一、DispatchServlet简介
servlet依托于容器，处理请求及相应的运行在支持java语言服务器的小程序。目前最常见的就是用来扩展Java Web服务器功能。
二、接收参数过程
HandlerMethodReturnValueHandler：响应返回值的处理
HandlerMethodArgumentResolver：对应请求方法参数的处理
public interface HandlerMethodArgumentResolver {
##该解析器是否支持parameter参数的解析
boolean supportsParameter(MethodParameter var1);
//将方法参数解析为参数值并返回
Object resolveArgument(MethodParameter var1, ModelAndViewContainer var2, NativeWebRequest var3, WebDataBinderFactory var4)throws Exception;
}
HandlerMethodArgumentResolver的初始化：bean生命周期afterPropertiesSet方法初始化参数解析器：
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
//初始化SpringMVC默认的方法参数解析器，并添加至argumentResolvers
if (this.argumentResolvers ==null) {
List resolvers = getDefaultArgumentResolvers();
this.argumentResolvers =new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers ==null) {
//初始化SpringMVC默认的初始化绑定器参数解析器
List resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers =new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers ==null) {
List handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers =new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
进入getDefalutArgumentResolvers方法，代码如下：
private List getDefaultArgumentResolvers() {
List resolvers =new ArrayList();
// Annotation-based argument resolution基于注解
//一般用于带有@RequestParam注解的简单参数绑定，简单参数比如byte、int、long、double、String以及对应的包装类型
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
//用于处理带有@RequestParam注解，且参数类型为Map的解析绑定
resolvers.add(new RequestParamMapMethodArgumentResolver());
//一般用于处理带有@PathVariable注解的默认参数绑定，后续还有一些参数解析器，可以通过以下解析器的supportsParameter(MethodParameter parameter)方法查看
resolvers.add(new PathVariableMethodArgumentResolver());
resolvers.add(new PathVariableMapMethodArgumentResolver());
resolvers.add(new MatrixVariableMethodArgumentResolver());
resolvers.add(new MatrixVariableMapMethodArgumentResolver());
resolvers.add(new ServletModelAttributeMethodProcessor(false));
//带有@RequestBody注解的
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()));
// Type-based argument resolution 基于类型
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());
// Custom arguments
if (getCustomArgumentResolvers() !=null) {
resolvers.addAll(getCustomArgumentResolvers());
}
// Catch-all
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));
return resolvers;
}
HandlerMethodArgumentResolverComposite：实际的参数解析类
//上面存放的默认的HandlerMethodArgumentResolver参数解析器
private final List<HandlerMethodArgumentResolver> argumentResolvers =new LinkedList();
//存放已经解析过的参数，已经对应的HandlerMethodArgumentResolver解析器
private final Map<MethodParameter, HandlerMethodArgumentResolver> argumentResolverCache =new ConcurrentHashMap(256);
ServletInvocableHandlerMethod类：
public final Object invokeForRequest(NativeWebRequest request,
ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
//从request中解析出HandlerMethod方法所需要的参数，并返回Object[] Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
StringBuilder builder = new StringBuilder("Invoking [");
builder.append(this.getMethod().getName()).append("] method with arguments ");
builder.append(Arrays.asList(args));
logger.trace(builder.toString());
}
//通过反射执行HandleMethod中的method，方法参数为args。并返回方法执行的返回值 Object returnValue = invoke(args);
if (logger.isTraceEnabled()) {
logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}
直接进入getMethodArgumentValues方法看看其过程，代码如下：
/**
* Get the method argument values for the current request.
*/
private Object[]getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer,
Object... providedArgs)throws Exception {
//获取方法参数数组
MethodParameter[] parameters = getMethodParameters();
//创建一个参数数组，保存从request解析出的方法参数
Object[] args =new Object[parameters.length];
for (int i =0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());
args[i] = resolveProvidedArgument(parameter, providedArgs);
if (args[i] !=null) {
continue;
}
//判断之前RequestMappingHandlerAdapter初始化的那24个HandlerMethodArgumentResolver（参数解析器），是否存在支持该参数解析的解析器
if (this.argumentResolvers.supportsParameter(parameter)) {
try {
args[i] =this.argumentResolvers.resolveArgument(
parameter, mavContainer, request, this.dataBinderFactory);
continue;
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);
}
throw ex;
}
}
if (args[i] ==null) {
String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);
throw new IllegalStateException(msg);
}
}
return args;
}
进入HandlerMethodArgumentResolverComposite的resolveArgument方法：
public ObjectresolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory)throws Exception {
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
if (resolver ==null) {
throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() +"]");
}
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
然后进入不同的HandlerMethodArgumentResolver的resolverArgument方法
三、不同类型参数代码debug
四、自定义参数解析器
1、自定义参数注解
@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface ArgumentResolverAnnotation {
Stringvalue()default "";
}
2、自定义参数解析器实现HandlerMethodArgumentResolver接口
public class MyArgumentResolverimplements HandlerMethodArgumentResolver {
/**
* 解析器是否支持当前参数
* @param parameter
* @return
*/
@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(ArgumentResolverAnnotation.class);
}
/**
* 解析参数
* @param parameter
* @param mavContainer
* @param webRequest
* @param binderFactory
* @return
* @throws Exception
*/
@Override
public ObjectresolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory)throws Exception {
//new参数对象
Object obj = BeanUtils.instantiate(parameter.getParameterType());
BeanWrapper wrapper = PropertyAccessorFactory.forBeanPropertyAccess(obj);
Iterator paramNames = webRequest.getParameterNames();
while (paramNames.hasNext()) {
String paramName = paramNames.next();
Object o = webRequest.getParameter(paramName);
try {
wrapper.setPropertyValue(paramName, o);
}catch (BeansException e) {
}
}
return obj;
}
}
3、注册到Spring参数解析器中
<mvc:annotation-driven>
<mvc:argument-resolvers>
<bean class="com.chen.example.argumentResolver.MyArgumentResolver"/>
</mvc:argument-resolvers>
</mvc:annotation-driven>
