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package org.springframework.web.method.support;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;

/**
 * Strategy interface for resolving method parameters into argument values in
 * the context of a given request.
 *
 * @author Arjen Poutsma
 * @since 3.1
 * @see HandlerMethodReturnValueHandler
 */
public interface HandlerMethodArgumentResolver {

   /**
    * Whether the given {@linkplain MethodParameter method parameter} is
    * supported by this resolver.
    * @param parameter the method parameter to check
    * @return {@code true} if this resolver supports the supplied parameter;
    * {@code false} otherwise
    */
   boolean supportsParameter(MethodParameter parameter);

   /**
    * Resolves a method parameter into an argument value from a given request.
    * A {@link ModelAndViewContainer} provides access to the model for the
    * request. A {@link WebDataBinderFactory} provides a way to create
    * a {@link WebDataBinder} instance when needed for data binding and
    * type conversion purposes.
    * @param parameter the method parameter to resolve. This parameter must
    * have previously been passed to {@link #supportsParameter} which must
    * have returned {@code true}.
    * @param mavContainer the ModelAndViewContainer for the current request
    * @param webRequest the current request
    * @param binderFactory a factory for creating {@link WebDataBinder} instances
    * @return the resolved argument value, or {@code null} if not resolvable
    * @throws Exception in case of errors with the preparation of argument values
    */
   @Nullable
   Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
         NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

}

import lombok.Data;

/**
 * @author donghaibin
 */
@Data
public class User {

    private String name;

    private String age;
}

import org.springframework.core.MethodParameter;
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;

/**
 * @author donghaibin
 */
public class UserArgumentResolver implements HandlerMethodArgumentResolver {

    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        // isAssignableFrom·½·¨ÅжÏÀàÐÍÊÇ·ñΪ±¾Éí»òÕß×ÓÀà
        return methodParameter.getParameterType().isAssignableFrom(User.class);
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        // ÕâÀï²âÊÔÖ±½Ó¹¹½¨Ò»¸ö¶ÔÏó·µ»Ø
        User user = new User();
        user.setAge("18");
        user.setName("DHB");
        return user;
    }

}

import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.List;

/**
 * @author donghaibin
 */
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        // Ìí¼Ó½ø²ÎÊý½âÎöÆ÷¼¯ºÏ
        resolvers.add(new UserArgumentResolver());
    }
}

import cn.dhbin.test.config.User;
import cn.dhbin.test.config.UserFlag;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author donghaibin
 */
@RestController
@Slf4j
public class TestController {

    @RequestMapping("/test")
    public String test(String a, User user) {
        log.info(user.toString());
        return a;
    }
}

2019-07-18 23:47:14.535  INFO 44852 --- [nio-8080-exec-1] cn.dhbin.test.controller.TestController  : User(name=DHB, age=11)