前言
HandlerMethodReturnValueHandler用于对接口返回值的处理。
一、HandlerMethodReturnValueHandler
public interface HandlerMethodReturnValueHandler {
//是否支持返回值的类型
boolean supportsReturnType(MethodParameter returnType);
//对返回值进行处理
void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;
}
二、ModelAndViewMethodReturnValueHandler
用于处理ModelAndView类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是ModelAndView类型
return ModelAndView.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
//返回值是null
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
ModelAndView mav = (ModelAndView) returnValue;
//view是否是String类型
if (mav.isReference()) {
String viewName = mav.getViewName();
mavContainer.setViewName(viewName);
//是否是重定向
if (viewName != null && isRedirectViewName(viewName)) {
mavContainer.setRedirectModelScenario(true);
}
}
else {
//处理View类型
View view = mav.getView();
mavContainer.setView(view);
//重定向
if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
mavContainer.setRedirectModelScenario(true);
}
}
mavContainer.setStatus(mav.getStatus());
mavContainer.addAllAttributes(mav.getModel());
}
三、ModelMethodProcessor
用于处理Model类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是Model类型
return Model.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
return;
}
else if (returnValue instanceof Model) {
//Model类型，将model的参数添加到ModelMap中
mavContainer.addAllAttributes(((Model) returnValue).asMap());
}
else {
// should not happen
throw new UnsupportedOperationException("Unexpected return type [" +
returnType.getParameterType().getName() + "] in method: " + returnType.getMethod());
}
}
四、ViewMethodReturnValueHandler
用于处理View类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是View类型
return View.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue instanceof View) {
View view = (View) returnValue;
//设置view
mavContainer.setView(view);
//校验重定向
if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
mavContainer.setRedirectModelScenario(true);
}
}
else if (returnValue != null) {
// should not happen
throw new UnsupportedOperationException("Unexpected return type: " +
returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
}
}
五、HttpEntityMethodProcessor
用于处理HttpEntity、ResponseEntity类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是HttpEntity类型，并且不能是RequestEntity类型
return (HttpEntity.class.isAssignableFrom(returnType.getParameterType()) &&
!RequestEntity.class.isAssignableFrom(returnType.getParameterType()));
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
mavContainer.setRequestHandled(true);
if (returnValue == null) {
return;
}
//request
ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
//response
ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
//returnValue是HttpEntity类型
Assert.isInstanceOf(HttpEntity.class, returnValue);
HttpEntity<?> responseEntity = (HttpEntity<?>) returnValue;
HttpHeaders outputHeaders = outputMessage.getHeaders();
HttpHeaders entityHeaders = responseEntity.getHeaders();
//设置响应的headers
if (!entityHeaders.isEmpty()) {
entityHeaders.forEach((key, value) -> {
if (HttpHeaders.VARY.equals(key) && outputHeaders.containsKey(HttpHeaders.VARY)) {
List<String> values = getVaryRequestHeadersToAdd(outputHeaders, entityHeaders);
if (!values.isEmpty()) {
outputHeaders.setVary(values);
}
}
else {
outputHeaders.put(key, value);
}
});
}
//ResponseEntity类型
if (responseEntity instanceof ResponseEntity) {
int returnStatus = ((ResponseEntity<?>) responseEntity).getStatusCodeValue();
outputMessage.getServletResponse().setStatus(returnStatus);
if (returnStatus == 200) {
HttpMethod method = inputMessage.getMethod();
//get和head方法，校验资源是否没有修改过，没有修改直接返回
if ((HttpMethod.GET.equals(method) || HttpMethod.HEAD.equals(method))
&& isResourceNotModified(inputMessage, outputMessage)) {
outputMessage.flush();
return;
}
}
else if (returnStatus / 100 == 3) {
String location = outputHeaders.getFirst("location");
if (location != null) {
//处理重定向
saveFlashAttributes(mavContainer, webRequest, location);
}
}
}
// Try even with null body. ResponseBodyAdvice could get involved.
//通过MessageConverters填充body
writeWithMessageConverters(responseEntity.getBody(), returnType, inputMessage, outputMessage);
// Ensure headers are flushed even if no body was written.
outputMessage.flush();
}
六、 MapMethodProcessor
用于处理Map类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//Map类型
return Map.class.isAssignableFrom(returnType.getParameterType());
}
@Override
@SuppressWarnings({
"rawtypes", "unchecked"})
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue instanceof Map){
//将Map中参数设置到ModelMap中
mavContainer.addAllAttributes((Map) returnValue);
}
else if (returnValue != null) {
// should not happen
throw new UnsupportedOperationException("Unexpected return type [" +
returnType.getParameterType().getName() + "] in method: " + returnType.getMethod());
}
}
七、 ViewNameMethodReturnValueHandler
用于处理void和CharSequence类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
Class<?> paramType = returnType.getParameterType();
return (void.class == paramType || CharSequence.class.isAssignableFrom(paramType));
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue instanceof CharSequence) {
String viewName = returnValue.toString();
mavContainer.setViewName(viewName);
if (isRedirectViewName(viewName)) {
mavContainer.setRedirectModelScenario(true);
}
}
else if (returnValue != null) {
// should not happen
throw new UnsupportedOperationException("Unexpected return type: " +
returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
}
}