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HandlerMethodArgumentResolver使用和原理
2020-11-07 17:19:00 【Lbj虞】
HandlerMethodArgumentResolver 用于将方法参数解析为参数值的策略接口,我们常说的自定义参数解析器,源码如下
/**
* Strategy interface for resolving method parameters into argument values in
* the context of a given request.
*
* @author Arjen Poutsma
* @since 3.1
* @see HandlerMethodReturnValueHandler
*/
public interface HandlerMethodArgumentResolver {
/**
* Whether the given {@linkplain MethodParameter method parameter} is
* supported by this resolver.
* @param parameter the method parameter to check
* @return {@code true} if this resolver supports the supplied parameter;
* {@code false} otherwise
*/
boolean supportsParameter(MethodParameter parameter);
/**
* Resolves a method parameter into an argument value from a given request.
* A {@link ModelAndViewContainer} provides access to the model for the
* request. A {@link WebDataBinderFactory} provides a way to create
* a {@link WebDataBinder} instance when needed for data binding and
* type conversion purposes.
* @param parameter the method parameter to resolve. This parameter must
* have previously been passed to {@link #supportsParameter} which must
* have returned {@code true}.
* @param mavContainer the ModelAndViewContainer for the current request
* @param webRequest the current request
* @param binderFactory a factory for creating {@link WebDataBinder} instances
* @return the resolved argument value, or {@code null} if not resolvable
* @throws Exception in case of errors with the preparation of argument values
*/
@Nullable
Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
}
下面是我的一个小例子,主要是通过自定义参数解析器去将分页参数,提取出来封装成实体对象
1.首先自定义一个注解
/**
* @Author: 虞云波(18088704)
* @Date: 2020/11/7 10:18
* @Description:
*/
@Target(ElementType.PARAMETER)
@Inherited
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface CustomArgumentPage {
}
2.写一个自定义参数解析器实现类
import com.suning.logistics.jwms.on.base.vo.PageBean;
import org.apache.commons.lang3.StringUtils;
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 javax.servlet.http.HttpServletRequest;
/**
* @Author: 虞云波(18088704)
* @Date: 2020/11/7 10:14
* @Description:
*/
public class CustomArgumentResolvers implements HandlerMethodArgumentResolver {
@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(CustomArgumentPage.class);
}
@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
String page = request.getParameter("page");
String pageSize = request.getParameter("pageSize");
PageBean pageBean = new PageBean();
if (StringUtils.isNotEmpty(page)) {
pageBean.setCurrentPage(Integer.valueOf(page).intValue());
}
if (StringUtils.isNotEmpty(pageSize)) {
pageBean.setPageSize(Integer.valueOf(pageSize).intValue());
}
pageBean.setStartPage((pageBean.getCurrentPage()-1)*pageBean.getPageSize());
return pageBean;
}
}
3.将自定义解析器注入到IOC 中
@Bean
public CustomArgumentResolvers initCustomArgumentResolvers(){
return new CustomArgumentResolvers();
}
4.将自定义的参数解析器,注入到MvcConfigure中
@Configuration
public class WebMvcCustomConfigurer implements WebMvcConfigurer {
@Autowired
private CustomArgumentResolvers customArgumentResolvers;
/**
* Add resolvers to support custom controller method argument types.
* <p>This does not override the built-in support for resolving handler
* method arguments. To customize the built-in support for argument
* resolution, configure {@link RequestMappingHandlerAdapter} directly.
*
* @param resolvers initially an empty list
*/
@Override
public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
resolvers.add(customArgumentResolvers);
}
}
5.编写测试Controller
@RequestMapping("/queryPageConfigList")
@ResponseBody
public Object getWarehouseCodeReadyonly(@CustomArgumentPage PageBean pageBean){
return warehouseConfigService.queryPage(pageBean,null);
}
6.效果如下
下面源码分析一波,讲述一下整个流程,
1.在Springboot AutoConfiguration 会自动注入 WebMvcAutoConfiguration
2.在WebMvcAutoConfiguration 中 静态内部类 EnableWebMvcConfiguration它继承了DelegatingWebMvcConfiguration这个类,这个很重要,中的 requestMappingHandlerAdapter方法,初始化HandlerAdapter
super.requestMappingHandlerAdapter()
3.在父类WebMvcConfigurationSupport 中,如下图 565行代码,会给HandlerAdapter 设置自定义的参数解析器
4.进入getArgumentResolvers方法,核心方法 addArgumentResolvers
5.是个空方法???,源码跟踪是进入了其子类 DelegatingWebMvcConfiguration 这个类中
6.继续代码跟踪下一步,会到WebMvcConfigurerComposite 中addArgumentResolvers 方法,会循环WebMvcConfigurer List 调用里面的 addArgumentResolvers 至于这个this.delegates 怎么初始化的,你们可以自己研究一下
7.最终调到我们自定义的WebMvcCustomConfigurer 中,将我们自定义的参数解析器,添加到整个参数解析List中
8.将数参数解析List 设置到HandlerAdapter 中
9.调用的时候,整个调用链如下图,刚兴趣的同学可以自己去分析一下
版权声明
本文为[Lbj虞]所创,转载请带上原文链接,感谢
https://my.oschina.net/u/3195939/blog/4707620
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