Content type 'application/x-www-form-urlencoded;charset=UTF-8' not supported

摘要： 前端form表單資料提交時，後端出現 Resolved [org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/x-www-form-urlencoded;chars...

前端form表單資料提交時，後端出現 Resolved [org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/x-www-form-urlencoded;charset=UTF-8' not supported] 這樣的提示，也沒有觸發Controller的響應方法。

A: 第一種解決辦法

ajax請求的時候，把Content-Type，設定為 application/json; charset=utf-8

A: 第二種解決辦法

自定義引數解析器：

1. 首先定義註解

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
public @interface P {
// ...
}
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2. 自定義引數解析器的實現

public class Form2PojoArgumentResolver implements HandlerMethodArgumentResolver
{
@Override
public boolean supportsParameter(MethodParameter parameter)
{
return parameter.hasParameterAnnotation(P.class);
}

@Nullable
@Override
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception
{
// 返回對應的引數型別的資料
}
}
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3. 配置引數解析器

@Configuration
public class ArgumentResolversConfig implements WebMvcConfigurer
{
@Override
public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers)
{
resolvers.add(new Form2PojoArgumentResolver());
}
}
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4. 相應的控制器的方法中

public class TestController 
{
@RequestMapping("xxx")
public testArgumentResolver(@P TestEntity entity) 
{
// ...
}
}
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通常情況下，前端form表單的資料到Controller中時就轉換成的物件。但是我這裡出現了特殊情形。 由於我的TestEntity實現了Map介面，而Spring Boot在啟動時會自動載入一系列的解析器，而這些解析其中有一個叫 MapMethodProcessor 的處理器，它的 supportsParameter 方法是這樣實現的：

@Override
public boolean supportsParameter(MethodParameter parameter) {
return Map.class.isAssignableFrom(parameter.getParameterType());
}
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這就導致了，在呼叫獲取方法引數的方法時（即呼叫 InvocableHandlerMethod.java 中的 getMethodArgumentValues 時）直接使用了 MapMethodProcessor 引數解析器（處理器），而自定義的引數解析器並沒有被呼叫。

翻了一下 HandlerMethodArgumentResolverComposite.java 的原始碼，引數解析器的選取是順序遍歷的，原始碼如下:

/**
 * Find a registered {@link HandlerMethodArgumentResolver} that supports the given method parameter.
 */
@Nullable
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
// 遍歷引數解析器，尋找符合要求的
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;
}
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又翻了一下 RequestMappingHandlerAdapter.java 的原始碼，引數解析器的載入順序是這個樣子的：

/**
 * Return the list of argument resolvers to use including built-in resolvers
 * and custom resolvers provided via {@link #setCustomArgumentResolvers}.
 */
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();

// 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());
// 臥槽，你在這兒啊
resolvers.add(new MapMethodProcessor());
resolvers.add(new ErrorsMethodArgumentResolver());
resolvers.add(new SessionStatusMethodArgumentResolver());
resolvers.add(new UriComponentsBuilderMethodArgumentResolver());

// Custom arguments
// 媽蛋，我在這兒
if (getCustomArgumentResolvers() != null) {
resolvers.addAll(getCustomArgumentResolvers());
}

// Catch-all
resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
resolvers.add(new ServletModelAttributeMethodProcessor(true));

return resolvers;
}
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好吧，怪不得輪不到自定義的引數解析器來處理。既然如此，那我改變一下自定義引數解析器的載入順序吧————渣渣我要騎到你們頭上去！

@Configuration
public class ArgumentResolversConfig
{
@Autowired
private RequestMappingHandlerAdapter adapter;

@PostConstruct
public void injectSelfMethodArgumentResolver() 
{
List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>();
argumentResolvers.add(new Form2PojoArgumentResolver());
argumentResolvers.addAll(adapter.getArgumentResolvers());
adapter.setArgumentResolvers(argumentResolvers);
}
}
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好了，如此，完美的解決了上述問題。

這個Bug就聊到這兒吧。