自定义HandlerMethodArgumentResolver，用Cookie组装一个简单的Pojo对象

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1. 概述

SpringMVC 为我们提供了@CookieValue 来注入 cookie 某一个 key 的值，但我们常需要@RequestBody 一样，把 Cookie 组装成一个 pojo 对象。
这篇教程将会演示我们怎样自定义一个 HandlerMethodArgumentResolver 完成从 Cookie 组装 pojo 对象的需求。

2. 自定义 HandlerMethodArgumentResolver

2.1 定义 Annotation

我们先定义一个 Annotation，叫 CookieObject。

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@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CookieObject {
}

2.2 实现 HandlerMethodArgumentResolver 接口

再定义个 CookieObjectMethodArgumentResolver 类，实现 HandlerMethodArgumentResolver 接口
HandlerMethodArgumentResolver 有两个 method.

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boolean supportsParameter(MethodParameter parameter);

返回 true/false,表示 resolver 是否支持处理该参数，我们将在他的实现里，判断参数是否携带@CookieObject.

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Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
  NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

组装参数的实现逻辑。

来，让我们看一下具体的实现

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public class CookieObjectMethodArgumentResolver implements HandlerMethodArgumentResolver {
    private String defaultEncoding = WebUtils.DEFAULT_CHARACTER_ENCODING;

    private String decodeInternal(HttpServletRequest request, String source) {
        String enc = determineEncoding(request);
        return UriUtils.decode(source, enc);
    }

    protected String determineEncoding(HttpServletRequest request) {
        String enc = request.getCharacterEncoding();
        if (enc == null) {
            enc = this.defaultEncoding;
        }
        return enc;
    }

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(CookieObject.class);
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);

        Class clazz = parameter.getParameterType();

        Object obj = clazz.newInstance();
        Cookie[] cookies = servletRequest.getCookies();
        if (cookies != null) {
            BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
            PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
            for (PropertyDescriptor property : propertyDescriptors) {
                Method setter = property.getWriteMethod();
                Class ppClazz = property.getPropertyType();
                if (setter != null) {
                    String propName = property.getName();
                    Cookie cooike = WebUtils.getCookie(servletRequest, propName);
                    if (cooike != null) {
                        String cookieValue = decodeInternal(servletRequest, cooike.getValue());
                        Object setValue = null;
                        if (Cookie.class.isAssignableFrom(ppClazz)) {
                            setValue = cookieValue;
                        } else if (cookieValue != null && binderFactory != null) {
                            WebDataBinder binder = binderFactory.createBinder(webRequest, null, propName);
                            setValue = binder.convertIfNecessary(cookieValue, ppClazz);
                        }
                        if (setValue != null) {
                            setter.invoke(obj, setValue);
                        }
                    }
                }
            }
        }
        return obj;
    }
}

2.3 加入 argumentResolvers 列表

最后再 SpringMVC 的配置中把我们定义的 CookieObjectMethodArgumentResolver 实例化后加入 argumentResolvers 列表。

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@Configuration
public class WebConfig extends WebMvcConfigurationSupport {
    @Override
    protected void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        CookieObjectMethodArgumentResolver cookieObjectMethodArgumentResolver = new CookieObjectMethodArgumentResolver()
        argumentResolvers.add(cookieObjectMethodArgumentResolver());
    }
}

3. 使用

3.1 定义一个 pojo

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@Data
@JsonIgnoreProperties(ignoreUnknown = true)
@EqualsAndHashCode(callSuper = false)
public class MyCookieParam  {
    private String foo;
    private String bar;
}

3.2 在 Controller 中接收

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@RequestMapping("/testCookieObject")
@ResponseBody
public String testCookieObject(@CookieObject MyCookieParam cookieParam) {
  return cookieParam
}