通用接口开放平台设计与实现——（31）API服务线程安全问题确认与修复

背景

在本系列的前面一篇博客评论中，有小伙伴指出，API服务存在线程安全问题：

https://blog.csdn.net/seawaving/article/details/122905199#comments_34477405

今天来确认下，线程是否安全？如不安全，如何修复？

‍

回顾

先来回顾下先前的实现，可能存在线程安全的是自己实现的过滤器链，如下：

package tech.abc.platform.cip.api.framework;


import tech.abc.platform.cip.common.entity.ApiRequest;
import tech.abc.platform.cip.common.entity.ApiResponse;

import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * API服务过滤器链条
 *
 * @author wqliu
 * @date 2022-2-12
 **/
public class ApiFilterChain {

    /**
     * 请求
     */
    private ApiRequest request;

    /**
     * 响应
     */
    private ApiResponse response = new ApiResponse();


    /**
     * 过滤器集合
     */
    private final List<ApiFilter> filters;

    /**
     * 过滤器迭代器
     */
    private Iterator<ApiFilter> iterator;

    public ApiFilterChain() {
        filters = Collections.EMPTY_LIST;
    }

    public ApiFilterChain(ApiFilter... filters) {
        this.filters = Arrays.asList(filters);

    }


    /**
     * 获取请求
     *
     * @return {@link ApiRequest}
     */
    public ApiRequest getRequest() {
        return this.request;
    }

    /**
     * 获取响应
     *
     * @return {@link ApiResponse}
     */
    public ApiResponse getResponse() {
        return this.response;
    }


    /**
     * 执行过滤
     *
     * @param request  请求
     * @param response 响应
     */
    public void doFilter(ApiRequest request, ApiResponse response) {
        // 如迭代器为空，则初始化
        if (this.iterator == null) {
            this.iterator = this.filters.iterator();
        }

        // 集合中还有过滤器，则继续往下传递
        if (this.iterator.hasNext()) {
            ApiFilter nextFilter = this.iterator.next();
            nextFilter.doFilter(request, response, this);
        }

        // 将处理结果更新到属性中
        this.request = request;
        this.response = response;
    }


    /**
     * 重置
     */
    public void reset() {
        this.request = null;
        this.response = null;
        this.iterator = null;
    }

}

该类是参照官方的MockFilterChain实现的，源码如下：

/*
 * Copyright 2002-2018 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.mock.web;

import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

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

/**
 * Mock implementation of the {@link javax.servlet.FilterChain} interface.
 *
 * <p>A {@link MockFilterChain} can be configured with one or more filters and a
 * Servlet to invoke. The first time the chain is called, it invokes all filters
 * and the Servlet, and saves the request and response. Subsequent invocations
 * raise an {@link IllegalStateException} unless {@link #reset()} is called.
 *
 * @author Juergen Hoeller
 * @author Rob Winch
 * @author Rossen Stoyanchev
 * @since 2.0.3
 * @see MockFilterConfig
 * @see PassThroughFilterChain
 */
public class MockFilterChain implements FilterChain {

    @Nullable
    private ServletRequest request;

    @Nullable
    private ServletResponse response;

    private final List<Filter> filters;

    @Nullable
    private Iterator<Filter> iterator;


    /**
     * Register a single do-nothing {@link Filter} implementation. The first
     * invocation saves the request and response. Subsequent invocations raise
     * an {@link IllegalStateException} unless {@link #reset()} is called.
     */
    public MockFilterChain() {
        this.filters = Collections.emptyList();
    }

    /**
     * Create a FilterChain with a Servlet.
     * @param servlet the Servlet to invoke
     * @since 3.2
     */
    public MockFilterChain(Servlet servlet) {
        this.filters = initFilterList(servlet);
    }

    /**
     * Create a {@code FilterChain} with Filter's and a Servlet.
     * @param servlet the {@link Servlet} to invoke in this {@link FilterChain}
     * @param filters the {@link Filter}'s to invoke in this {@link FilterChain}
     * @since 3.2
     */
    public MockFilterChain(Servlet servlet, Filter... filters) {
        Assert.notNull(filters, "filters cannot be null");
        Assert.noNullElements(filters, "filters cannot contain null values");
        this.filters = initFilterList(servlet, filters);
    }

    private static List<Filter> initFilterList(Servlet servlet, Filter... filters) {
        Filter[] allFilters = ObjectUtils.addObjectToArray(filters, new ServletFilterProxy(servlet));
        return Arrays.asList(allFilters);
    }


    /**
     * Return the request that {@link #doFilter} has been called with.
     */
    @Nullable
    public ServletRequest getRequest() {
        return this.request;
    }

    /**
     * Return the response that {@link #doFilter} has been called with.
     */
    @Nullable
    public ServletResponse getResponse() {
        return this.response;
    }

    /**
     * Invoke registered {@link Filter Filters} and/or {@link Servlet} also saving the
     * request and response.
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
        Assert.notNull(request, "Request must not be null");
        Assert.notNull(response, "Response must not be null");
        Assert.state(this.request == null, "This FilterChain has already been called!");

        if (this.iterator == null) {
            this.iterator = this.filters.iterator();
        }

        if (this.iterator.hasNext()) {
            Filter nextFilter = this.iterator.next();
            nextFilter.doFilter(request, response, this);
        }

        this.request = request;
        this.response = response;
    }

    /**
     * Reset the {@link MockFilterChain} allowing it to be invoked again.
     */
    public void reset() {
        this.request = null;
        this.response = null;
        this.iterator = null;
    }


    /**
     * A filter that simply delegates to a Servlet.
     */
    private static final class ServletFilterProxy implements Filter {

        private final Servlet delegateServlet;

        private ServletFilterProxy(Servlet servlet) {
            Assert.notNull(servlet, "servlet cannot be null");
            this.delegateServlet = servlet;
        }

        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
                throws IOException, ServletException {

            this.delegateServlet.service(request, response);
        }

        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
        }

        @Override
        public void destroy() {
        }

        @Override
        public String toString() {
            return this.delegateServlet.toString();
        }
    }

}

‍

这个类用在了我们API服务中，如下：

package tech.abc.platform.cip.api.service.impl;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import tech.abc.platform.cip.api.exception.ApiException;
import tech.abc.platform.cip.api.framework.ApiFilterChain;
import tech.abc.platform.cip.api.framework.BasicValidateFilter;
import tech.abc.platform.cip.api.framework.BusinessFilter;
import tech.abc.platform.cip.api.framework.FrameworkValidateFilter;
import tech.abc.platform.cip.api.service.ApiRestService;
import tech.abc.platform.cip.common.entity.ApiRequest;
import tech.abc.platform.cip.common.entity.ApiResponse;
import tech.abc.platform.cip.enums.ApiServiceExecuteResultEnum;
import tech.abc.platform.cip.service.ApiServiceLogService;
import tech.abc.platform.common.exception.CustomException;

import java.time.LocalDateTime;

/**
 * '
 * API服务技术框架实现
 *
 * @author wqliu
 * @date 2022-2-10
 **/
@Service
public class ApiRestServiceImpl implements ApiRestService {
    private ApiFilterChain filterChain;

    @Autowired
    private ApiServiceLogService apiServiceLogService;

    public ApiRestServiceImpl(FrameworkValidateFilter frameworkValidateFilter,
                              BusinessFilter businessFilter, BasicValidateFilter basicValidateFilter) {
        filterChain = new ApiFilterChain(basicValidateFilter, frameworkValidateFilter, businessFilter);

    }

    @Override
    public ApiResponse handle(ApiRequest apiRequest) {

        LocalDateTime receiveTime = LocalDateTime.now();
        ApiResponse apiResponse = new ApiResponse();
        try {
            filterChain.doFilter(apiRequest, apiResponse);
            apiResponse = this.filterChain.getResponse();
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.SUCCESS.name());
        } catch (CustomException ex) {
            // 自定义异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode("S00");
            apiResponse.setErrorMessage(ex.getMessage());
        } catch (ApiException ex) {
            // API异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode(ex.getErrorCode());
            apiResponse.setErrorMessage(ex.getMessage());
        } catch (Exception ex) {
            // 非预期异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode("S99");
            apiResponse.setErrorMessage("未定义异常：" + ex.getMessage());
        } finally {
            // 需要重置，为下次请求服务
            filterChain.reset();
            // 记录日志
            apiServiceLogService.recordLog(apiRequest, apiResponse, receiveTime);

        }

        return apiResponse;
    }
}

分析

其中ApiRestServiceImpl使用的@Service注解，Spring的默认处理是单例模式，ApiFilterChain是在构造函数中new出来的。线程安全的关键点，在于ApiFilterChain持有和保存了ApiRequest和ApiResponse对象。

从代码层面分析了一下，ApiFilterChain确实没有持有ApiRequest和ApiResponse对象的必要，通过方法接收ApiRequest对象，然后处理过程中修改ApiResponse对象，都是引用，没必要再保存一份。

至于当时为什么这么写，大概是参照官方MockFilterChain写法，高度信任而没有深度思考是否需要这么做。

‍

验证

上面是从代码层面分析，接下来就动手验证下，线程安全问题是否存在，借此也夯实下实际工作中很少用到的多线程并发及线程安全基础。

如何验证呢？

其实思路也挺简单，发起多次接口调用，通过日志输出对象的HashCode，看看HashCode是否是同一个就好了。

‍

使用Postman来做接口测试，调用平台内置的查询待处理消息的服务接口platform.message.query，如下：

注：为方便测试，把签名验证处理临时注释掉了，因此入参sign属性随便写了个1111，以通过非空验证。

‍

在服务接口处理中添加日志输出，这里用error而不是info目的是更容易找到，如下：

然后使用postman发起两次接口调用，查看日志，如下：

可以看到，无论是ApiRestService，还是其所属的filterChain，哈希码是完全相同的，已经足以说明就是同一个对象，因此存在线程安全问题。当接口同时收到多个请求时，也就是多线程并发时，持有的请求对象和响应对象会混乱掉，是个大问题。

‍

修正

既然问题已经确认，那接下来就修正它。

在前面分析环节，实际已经分析出来，filterChain并不需要持有请求对象和响应对象，去除掉后，就从根本上解决了线程安全问题，调整如下：

package tech.abc.platform.cip.api.framework;


import tech.abc.platform.cip.common.entity.ApiRequest;
import tech.abc.platform.cip.common.entity.ApiResponse;

import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * API服务过滤器链条
 *
 * @author wqliu
 * @date 2022-2-12
 **/
public class ApiFilterChain {


    /**
     * 过滤器集合
     */
    private final List<ApiFilter> filters;

    /**
     * 过滤器迭代器
     */
    private Iterator<ApiFilter> iterator;

    public ApiFilterChain() {
        filters = Collections.EMPTY_LIST;
    }

    public ApiFilterChain(ApiFilter... filters) {
        this.filters = Arrays.asList(filters);

    }


    /**
     * 执行过滤
     *
     * @param request  请求
     * @param response 响应
     */
    public void doFilter(ApiRequest request, ApiResponse response) {
        // 如迭代器为空，则初始化
        if (this.iterator == null) {
            this.iterator = this.filters.iterator();
        }

        // 集合中还有过滤器，则继续往下传递
        if (this.iterator.hasNext()) {
            ApiFilter nextFilter = this.iterator.next();
            nextFilter.doFilter(request, response, this);
        }


    }


    /**
     * 重置
     */
    public void reset() {

        this.iterator = null;
    }

}

测试功能正常，如下：

‍

新的疑问点

在调整ApiFilterChain的过程中，去除了存在线程安全的ApiRequest和ApiResponse对象，同时发现还持有一个过滤器集合对象

private final List filters，该对象在构造方法中初始化，在接口服务的finally里执行reset清理工作，不过reset方法是重置过滤器集合的迭代器，而不是清空过滤器集合本身。

假设是多线程并发情况下，A、B两个请求先后到达，A请求处理结束了，调用reset清空了过滤器的迭代器，而B请求还在只走完了3个过滤器中的2个，会不会有问题呢？

按照前面的验证方法，输出哈希码，确定是同一个对象。

要做并发测试，比较麻烦，得辅助Jmeter等工具来实现了

这个地方高度怀疑存在线程安全问题，比较彻底的解决办法，就是把API服务变更为非单例模式。

彻底改造

接口服务对应的控制器中直接new对象，不使用依赖注入，如下；

@RestController
@RequestMapping("/api")
@Slf4j
public class ApiRestController {


    @PostMapping("/rest")
    @AllowAll
    public ResponseEntity<ApiResponse> post(@RequestBody ApiRequest apiRequest) {
        ApiRestService apiRestService = new ApiRestServiceImpl();
        ApiResponse apiResponse = apiRestService.handle(apiRequest);
        return new ResponseEntity<ApiResponse>(apiResponse, HttpStatus.OK);
    }

}

ApiRestServiceImpl去除@Service注解，从而也不再是单例模式，调整构造方法，以及内部获取类的方式，如下：

package tech.abc.platform.cip.api.service.impl;

import lombok.extern.slf4j.Slf4j;
import tech.abc.platform.cip.api.exception.ApiException;
import tech.abc.platform.cip.api.framework.ApiFilterChain;
import tech.abc.platform.cip.api.framework.BasicValidateFilter;
import tech.abc.platform.cip.api.framework.BusinessFilter;
import tech.abc.platform.cip.api.framework.FrameworkValidateFilter;
import tech.abc.platform.cip.api.service.ApiRestService;
import tech.abc.platform.cip.common.entity.ApiRequest;
import tech.abc.platform.cip.common.entity.ApiResponse;
import tech.abc.platform.cip.enums.ApiServiceExecuteResultEnum;
import tech.abc.platform.cip.service.ApiServiceLogService;
import tech.abc.platform.common.exception.CustomException;
import tech.abc.platform.common.utils.SpringUtil;

import java.time.LocalDateTime;

/**
 * '
 * API服务技术框架实现
 *
 * @author wqliu
 * @date 2022-2-10
 **/

@Slf4j
public class ApiRestServiceImpl implements ApiRestService {
    private ApiFilterChain filterChain;


    public ApiRestServiceImpl() {
        BusinessFilter businessFilter = SpringUtil.getBean(BusinessFilter.class);
        FrameworkValidateFilter frameworkValidateFilter = SpringUtil.getBean(FrameworkValidateFilter.class);
        BasicValidateFilter basicValidateFilter = SpringUtil.getBean(BasicValidateFilter.class);
        filterChain = new ApiFilterChain(basicValidateFilter, frameworkValidateFilter, businessFilter);
    }

    @Override
    public ApiResponse handle(ApiRequest apiRequest) {


        LocalDateTime receiveTime = LocalDateTime.now();
        ApiResponse apiResponse = new ApiResponse();
        try {
            filterChain.doFilter(apiRequest, apiResponse);
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.SUCCESS.name());
        } catch (CustomException ex) {
            // 自定义异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode("S00");
            apiResponse.setErrorMessage(ex.getMessage());
        } catch (ApiException ex) {
            // API异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode(ex.getErrorCode());
            apiResponse.setErrorMessage(ex.getMessage());
        } catch (Exception ex) {
            // 非预期异常处理
            apiResponse.setExecuteResult(ApiServiceExecuteResultEnum.ERROR.name());
            apiResponse.setErrorCode("S99");
            apiResponse.setErrorMessage("未定义异常：" + ex.getMessage());
        } finally {
            ApiServiceLogService apiServiceLogService = SpringUtil.getBean(ApiServiceLogService.class);
            // 记录日志
            apiServiceLogService.recordLog(apiRequest, apiResponse, receiveTime);

        }

        return apiResponse;
    }
}

运行，发现多次接口调用进行测试，每次接口调用，无论是ApiRestService还是ApiFilterChain，都不是同一个对象了，因此线程肯定是安全的了。

‍

开源平台资料

平台名称：一二三开发平台
简介：企业级通用开发平台
设计资料：[csdn专栏]
开源地址：[Gitee]
开源协议：MIT
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