SpringMVC源码解读 - HandlerMapping

Posted 2020-06-16

SpringMVC在请求到handler处理器的分发这步是通过HandlerMapping模块解决的.handlerMapping 还处理拦截器.

先看看HandlerMapping的继承树吧

可以大致这样做个分类:

　　1. 一个接口HandlerMapping,定义一个api: HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;

　　2. 一个基础抽象类:主要是准备上下文环境,提供getHandlerInternal钩子,封装拦截器到HandlerExecutionChain

　　3. 基于注解@Controller,@RequestMapping的使用

　　4. 配置文件中直接配置url到 handler的SimpleUrlHandlerMapping

　　5. 默认实现BeanNameUrlHandlerMapping

　　6. Controller子类的映射

 

看看HandlerMapping吧,就一个getHandler api 非常简单.

// HandlerMapping

1 package org.springframework.web.servlet;
2 public interface HandlerMapping {
3     HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
4 
5 }

 

AbstractHandlerMapping就没有这么简单了

先看AbstractHandlerMapping继承的类,实现的接口

1 package org.springframework.web.servlet.handler;
2 public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport
3         implements HandlerMapping, Ordered {
4     // ...
5 }

WebApplicationObjectSupport用于提供上下文ApplicationContext和ServletContext.

　　还有这边的initApplicationContext方法,在后续经常会使用到.AbstractHandlerMapping就直接覆写了.

　　父类里还是实现了ApplicationContextAware和ServletContextAware接口,spring概念很统一.

Ordered用于集合排序.

 

再接着看AbstractHandlerMapping的属性吧

// AbstractHandlerMapping

 1     // order赋了最大值,优先级是最小的
 2     private int order = Integer.MAX_VALUE;  // default: same as non-Ordered
 3     // 默认的Handler,这边使用的Obejct,子类实现的时候,使用HandlerMethod,HandlerExecutionChain等
 4     private Object defaultHandler;
 5     // url计算的辅助类
 6     private UrlPathHelper urlPathHelper = new UrlPathHelper();
 7     // 基于ant进行path匹配,解决如/books/{id}场景
 8     private PathMatcher pathMatcher = new AntPathMatcher();
 9     // 拦截器配置:1,HandlerMapping属性设置;2,extendInterceptors设置
10     private final List<Object> interceptors = new ArrayList<Object>();
11     // 从interceptors中解析得到,直接添加给全部handler
12     private final List<HandlerInterceptor> adaptedInterceptors = new ArrayList<HandlerInterceptor>();
13     // 使用前需要跟url进行匹配,匹配通过才会使用
14     private final List<MappedInterceptor> mappedInterceptors = new ArrayList<MappedInterceptor>();

 

看下拦截器的初始化:

// AbstractHandlerMapping

 1     @Override
 2     protected void initApplicationContext() throws BeansException {
 3         extendInterceptors(this.interceptors);
 4         detectMappedInterceptors(this.mappedInterceptors);
 5         initInterceptors();
 6     }
 7 
 8     /**
 9      * 提供给子类扩展拦截器,可惜都没有使用
10      */
11     protected void extendInterceptors(List<Object> interceptors) {
12     }
13 
14     /**
15      * 扫描应用下的MappedInterceptor,并添加到mappedInterceptors
16      */
17     protected void detectMappedInterceptors(List<MappedInterceptor> mappedInterceptors) {
18         mappedInterceptors.addAll(
19                 BeanFactoryUtils.beansOfTypeIncludingAncestors(
20                         getApplicationContext(),MappedInterceptor.class, true, false).values());
21     }
22 
23     /**
24      * 归集MappedInterceptor,并适配HandlerInterceptor和WebRequestInterceptor
25      */
26     protected void initInterceptors() {
27         if (!this.interceptors.isEmpty()) {
28             for (int i = 0; i < this.interceptors.size(); i++) {
29                 Object interceptor = this.interceptors.get(i);
30                 if (interceptor == null) {
31                     throw new IllegalArgumentException("Entry number " + i + " in interceptors array is null");
32                 }
33                 if (interceptor instanceof MappedInterceptor) {
34                     mappedInterceptors.add((MappedInterceptor) interceptor);
35                 }
36                 else {
37                     adaptedInterceptors.add(adaptInterceptor(interceptor));
38                 }
39             }
40         }
41     }
42 
43     protected HandlerInterceptor adaptInterceptor(Object interceptor) {
44         if (interceptor instanceof HandlerInterceptor) {
45             return (HandlerInterceptor) interceptor;
46         }
47         else if (interceptor instanceof WebRequestInterceptor) {
48             return new WebRequestHandlerInterceptorAdapter((WebRequestInterceptor) interceptor);
49         }
50         else {
51             throw new IllegalArgumentException("Interceptor type not supported: " + interceptor.getClass().getName());
52         }
53     }

 

 然后是getHandler(HttpServletRequest request)的实现,这边同时预留getHandlerInternal(HttpServletRequest request)给子类实现

// AbstractHandlerMapping

 1     public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
 2         Object handler = getHandlerInternal(request);
 3         if (handler == null) {
 4             handler = getDefaultHandler();
 5         }
 6         if (handler == null) {
 7             return null;
 8         }
 9         // Bean name or resolved handler?
10         if (handler instanceof String) {
11             String handlerName = (String) handler;
12             handler = getApplicationContext().getBean(handlerName);
13         }
14         return getHandlerExecutionChain(handler, request);
15     }
16 
17     protected abstract Object getHandlerInternal(HttpServletRequest request) throws Exception;

 

最后是封装拦截器到HandlerExecutionChain

　　adaptedInterceptors直接添加

　　mappedInterceptors需要根据url匹配通过后添加

// AbstractHandlerMapping

 1     protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
 2         HandlerExecutionChain chain =
 3             (handler instanceof HandlerExecutionChain) ?
 4                 (HandlerExecutionChain) handler : new HandlerExecutionChain(handler);
 5 
 6         chain.addInterceptors(getAdaptedInterceptors());
 7 
 8         String lookupPath = urlPathHelper.getLookupPathForRequest(request);
 9         for (MappedInterceptor mappedInterceptor : mappedInterceptors) {
10             if (mappedInterceptor.matches(lookupPath, pathMatcher)) {
11                 chain.addInterceptor(mappedInterceptor.getInterceptor());
12             }
13         }
14 
15         return chain;
16     }

 

Controller子类的映射,这一分支先看类继承

我们来说说,这边每个类主要的职责

　　1. AbstractHandlerMapping 准备上下文环境;提供getHandlerInternal钩子;封装拦截器到HandlerExecutionChain

　　2. AbstractUrlHandlerMapping 实现注册handler的方法供子类使用;实现getHandlerInternal,根据子类初始化的配置信息,查找handler

　　3. AbstractDetectingUrlHandlerMapping 扫描应用下的Object,迭代后提供钩子方法determineUrlsForHandler由子类决定如何过滤

　　4. AbstractControllerUrlHandlerMapping 实现determineUrlsForHandler,添加过滤排除的handler操作(配置文件配置),预留钩子方法buildUrlsForHandler给子类实现;同时判断controller的子类

　　5. ControllerBeanNameHandlerMapping 根据bean name生成url

　　　　ControllerClassNameHandlerMapping根据class name生成url

 

从AbstractUrlHandlerMapping开始看吧,这边只是大致看下代码,如果需要仔细分析,请移步<SpringMVC源码解读 - HandlerMapping - AbstractUrlHandlerMapping系列request分发>

handler的注册

1     protected void registerHandler(String[] urlPaths, String beanName) throws BeansException, IllegalStateException { }
2 
3     protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException { }

handler的查找

1 protected Object getHandlerInternal(HttpServletRequest request) throws Exception {}
2 // 根据url查找handler
3 protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {}
4 // 校验handler
5 protected void validateHandler(Object handler, HttpServletRequest request) throws Exception {}
6 // 封装拦截器到HandlerExecutionChain
7 protected Object buildPathExposingHandler(Object rawHandler, String bestMatchingPattern,
8             String pathWithinMapping, Map<String, String> uriTemplateVariables) {}

 

AbstractDetectingUrlHandlerMapping,这边一样不展开,具体移步<SpringMVC源码解读 - HandlerMapping - AbstractDetectingUrlHandlerMapping系列初始化>

具体做的事情:

　　1. 通过覆写initApplicationContext,调用detectHandlers扫描Obejct

　　2. 提供钩子方法determineUrlsForHandler给子类根据handler生成url

　　3. 调用父类的registerHandler进行注册

 1     @Override
 2     public void initApplicationContext() throws ApplicationContextException {
 3         super.initApplicationContext();
 4         detectHandlers();
 5     }
 6 
 7     protected void detectHandlers() throws BeansException {
 8         // ...
 9     }
10 
11 
12     /**
13      * Determine the URLs for the given handler bean.
14      * 钩子而已
15      */
16     protected abstract String[] determineUrlsForHandler(String beanName);

 

AbstractControllerUrlHandlerMapping,这边一样不展开,具体移步<SpringMVC源码解读 - HandlerMapping - AbstractDetectingUrlHandlerMapping系列初始化>

具体做的事情;

　　1. 覆写determineUrlsForHandler添加剔除部分类的逻辑,通过配置文件配置的excludedClasses和excludedPackages在这边使用

　　2. 判断是否controller的子类

　　3. 预留buildUrlsForHandler给子类生成url

 1     @Override
 2     protected String[] determineUrlsForHandler(String beanName) {
 3         Class beanClass = getApplicationContext().getType(beanName);
 4         if (isEligibleForMapping(beanName, beanClass)) {
 5             return buildUrlsForHandler(beanName, beanClass);
 6         }
 7         else {
 8             return null;
 9         }
10     }
11 
12     protected boolean isEligibleForMapping(String beanName, Class beanClass) {}
13 
14     protected boolean isControllerType(Class beanClass) {}
15 
16     protected abstract String[] buildUrlsForHandler(String beanName, Class beanClass);

 

ControllerBeanNameHandlerMapping和ControllerClassNameHandlerMapping 直接看源码吧,或者移步<SpringMVC源码解读 - HandlerMapping - AbstractDetectingUrlHandlerMapping系列初始化>

 

配置文件中直接配置url到 handler的SimpleUrlHandlerMapping,就是使用registerHandlers注册配置文档中的handler,直接看代码或者移步<SpringMVC源码解读 - HandlerMapping - SimpleUrlHandlerMapping初始化>吧

 

BeanNameUrlHandlerMapping 实现determineUrlsForHandler生成url,直接看代码或者移步<SpringMVC源码解读 - HandlerMapping - AbstractDetectingUrlHandlerMapping系列初始化>吧

 

基于注解@Controller,@RequestMapping的使用

最难吭的骨头

先看类继承吧

说下各个类的职责吧,具体的分析还是移步下面的文章

<SpringMVC源码解读 - HandlerMapping - RequestMappingHandlerMapping初始化>

<SpringMVC源码解读 - HandlerMapping - RequestMappingHandlerMapping请求分发>

　　1. AbstractHandlerMethodMaping 定义初始化流程,请求时如何映射

　　初始化:

　　　　1.1.1 扫描应用下的Object

　　　　1.1.2 预留isHandler钩子方法给子类判断Object是否handler

　　　　1.1.3 迭代扫描每一个handler,找出符合要求的方法,这边判断依然是留给子类实现getMappingForMethod

　　　　1.1.4 注册查找到的处理器,需要确保一个匹配条件RequestMappingInfo只能映射到一个handler

　　　　1.1.5 根据匹配条件获取url,同样的只是定义流程,具体的算法留给子类实现getMappingPathPatterns

　　请求request分发处理: 

　　　　1.2.1 直接字符串匹配的方式,查找handler　

　　　　1.2.2 匹配条件查找,这边具体的算法交由子类处理getMatchingMapping

　　　　1.2.3 排序并获取最佳匹配handler,这边的排序方式还是子类处理getMappingConmparator

　　　　1.2.4 分别封装匹配到和未匹配到handler的情况

　　2. RequestMappingInfoHandlerMapping使用RequestMappingInfo实现匹配条件,RequestMappingInfo的初始化留给子类

　　　　2.1 根据RequestMappingInfo生成url   ->getMappingPathPatterns

　　　　2.2 使用匹配条件查找Handler -> getMatchingMapping

　　　　2.3 完成比较器算法 -> getMappingComparator

　　　　2.4 覆写handleMatch,缓存n多信息到request

　　　　　　注册pattern,最佳匹配的pattern,url中解析出来的参数,url中解析出来的多值参数,mediaType

　　　　2.1.5 覆写handlerNoMatch,最后的挣扎,再尝试匹配一次

　　3. RequestMappingHandlerMapping 根据注解@Controller @RequestMapping生成RequestMappingInfo,并校验isHandler

　　　　3.1 覆写afterPropertiesSet,添加文件后缀判断

　　　　3.2 实现isHandler,类上有@Controller @RequestMapping其中一个注解就对

　　　　3.3 解析注解内容,生产RequestMappingInfo实例