Spring拦截器HandlerInterceptor

前言

本文风格类似 模仿SpringSecurity自定义过滤器链

首先我们看下源码, 然后手写模拟练习

如何看源码实现

1. 首先debug调试是最简单的学习途径, 我们先定义一个拦截器

package com.example.demoboot.handler;

import org.springframework.lang.Nullable;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author cuishiying
 * @date 2021-01-22
 */
@Component
public class DemoInterceptor implements HandlerInterceptor {


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

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
        System.out.println("afterHandle");
    }
}

2. 注册拦截器

package com.example.demoboot.handler;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

/**
 * @author cuishiying
 * @date 2021-01-22
 */
@Configuration
public class InterceptorConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // 如果有多个拦截器，继续registry.add往下添加就可以啦
        registry.addInterceptor(new DemoInterceptor()).addPathPatterns("/**");
    }

}

3. 在 preHandle 方法中打断点, 服务启动后请求任何uri, 即可进入查看调用链. 首先会进入类 HandlerExecutionChain 中的 applyPreHandle 方法

/*
 * Copyright 2002-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet;

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

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;

/**
 * Handler execution chain, consisting of handler object and any handler interceptors.
 * Returned by HandlerMapping's {@link HandlerMapping#getHandler} method.
 *
 * @author Juergen Hoeller
 * @since 20.06.2003
 * @see HandlerInterceptor
 */
public class HandlerExecutionChain {

    private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);

    private final Object handler;

    @Nullable
    private HandlerInterceptor[] interceptors;

    @Nullable
    private List<HandlerInterceptor> interceptorList;

    private int interceptorIndex = -1;


    /**
     * Create a new HandlerExecutionChain.
     * @param handler the handler object to execute
     */
    public HandlerExecutionChain(Object handler) {
        this(handler, (HandlerInterceptor[]) null);
    }

    /**
     * Create a new HandlerExecutionChain.
     * @param handler the handler object to execute
     * @param interceptors the array of interceptors to apply
     * (in the given order) before the handler itself executes
     */
    public HandlerExecutionChain(Object handler, @Nullable HandlerInterceptor... interceptors) {
        if (handler instanceof HandlerExecutionChain) {
            HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
            this.handler = originalChain.getHandler();
            this.interceptorList = new ArrayList<>();
            CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
            CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
        }
        else {
            this.handler = handler;
            this.interceptors = interceptors;
        }
    }


    /**
     * Return the handler object to execute.
     */
    public Object getHandler() {
        return this.handler;
    }

    /**
     * Add the given interceptor to the end of this chain.
     */
    public void addInterceptor(HandlerInterceptor interceptor) {
        initInterceptorList().add(interceptor);
    }

    /**
     * Add the given interceptor at the specified index of this chain.
     * @since 5.2
     */
    public void addInterceptor(int index, HandlerInterceptor interceptor) {
        initInterceptorList().add(index, interceptor);
    }

    /**
     * Add the given interceptors to the end of this chain.
     */
    public void addInterceptors(HandlerInterceptor... interceptors) {
        if (!ObjectUtils.isEmpty(interceptors)) {
            CollectionUtils.mergeArrayIntoCollection(interceptors, initInterceptorList());
        }
    }

    private List<HandlerInterceptor> initInterceptorList() {
        if (this.interceptorList == null) {
            this.interceptorList = new ArrayList<>();
            if (this.interceptors != null) {
                // An interceptor array specified through the constructor
                CollectionUtils.mergeArrayIntoCollection(this.interceptors, this.interceptorList);
            }
        }
        this.interceptors = null;
        return this.interceptorList;
    }

    /**
     * Return the array of interceptors to apply (in the given order).
     * @return the array of HandlerInterceptors instances (may be {@code null})
     */
    @Nullable
    public HandlerInterceptor[] getInterceptors() {
        if (this.interceptors == null && this.interceptorList != null) {
            this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[0]);
        }
        return this.interceptors;
    }


    /**
     * Apply preHandle methods of registered interceptors.
     * @return {@code true} if the execution chain should proceed with the
     * next interceptor or the handler itself. Else, DispatcherServlet assumes
     * that this interceptor has already dealt with the response itself.
     */
    boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = 0; i < interceptors.length; i++) {
                HandlerInterceptor interceptor = interceptors[i];
                if (!interceptor.preHandle(request, response, this.handler)) {
                    triggerAfterCompletion(request, response, null);
                    return false;
                }
                this.interceptorIndex = i;
            }
        }
        return true;
    }

    /**
     * Apply postHandle methods of registered interceptors.
     */
    void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
            throws Exception {

        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = interceptors.length - 1; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                interceptor.postHandle(request, response, this.handler, mv);
            }
        }
    }

    /**
     * Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
     * Will just invoke afterCompletion for all interceptors whose preHandle invocation
     * has successfully completed and returned true.
     */
    void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
            throws Exception {

        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = this.interceptorIndex; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                try {
                    interceptor.afterCompletion(request, response, this.handler, ex);
                }
                catch (Throwable ex2) {
                    logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
                }
            }
        }
    }

    /**
     * Apply afterConcurrentHandlerStarted callback on mapped AsyncHandlerInterceptors.
     */
    void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = interceptors.length - 1; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                if (interceptor instanceof AsyncHandlerInterceptor) {
                    try {
                        AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptor;
                        asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
                    }
                    catch (Throwable ex) {
                        if (logger.isErrorEnabled()) {
                            logger.error("Interceptor [" + interceptor + "] failed in afterConcurrentHandlingStarted", ex);
                        }
                    }
                }
            }
        }
    }


    /**
     * Delegates to the handler's {@code toString()} implementation.
     */
    @Override
    public String toString() {
        Object handler = getHandler();
        StringBuilder sb = new StringBuilder();
        sb.append("HandlerExecutionChain with [").append(handler).append("] and ");
        if (this.interceptorList != null) {
            sb.append(this.interceptorList.size());
        }
        else if (this.interceptors != null) {
            sb.append(this.interceptors.length);
        }
        else {
            sb.append(0);
        }
        return sb.append(" interceptors").toString();
    }

}

4. 继续向上看即可看到 DispatcherServlet 中的 doDispatch 在调用

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
                // Clean up any resources used by a multipart request.
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

参考

• https://blog.csdn.net/ooiuy450/article/details/70054613
• https://mp.weixin.qq.com/s/gXCog_DxNjpMnYX9IpF6TQ
• https://zhuanlan.zhihu.com/p/47324985