这要从DispatcherServlet开始说起：
在WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);增加断点
搜索http://localhost:8080/car/3/owner/lisi?age=18&inters=basketball&inters=game
public class DispatcherServlet extends frameworkServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 决定哪一个handler(方法)能处理这个请求，返回给mappedHandler
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 决定哪一个HandlerAdapter能处理这个请求
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
...
getHandler方法
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
Iterator var2 = this.handlerMappings.iterator();
while(var2.hasNext()) {
//找出是哪个mapping（一般为RequestMappingHandlerMapping和welcomePageHandlerMapping）
HandlerMapping mapping = (HandlerMapping)var2.next();
//通过mapping，找出哪个handler(方法)能处理这个请求
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
alt+左键，点击handler，获得handler的值就是处理该请求的方法
@ResponseBody
@GetMapping("/car/{id}/owner/{username}")
public Map car(
@PathVariable(value = "id")Integer id,
@PathVariable(value = "username") String username,
@PathVariable Map pv,
@RequestParam(value = "age")Integer age,
@RequestParam(value = "inters")List inters,
@RequestParam Map map1
)
{
Map map = new HashMap();
map.put("age",age);
map.put("inters",inters);
map.put("pv",pv);
map.put("map1",map1);
return map;
}
再step into 进入getHandlerAdapter方法
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
Iterator var2 = this.handlerAdapters.iterator();
while(var2.hasNext()) {
HandlerAdapter adapter = (HandlerAdapter)var2.next();
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
在这四种handlerAdapter中确定
0.支持方法上标注@RequestMapping
1.支持函数式编程的方法
xxxxxxx
再step into adapter.supports方法
如果该handler是HandlerMethod 类型，并且supportsInternal()为true
子类重写supportsInternal()方法，返回true，该方法逻辑满足:
是使用@RequestMapping修饰的普通方法转换的HandlerMethod对象
才可以使用该Adapter进行处理
public final boolean supports(Object handler) {
return handler instanceof HandlerMethod && this.supportsInternal((HandlerMethod)handler);
}
最终返回第一个adapter：RequestMappingHandlerAdapter
然后开始真正的处理这个请求ha.handle，step into，再step into handleInternal方法
public class DispatcherServlet extends frameworkServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
ModelAndView mv = null;
...
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
...
//本节重点
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
HandlerAdapter接口实现类RequestMappingHandlerAdapter（主要用来处理@RequestMapping）
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
...
//AbstractHandlerMethodAdapter类的方法，RequestMappingHandlerAdapter继承AbstractHandlerMethodAdapter
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
//handleInternal的核心
mav = invokeHandlerMethod(request, response, handlerMethod);
//...
return mav;
}
}
再step into invokeHandlerMethod方法
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {//<-----关注点
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
...
参数解析器argumentResolvers
确定将要执行的目标方法的每一个参数的值是什么;
SpringMVC目标方法能写多少种参数类型。取决于参数解析器argumentResolvers。
this.argumentResolvers在afterPropertiesSet()方法内初始化
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
@Nullable
private HandlerMethodArgumentResolverComposite argumentResolvers;
@Override
public void afterPropertiesSet() {
...
if (this.argumentResolvers == null) {//初始化argumentResolvers
List resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
...
}
//初始化了一堆的实现HandlerMethodArgumentResolver接口的参数对象
private List getDefaultArgumentResolvers() {
List resolvers = new ArrayList<>(30);
// Annotation-based argument resolution
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
resolvers.add(new RequestParamMapMethodArgumentResolver());
resolvers.add(new PathVariableMethodArgumentResolver());
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ServletModelAttributeMethodProcessor(false));
resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
resolvers.add(new RequestHeaderMapMethodArgumentResolver());
resolvers.add(new ServletcookievalueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new expressionValueMethodArgumentResolver(getBeanFactory()));
resolvers.add(new SessionAttributeMethodArgumentResolver());
resolvers.add(new RequestAttributeMethodArgumentResolver());
// Type-based argument resolution
resolvers.add(new ServletRequestMethodArgumentResolver());
resolvers.add(new ServletResponseMethodArgumentResolver());
resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
resolvers.add(new RedirectAttributesMethodArgumentResolver());
resolvers.add(new ModelMethodProcessor());
resolvers.add(new MapMethodProcessor());
resolvers.add(new ErrorsMethodArgumentResolver());
resolvers.add(new SessionStatusMethodArgumentResolver());
resolvers.add(new UriComponentsBuilderMethodArgumentResolver());
if (KotlinDetector.isKotlinPresent()) {
resolvers.add(new ContinuationHandlerMethodArgumentResolver());
}
// Custom arguments
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new PrincipalMethodArgumentResolver());
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));
return resolvers;
}
}
参数解析器HandlerMethodArgumentResolver方法：
public interface HandlerMethodArgumentResolver {
//当前解析器是否支持解析这种参数
boolean supportsParameter(MethodParameter parameter);
@Nullable//如果支持，就调用 resolveArgument进行解析
Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
}
返回值处理器
ValueHandler
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {//<---关注点
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
...
返回值处理器代表方法可以返回的类型：
this.returnValueHandlers在afterPropertiesSet()方法内初始化
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
@Nullable
private HandlerMethodReturnValueHandlerComposite returnValueHandlers;
@Override
public void afterPropertiesSet() {
...
if (this.returnValueHandlers == null) {
List handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
//初始化了一堆的实现HandlerMethodReturnValueHandler接口的返回值参数对象
private List getDefaultReturnValueHandlers() {
List handlers = new ArrayList<>(20);
// Single-purpose return value types
handlers.add(new ModelAndViewMethodReturnValueHandler());
handlers.add(new ModelMethodProcessor());
handlers.add(new ViewMethodReturnValueHandler());
handlers.add(new ResponseBodyEmitterReturnValueHandler(getMessageConverters(),
this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager));
handlers.add(new StreamingResponseBodyReturnValueHandler());
handlers.add(new HttpEntityMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));
// Annotation-based return value types
handlers.add(new ServletModelAttributeMethodProcessor(false));
handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
// Multi-purpose return value types
handlers.add(new ViewNameMethodReturnValueHandler());
handlers.add(new MapMethodProcessor());
// Custom return value types
if (getCustomReturnValueHandlers() != null) {
handlers.addAll(getCustomReturnValueHandlers());
}
// Catch-all
if (!CollectionUtils.isEmpty(getModelAndViewResolvers())) {
handlers.add(new ModelAndViewResolverMethodReturnValueHandler(getModelAndViewResolvers()));
}
else {
handlers.add(new ServletModelAttributeMethodProcessor(true));
}
return handlers;
}
}
HandlerMethodReturnValueHandlerComposite类如下：
public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {
private final List returnValueHandlers = new ArrayList<>();
...
public HandlerMethodReturnValueHandlerComposite addHandlers(
@Nullable List handlers) {
if (handlers != null) {
this.returnValueHandlers.addAll(handlers);
}
return this;
}
}
HandlerMethodReturnValueHandler接口：
public interface HandlerMethodReturnValueHandler {
boolean supportsReturnType(MethodParameter returnType);
void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;
}
