0 摘要

本文从源码层面简单讲解SpringMVC的处理器映射环节，也就是查找Controller详细过程

1 SpringMVC请求流程

Controller查找在上图中对应的步骤1至2的过程

SpringMVC详细运行流程图

2 SpringMVC初始化过程

2.1 先认识两个类

1.RequestMappingInfo

封装RequestMapping注解

包含HTTP请求头的相关信息

一个实例对应一个RequestMapping注解

2.HandlerMethod

封装Controller的处理请求方法

包含该方法所属的bean对象、该方法对应的method对象、该方法的参数等

RequestMappingHandlerMapping的继承关系

在SpringMVC初始化的时候

首先执行RequestMappingHandlerMapping的afterPropertiesSet

然后进入AbstractHandlerMethodMapping的afterPropertiesSet

这个方法会进入该类的initHandlerMethods

负责从applicationContext中扫描beans,然后从bean中查找并注册处理器方法

//Scan beans in the ApplicationContext, detect and register handler methods.

protected void initHandlerMethods() {

...

//获取applicationContext中所有的bean name

String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?

BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :

getApplicationContext().getBeanNamesForType(Object.class));

//遍历beanName数组

for (String beanName : beanNames) {

//isHandler会根据bean来判断bean定义中是否带有Controller注解或RequestMapping注解

if (isHandler(getApplicationContext().getType(beanName))){

detectHandlerMethods(beanName);

}

}

handlerMethodsInitialized(getHandlerMethods());

}

RequestMappingHandlerMapping#isHandler

上图方法即判断当前bean定义是否带有Controlller注解或RequestMapping注解

如果只有RequestMapping生效吗？不会的!

因为这种情况下Spring初始化的时候不会把该类注册为Spring bean,遍历beanNames时不会遍历到这个类，所以这里把Controller换成Compoent也可以，不过一般不这么做

当确定bean为handler后,便会从该bean中查找出具体的handler方法(即Controller类下的具体定义的请求处理方法),查找代码如下

/**

* Look for handler methods in a handler

* @param handler the bean name of a handler or a handler instance

*/

protected void detectHandlerMethods(final Object handler) {

//获取当前Controller bean的class对象

Class> handlerType = (handler instanceof String) ?

getApplicationContext().getType((String) handler) : handler.getClass();

//避免重复调用 getMappingForMethod 来重建 RequestMappingInfo 实例

final Map mappings = new IdentityHashMap();

//同上，也是该Controller bean的class对象

final Class> userType = ClassUtils.getUserClass(handlerType);

//获取当前bean的所有handler method

//根据 method 定义是否带有 RequestMapping

//若有则创建RequestMappingInfo实例

Set methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {

@Override

public boolean matches(Method method) {

T mapping = getMappingForMethod(method, userType);

if (mapping != null) {

mappings.put(method, mapping);

return true;

}

else {

return false;

}

}

});

//遍历并注册当前bean的所有handler method

for (Method method : methods) {

//注册handler method，进入以下方法

registerHandlerMethod(handler, method, mappings.get(method));

}

以上代码有两个地方有调用了getMappingForMethod

使用方法和类型级别RequestMapping注解来创建RequestMappingInfo

@Override

protected RequestMappingInfo getMappingForMethod(Method method, Class> handlerType) {

RequestMappingInfo info = null;

//获取method的@RequestMapping

RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);

if (methodAnnotation != null) {

RequestCondition> methodCondition = getCustomMethodCondition(method);

info = createRequestMappingInfo(methodAnnotation, methodCondition);

//获取method所属bean的@RequtestMapping注解

RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);

if (typeAnnotation != null) {

RequestCondition> typeCondition = getCustomTypeCondition(handlerType);

//合并两个@RequestMapping注解

info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);

}

}

return info;

}

这个方法的作用就是根据handler method方法创建RequestMappingInfo对象。首先判断该mehtod是否含有RequestMpping注解。如果有则直接根据该注解的内容创建RequestMappingInfo对象。创建以后判断当前method所属的bean是否也含有RequestMapping注解。如果含有该注解则会根据该类上的注解创建一个RequestMappingInfo对象。然后在合并method上的RequestMappingInfo对象，最后返回合并后的对象。现在回过去看detectHandlerMethods方法，有两处调用了getMappingForMethod方法，个人觉得这里是可以优化的，在第一处判断method时否为handler时，创建的RequestMappingInfo对象可以保存起来，直接拿来后面使用，就少了一次创建RequestMappingInfo对象的过程。然后紧接着进入registerHandlerMehtod方法，如下

protected void registerHandlerMethod(Object handler, Method method, T mapping) {

//创建HandlerMethod

HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);

HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);

//检查配置是否存在歧义性

if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {

throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean()

+ "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '"

+ oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");

}

this.handlerMethods.put(mapping, newHandlerMethod);

if (logger.isInfoEnabled()) {

logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);

}

//获取@RequestMapping注解的value，然后添加value->RequestMappingInfo映射记录至urlMap中

Set patterns = getMappingPathPatterns(mapping);

for (String pattern : patterns) {

if (!getPathMatcher().isPattern(pattern)) {

this.urlMap.add(pattern, mapping);

}

}

}

这里T的类型是RequestMappingInfo。这个对象就是封装的具体Controller下的方法的RequestMapping注解的相关信息。一个RequestMapping注解对应一个RequestMappingInfo对象。HandlerMethod和RequestMappingInfo类似，是对Controlelr下具体处理方法的封装。先看方法的第一行,根据handler和mehthod创建HandlerMethod对象。第二行通过handlerMethods map来获取当前mapping对应的HandlerMethod。然后判断是否存在相同的RequestMapping配置。如下这种配置就会导致此处抛

Invocation of init method failed; nested exception is java.lang.IllegalStateException: Ambiguous mapping found. Cannot map...

异常

@Controller

@RequestMapping("/AmbiguousTest")

public class AmbiguousTestController {

@RequestMapping(value = "/test1")

@ResponseBody

public String test1(){

return "method test1";

}

@RequestMapping(value = "/test1")

@ResponseBody

public String test2(){

return "method test2";

}

}

在SpingMVC启动(初始化)阶段检查RequestMapping配置是否有歧义，这是其中一处检查歧义的(后面还会提到一个在运行时检查歧义性的地方)。然后确认配置正常以后会把该RequestMappingInfo和HandlerMethod对象添加至handlerMethods(LinkedHashMap)中，静接着把RequestMapping注解的value和ReuqestMappingInfo对象添加至urlMap中。

registerHandlerMethod方法简单总结

该方法的主要有3个职责

1. 检查RequestMapping注解配置是否有歧义。

2. 构建RequestMappingInfo到HandlerMethod的映射map。该map便是AbstractHandlerMethodMapping的成员变量handlerMethods。LinkedHashMap。

3. 构建AbstractHandlerMethodMapping的成员变量urlMap，MultiValueMap。这个数据结构可以把它理解成Map>。其中String类型的key存放的是处理方法上RequestMapping注解的value。就是具体的uri

先有如下Controller

@Controller

@RequestMapping("/UrlMap")

public class UrlMapController {

@RequestMapping(value = "/test1", method = RequestMethod.GET)

@ResponseBody

public String test1(){

return "method test1";

}

@RequestMapping(value = "/test1")

@ResponseBody

public String test2(){

return "method test2";

}

@RequestMapping(value = "/test3")

@ResponseBody

public String test3(){

return "method test3";

}

}

初始化完成后，对应AbstractHandlerMethodMapping的urlMap的结构如下

以上便是SpringMVC初始化的主要过程

查找过程

为了理解查找流程，带着一个问题来看，现有如下Controller

@Controller

@RequestMapping("/LookupTest")

public class LookupTestController {

@RequestMapping(value = "/test1", method = RequestMethod.GET)

@ResponseBody

public String test1(){

return "method test1";

}

@RequestMapping(value = "/test1", headers = "Referer=https://www.baidu.com")

@ResponseBody

public String test2(){

return "method test2";

}

@RequestMapping(value = "/test1", params = "id=1")

@ResponseBody

public String test3(){

return "method test3";

}

@RequestMapping(value = "/*")

@ResponseBody

public String test4(){

return "method test4";

}

}

有如下请求

这个请求会进入哪一个方法？

web容器(Tomcat、jetty)接收请求后，交给DispatcherServlet处理。FrameworkServlet调用对应请求方法(eg:get调用doGet)，然后调用processRequest方法。进入processRequest方法后，一系列处理后，在line:936进入doService方法。然后在Line856进入doDispatch方法。在line:896获取当前请求的处理器handler。然后进入AbstractHandlerMethodMapping的lookupHandlerMethod方法。代码如下

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {

List matches = new ArrayList();

//根据uri获取直接匹配的RequestMappingInfos

List directPathMatches = this.urlMap.get(lookupPath);

if (directPathMatches != null) {

addMatchingMappings(directPathMatches, matches, request);

}

//不存在直接匹配的RequetMappingInfo，遍历所有RequestMappingInfo

if (matches.isEmpty()) {

// No choice but to go through all mappings

addMatchingMappings(this.handlerMethods.keySet(), matches, request);

}

//获取最佳匹配的RequestMappingInfo对应的HandlerMethod

if (!matches.isEmpty()) {

Comparator comparator = new MatchComparator(getMappingComparator(request));

Collections.sort(matches, comparator);

if (logger.isTraceEnabled()) {

logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);

}

//再一次检查配置的歧义性

Match bestMatch = matches.get(0);

if (matches.size() > 1) {

Match secondBestMatch = matches.get(1);

if (comparator.compare(bestMatch, secondBestMatch) == 0) {

Method m1 = bestMatch.handlerMethod.getMethod();

Method m2 = secondBestMatch.handlerMethod.getMethod();

throw new IllegalStateException(

"Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" +

m1 + ", " + m2 + "}");

}

}

handleMatch(bestMatch.mapping, lookupPath, request);

return bestMatch.handlerMethod;

}

else {

return handleNoMatch(handlerMethods.keySet(), lookupPath, request);

}

}

进入lookupHandlerMethod方法，其中lookupPath="/LookupTest/test1",根据lookupPath，也就是请求的uri。直接查找urlMap，获取直接匹配的RequestMappingInfo list。这里会匹配到3个RequestMappingInfo。如下

然后进入addMatchingMappings方法

private void addMatchingMappings(Collection mappings, List matches, HttpServletRequest request) {

for (T mapping : mappings) {

T match = getMatchingMapping(mapping, request);

if (match != null) {

matches.add(new Match(match, handlerMethods.get(mapping)));

}

}

}

这个方法的职责是遍历当前请求的uri和mappings中的RequestMappingInfo能否匹配上，如果能匹配上，创建一个相同的RequestMappingInfo对象。再获取RequestMappingInfo对应的handlerMethod。然后创建一个Match对象添加至matches list中。执行完addMatchingMappings方法，回到lookupHandlerMethod。这时候matches还有3个能匹配上的RequestMappingInfo对象。接下来的处理便是对matchers列表进行排序，然后获取列表的第一个元素作为最佳匹配。返回Match的HandlerMethod。这里进入RequestMappingInfo的compareTo方法，看一下具体的排序逻辑。代码如下

public int compareTo(RequestMappingInfo other, HttpServletRequest request) {

int result = patternsCondition.compareTo(other.getPatternsCondition(), request);

if (result != 0) {

return result;

}

result = paramsCondition.compareTo(other.getParamsCondition(), request);

if (result != 0) {

return result;

}

result = headersCondition.compareTo(other.getHeadersCondition(), request);

if (result != 0) {

return result;

}

result = consumesCondition.compareTo(other.getConsumesCondition(), request);

if (result != 0) {

return result;

}

result = producesCondition.compareTo(other.getProducesCondition(), request);

if (result != 0) {

return result;

}

result = methodsCondition.compareTo(other.getMethodsCondition(), request);

if (result != 0) {

return result;

}

result = customConditionHolder.compareTo(other.customConditionHolder, request);

if (result != 0) {

return result;

}

return 0;

}

代码里可以看出，匹配的先后顺序是value>params>headers>consumes>produces>methods>custom，看到这里，前面的问题就能轻易得出答案了。在value相同的情况，params更能先匹配。所以那个请求会进入test3()方法。再回到lookupHandlerMethod，在找到HandlerMethod。SpringMVC还会这里再一次检查配置的歧义性，这里检查的原理是通过比较匹配度最高的两个RequestMappingInfo进行比较。此处可能会有疑问在初始化SpringMVC有检查配置的歧义性，这里为什么还会检查一次。假如现在Controller中有如下两个方法，以下配置是能通过初始化歧义性检查的。

@RequestMapping(value = "/test5", method = {RequestMethod.GET, RequestMethod.POST})

@ResponseBody

public String test5(){

return "method test5";

}

@RequestMapping(value = "/test5", method = {RequestMethod.GET, RequestMethod.DELETE})

@ResponseBody

public String test6(){

return "method test6";

}

现在执行 http://localhost:8080/SpringMVC-Demo/LookupTest/test5 请求，便会在lookupHandlerMethod方法中抛

java.lang.IllegalStateException: Ambiguous handler methods mapped for HTTP path 'http://localhost:8080/SpringMVC-Demo/LookupTest/test5'异常。这里抛该异常是因为RequestMethodsRequestCondition的compareTo方法是比较的method数。代码如下

public int compareTo(RequestMethodsRequestCondition other, HttpServletRequest request) {

return other.methods.size() - this.methods.size();

}

什么时候匹配通配符？当通过urlMap获取不到直接匹配value的RequestMappingInfo时才会走通配符匹配进入addMatchingMappings方法。

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对脚本之家的支持。