Spring MVC系列（五）之自定义数据绑定---HandlerMethodArgumentResolver

介绍

      前面几节我们介绍了Spring MVC的几种常见的数据绑定的方法，可以灵活地获取用户请求中的参数，例如@PathVariable，@ModelAttribute，@RequestParam等这些数据绑定注解，有了这些注解，我们可以很方便的去获取参数，但是偶尔我们需要自定义的去进行数据绑定，Spring一直遵循开闭原则，可以让使用者自定义去做自己的事情，今天我们一起浅析一下HandlerMethodArgumentResolver

认识HandlerMethodArgumentResolver，我们可以看下HandlerMethodArgumentResolver的继承关系图

我们可以很清楚的看到我们常见的几个数据绑定的annotation的具体实现都是实现了HandlerMethodArgumentResolver这个接口，我们可以先尝试一下写一个demo，自定义annotation绑定一个数据

首先我们新建一个annotation-----CurrentUser  默认只能注解参数，且运行时有效:

package org.study.lyncc.web.resolver.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CurrentUser {

    
    String value() default "";

}

我们按照他的定义，自定义一个CurrentUserHandlerMethodArgumentResolver实现HandlerMethodArgumentResolver：

package org.study.lyncc.web.resolver;

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;
import org.study.lyncc.web.entity.User;
import org.study.lyncc.web.resolver.annotation.CurrentUser;

public class CurrentUserHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver{

    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(CurrentUser.class);
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        return new User(1,"lyncc");
    }

}

这边只是一个简单的demo，默认返回一个user，这样，我们写个controller来测试一下

package org.study.lyncc.web.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
import org.study.lyncc.web.entity.User;
import org.study.lyncc.web.resolver.annotation.CurrentUser;

@Controller
@RequestMapping(value="/data/binding")
public class CostomDataBindingController {
    
    @RequestMapping(value="/test")
    public ModelAndView costomData(@CurrentUser User u){
        System.out.println(u.getUsername());
        ModelAndView mav = new ModelAndView("session");
        return mav;
    }

}

我们写了一个测试方法，costomData中间的入参是User，前面加了我们自定义的注解@CurrentUser，这样此处的User应该就是我们在CurrentUserHandlerMethodArgumentResolver中resolveArgument方法返回的对象了

不过我们还需要让spring容器加载我们自定义的数据绑定的类CurrentUserHandlerMethodArgumentResolver，我们修改一下我们spring mvc的配置文件spring-servlet.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc.xsd">
       
     <!-- 基于注解驱动 -->
    <mvc:annotation-driven>
       <mvc:argument-resolvers>  
            <bean class="org.study.lyncc.web.resolver.CurrentUserHandlerMethodArgumentResolver"/>  
        </mvc:argument-resolvers>  
    </mvc:annotation-driven>
	
	<!-- 默认spring的扫描包， 此处指定处理扫描org.study.lyncc.web.controller包下的类有@Controller注解的-->
	 <context:component-scan base-package="org.study.lyncc.web.controller" >
    	<context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" /> 
    </context:component-scan>  
	
	<!-- 静态资源的处理 -->
	<mvc:resources mapping="/fonts/**" location="/WEB-INF/fonts/"/>
	<mvc:resources mapping="/js/**" location="/WEB-INF/js/"/>

     <!--视图解析器  -->
    <bean id="viewResolver"  
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">  
        <property name="prefix" value="/WEB-INF/jsp/"></property>  
        <property name="suffix" value=".jsp"></property>  
    </bean> 
    
</beans>

在<mvc:annotation-driven>中加入我们的自定义的类的全路径

启动spring mvc 浏览器中输入：http://localhost:8080/spring-mvc/data/binding/test，发现在控制台中正常打印了

好了，我们再举一个例子，加入我们的url是http://localhost:8080/spring-mvc/data/binding/custom?names=lyncc,fly,ted&ids=1,2,3，我们想要在后台直接获取一个List<User>

也就说我们可以提前转化

同样我们定义一个annotation

package org.study.lyncc.web.resolver.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


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

    String value() default "";
}

ManyUserHandlerMethodArgumentResolver

package org.study.lyncc.web.resolver;

import java.util.ArrayList;
import java.util.List;

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;
import org.study.lyncc.web.entity.User;
import org.study.lyncc.web.resolver.annotation.ManyUser;

public class ManyUserHandlerMethodArgumentResolver implements HandlerMethodArgumentResolver{

    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(ManyUser.class);
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        List<User> users = new ArrayList<User>();
        String names = (String)webRequest.getParameter("names");
        String ids = (String)webRequest.getParameter("ids");
        if(null != names && null != ids){
            String[] nameStrs = names.trim().split(",");
            String[] idStrs = ids.trim().split(",");
            for(int i = 0;i<nameStrs.length;i++){
                User user = new User(Integer.parseInt(idStrs[i]), nameStrs[i]);
                users.add(user);
            }
        }
        return users;
    }

}

测试controller

package org.study.lyncc.web.controller;

import java.util.List;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
import org.study.lyncc.web.entity.User;
import org.study.lyncc.web.resolver.annotation.CurrentUser;
import org.study.lyncc.web.resolver.annotation.ManyUser;

@Controller
@RequestMapping(value="/data/binding")
public class CostomDataBindingController {
    
    @RequestMapping(value="/test")
    public ModelAndView costomData(@CurrentUser User u){
        System.out.println(u.getUsername());
        ModelAndView mav = new ModelAndView("session");
        return mav;
    }
    
    @RequestMapping(value="/custom")
    public ModelAndView customData1(@ManyUser List<User> users){
        if(null != users && !users.isEmpty()){
            for(User u : users){
                System.out.println(u);
            }
        }
        ModelAndView mav = new ModelAndView("session");
        return mav;
    }

    
}

别忘记修改spring-servlet.xml

  <mvc:annotation-driven>
       <mvc:argument-resolvers>  
            <bean class="org.study.lyncc.web.resolver.CurrentUserHandlerMethodArgumentResolver"/>
            <bean class="org.study.lyncc.web.resolver.ManyUserHandlerMethodArgumentResolver"/>  
        </mvc:argument-resolvers>  
    </mvc:annotation-driven>

启动项目，输入http://localhost:8080/spring-mvc/data/binding/custom?names=lyncc,fly,ted&ids=1,2,3