平常使用：SpringBoot自定义参数解析器

时间 2020-02-07

原文原文链接

SpringBoot自定义参数解析器

咱们都知道SpringMvc的Controller的方法上能够接收各类各样的参数，好比HttpServletRequest或HttpServletResponse，各类注解@RequestParam、@RequestHeader、@RequestBody、@PathVariable、@ModelAttribute，这些参数是从哪里获取的？java

这些参数都是由不一样的参数解析器为咱们解析出来的，能够解析类也能够解析带注解的类

咱们能够利用解析器解析自定义的参数(类、注解)，在咱们须要的传入的controller方法上传入它(不须要每次都要在方法内部经过request、response等参数作一系列操做来获取该类对象)

添加解析器

咱们想要自定义解析参数的时候咱们就须要经过更改SpringBoot的配置来添加本身实现的解析类

自定义配置类实现WebMvcConfigurer接口，重写其中的addArgumentResolvers方法来添加本身的解析类(经过自动注入的方法注入)web

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private SecKillUserArgumentResolvers secKillUserArgumentResolvers;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(secKillUserArgumentResolvers);
    }
}

实现自定义解析器

咱们自定义解析器须要实现HandlerMethodArgumentResolver处理器方法解析器接口，并实现其中的supportsParameter和resolveArgument方法

HandlerMethodArgumentResolver的接口定义以下：redis

（1）supportsParameter 用于判断是否支持对某种参数的解析(支持则返回true)cookie

（2）resolveArgument 将请求中的参数值解析为某种对象(具体的操做获取解析对象)app

下面这个自定义解析器用于获取User对象(经过token获取保存在redis中的user)，无需每次使用resquest和response在controller方法内部获取，能够直接获取到做为参数传入ide

/**
 * 自定义参数解析器
 * 解析每次都要获取的user自动传入，无需每次获取
 */
@Component
public class SecKillUserArgumentResolvers implements HandlerMethodArgumentResolver {

    @Autowired
    private UserService userService;

    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        Class<?> c = methodParameter.getParameterType();
        return c == User.class;
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        HttpServletRequest request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
        HttpServletResponse response = nativeWebRequest.getNativeResponse(HttpServletResponse.class);
        assert request != null;
        String paramToken = request.getParameter(UserServiceImpl.COOKIE_NAME_TOKEN);//COOKIE_NAME_TOKEN="token"
        String cookieToken = getCookieValue(request);
        if(StringUtils.isEmpty(cookieToken)&&StringUtils.isEmpty(paramToken)){//经过两种方式获取，若是都获取失败则返回null
            return null;
        }else {
            String token = StringUtils.isEmpty(paramToken)?cookieToken:paramToken;
            return UserService.getUserByToken(response,token);
        }
    }
//遍历cookie获取名称相同的那个cookie的值
    private String getCookieValue(HttpServletRequest request) {
        Cookie[] cookies = request.getCookies();
        for(Cookie cookie:cookies){
            if(cookie.getName().equals(SecKillUserServiceImpl.COOKIE_NAME_TOKEN)){
                return cookie.getValue();
            }
        }
        return null;
    }
}

到此，一个自定义参数解析器就实现好了，咱们能够经过传入参数的形式直接经过解析器帮咱们获取到

解析对象的使用

咱们在controller方法中传入该参数，能够直接为咱们获取到User对象

@RequestMapping("/to_list")
    public String toList(Model model,User user){
    }

Springboot中其余参数解析器

Model

咱们知道咱们能够传入Model对象参数就能够直接使用它，咱们看看它的参数解析器

ModelAttributeMethodProcessor类ui

public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(ModelAttribute.class) || this.annotationNotRequired && !BeanUtils.isSimpleProperty(parameter.getParameterType());
    }

    @Nullable
    public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
        Assert.state(mavContainer != null, "ModelAttributeMethodProcessor requires ModelAndViewContainer");
        Assert.state(binderFactory != null, "ModelAttributeMethodProcessor requires WebDataBinderFactory");
        String name = ModelFactory.getNameForParameter(parameter);
        ModelAttribute ann = (ModelAttribute)parameter.getParameterAnnotation(ModelAttribute.class);
        if (ann != null) {
            mavContainer.setBinding(name, ann.binding());
        }
        Object attribute = null;
        BindingResult bindingResult = null;
        if (mavContainer.containsAttribute(name)) {
            attribute = mavContainer.getModel().get(name);
        } else {
            try {
                attribute = this.createAttribute(name, parameter, binderFactory, webRequest);
            } catch (BindException var10) {
                if (this.isBindExceptionRequired(parameter)) {
                    throw var10;
                }
                if (parameter.getParameterType() == Optional.class) {
                    attribute = Optional.empty();
                }
                bindingResult = var10.getBindingResult();
            }
        }
        if (bindingResult == null) {
            WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
            if (binder.getTarget() != null) {
                if (!mavContainer.isBindingDisabled(name)) {
                    this.bindRequestParameters(binder, webRequest);
                }
                this.validateIfApplicable(binder, parameter);
                if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
                    throw new BindException(binder.getBindingResult());
                }
            }
            if (!parameter.getParameterType().isInstance(attribute)) {
                attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
            }
            bindingResult = binder.getBindingResult();
        }
        Map<String, Object> bindingResultModel = bindingResult.getModel();
        mavContainer.removeAttributes(bindingResultModel);
        mavContainer.addAllAttributes(bindingResultModel);
        return attribute;
    }

RequestParam

RequestParamMethodArgumentResolver类，基于注解的方式this

若是传入参数parameter上有该注解，则能够解析code

public boolean supportsParameter(MethodParameter parameter) {
        if (parameter.hasParameterAnnotation(RequestParam.class)) {
            if (!Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {
                return true;
            } else {
                RequestParam requestParam = (RequestParam)parameter.getParameterAnnotation(RequestParam.class);
                return requestParam != null && StringUtils.hasText(requestParam.name());
            }
        } else if (parameter.hasParameterAnnotation(RequestPart.class)) {
            return false;
        } else {
            parameter = parameter.nestedIfOptional();
            if (MultipartResolutionDelegate.isMultipartArgument(parameter)) {
                return true;
            } else {
                return this.useDefaultResolution ? BeanUtils.isSimpleProperty(parameter.getNestedParameterType()) : false;
            }
        }
    }

PathVariable

PathVariableMethodArgumentResolver类，也是基于注解，与RequestParam相似对象

public boolean supportsParameter(MethodParameter parameter) {
        if (!parameter.hasParameterAnnotation(PathVariable.class)) {
            return false;
        } else if (!Map.class.isAssignableFrom(parameter.nestedIfOptional().getNestedParameterType())) {
            return true;
        } else {
            PathVariable pathVariable = (PathVariable)parameter.getParameterAnnotation(PathVariable.class);
            return pathVariable != null && StringUtils.hasText(pathVariable.value());
        }
    }

基于注解自定义参数解析器

编写注解类，须要解析的类须要有此注解

@Target(value = ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface ParamModel {
}

实现解析器

public class MyArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.hasParameterAnnotation(ParamModel.class);//带有注解就解析
    }
    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer container,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) {
        //实现解析对象代码
    }

配置到WebMvcConfigurer

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private MyArgumentResolvers myArgumentResolvers;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(myArgumentResolvers);
    }
}