摘要
- 本文從源碼層面簡(jiǎn)單講解SpringMVC的處理器映射環(huán)節(jié)，也就是查找Controller詳細(xì)過(guò)程。
SpringMVC請(qǐng)求流程
image.png
- Controller查找在上圖中對(duì)應(yīng)的步驟1至2的過(guò)程
SpringMVC初始化過(guò)程
理解初始化過(guò)程之前，先認(rèn)識(shí)兩個(gè)類
- RequestMappingInfo類，對(duì)RequestMapping注解封裝。里面包含http請(qǐng)求頭的相關(guān)信息。如uri、method、params、header等參數(shù)。一個(gè)對(duì)象對(duì)應(yīng)一個(gè)RequestMapping注解
-
HandlerMethod類，是對(duì)Controller的處理請(qǐng)求方法的封裝。里面包含了該方法所屬的bean對(duì)象、該方法對(duì)應(yīng)的method對(duì)象、該方法的參數(shù)等。
image.png
- 上圖是RequestMappingHandlerMapping的繼承關(guān)系。在SpringMVC初始化的時(shí)候，首先執(zhí)行RequestMappingHandlerMapping中的afterPropertiesSet方法，然后會(huì)進(jìn)入AbstractHandlerMethodMapping的afterPropertiesSet方法(line:93)，這個(gè)方法會(huì)進(jìn)入當(dāng)前類的initHandlerMethods方法（line:103）。這個(gè)方法的職責(zé)便是從applicationContext中掃描beans，然后從bean中查找并注冊(cè)處理器方法，代碼如下。
protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
//獲取applicationContext中所有的bean name
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
//遍歷beanName數(shù)組
for (String beanName : beanNames) {
//isHandler會(huì)根據(jù)bean來(lái)判斷bean定義中是否帶有Controller注解或RequestMapping注解
if (isHandler(getApplicationContext().getType(beanName))){
detectHandlerMethods(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
- isHandler方法其實(shí)很簡(jiǎn)單，如下
@Override
protected boolean isHandler(Class<?> beanType) {
return ((AnnotationUtils.findAnnotation(beanType, Controller.class) != null) ||
(AnnotationUtils.findAnnotation(beanType, RequestMapping.class) != null));
}
- 就是判斷當(dāng)前bean定義是否帶有Controlller注解或RequestMapping注解，看了這里邏輯可能會(huì)想如果只有RequestMapping會(huì)生效嗎？答案是不會(huì)的，因?yàn)樵谶@種情況下Spring初始化的時(shí)候不會(huì)把該類注冊(cè)為Spring bean，遍歷beanNames時(shí)不會(huì)遍歷到這個(gè)類，所以這里把Controller換成Compoent注解也是可以，不過(guò)一般不會(huì)這么做。當(dāng)確定bean為handlers后，便會(huì)從該bean中查找出具體的handler方法（也就是我們通常定義的Controller類下的具體定義的請(qǐng)求處理方法），查找代碼如下
protected void detectHandlerMethods(final Object handler) {
//獲取到當(dāng)前Controller bean的class對(duì)象
Class<?> handlerType = (handler instanceof String) ?
getApplicationContext().getType((String) handler) : handler.getClass();
//同上，也是該Controller bean的class對(duì)象
final Class<?> userType = ClassUtils.getUserClass(handlerType);
//獲取當(dāng)前bean的所有handler method。這里查找的依據(jù)便是根據(jù)method定義是否帶有RequestMapping注解。如果有根據(jù)注解創(chuàng)建RequestMappingInfo對(duì)象
Set<Method> methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {
public boolean matches(Method method) {
return getMappingForMethod(method, userType) != null;
}
});
//遍歷并注冊(cè)當(dāng)前bean的所有handler method
for (Method method : methods) {
T mapping = getMappingForMethod(method, userType);
//注冊(cè)handler method，進(jìn)入以下方法
registerHandlerMethod(handler, method, mapping);
}
}
- 以上代碼有兩個(gè)地方有調(diào)用了getMappingForMethod方法
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
RequestMappingInfo info = null;
//獲取method的@RequestMapping注解
RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);
if (methodAnnotation != null) {
RequestCondition<?> methodCondition = getCustomMethodCondition(method);
info = createRequestMappingInfo(methodAnnotation, methodCondition);
//獲取method所屬bean的@RequtestMapping注解
RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);
if (typeAnnotation != null) {
RequestCondition<?> typeCondition = getCustomTypeCondition(handlerType);
//合并兩個(gè)@RequestMapping注解
info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);
}
}
return info;
}
- 這個(gè)方法的作用就是根據(jù)handler method方法創(chuàng)建RequestMappingInfo對(duì)象。首先判斷該mehtod是否含有RequestMpping注解。如果有則直接根據(jù)該注解的內(nèi)容創(chuàng)建RequestMappingInfo對(duì)象。創(chuàng)建以后判斷當(dāng)前method所屬的bean是否也含有RequestMapping注解。如果含有該注解則會(huì)根據(jù)該類上的注解創(chuàng)建一個(gè)RequestMappingInfo對(duì)象。然后在合并method上的RequestMappingInfo對(duì)象，最后返回合并后的對(duì)象?，F(xiàn)在回過(guò)去看detectHandlerMethods方法，有兩處調(diào)用了getMappingForMethod方法，個(gè)人覺(jué)得這里是可以優(yōu)化的，在第一處判斷method時(shí)否為handler時(shí)，創(chuàng)建的RequestMappingInfo對(duì)象可以保存起來(lái)，直接拿來(lái)后面使用，就少了一次創(chuàng)建RequestMappingInfo對(duì)象的過(guò)程。然后緊接著進(jìn)入registerHandlerMehtod方法，如下
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
//創(chuàng)建HandlerMethod
HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);
HandlerMethod oldHandlerMethod = handlerMethods.get(mapping);
//檢查配置是否存在歧義性
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);
}
//獲取@RequestMapping注解的value，然后添加value->RequestMappingInfo映射記錄至urlMap中
Set<String> patterns = getMappingPathPatterns(mapping);
for (String pattern : patterns) {
if (!getPathMatcher().isPattern(pattern)) {
this.urlMap.add(pattern, mapping);
}
}
}
- 這里T的類型是RequestMappingInfo。這個(gè)對(duì)象就是封裝的具體Controller下的方法的RequestMapping注解的相關(guān)信息。一個(gè)RequestMapping注解對(duì)應(yīng)一個(gè)RequestMappingInfo對(duì)象。HandlerMethod和RequestMappingInfo類似，是對(duì)Controlelr下具體處理方法的封裝。先看方法的第一行,根據(jù)handler和mehthod創(chuàng)建HandlerMethod對(duì)象。第二行通過(guò)handlerMethods map來(lái)獲取當(dāng)前mapping對(duì)應(yīng)的HandlerMethod。然后判斷是否存在相同的RequestMapping配置。如下這種配置就會(huì)導(dǎo)致此處拋
Invocation of init method failed; nested exception is java.lang.IllegalStateException: Ambiguous mapping found. Cannot map...
異常
@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啟動(dòng)（初始化）階段檢查RequestMapping配置是否有歧義，這是其中一處檢查歧義的（后面還會(huì)提到一個(gè)在運(yùn)行時(shí)檢查歧義性的地方）。然后確認(rèn)配置正常以后會(huì)把該RequestMappingInfo和HandlerMethod對(duì)象添加至handlerMethods（LinkedHashMap<RequestMappingInfo,HandlerMethod>）中，靜接著把RequestMapping注解的value和ReuqestMappingInfo對(duì)象添加至urlMap中。
registerHandlerMethod方法簡(jiǎn)單總結(jié)
該方法的主要有3個(gè)職責(zé)
- 檢查RequestMapping注解配置是否有歧義。
- 構(gòu)建RequestMappingInfo到HandlerMethod的映射map。該map便是AbstractHandlerMethodMapping的成員變量handlerMethods。LinkedHashMap<RequestMappingInfo,HandlerMethod>。
- 構(gòu)建AbstractHandlerMethodMapping的成員變量urlMap，MultiValueMap<String,RequestMappingInfo>。這個(gè)數(shù)據(jù)結(jié)構(gòu)可以把它理解成Map<String,List<RequestMappingInfo>>。其中String類型的key存放的是處理方法上RequestMapping注解的value。就是具體的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，對(duì)應(yīng)AbstractHandlerMethodMapping的urlMap的結(jié)構(gòu)如下
image.png 以上便是SpringMVC初始化的主要過(guò)程
查找過(guò)程
- 為了理解查找流程，帶著一個(gè)問(wèn)題來(lái)看，現(xiàn)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";
}
}
-
有如下請(qǐng)求
image.png 這個(gè)請(qǐng)求會(huì)進(jìn)入哪一個(gè)方法？
web容器（Tomcat、jetty）接收請(qǐng)求后，交給DispatcherServlet處理。FrameworkServlet調(diào)用對(duì)應(yīng)請(qǐng)求方法（eg:get調(diào)用doGet），然后調(diào)用processRequest方法。進(jìn)入processRequest方法后，一系列處理后，在line:936進(jìn)入doService方法。然后在Line856進(jìn)入doDispatch方法。在line:896獲取當(dāng)前請(qǐng)求的處理器handler。然后進(jìn)入AbstractHandlerMethodMapping的lookupHandlerMethod方法。代碼如下
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<Match>();
//根據(jù)uri獲取直接匹配的RequestMappingInfos
List<T> directPathMatches = this.urlMap.get(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
//不存在直接匹配的RequetMappingInfo，遍歷所有RequestMappingInfo
if (matches.isEmpty()) {
// No choice but to go through all mappings
addMatchingMappings(this.handlerMethods.keySet(), matches, request);
}
//獲取最佳匹配的RequestMappingInfo對(duì)應(yīng)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);
}
//再一次檢查配置的歧義性
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);
}
}
-
進(jìn)入lookupHandlerMethod方法，其中l(wèi)ookupPath="/LookupTest/test1",根據(jù)lookupPath，也就是請(qǐng)求的uri。直接查找urlMap，獲取直接匹配的RequestMappingInfo list。這里會(huì)匹配到3個(gè)RequestMappingInfo。如下
image.png
- 然后進(jìn)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)));
}
}
}
- 這個(gè)方法的職責(zé)是遍歷當(dāng)前請(qǐng)求的uri和mappings中的RequestMappingInfo能否匹配上，如果能匹配上，創(chuàng)建一個(gè)相同的RequestMappingInfo對(duì)象。再獲取RequestMappingInfo對(duì)應(yīng)的handlerMethod。然后創(chuàng)建一個(gè)Match對(duì)象添加至matches list中。執(zhí)行完addMatchingMappings方法，回到lookupHandlerMethod。這時(shí)候matches還有3個(gè)能匹配上的RequestMappingInfo對(duì)象。接下來(lái)的處理便是對(duì)matchers列表進(jìn)行排序，然后獲取列表的第一個(gè)元素作為最佳匹配。返回Match的HandlerMethod。這里進(jìn)入RequestMappingInfo的compareTo方法，看一下具體的排序邏輯。代碼如下
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;
}
- 代碼里可以看出，匹配的先后順序是value>params>headers>consumes>produces>methods>custom，看到這里，前面的問(wèn)題就能輕易得出答案了。在value相同的情況，params更能先匹配。所以那個(gè)請(qǐng)求會(huì)進(jìn)入test3()方法。再回到lookupHandlerMethod，在找到HandlerMethod。SpringMVC還會(huì)這里再一次檢查配置的歧義性，這里檢查的原理是通過(guò)比較匹配度最高的兩個(gè)RequestMappingInfo進(jìn)行比較。此處可能會(huì)有疑問(wèn)在初始化SpringMVC有檢查配置的歧義性，這里為什么還會(huì)檢查一次。假如現(xiàn)在Controller中有如下兩個(gè)方法，以下配置是能通過(guò)初始化歧義性檢查的。
@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";
}
- 現(xiàn)在執(zhí)行 http://localhost:8080/SpringMVC-Demo/LookupTest/test5 請(qǐng)求，便會(huì)在lookupHandlerMethod方法中拋
java.lang.IllegalStateException: Ambiguous handler methods mapped for HTTP path 'http://localhost:8080/SpringMVC-Demo/LookupTest/test5'異常。這里拋該異常是因?yàn)镽equestMethodsRequestCondition的compareTo方法是比較的method數(shù)。代碼如下
public int compareTo(RequestMethodsRequestCondition other, HttpServletRequest request) {
return other.methods.size() - this.methods.size();
}
- 什么時(shí)候匹配通配符？當(dāng)通過(guò)urlMap獲取不到直接匹配value的RequestMappingInfo時(shí)才會(huì)走通配符匹配進(jìn)入addMatchingMappings方法。
總結(jié)
- 解析所使用代碼已上傳至github，https://github.com/wycm/SpringMVC-Demo
- 以上源碼是基于SpringMVC 3.2.2.RELEASE版本。以上便是SpringMVC請(qǐng)求查找的主要過(guò)程，希望對(duì)大家有幫助。本文可能有錯(cuò)誤，希望讀者能夠指出來(lái)。
版權(quán)聲明
作者：wycm
出處：http://www.itdecent.cn/p/08338ea28647
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