checkRequestMethod(mappedMethods, request)) {
String[] supportedMethods = new String[mappedMethods.length];
for (int i = 0; i < mappedMethods.length; i++) {
supportedMethods[i] = mappedMethods[i].name();
}
throw new HttpRequestMethodNotSupportedException(request.getMethod(), supportedMethods);
}
String[] mappedParams = mapping.params();
if (!ServletAnnotationMappingUtils.checkParameters(mappedParams, request)) {
throw new UnsatisfiedServletRequestParameterException(mappedParams, request.getParameterMap());
}
String[] mappedHeaders = mapping.headers();
if (!ServletAnnotationMappingUtils.checkHeaders(mappedHeaders, request)) {
throw new ServletRequestBindingException("Header conditions \"" +
StringUtils.arrayToDelimitedString(mappedHeaders, ", ") +
"\" not met for actual request");
}
}
@Override
protected boolean supportsTypeLevelMappings() {
return true;
}
}
public abstract class WebApplicationObjectSupport extends ApplicationObjectSupport
implements ServletContextAware {
private ServletContext servletContext;
//由于该类实现了ServletContextAware接口，在ServletContext初始化完成后，调用该方法
public final void setServletContext(ServletContext servletContext) {
if (servletContext != this.servletContext) {
this.servletContext = servletContext;
if (servletContext != null) {
initServletContext(servletContext);
}
}
}
@Override
protected boolean isContextRequired() {
return true;
}
/**
* 在ApplicationContext初始完成后调用该方法，如果已用上下文是WebApplicationContext则调用initServeltContext
*/
@Override
protected void initApplicationContext(ApplicationContext context) {
// 调用父类initApplicationContext，也就是调用ApplicationObjectSupport.initApplictionContext()方法
super.initApplicationContext(context);
if (this.servletContext == null && context instanceof WebApplicationContext) {
this.servletContext = ((WebApplicationContext) context).getServletContext();
if (this.servletContext != null) {
// 模板方法模式，具体实现延迟到子类中进行
initServletContext(this.servletContext);
}
}
}
/**
* Subclasses may override this for custom initialization based
* on the ServletContext that this application object runs in.
* <p>The default implementation is empty. Called by
* {@link #initApplicationContext(org.springframework.context.ApplicationContext)}
* as well as {@link #setServletContext(javax.servlet.ServletContext)}.
* @param servletContext the ServletContext that this application object runs in
* (never <code>null</code>)
*/
protected void initServletContext(ServletContext servletContext) {
}
