Role of handlermethodargumentresolver + use case

Preface
I encountered a parameter resolution problem when I was working on the project today HandlerMethodArgumentResolver Doubts about the use of . I want to be a novice here to communicate with you and record . Next, the train starts to leave ......

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First, let's get to know the interface ,HandlerMethodArgumentResolver.

public interface HandlerMethodArgumentResolver {
    boolean supportsParameter(MethodParameter var1);
 
    Object resolveArgument(MethodParameter var1, ModelAndViewContainer var2, NativeWebRequest var3, WebDataBinderFactory var4) throws Exception;
}
You can see , This interface has two methods ,supportsParameter and resolveArgument.

Method supportsParameter Well understood. , The return value is boolean type , Its function is to judge Controller Parameters in layer , Whether the conditions are met , If the conditions are met, execute resolveArgument Method , If you are not satisfied, skip .

and resolveArgument Methods? , It's only in supportsParameter Method returns true It will be called . Used to handle some business , Assign return value to Controller This parameter in the layer .

So? , We can HandlerMethodArgumentResolver Understood as a parameter parser , We can implement... By writing a class HandlerMethodArgumentResolver Interface to implement Controller Modification of method parameters in layer .

Example of project code
When the parameter parser is not used Controller controller ：

@Controller
@RequestMapping("/goods")
public class GoodsController {
    private static Logger logger = LoggerFactory.getLogger(GoodsController.class);
    @Autowired
    UserService userService;
    @RequestMapping("/to_list")
    public String to_login(Model model,HttpServletResponse response,
                        @CookieValue(value=UserService.TOKEN,required = false)String cookieToken,
                        @RequestParam(value = UserService.TOKEN,required = false) String paramToken) {
        if(StringUtils.isEmpty(cookieToken)&&StringUtils.isEmpty(paramToken)){
            return "login";
        }
        String token = StringUtils.isEmpty(cookieToken) ? paramToken : cookieToken;
        User user=userService.getByToken(response,token);
        logger.info(user.toString());
        model.addAttribute("user",user);
        return "goods_list";
    }
}
Please look carefully to_login Method  cookieToken and paramToken, Take a closer look at the lower body of Dharma . It's not hard to see. , The two parameters and the statement code in the method body are for , adopt cookie or request Among them token This variable is used to query the user user Information about .

But we didn't find it , This method , Just for this simple little function , Just wrote so much code . Is it a little too bloated ？ And if there are other ways to use the user user This information variable ？

well , At this time we can use HandlerMethodArgumentResolver Interface to perform a small optimization .

Use HandlerMethodArgumentResolver After the parser ：

Write a class implementation HandlerMethodArgumentResolver Interface

 
@Service
public class UserArgumentResolver implements HandlerMethodArgumentResolver {
    @Autowired
    MiaoshaUserService userService;
    public boolean supportsParameter(MethodParameter parameter) {
        Class<?> clazz = parameter.getParameterType();
        return clazz==MiaoshaUser.class;
    }
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
 
        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
 
        String paramToken = request.getParameter(MiaoshaUserService.COOKI_NAME_TOKEN);
        String cookieToken = getCookieValue(request, MiaoshaUserService.COOKI_NAME_TOKEN);
        if(StringUtils.isEmpty(cookieToken) && StringUtils.isEmpty(paramToken)) {
            return null;
        }
        String token = StringUtils.isEmpty(paramToken)?cookieToken:paramToken;
        return userService.getByToken(response, token);
    }
    private String getCookieValue(HttpServletRequest request, String cookiName) {
        Cookie[]  cookies = request.getCookies();
        for(Cookie cookie : cookies) {
            if(cookie.getName().equals(cookiName)) {
                return cookie.getValue();
            }
        }
        return null;
    }
}
Put the class we wrote , Register in the configuration file

@Configuration
public class WebConfig  extends WebMvcConfigurerAdapter{
    @Autowired
    UserArgumentResolver userArgumentResolver;
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(userArgumentResolver);
    }
}
Last , Our control class can be written like this

    @RequestMapping("/to_list")
    public String list(Model model,MiaoshaUser user) {
        model.addAttribute("user", user);
        // Query product list
        List<GoodsVo> goodsList = goodsService.listGoodsVo();
        model.addAttribute("goodsList", goodsList);
        return "goods_list";
    }
 
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Link to the original text ：https://blog.csdn.net/qq_36408229/article/details/104436508