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在javaweb开发中数据库表数据量会越来越大，为了减轻数据库读写压力，对数据库进行主从模式部署（一主一从，多主多从），在应用层面可以通过spring提供的路由数据源+注解+切面进行控制，在代码层面切换不同数据库源，不同操作选择不同数据库。

代码如下：

               
    
     com.alibaba
                
    
     druid-spring-boot-starter
                
    
     1.1.9
            
           
           
               
    
     org.mybatis.spring.boot
                
    
     mybatis-spring-boot-starter
                
    
     1.1.1
            
           
           
               
    
     mysql
                
    
     mysql-connector-java
                
            
   

spring.datasource.master.url=jdbc:mysql://localhost:3306/master?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=falsespring.datasource.master.username=rootspring.datasource.master.password=123456spring.datasource.master.driver-class-name=com.mysql.cj.jdbc.Driverspring.datasource.slave.url=jdbc:mysql://localhost:3306/slave?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=falsespring.datasource.slave.username=rootspring.datasource.slave.password=123456spring.datasource.slave.driver-class-name=com.mysql.cj.jdbc.Driver

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class, TransactionAutoConfiguration.class})@MapperScan("com.*.mapper")public class AnnotationAopReflectionApplication {    public static void main(String[] args) {        SpringApplication.run(AnnotationAopReflectionApplication.class, args);    }}

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)@Documentedpublic @interface DataSourceAnnotation {    /**     * 默认数据源     */    DataSourceEnum value() default DataSourceEnum.MASTER;    /**     * 清除     */    boolean clear() default true;}public enum DataSourceEnum {    //数据源主库、从库    MASTER("1","master"),    SLAVE("2","slave");    private String code;    private String name;    private DataSourceEnum(String code,String name){        this.code = code;        this.name = name;    }    public static DataSourceEnum getByCode(String code) {        for (DataSourceEnum event : DataSourceEnum.values()) {            if (event.code.equals(code)) {                return event;            }        }        return null;    }    public String getCode() {        return code;    }    public void setCode(String code) {        this.code = code;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}public class DataSourceContextHolder {    private static final ThreadLocal
   
     context = new ThreadLocal<>();    /**     * 赋值     */    public static void set(String datasourceType) {        context.set(datasourceType);    }    /**     * 获取值     */    public static String get() {        return context.get();    }    /**     * 清空     */    public static void clear() {        context.remove();    }}public class RoutingDataSource extends AbstractRoutingDataSource {    /**     * 最终的determineCurrentLookupKey返回的是从DataSourceContextHolder中拿到的,因此在动态切换数据源的时候注解     * 应该给DataSourceContextHolder设值     */    @Override    protected Object determineCurrentLookupKey() {        return DataSourceContextHolder.get();    }}@Configuration@MapperScan(basePackages = "com.", sqlSessionTemplateRef = "sqlSessionTemplate")public class DataSourceConfig {    /**     * 主库     */    @Bean    @ConfigurationProperties(prefix = "spring.datasource.master")    public DataSource master() {        return DruidDataSourceBuilder.create().build();    }    /**     * 从库     */    @Bean    @ConfigurationProperties(prefix = "spring.datasource.slave")    public DataSource slaver() {        return DruidDataSourceBuilder.create().build();    }    /**     * 实例化数据源路由     */    @Bean    public RoutingDataSource routingDataSource(@Qualifier("master") DataSource masterDataSource,@Autowired(required = false) @Qualifier("slaver") DataSource slaveDataSource) {        RoutingDataSource routingDataSource = new RoutingDataSource();        Map
    
      targetDataSources = new HashMap<>();        targetDataSources.put(DataSourceEnum.MASTER.getName(), masterDataSource);        if (slaveDataSource != null) {            targetDataSources.put(DataSourceEnum.SLAVE.getName(), slaveDataSource);        }        routingDataSource.setTargetDataSources(targetDataSources);        routingDataSource.setDefaultTargetDataSource(masterDataSource);        return routingDataSource;    }    /**     * 配置sessionFactory     */    @Bean    public SqlSessionFactory sqlSessionFactory(@Qualifier("routingDataSource") DataSource routingDataSource) throws Exception {        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();        sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/*.xml"));        sqlSessionFactoryBean.setDataSource(routingDataSource);        return sqlSessionFactoryBean.getObject();    }    /**     * 创建sqlSessionTemplate     */    @Bean    public SqlSessionTemplate sqlSessionTemplate(@Qualifier("sqlSessionFactory") SqlSessionFactory sqlSessionFactory) {        return new SqlSessionTemplate(sqlSessionFactory);    }    /**     * 事务配置     */    @Bean(name = "dataSourceTransactionManager")    public DataSourceTransactionManager dataSourceTransactionManager(@Qualifier("routingDataSource") DataSource dynamicDataSource) {        DataSourceTransactionManager dataSourceTransactionManager = new DataSourceTransactionManager();        dataSourceTransactionManager.setDataSource(dynamicDataSource);        return dataSourceTransactionManager;    }}@Aspect@Order(value = 1)@Componentpublic class DataSourceAspect {    @Around("@annotation(com.*.DataSourceAnnotation)")    public Object setDynamicDataSource(ProceedingJoinPoint pjp) throws Throwable {        boolean clear = false;        try {            Method method = this.getMethod(pjp);            DataSourceAnnotation dataSourceAnnotation = method.getAnnotation(DataSourceAnnotation.class);            clear = dataSourceAnnotation.clear();            DataSourceContextHolder.set(dataSourceAnnotation.value().getName());            System.out.println(String.format("数据源切换至：{%s}", dataSourceAnnotation.value().getName()));            return pjp.proceed();        } finally {            if (clear) {                DataSourceContextHolder.clear();            }        }    }    private Method getMethod(JoinPoint pjp) {        MethodSignature signature = (MethodSignature) pjp.getSignature();        return signature.getMethod();    }}
    
   

@Servicepublic class DemoService {    @Autowired    private UserMapper userMapper;    @Autowired    private AuthUserMapper authUserMapper;    /**     * 读操作     */    @DataSourceAnnotation(DataSourceEnum.SLAVE)    public AuthUser getAuthUser() {        String userId = "001";        AuthUser authUser = authUserMapper.getAuthUserById(userId);        //User user = userMapper.getUserById(1);        return authUser;    }    /**     * 写操作     */    @DataSourceAnnotation(DataSourceEnum.MASTER)    public User updateUser() {        User user = userMapper.getUserById(1);        return user;    }}@RestControllerpublic class DemoController {        @Autowired    private DemoService demoService;    @GetMapping("/readSlave")    public Object readSlave() {        return demoService.getAuthUser();    }    @GetMapping("/writeMaster")    public Object writeMaster() {        return demoService.updateUser();    }}

前提是部署好mysql主从数据库或准备不同数据库。注意读写分离的核心点就是数据路由，需要继承AbstractRountingDataSource，覆写它的determinCurrentLookupKey方法，同时需要注意全局的上下文管理器DataSourceContextHolder，它是保存数据源上下文的主要类，也是路由方法中寻找的数据源取值，相当于数据源的中转站，此例配置了3个数据源。再结合jdbc底层、事务等，数据库读写分离就实现了。

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