省掉bean自定義spring mvc註解注入json值

註解hello(@JsonArg String msg)直接獲取body{"msg": "ok!"}中的ok!，不用定義一個bean來接收沒有的欄位。

JsonPathArgumentResolver.java

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.tianxia.server.util.Requests;
import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

import javax.servlet.http.HttpServletRequest;
import java.io.BufferedReader;
import java.io.IOException;

public class JsonPathArgumentResolver implements HandlerMethodArgumentResolver {

    private static final String JSONBODYATTRIBUTE = "JSON_REQUEST_BODY";

    private static final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.hasParameterAnnotation(JsonArg.class);
    }

    @Nullable
    @Override
    public Object resolveArgument(MethodParameter methodParameter, @Nullable ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, @Nullable WebDataBinderFactory webDataBinderFactory) throws Exception {
        String jsonBody = getRequestBody(nativeWebRequest);

        JsonNode rootNode = objectMapper.readTree(jsonBody);
        JsonNode node = rootNode.path(methodParameter.getParameterName());
        if (node.toString().equals("")) return null;
        return objectMapper.readValue(node.toString(), methodParameter.getParameterType());
    }

    private String getRequestBody(NativeWebRequest webRequest){
        HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);

        String jsonBody = (String) webRequest.getAttribute(JSONBODYATTRIBUTE, NativeWebRequest.SCOPE_REQUEST);
        if (jsonBody == null){
            jsonBody = Requests.readBody(servletRequest);
            webRequest.setAttribute(JSONBODYATTRIBUTE, jsonBody, NativeWebRequest.SCOPE_REQUEST);
        }
        return jsonBody;
    }

}

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WebConfig.java

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        resolvers.add(new JsonPathArgumentResolver());
    }
}
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