再次来回顾下Spring mvc的请求映射流程吧，首先，客户端发送请求被DispathcerServlet拦截，然后把请求作为参数调用handlerMappings找到对应的HandlerMapping得到Handler封装成HandlerExecutionChain对象返回给DispatcherServlet处理器。

1. HandlerMapping接口

接口定义如下

public interface HandlerMapping {

    String BEST_MATCHING_HANDLER_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingHandler";


    String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";


    String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";


    String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";


    String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";


    String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";

    String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";

    @Nullable
    HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;

}

从接口定义中可以发现，该接口只有一个抽象方法getHandler，返回参数为一个HandlerExecutionChain对象。

image.png

MatchableHandlerMapping接口通过继承HandlerMapping接口，增加了新的match抽象方法，

    @Nullable
    RequestMatchResult match(HttpServletRequest request, String pattern);

该方法作用是在确定给定的请求是否符合请求条件

2 Handler映射执行流程

image.png

获取到Handler对象后封装成HandlerExecutionChain对象的核心代码：

    protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));

        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
            if (interceptor instanceof MappedInterceptor) {
                MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            }
            else {
                chain.addInterceptor(interceptor);
            }
        }
        return chain;
    }

3. 自定义拦截器

实现拦截器的步骤：

1. 实现HandlerInterceptor 接口
2. 注册到Spring容器中

3.1 实现方案

HandlerInterceptor的接口定义如下:

public interface HandlerInterceptor {

    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        return true;
    }

    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            @Nullable ModelAndView modelAndView) throws Exception {
    }

    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
            @Nullable Exception ex) throws Exception {
    }
}

自定义拦截器必须实现该接口，下面自定义拦截器代码：

public class TestHandlerInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}

实现Springboot 自动配置拦截器

package com.joe.code.common.configuration;

import com.joe.code.common.component.TestResolver;
import com.joe.code.common.intercepter.TestHandlerInterceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.List;

// 注册resolver
@Configuration
public class WebConfiguration implements WebMvcConfigurer {

    @Autowired
    private ApplicationContext context;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new TestHandlerInterceptor());
    }
}