springBoot连接mysql主从配置

1. 在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

2. 在application.properties中添加以下配置：

# 主库配置
spring.datasource.master.url=jdbc:mysql://localhost:3306/master?useUnicode=true&characterEncoding=utf-8&useSSL=false
spring.datasource.master.username=root
spring.datasource.master.password=root
spring.datasource.master.driver-class-name=com.mysql.jdbc.Driver

# 从库配置
spring.datasource.slave.url=jdbc:mysql://localhost:3306/slave?useUnicode=true&characterEncoding=utf-8&useSSL=false
spring.datasource.slave.username=root
spring.datasource.slave.password=root
spring.datasource.slave.driver-class-name=com.mysql.jdbc.Driver

# 配置多个从库，用逗号分隔
spring.datasource.slave2.url=jdbc:mysql://localhost:3306/slave2?useUnicode=true&characterEncoding=utf-8&useSSL=false
spring.datasource.slave2.username=root
spring.datasource.slave2.password=root
spring.datasource.slave2.driver-class-name=com.mysql.jdbc.Driver

# 配置读写分离
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.read-type=READ_ONLY
spring.datasource.master.slaves=slave,slave2

3. 在代码中使用@Primary注解来指定默认的数据源：

@Configuration
public class DataSourceConfig {

    @Bean(name = "masterDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource masterDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "slaveDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.slave")
    public DataSource slaveDataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "slave2DataSource")
    @ConfigurationProperties(prefix = "spring.datasource.slave2")
    public DataSource slave2DataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "dynamicDataSource")
    @Primary // 指定默认的数据源
    public DataSource dynamicDataSource() {
        DynamicDataSource dynamicDataSource = new DynamicDataSource();
        dynamicDataSource.setDefaultTargetDataSource(masterDataSource());
        Map<Object, Object> dataSourceMap = new HashMap<>();
        dataSourceMap.put("master", masterDataSource());
        dataSourceMap.put("slave", slaveDataSource());
        dataSourceMap.put("slave2", slave2DataSource());
        dynamicDataSource.setTargetDataSources(dataSourceMap);
        return dynamicDataSource;
    }
}

4. 实现自定义的动态数据源：

public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return DataSourceContextHolder.getDataSourceType();
    }
}

5. 创建一个数据源上下文，用于保存当前线程使用的数据源类型：

public class DataSourceContextHolder {

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

    public static void setDataSourceType(String dataSourceType) {
        contextHolder.set(dataSourceType);
    }

    public static String getDataSourceType() {
        return contextHolder.get();
    }

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

6. 在service层中根据需要调用不同的数据源：

@Service
public class UserService {

    @Autowired
    private UserDao userDao;

    public List<User> findAll() {
        // 从主库读取数据
        DataSourceContextHolder.setDataSourceType("master");
        return userDao.findAll();
    }

    public User findById(Long id) {
        // 从从库1读取数据
        DataSourceContextHolder.setDataSourceType("slave");
        return userDao.findById(id);
    }

    public void save(User user) {
        // 写入主库
        DataSourceContextHolder.setDataSourceType("master");
        userDao.save(user);
    }

    public void deleteById(Long id) {
        // 写入主库
        DataSourceContextHolder.setDataSourceType("master");
        userDao.deleteById(id);
    }
}