首先来看下RequestMappingHandlerAdapter这个类的源码
/**
* An {@link AbstractHandlerMethodAdapter} that supports {@link HandlerMethod}s
* with the signature -- method argument and return types, defined in
* {@code @RequestMapping}.
*
*
Support for custom argument and return value types can be added via
* {@link #setCustomArgumentResolvers} and {@link #setCustomReturnValueHandlers}.
* Or alternatively to re-configure all argument and return value types use
* {@link #setArgumentResolvers} and {@link #setReturnValueHandlers(List)}.
*
* @author Rossen Stoyanchev
* @since 3.1
* @see HandlerMethodArgumentResolver
* @see HandlerMethodReturnValueHandler
*/
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
private List customArgumentResolvers;
private HandlerMethodArgumentResolverComposite argumentResolvers;
private HandlerMethodArgumentResolverComposite initBinderArgumentResolvers;
private List customReturnValueHandlers;
private HandlerMethodReturnValueHandlerComposite returnValueHandlers;
private List modelAndViewResolvers;
private ContentNegotiationManager contentNegotiationManager = new ContentNegotiationManager();
private List> messageConverters;
private WebBindingInitializer webBindingInitializer;
private AsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor("MvcAsync");
private Long asyncRequestTimeout;
............................................
从注释中可以了解到通过设置setCustomArgumentResolvers and setCustomReturnValueHandlers可以实现自定义出参和入参的相关规则
由于RequestMappingHandlerAdapter实现了InitializingBean接口所以在初始化的时候会调用afterPropertiesSet()方法
public void afterPropertiesSet() {
if (this.argumentResolvers == null) {
List resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
initControllerAdviceCache();
}
RequestMappingHandlerAdapter方法中有两个方法，getDefaultArgumentResolvers和getDefaultReturnValueHandlers方法，当然我们这边自定义是通过RequestMappingHandlerAdapter的customArgumentResolvers和customReturnValueHandlers属性来实现的，如果通过argumentResolvers和returnValueHandlers属性来直接设置的话，会将spring默认的请求入参和出参覆盖掉
getDefaultArgumentResolvers()方法可以看到我们自定义的入参处理类是被放在中后位置的，同样的getDefaultReturnValueHandlers()方法也是这样
/**
* Return the list of return value handlers to use including built-in and
* custom handlers provided via {@link #setReturnValueHandlers}.
*/
private List getDefaultReturnValueHandlers() {
List handlers = new ArrayList();
// Single-purpose return value types
handlers.add(new ModelAndViewMethodReturnValueHandler());
handlers.add(new ModelMethodProcessor());
handlers.add(new ViewMethodReturnValueHandler());
handlers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.contentNegotiationManager));
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));
// Annotation-based return value types
handlers.add(new ModelAttributeMethodProcessor(false));
handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.contentNegotiationManager));
// 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 ModelAttributeMethodProcessor(true));
}
return handlers;
}
此处需要注意的是返回值的处理，由于我们自定义的是处于偏后的位置，如果其他处理类已经返回了，那么我们这边是不会再进入我们自定义的处理类中的
我们可以看到HandlerMethodArgumentResolverComposite 类
public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {
............................
/**
* Whether the given {@linkplain MethodParameter method parameter} is supported by any registered
* {@link HandlerMethodArgumentResolver}.
*/
public boolean supportsParameter(MethodParameter parameter) {
return getArgumentResolver(parameter) != null;
}
/**
* Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it.
* @exception IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found.
*/
public Object resolveArgument(
MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory)
throws Exception {
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
Assert.notNull(resolver, "Unknown parameter type [" + parameter.getParameterType().getName() + "]");
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
......................................
实现了HandlerMethodArgumentResolver接口
而在其中
/**
* Find a registered {@link HandlerMethodArgumentResolver} that supports the given method parameter.
*/
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
for (HandlerMethodArgumentResolver methodArgumentResolver : this.argumentResolvers) {
if (logger.isTraceEnabled()) {
logger.trace("Testing if argument resolver [" + methodArgumentResolver + "] supports [" +
parameter.getGenericParameterType() + "]");
}
if (methodArgumentResolver.supportsParameter(parameter)) {
result = methodArgumentResolver;
this.argumentResolverCache.put(parameter, result);
break;
}
}
}
return result;
}
这里的argumentResolvers就是前文指定添加的
public void afterPropertiesSet() {
if (this.argumentResolvers == null) {
List resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List handlers = getDefaultReturnValueHandlers();
/*********就是这里************/
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
/*********就是这里************/
}
initControllerAdviceCache();
}