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一、前言

下面是一个示例代码，展示如何在 Spring Boot 应用中实现 MySQL 主从复制的数据源动态切换。我们将使用 Spring Boot 和 MyBatis-Plus，并且结合 Spring 的动态数据源切换功能。

1. 添加依赖

首先，确保在 pom.xml 文件中添加了必要的依赖：

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.30</version>
        </dependency>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.3</version>
        </dependency>

        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.8.20</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>

    </dependencies>

2. 配置主从数据源

在 application.yml 或 application.properties 中配置主从数据源：

server:
  port: 8082

spring:
  datasource:
    master:
      url: jdbc:mysql://master-db-host:3306/your_database?useSSL=false
      username: your_username
      password: your_password
      driver-class-name: com.mysql.cj.jdbc.Driver
    slave:
      url: jdbc:mysql://slave-db-host:3306/your_database?useSSL=false
      username: your_username
      password: your_password
      driver-class-name: com.mysql.cj.jdbc.Driver
      
mybatis-plus:
  mapper-locations: classpath*:/mapper/**/*.xml

3. 创建数据源配置类

在 DataSourceConfig 中配置数据源和动态路由：

@Configuration
@Data
public class DataSourceConfig {
    @Value("${spring.datasource.master.url}")
    private String dbUrl;
    @Value("${spring.datasource.master.username}")
    private String username;
    @Value("${spring.datasource.master.password}")
    private String password;
    @Value("${spring.datasource.master.driver-class-name}")
    private String driverClassName;


    @Value("${spring.datasource.slave.url}")
    private String slaveDbUrl;
    @Value("${spring.datasource.slave.username}")
    private String slaveUsername;
    @Value("${spring.datasource.slave.password}")
    private String slavePassword;
    @Value("${spring.datasource.slave.driver-class-name}")
    private String slaveDriverClassName;


    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource() {
        return DataSourceBuilder.create()
                .driverClassName(driverClassName)
                .url(dbUrl)
                .username(username)
                .password(password)
                .build();
    }

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource.slave")
    public DataSource slaveDataSource() {

        return DataSourceBuilder.create()
                .driverClassName(slaveDriverClassName)
                .url(slaveDbUrl)
                .username(slaveUsername)
                .password(slavePassword)
                .build();

    }
}

4. 创建数据源上下文

DatabaseContextHolder 用于管理当前线程的数据源类型：

public class DatabaseContextHolder {

    private static final ThreadLocal<DatabaseType> contextHolder = new ThreadLocal<>();

    public static void setDatabaseType(DatabaseType databaseType) {
        contextHolder.set(databaseType);
    }

    public static DatabaseType getDatabaseType() {
        return contextHolder.get();
    }

    public static void clearDatabaseType() {
        contextHolder.remove();
    }
}

5. 定义数据源类型

DatabaseType 枚举定义了数据源类型：

public enum DatabaseType {
    MASTER,
    SLAVE
}

6. 配置数据源切换

使用 AOP 来控制数据源切换，可以定义一个切面来切换数据源：

@Aspect
@Component
@EnableAspectJAutoProxy
public class DataSourceAspect {



    @Pointcut("@annotation(com.zbbmeta.annotation.DataSource)")
    public void dataSourcePointCut() {}

    @Around("dataSourcePointCut()")
    public Object around(ProceedingJoinPoint point) throws Throwable {
        MethodSignature signature = (MethodSignature) point.getSignature();
        Method method = signature.getMethod();

        DataSource dataSource = method.getAnnotation(DataSource.class);
        if (dataSource != null) {
            DatabaseContextHolder.setDatabaseType(dataSource.type());
        }

        try {
            return point.proceed();
        } finally {
            DatabaseContextHolder.clearDatabaseType();
        }
    }

}

7. 创建DynamicDataSourceConfig

@Configuration
@MapperScan("com.zbbmeta.mapper")
public class DynamicDataSourceConfig {
    @Autowired
    private DataSource masterDataSource;

    @Autowired
    private DataSource slaveDataSource;

    // 配置动态数据源
    @Bean
    @Primary
    public DataSource dynamicDataSource() {
        Map<Object, Object> targetDataSources = new HashMap<>();
        targetDataSources.put(DatabaseType.MASTER, masterDataSource);
        targetDataSources.put(DatabaseType.SLAVE, slaveDataSource);

        DynamicRoutingDataSource dynamicDataSource = new DynamicRoutingDataSource();
        dynamicDataSource.setTargetDataSources(targetDataSources);
        dynamicDataSource.setDefaultTargetDataSource(masterDataSource); // 设置默认数据源
        return dynamicDataSource;
    }

    // 配置 MyBatis 的 SqlSessionFactory
    @Bean
    public SqlSessionFactory sqlSessionFactory(DataSource dynamicDataSource) throws Exception {
        MybatisSqlSessionFactoryBean sessionFactoryBean = new MybatisSqlSessionFactoryBean();
        sessionFactoryBean.setDataSource(dynamicDataSource);

        // 设置要扫描的 mapper 接口和 XML 文件路径
        sessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));
        sessionFactoryBean.setTypeAliasesPackage("com.zbbmeta.entity");  // 设置实体类包路径

        return sessionFactoryBean.getObject();
    }

    // 配置 MyBatis 的 SqlSessionTemplate
    @Bean
    public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
        return new SqlSessionTemplate(sqlSessionFactory);
    }
}

8. 创建DynamicRoutingDataSource

public class DynamicRoutingDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return DatabaseContextHolder.getDatabaseType();
    }
}

9. 创建注解

注解用于标记需要读操作的方法：

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DataSource {

    DatabaseType type() default DatabaseType.SLAVE;

}

10. 使用注解

@RestController
public class TutorialController {


    @Autowired
    private TutorialService tutorialService;


    @DataSource
    @GetMapping("/list")
    public List<Tutorial> list(){
        return tutorialService.list();

    }

    @DataSource(type = DatabaseType.MASTER)
    @GetMapping("/create")
    public Boolean create(){

        Tutorial tutorial = new Tutorial();
        tutorial.setTitle("master");
        tutorial.setDescription("master");

        return tutorialService.save(tutorial);
    }
}

这个示例展示了如何使用 Spring Boot 和 MyBatis-Plus 实现 MySQL 主从复制的数据源切换。你可以根据实际情况调整配置和代码。