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  • 读写分离很难吗?springboot结合aop简单就实现了

    摘自:https://www.cnblogs.com/yeya/p/11936239.html

    读写分离很难吗?springboot结合aop简单就实现了

     

    前言

    入职新公司到现在也有一个月了,完成了手头的工作,前几天终于有时间研究下公司旧项目的代码。在研究代码的过程中,发现项目里用到了Spring Aop来实现数据库的读写分离,本着自己爱学习(我自己都不信...)的性格,决定写个实例工程来实现spring aop读写分离的效果。

    环境部署

    数据库:MySql

    库数量:2个,一主一从

    关于mysql的主从环境部署之前已经写过文章介绍过了,这里就不再赘述,参考《windows版的mysql主从复制环境搭建》

    开始项目

    首先,毫无疑问,先开始搭建一个SpringBoot工程,然后在pom文件中引入如下依赖:

    <dependencies>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid-spring-boot-starter</artifactId>
                <version>1.1.10</version>
            </dependency>
            <dependency>
                <groupId>org.mybatis.spring.boot</groupId>
                <artifactId>mybatis-spring-boot-starter</artifactId>
                <version>1.3.2</version>
            </dependency>
            <dependency>
                <groupId>tk.mybatis</groupId>
                <artifactId>mapper-spring-boot-starter</artifactId>
                <version>2.1.5</version>
            </dependency>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.16</version>
            </dependency>
            <!-- 动态数据源 所需依赖 ### start-->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-jdbc</artifactId>
                <scope>provided</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-aop</artifactId>
                <scope>provided</scope>
            </dependency>
            <!-- 动态数据源 所需依赖 ### end-->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>fastjson</artifactId>
                <version>1.2.4</version>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-jpa</artifactId>
            </dependency>
        </dependencies>

    目录结构

    引入基本的依赖后,整理一下目录结构,完成后的项目骨架大致如下:

    建表

    创建一张表user,在主库执行sql语句同时在从库生成对应的表数据

    DROP TABLE IF EXISTS `user`;
    CREATE TABLE `user` (
      `user_id` bigint(20) NOT NULL COMMENT '用户id',
      `user_name` varchar(255) DEFAULT '' COMMENT '用户名称',
      `user_phone` varchar(50) DEFAULT '' COMMENT '用户手机',
      `address` varchar(255) DEFAULT '' COMMENT '住址',
      `weight` int(3) NOT NULL DEFAULT '1' COMMENT '权重,大者优先',
      `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
      `updated_at` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
      PRIMARY KEY (`user_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
    
    INSERT INTO `user` VALUES ('1196978513958141952', '测试1', '18826334748', '广州市海珠区', '1', '2019-11-20 10:28:51', '2019-11-22 14:28:26');
    INSERT INTO `user` VALUES ('1196978513958141953', '测试2', '18826274230', '广州市天河区', '2', '2019-11-20 10:29:37', '2019-11-22 14:28:14');
    INSERT INTO `user` VALUES ('1196978513958141954', '测试3', '18826273900', '广州市天河区', '1', '2019-11-20 10:30:19', '2019-11-22 14:28:30');

    主从数据源配置

    application.yml,主要信息是主从库的数据源配置

    server:
      port: 8001
    spring:
      jackson:
        date-format: yyyy-MM-dd HH:mm:ss
        time-zone: GMT+8
      datasource:
        type: com.alibaba.druid.pool.DruidDataSource
        driver-class-name: com.mysql.cj.jdbc.Driver
        master:
          url: jdbc:mysql://127.0.0.1:3307/user?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&useSSL=false&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true
          username: root
          password:
        slave:
          url: jdbc:mysql://127.0.0.1:3308/user?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&useSSL=false&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true
          username: root
          password:

    因为有一主一从两个数据源,我们用枚举类来代替,方便我们使用时能对应

    @Getter
    public enum DynamicDataSourceEnum {
        MASTER("master"),
        SLAVE("slave");
        private String dataSourceName;
        DynamicDataSourceEnum(String dataSourceName) {
            this.dataSourceName = dataSourceName;
        }
    }

    数据源配置信息类 DataSourceConfig,这里配置了两个数据源,masterDb和slaveDb

    @Configuration
    @MapperScan(basePackages = "com.xjt.proxy.mapper", sqlSessionTemplateRef = "sqlTemplate")
    public class DataSourceConfig {
        
         // 主库
          @Bean
          @ConfigurationProperties(prefix = "spring.datasource.master")
          public DataSource masterDb() {
      return DruidDataSourceBuilder.create().build();
          }
    
        /**
         * 从库
         */
        @Bean
        @ConditionalOnProperty(prefix = "spring.datasource", name = "slave", matchIfMissing = true)
        @ConfigurationProperties(prefix = "spring.datasource.slave")
        public DataSource slaveDb() {
            return DruidDataSourceBuilder.create().build();
        }
    
        /**
         * 主从动态配置
         */
        @Bean
        public DynamicDataSource dynamicDb(@Qualifier("masterDb") DataSource masterDataSource,
            @Autowired(required = false) @Qualifier("slaveDb") DataSource slaveDataSource) {
            DynamicDataSource dynamicDataSource = new DynamicDataSource();
            Map<Object, Object> targetDataSources = new HashMap<>();
            targetDataSources.put(DynamicDataSourceEnum.MASTER.getDataSourceName(), masterDataSource);
            if (slaveDataSource != null) {
                targetDataSources.put(DynamicDataSourceEnum.SLAVE.getDataSourceName(), slaveDataSource);
            }
            dynamicDataSource.setTargetDataSources(targetDataSources);
            dynamicDataSource.setDefaultTargetDataSource(masterDataSource);
            return dynamicDataSource;
        }
        @Bean
        public SqlSessionFactory sessionFactory(@Qualifier("dynamicDb") DataSource dynamicDataSource) throws Exception {
            SqlSessionFactoryBean bean = new SqlSessionFactoryBean();
            bean.setMapperLocations(
                new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/*Mapper.xml"));
            bean.setDataSource(dynamicDataSource);
            return bean.getObject();
        }
        @Bean
        public SqlSessionTemplate sqlTemplate(@Qualifier("sessionFactory") SqlSessionFactory sqlSessionFactory) {
            return new SqlSessionTemplate(sqlSessionFactory);
        }
        @Bean(name = "dataSourceTx")
        public DataSourceTransactionManager dataSourceTx(@Qualifier("dynamicDb") DataSource dynamicDataSource) {
            DataSourceTransactionManager dataSourceTransactionManager = new DataSourceTransactionManager();
            dataSourceTransactionManager.setDataSource(dynamicDataSource);
            return dataSourceTransactionManager;
        }
    }

    设置路由

    设置路由的目的为了方便查找对应的数据源,我们可以用ThreadLocal保存数据源的信息到每个线程中,方便我们需要时获取

    public class DataSourceContextHolder {
        private static final ThreadLocal<String> DYNAMIC_DATASOURCE_CONTEXT = new ThreadLocal<>();
        public static void set(String datasourceType) {
            DYNAMIC_DATASOURCE_CONTEXT.set(datasourceType);
        }
        public static String get() {
            return DYNAMIC_DATASOURCE_CONTEXT.get();
        }
        public static void clear() {
            DYNAMIC_DATASOURCE_CONTEXT.remove();
        }
    }

    获取路由

    public class DynamicDataSource extends AbstractRoutingDataSource {
        @Override
        protected Object determineCurrentLookupKey() {
            return DataSourceContextHolder.get();
        }
    }

    AbstractRoutingDataSource的作用是基于查找key路由到对应的数据源,它内部维护了一组目标数据源,并且做了路由key与目标数据源之间的映射,提供基于key查找数据源的方法。

    数据源的注解

    为了可以方便切换数据源,我们可以写一个注解,注解中包含数据源对应的枚举值,默认是主库,

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.METHOD)
    @Documented
    public @interface DataSourceSelector {
    
        DynamicDataSourceEnum value() default DynamicDataSourceEnum.MASTER;
        boolean clear() default true;
    }

    aop切换数据源

    到这里,aop终于可以现身出场了,这里我们定义一个aop类,对有注解的方法做切换数据源的操作,具体代码如下:

    @Slf4j
    @Aspect
    @Order(value = 1)
    @Component
    public class DataSourceContextAop {
    
     @Around("@annotation(com.xjt.proxy.dynamicdatasource.DataSourceSelector)")
        public Object setDynamicDataSource(ProceedingJoinPoint pjp) throws Throwable {
            boolean clear = true;
            try {
                Method method = this.getMethod(pjp);
                DataSourceSelector dataSourceImport = method.getAnnotation(DataSourceSelector.class);
                clear = dataSourceImport.clear();
                DataSourceContextHolder.set(dataSourceImport.value().getDataSourceName());
                log.info("========数据源切换至:{}", dataSourceImport.value().getDataSourceName());
                return pjp.proceed();
            } finally {
                if (clear) {
                    DataSourceContextHolder.clear();
                }
    
            }
        }
        private Method getMethod(JoinPoint pjp) {
            MethodSignature signature = (MethodSignature)pjp.getSignature();
            return signature.getMethod();
        }
    
    }

    到这一步,我们的准备配置工作就完成了,下面开始测试效果。

    先写好Service文件,包含读取和更新两个方法,

    @Service
    public class UserService {
    
        @Autowired
        private UserMapper userMapper;
    
        @DataSourceSelector(value = DynamicDataSourceEnum.SLAVE)
        public List<User> listUser() {
            List<User> users = userMapper.selectAll();
            return users;
        }
    
        @DataSourceSelector(value = DynamicDataSourceEnum.MASTER)
        public int update() {
            User user = new User();
            user.setUserId(Long.parseLong("1196978513958141952"));
            user.setUserName("修改后的名字2");
            return userMapper.updateByPrimaryKeySelective(user);
        }
    
        @DataSourceSelector(value = DynamicDataSourceEnum.SLAVE)
        public User find() {
            User user = new User();
            user.setUserId(Long.parseLong("1196978513958141952"));
            return userMapper.selectByPrimaryKey(user);
        }
    }

    根据方法上的注解可以看出,读的方法走从库,更新的方法走主库,更新的对象是userId为1196978513958141953 的数据,

    然后我们写个测试类测试下是否能达到效果,

    @RunWith(SpringRunner.class)
    @SpringBootTest
    class UserServiceTest {
    
        @Autowired
        UserService userService;
    
        @Test
        void listUser() {
            List<User> users = userService.listUser();
            for (User user : users) {
                System.out.println(user.getUserId());
                System.out.println(user.getUserName());
                System.out.println(user.getUserPhone());
            }
        }
        @Test
        void update() {
            userService.update();
            User user = userService.find();
            System.out.println(user.getUserName());
        }
    }

    测试结果:

    1、读取方法

    2、更新方法

    执行之后,比对数据库就可以发现主从库都修改了数据,说明我们的读写分离是成功的。当然,更新方法可以指向从库,这样一来就只会修改到从库的数据,而不会涉及到主库。

    注意

    上面测试的例子虽然比较简单,但也符合常规的读写分离配置。值得说明的是,读写分离的作用是为了缓解写库,也就是主库的压力,但一定要基于数据一致性的原则,就是保证主从库之间的数据一定要一致。如果一个方法涉及到写的逻辑,那么该方法里所有的数据库操作都要走主库

    假设写的操作执行完后数据有可能还没同步到从库,然后读的操作也开始执行了,如果这个读取的程序走的依然是从库的话,那么就会出现数据不一致的现象了,这是我们不允许的。

    最后发一下项目的github地址,有兴趣的同学可以看下,记得给个star哦

    地址:https://github.com/Taoxj/mysql-proxy

    參考:

    https://www.cnblogs.com/cjsblog/p/9712457.html

     
     
    分类: mysql, SpringBoot
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  • 原文地址:https://www.cnblogs.com/xichji/p/11942299.html
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