PROSAGA码农传奇-策略引擎-在Spring Boot中使用Gson配置snake

<div class =“post-text”itemprop =“text”>
  <P>
    这是一个很好的问题。如果我了解Spring MVC如何在幕后工作，则不使用HTTP转换器
     <code>
      @ModelAttribute
    </code>
    驱动的。当您从中获取异常时，可以轻松检查它
     <code>
      ExampleParam
    </code>
     构造函数或
     <code>
      ExampleParam.setCamelCase
    </code>
     方法（de-Lombok first） -  Spring使用它的bean实用程序
     <code>
      public
    </code>
     （！）
     <code>
      ExampleParam.setCamelCase
    </code>
     设置DTO值。另一个证明是没有
     <code>
      Gson.fromJson
    </code>
     无论您的Gson转换器配置如何，都不会调用。所以，你的
     <code>
      camelCase
    </code>
     让你感到困惑，因为默认的Gson实例和Spring一样使用这个策略 - 所以这只是一个混乱的问题。
  </p>
  <P>
    为了使其工作，您必须创建自定义Gson感知
     <code>
      HandlerMethodArgumentResolver
    </code>
     实现。假设我们只支持POJO（不是列表，地图或基元）。
  </p>
   <pre class="lang-java prettyprint-override">
    <code>
      @Configuration
@EnableWebMvc
class WebMvcConfiguration
        extends WebMvcConfigurerAdapter {

private static final Gson gson = new GsonBuilder()
            .setFieldNamingPolicy(LOWER_CASE_WITH_UNDERSCORES)
            .create();

@Override
    public void addArgumentResolvers(final List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(new HandlerMethodArgumentResolver() {
            @Override
            public boolean supportsParameter(final MethodParameter parameter) {
                // It must be never a primitive, array, string, boxed number, map or list -- and whatever you configure ;)
                final Class<?> parameterType = parameter.getParameterType();
                return !parameterType.isPrimitive()
                        && !parameterType.isArray()
                        && parameterType != String.class
                        && !Number.class.isAssignableFrom(parameterType)
                        && !Map.class.isAssignableFrom(parameterType)
                        && !List.class.isAssignableFrom(parameterType);
            }

@Override
            public Object resolveArgument(final MethodParameter parameter, final ModelAndViewContainer mavContainer, final NativeWebRequest webRequest,
                    final WebDataBinderFactory binderFactory) {
                // Now we're deconstructing the request parameters creating a JSON tree, because Gson can convert from JSON trees to POJOs transparently
                // Also note parameter.getGenericParameterType() -- it's better that Class<?> that cannot hold generic types parameterization
                return gson.fromJson(
                        parameterMapToJsonElement(webRequest.getParameterMap()),
                        parameter.getGenericParameterType()
                );
            }
        });
    }

...

private static JsonElement parameterMapToJsonElement(final Map<String, String[]> parameters) {
        final JsonObject jsonObject = new JsonObject();
        for ( final Entry<String, String[]> e : parameters.entrySet() ) {
            final String key = e.getKey();
            final String[] value = e.getValue();
            final JsonElement jsonValue;
            switch ( value.length ) {
            case 0:
                // As far as I understand, this must never happen, but I'm not sure
                jsonValue = JsonNull.INSTANCE;
                break;
            case 1:
                // If there's a single value only, let's convert it to a string literal
                // Gson is good at "weak typing": strings can be parsed automatically to numbers and booleans
                jsonValue = new JsonPrimitive(value[0]);
                break;
            default:
                // If there are more than 1 element -- make it an array
                final JsonArray jsonArray = new JsonArray();
                for ( int i = 0; i < value.length; i++ ) {
                    jsonArray.add(value[i]);
                }
                jsonValue = jsonArray;
                break;
            }
            jsonObject.add(key, jsonValue);
        }
        return jsonObject;
    }

}

</code>
  </pre>
  <P>
    那么，结果如下：
  </p>
  <UL>
    <LI>
       <code>
        http://localhost:8080/?camelCase=hello
      </code>
       =＆GT;
      <EM>
        （空）
      </EM>
    </LI>
    <LI>
       <code>
        http://localhost:8080/?camel_case=hello
      </code>
       =＆GT;
       <code>
        "hello"
      </code>
    </LI>
  </UL>
</DIV>

在Spring Boot中使用Gson配置snake_case查询参数