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;我们按照他的定义，自定义一个CurrentUserHandlerMethodArgumentResolver实现HandlerMethodArgumentResolver：
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 "";
}
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;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
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;
}
}
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"在<mvc:annotation-driven>中加入我们的自定义的类的全路径
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>
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;ManyUserHandlerMethodArgumentResolver
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 "";
}
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;别忘记修改spring-servlet.xml
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;
}
}
<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
<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>
