Spring MVC学习笔记之Controller查找(基于Spring4.0.3)

转载  2018-03-12   作者:芥末无疆sss   我要评论

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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<Method, T> mappings = new IdentityHashMap<Method, T>();
 //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<Method> 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<String> 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<Match> matches = new ArrayList<Match>();
 //根据uri获取直接匹配的RequestMappingInfos
 List<T> 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<Match> 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<T> mappings, List<Match> 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。

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