介绍 SpringMvc 如何处理参数解析 和 如何处理返回值的。
文章最后列举了HandlerMethodArgumentResolver 接口和 HandlerMethodReturnValueHandler 接口的实现类列表
SpringMVC请求过程
- 前端请求 首先被 DispatcherServlet 截获，DispatcherServlet 通过 handlerMapping 获得HandlerExecutionChain，然后获得 HandlerAdapter。
- HandlerAdapter 在内部对于每个请求，都会实例化一个 ServletInvocableHandlerMethod 进行处理，ServletInvocableHandlerMethod 在进行处理的时候，会分两部分(参数值和返回值)分别对请求跟响应进行处理。
- 之后 HandlerAdapter 得到 ModelAndView ，然后做相应的处理。
ServletInvocableHandlerMethod 分析
ServletInvocableHandlerMethod 在处理时，将 方法参数的处理 交给 HandlerMethodArgumentResolver 处理，而方法的返回值会交给 HandlerMethodReturnValueHandler 处理。
- HandlerMethodArgumentResolver 请求方法参数的处理
- HandlerMethodReturnValueHandler 响应返回值的处理
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| public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
public Object invokeForRequest(
NativeWebRequest request,
@Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
return doInvoke(args);
}
public void invokeAndHandle(
ServletWebRequest webRequest,
ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest)
|| getResponseStatus() != null
|| mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
|
RequestResponseBodyMethodProcessor详解
本文以 RequestResponseBodyMethodProcessor 为例讲解 。
HandlerMethodArgumentResolver接口
定义了两个方法:
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| public interface HandlerMethodArgumentResolver {
boolean supportsParameter(MethodParameter parameter);
@Nullable
Object resolveArgument(
MethodParameter parameter,
@Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest,
@Nullable WebDataBinderFactory binderFactory) throws Exception;
}
|
HandlerMethodReturnValueHandler接口
定义了两个方法:
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| public interface HandlerMethodReturnValueHandler {
boolean supportsReturnType(MethodParameter returnType);
void handleReturnValue(
@Nullable Object returnValue,
MethodParameter returnType,
ModelAndViewContainer mavContainer,
NativeWebRequest webRequest) throws Exception;
}
|
AbstractMessageConverterMethodArgumentResolver
HandlerMethodArgumentResolver接口的抽象类： 仅仅引入了HttpMessageConverter，即具体的转换工作由这些HttpMessageConverter来完成。
简单介绍AbstractMessageConverterMethodArgumentResolver中其他关联的类:
- HttpMessageConverter : 消息转换器。将 Request的 body 转换为想要的结果。常接触到的例子。FastJsonHttpMessageConverter 将 json字符串转换为对应的类对象。
- RequestBodyAdvice: 在消息转换器的作用前后执行。常用于 请求的加解密，与ControllerAdvice注解同时使用。
AbstractMessageConverterMethodArgumentResolver源码:
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| public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {
@Nullable
protected <T> Object readWithMessageConverters(
HttpInputMessage inputMessage,
MethodParameter parameter,
Type targetType)
throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
MediaType contentType;
boolean noContentType = false;
try {
contentType = inputMessage.getHeaders().getContentType();
}
catch (InvalidMediaTypeException ex) {
throw new HttpMediaTypeNotSupportedException(ex.getMessage());
}
if (contentType == null) {
noContentType = true;
contentType = MediaType.APPLICATION_OCTET_STREAM;
}
Class<?> contextClass = parameter.getContainingClass();
Class<T> targetClass = (targetType instanceof Class ? (Class<T>) targetType : null);
if (targetClass == null) {
ResolvableType resolvableType = ResolvableType.forMethodParameter(parameter);
targetClass = (Class<T>) resolvableType.resolve();
}
HttpMethod httpMethod = (inputMessage instanceof HttpRequest ? ((HttpRequest) inputMessage).getMethod() : null);
Object body = NO_VALUE;
EmptyBodyCheckingHttpInputMessage message;
try {
message = new EmptyBodyCheckingHttpInputMessage(inputMessage);
for (HttpMessageConverter<?> converter : this.messageConverters) {
Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
GenericHttpMessageConverter<?> genericConverter =
(converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);
if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) :
(targetClass != null && converter.canRead(targetClass, contentType))) {
if (message.hasBody()) {
HttpInputMessage msgToUse =
getAdvice().beforeBodyRead(message, parameter, targetType, converterType);
body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :
((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));
body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);
}
else {
body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);
}
break;
}
}
}
catch (IOException ex) {
throw new HttpMessageNotReadableException("I/O error while reading input message", ex, inputMessage);
}
if (body == NO_VALUE) {
if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||
(noContentType && !message.hasBody())) {
return null;
}
throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
}
MediaType selectedContentType = contentType;
Object theBody = body;
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(theBody, !traceOn);
return "Read \"" + selectedContentType + "\" to [" + formatted + "]";
});
return body;
}
}
|
AbstractMessageConverterMethodProcessor抽象类
在 AbstractMessageConverterMethodArgumentResolver抽象类 的基础上，添加HandlerMethodReturnValueHandler接口。
因此 AbstractMessageConverterMethodProcessor类 不仅可以用来转换请求数据，也可以用来转换响应数据。
RequestResponseBodyMethodProcessor类
继承自 AbstractMessageConverterMethodProcessor，专注解析 包含@RequestBody 和 @ResponseBody注解的方法。
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| public class RequestResponseBodyMethodProcessor
extends AbstractMessageConverterMethodProcessor {
@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(RequestBody.class);
}
@Override
public boolean supportsReturnType(MethodParameter returnType) {
return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class)
|| returnType.hasMethodAnnotation(ResponseBody.class));
}
@Override
public Object resolveArgument(
MethodParameter parameter,
@Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest,
@Nullable WebDataBinderFactory binderFactory) throws Exception {
}
@Override
protected <T> Object readWithMessageConverters(
NativeWebRequest webRequest,
MethodParameter parameter,
Type paramType)
throws IOException, HttpMediaTypeNotSupportedException,HttpMessageNotReadableException
{
}
@Override
public void handleReturnValue(
@Nullable Object returnValue,
MethodParameter returnType,
ModelAndViewContainer mavContainer,
NativeWebRequest webRequest)
throws IOException, HttpMediaTypeNotAcceptableException,HttpMessageNotWritableException {
}
|
相关接口的实现类总览
HandlerMethodArgumentResolver实现类
| 实现类 |
说明 |
| RequestParamMethodArgumentResolver |
支持带有@RequestParam注解的参数或带有MultipartFile类型的参数 |
| RequestParamMapMethodArgumentResolver |
支持带有@RequestParam注解的参数 && @RequestParam注解的属性value存在 && 参数类型是实现Map接口的属性 |
| PathVariableMethodArgumentResolver |
支持带有@PathVariable注解的参数 且如果参数实现了Map接口，@PathVariable注解需带有value属性 |
| MatrixVariableMethodArgumentResolver |
支持带有@MatrixVariable注解的参数 且如果参数实现了Map接口，@MatrixVariable注解需带有value属性 |
| RequestResponseBodyMethodProcessor |
本章已分析过 |
| ServletRequestMethodArgumentResolver |
参数类型是实现或继承或是WebRequest、ServletRequest、MultipartRequest、HttpSession、Principal、Locale、TimeZone、InputStream、Reader、HttpMethod这些类。（这就是为何我们在Controller中的方法里添加一个HttpServletRequest参数，Spring会为我们自动获得HttpServletRequest对象的原因） |
| ServletResponseMethodArgumentResolver |
参数类型是实现或继承或是ServletResponse、OutputStream、Writer这些类 |
| RedirectAttributesMethodArgumentResolver |
参数是实现了RedirectAttributes接口的类 |
| HttpEntityMethodProcessor |
参数类型是HttpEntity |
HandlerMethodReturnValueHandler实现类
| 实现类 |
说明 |
| ModelAndViewMethodReturnValueHandler |
返回值类型是ModelAndView或其子类 |
| ModelMethodProcessor |
返回值类型是Model或其子类 |
| ViewMethodReturnValueHandler |
返回值类型是View或其子类 |
| HttpHeadersReturnValueHandler |
返回值类型是HttpHeaders或其子类 |
| ModelAttributeMethodProcessor |
返回值有@ModelAttribute注解 |
| ViewNameMethodReturnValueHandler |
返回值是void或String |
接口总览小结
从名字我们也看的出来
- Resolver结尾的是实现了HandlerMethodArgumentResolver接口的类
- Handler结尾的是实现了HandlerMethodReturnValueHandler接口的类
- Processor结尾的是实现了HandlerMethodArgumentResolver和HandlerMethodReturnValueHandler的类
来源
https://www.cnblogs.com/fangjian0423/p/springMVC-request-param-analysis.html