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@ -370,14 +370,398 @@ HandlerMappings完成对MVC中Controller的定义和配置，只不过在Web这
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## 4 SpringMVC处理分发HTTP请求
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### 4.1 HandlerMapping的配置和设计原理
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前面分析了DispatcherServlet对Spring MVC框架的初始化过程，在此基础上，我们再进一步分析HandlerMapping的实现原理，看看这个MVC框架中比较关键的控制部分是如何实现的。
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在初始化完成时，在上下文环境中已定义的所有HandlerMapping都已经被加载了，这些加载的handlerMappings被放在一个List中并被排序，存储着HTTP请求对应的映射数据。这个List中的每一个元素都对应着一个具体handlerMapping的配置，一般每一个handlerMapping
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可以持有一系列从URL请求到Controller的映射，而Spring MVC提供了一系列的HandlerMapping实现。
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### 4.2 使用HandlerMapping完成请求的映射处理
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以SimpleUrlHandlerMapping这个handlerMapping为例来分析HandlerMapping的设计与实现。在SimpleUrlHandlerMapping中，定义了一个map来 持有 一系列的映射关系。通过这些在HandlerMapping中定义的映射关系，即这些URL请求和控制器的对应关系，使Spring MVC
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应用可以根据HTTP请求确定一个对应的Controller。具体来说，这些映射关系是通过接口HandlerMapping来封装的，在HandlerMapping接 口中定义了一个getHandler方法，通过这个方法，可以获得与HTTP请求对应的HandlerExecutionChain，在这个HandlerExecutionChain
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中，封装了具体的Controller对象。
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```java
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public interface HandlerMapping {
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String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
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String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";
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String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";
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String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";
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String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";
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String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";
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/**
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* 返回的这个HandlerExecutionChain不但持有handler本身，还包括了处理这个HTTP请求的拦截器
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*/
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HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
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}
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```
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这个HandlerExecutionChain的实现看起来比较简洁，它持有一个Interceptor链和一个handler对象，这个handler对象实际上就是HTTP请求对应的Controller，在持有这个handler对象的同时，还在HandlerExecutionChain中设置了一个拦截器链，通过这个拦截器链中的拦截器,
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可以为handler对象提供功能的增强。要完成这些工作，需要对拦截器链和handler都进行配置，这些配置都是在HandlerExecutionChain的初始化函数中完成的。为了维护这个拦截器链和handler，HandlerExecutionChain还提供了一系列与拦截器链维护相关的操作，比如，为拦
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截器链增加拦截器的addInterceptor()方法。
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```java
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public class HandlerExecutionChain {
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private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
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private final Object handler;
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private HandlerInterceptor[] interceptors;
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private List<HandlerInterceptor> interceptorList;
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private int interceptorIndex = -1;
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public HandlerExecutionChain(Object handler) {
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this(handler, null);
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}
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public HandlerExecutionChain(Object handler, HandlerInterceptor[] interceptors) {
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if (handler instanceof HandlerExecutionChain) {
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HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
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this.handler = originalChain.getHandler();
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this.interceptorList = new ArrayList<HandlerInterceptor>();
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CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
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CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
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}
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else {
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this.handler = handler;
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this.interceptors = interceptors;
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}
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}
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public Object getHandler() {
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return this.handler;
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}
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/**
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* 为拦截器链 添加拦截器
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*/
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public void addInterceptor(HandlerInterceptor interceptor) {
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initInterceptorList();
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this.interceptorList.add(interceptor);
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}
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/**
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* 批量添加拦截器
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*/
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public void addInterceptors(HandlerInterceptor[] interceptors) {
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if (interceptors != null) {
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initInterceptorList();
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this.interceptorList.addAll(Arrays.asList(interceptors));
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}
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}
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/**
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* 延迟初始化interceptorList和interceptors集合
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*/
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private void initInterceptorList() {
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if (this.interceptorList == null) {
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this.interceptorList = new ArrayList<HandlerInterceptor>();
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}
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if (this.interceptors != null) {
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this.interceptorList.addAll(Arrays.asList(this.interceptors));
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this.interceptors = null;
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}
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}
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public HandlerInterceptor[] getInterceptors() {
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if (this.interceptors == null && this.interceptorList != null) {
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this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
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}
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return this.interceptors;
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}
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@Override
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public String toString() {
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if (this.handler == null) {
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return "HandlerExecutionChain with no handler";
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}
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StringBuilder sb = new StringBuilder();
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sb.append("HandlerExecutionChain with handler [").append(this.handler).append("]");
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if (!CollectionUtils.isEmpty(this.interceptorList)) {
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sb.append(" and ").append(this.interceptorList.size()).append(" interceptor");
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if (this.interceptorList.size() > 1) {
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sb.append("s");
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}
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}
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return sb.toString();
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}
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}
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```
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HandlerExecutionChain中定义的Handler和Interceptor需要在定义HandlerMapping时配置好，例如对具体的SimpleURLHandlerMapping，要做的就是根据URL映射的方式，注册Handler和Interceptor，从而维护一个反映这种映射关系的handlerMap。当需要匹配HTTP请求时，需要查询这个handlerMap中的信息来得到对应的HandlerExecutionChain。这些信息是什么时候配置好的呢?这里有一个注册过程，这个注册过程在容器对Bean进行依赖注入时发生，它实际上是通过一个Bean的postProcessor()来完成的。以SimpleHandlerMapping为例，需要注意的是，这里用到了对容器的回调，只有SimpleHandlerMapping是ApplicationContextAware的子类才能启动这个注册过程。这个注册过程完成的是反映URL和Controller之间映射关系的handlerMap的建立。
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```java
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public class SimpleUrlHandlerMapping extends AbstractUrlHandlerMapping {
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@Override
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public void initApplicationContext() throws BeansException {
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super.initApplicationContext();
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registerHandlers(this.urlMap);
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}
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/**
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* 为相应的路径注册URL映射中指定的所有handlers处理程序
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*/
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protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
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if (urlMap.isEmpty()) {
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logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
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}
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else {
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// 这里对bean的配置进行解析，然后调用父类的registerHandler()方法进行解析
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for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
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String url = entry.getKey();
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Object handler = entry.getValue();
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// 如果url没有斜线，就在前面加上斜线
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if (!url.startsWith("/")) {
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url = "/" + url;
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}
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// Remove whitespace from handler bean name.
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if (handler instanceof String) {
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handler = ((String) handler).trim();
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}
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// 这里调用的是父类的方法
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registerHandler(url, handler);
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}
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}
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}
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}
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```
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这个SimpleUrlHandlerMapping注册过程的完成，很大一部分需要它的基类来配合，这个基类就是AbstractUrlHandlerMapping。在AbstractUrlHandlerMapping的处理过程中，如果使用Bean的名称作为映射，那么直接从容器中获取这个HTTP映射对应的Bean，然后还要对不同的URL配置进行解析处理，比如在HTTP请求中配置成“/”和通配符“/*” 的URL，以及正常的URL请求，完成这个解析处理过程以后，会
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把URL和handler作为键值对放到一个handlerMap中去。
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```java
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public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {
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/**
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* 为给定的URL路径注册指定的handler处理程序
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*/
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protected void registerHandler(String[] urlPaths, String beanName) throws BeansException, IllegalStateException {
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Assert.notNull(urlPaths, "URL path array must not be null");
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for (String urlPath : urlPaths) {
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registerHandler(urlPath, beanName);
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}
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}
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/**
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* 为给定的URL路径注册指定的handler处理程序
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*/
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protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
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Assert.notNull(urlPath, "URL path must not be null");
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Assert.notNull(handler, "Handler object must not be null");
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Object resolvedHandler = handler;
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// 如果使用bean名称进行映射，就直接从IoC容器中获取该bean名称对应的handler
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if (!this.lazyInitHandlers && handler instanceof String) {
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String handlerName = (String) handler;
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if (getApplicationContext().isSingleton(handlerName)) {
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resolvedHandler = getApplicationContext().getBean(handlerName);
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}
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}
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Object mappedHandler = this.handlerMap.get(urlPath);
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if (mappedHandler != null) {
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if (mappedHandler != resolvedHandler) {
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throw new IllegalStateException(
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"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
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"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
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}
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}
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else {
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// 处理URL是"/"的映射，把这个"/"映射的controller设置到rootHandler中
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if (urlPath.equals("/")) {
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if (logger.isInfoEnabled()) {
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logger.info("Root mapping to " + getHandlerDescription(handler));
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}
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setRootHandler(resolvedHandler);
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}
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// 处理URL是"/"的映射，把这个"/"映射的controller设置到defaultHandler中
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else if (urlPath.equals("/*")) {
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if (logger.isInfoEnabled()) {
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logger.info("Default mapping to " + getHandlerDescription(handler));
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}
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setDefaultHandler(resolvedHandler);
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}
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// 处理正常的URL映射，此handlerMap的key和value分别代表URL和映射的Controller
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else {
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this.handlerMap.put(urlPath, resolvedHandler);
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if (logger.isInfoEnabled()) {
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logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
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}
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}
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}
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}
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/**
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* 为此handler映射设置根handler，即要为根路径（"/"）注册的handler
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* <p>Default is {@code null}, indicating no root handler.
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*/
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public void setRootHandler(Object rootHandler) {
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this.rootHandler = rootHandler;
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}
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public Object getRootHandler() {
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return this.rootHandler;
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}
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/**
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* 设置此handler映射的默认handler。如果未找到特定映射，则将返回此handler
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*/
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public void setDefaultHandler(Object defaultHandler) {
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this.defaultHandler = defaultHandler;
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}
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public Object getDefaultHandler() {
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return this.defaultHandler;
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}
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}
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```
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这里的handlerMap是一个HashMap，其中保存了URL请求和Controller的映射关系，这个handlerMap是在AbstractUrlHandlerMapping中定义的（ Map<String, object> handlerMap = new LinkedHashMap<String, object>() ），这个配置好URL请求和handler映射数据的handlerMap，为Spring MVC响应HTTP请求准备好了基本的映射数据，根据这个handlerMap以及设置于其中的映射数据，可以方便地由
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URL请求得到它所对应的handler。有了这些准备工作，Spring MVC就可以等待HTTP请求的到来了。
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### 4.2 使用HandlerMapping完成请求的映射处理
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|
|
|
|
继续通过SimpleUrlHandlerMapping的实现来分析HandlerMapping的接口方法getHandler()，该方法会根据初始化时得到的映射关系来生成DispatcherServlet需要的HandlerExecutionChain，也就是说，这个getHandler()方法是实际使用HandlerMapping完成请求的映射处理的地方。在前面的HandlerExecutionChain的执行过程中，首先在AbstractHandlerMapping中启动getHandler的调用。
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|
|
```java
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public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {
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/**
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* 查找给定请求的handler，如果找不到特定的handler，则返回到defaultHandler
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*/
|
|
|
|
|
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
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// 模板方法模式
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Object handler = getHandlerInternal(request);
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// 如果找不到特定的handler，则取defaultHandler
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if (handler == null) {
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handler = getDefaultHandler();
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}
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// defaultHandler也没有则返回null
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if (handler == null) {
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return null;
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}
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// 如果该handler是String类型的，说明它是一个beanname
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// 根据该beanname从IoC容器中获取真正的handler对象
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if (handler instanceof String) {
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String handlerName = (String) handler;
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handler = getApplicationContext().getBean(handlerName);
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}
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// 这里把handler添加到到HandlerExecutionChain中
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return getHandlerExecutionChain(handler, request);
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}
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}
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```
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取得handler的具体过程在getHandlerInternal()方法中实现，这个方法接受HTTP请求作为参数，它的实现在AbstractHandlerMapping的子类AbstractUrlHandlerMapping中，这个实现过程包括从HTTP请求中得到URL，并根据URL到urlMapping中获得handler。
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```java
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public abstract class AbstractUrlHandlerMapping extends AbstractHandlerMapping {
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/**
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* 查找给定请求的URL路径 对应的handler
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*/
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@Override
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protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
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// 从request中获取请求的URL路径
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String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
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// 将得到的URL路径与handler进行匹配，得到对应的handler，如果没有对应的handler
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// 则返回null，这样默认的handler会被使用
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Object handler = lookupHandler(lookupPath, request);
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if (handler == null) {
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// We need to care for the default handler directly, since we need to
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// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
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Object rawHandler = null;
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if ("/".equals(lookupPath)) {
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rawHandler = getRootHandler();
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}
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// 使用默认的handler
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if (rawHandler == null) {
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rawHandler = getDefaultHandler();
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}
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if (rawHandler != null) {
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// Bean name or resolved handler?
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if (rawHandler instanceof String) {
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String handlerName = (String) rawHandler;
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rawHandler = getApplicationContext().getBean(handlerName);
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}
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validateHandler(rawHandler, request);
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handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
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}
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}
|
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|
|
if (handler != null && logger.isDebugEnabled()) {
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|
|
logger.debug("Mapping [" + lookupPath + "] to " + handler);
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|
}
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|
else if (handler == null && logger.isTraceEnabled()) {
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|
|
logger.trace("No handler mapping found for [" + lookupPath + "]");
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|
|
}
|
|
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|
|
return handler;
|
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|
|
}
|
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|
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|
|
/**
|
|
|
|
|
* 查找给定URL路径的handler实例
|
|
|
|
|
*/
|
|
|
|
|
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
|
|
|
|
|
// 直接匹配
|
|
|
|
|
Object handler = this.handlerMap.get(urlPath);
|
|
|
|
|
if (handler != null) {
|
|
|
|
|
// Bean name or resolved handler?
|
|
|
|
|
if (handler instanceof String) {
|
|
|
|
|
String handlerName = (String) handler;
|
|
|
|
|
handler = getApplicationContext().getBean(handlerName);
|
|
|
|
|
}
|
|
|
|
|
validateHandler(handler, request);
|
|
|
|
|
return buildPathExposingHandler(handler, urlPath, urlPath, null);
|
|
|
|
|
}
|
|
|
|
|
// 正则匹配
|
|
|
|
|
List<String> matchingPatterns = new ArrayList<String>();
|
|
|
|
|
for (String registeredPattern : this.handlerMap.keySet()) {
|
|
|
|
|
if (getPathMatcher().match(registeredPattern, urlPath)) {
|
|
|
|
|
matchingPatterns.add(registeredPattern);
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
String bestPatternMatch = null;
|
|
|
|
|
Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
|
|
|
|
|
if (!matchingPatterns.isEmpty()) {
|
|
|
|
|
Collections.sort(matchingPatterns, patternComparator);
|
|
|
|
|
if (logger.isDebugEnabled()) {
|
|
|
|
|
logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
|
|
|
|
|
}
|
|
|
|
|
bestPatternMatch = matchingPatterns.get(0);
|
|
|
|
|
}
|
|
|
|
|
if (bestPatternMatch != null) {
|
|
|
|
|
handler = this.handlerMap.get(bestPatternMatch);
|
|
|
|
|
// Bean name or resolved handler?
|
|
|
|
|
if (handler instanceof String) {
|
|
|
|
|
String handlerName = (String) handler;
|
|
|
|
|
handler = getApplicationContext().getBean(handlerName);
|
|
|
|
|
}
|
|
|
|
|
validateHandler(handler, request);
|
|
|
|
|
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);
|
|
|
|
|
|
|
|
|
|
// There might be multiple 'best patterns', let's make sure we have the correct URI template variables
|
|
|
|
|
// for all of them
|
|
|
|
|
Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
|
|
|
|
|
for (String matchingPattern : matchingPatterns) {
|
|
|
|
|
if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
|
|
|
|
|
Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
|
|
|
|
|
Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
|
|
|
|
|
uriTemplateVariables.putAll(decodedVars);
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
if (logger.isDebugEnabled()) {
|
|
|
|
|
logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
|
|
|
|
|
}
|
|
|
|
|
return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
|
|
|
|
|
}
|
|
|
|
|
// No handler found...
|
|
|
|
|
return null;
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
经过这一系列对HTTP请求进行解析和匹配handler的过程，得到了与请求对应的handler处理器。在返回的handler中，已经完成了在HandlerExecutionChain中进行封装的工作，为handler对HTTP请求的响应做好了准备。
|
|
|
|
|
|
|
|
|
|
### 4.3 DispatcherServlet对HTTP请求的分发处理
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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AmyliaY
5 years ago
