本文共 10995 字，大约阅读时间需要 36 分钟。

为了提高数据库的查询效率，利用数据库主从机制，写走主库，查询走从库。如果只是实现一主一从类似简单的主从模式，可以继承AbstractRoutingDataSource实现读写分离。而不需使用mycat，sharedingJDBC等数据库插件。

分析AbstractRoutingDataSource可知，defaultTargetDataSource，表示默认的数据源；targetDataSources表示配置的所有数据源集合；afterPropertiesSet方法spring bean对象初始化方法，会把targetDataSources和defaultTargetDataSource，设置为resolvedDataSources和resolvedDefaultDataSource。getConnection()获取jdbc的连接，并通过determineTargetDataSource()获取指定的数据源，AbstractRoutingDataSource使用模板类的模式，在父类定义了determineCurrentLookupKey()虚拟方法，获取lookupkey对象；其子类必须实现该方法。源码如下：

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {    /**     *配置的数据源     */	@Nullable	private Map
   
     targetDataSources;    /**     *默认数据源     */	@Nullable	private Object defaultTargetDataSource;    ......     /**     *spring InitializingBean 实现方法，bean初始化时调用     */    @Override	public void afterPropertiesSet() {		if (this.targetDataSources == null) {			throw new IllegalArgumentException("Property 'targetDataSources' is required");		}		this.resolvedDataSources = new HashMap<>(this.targetDataSources.size());		this.targetDataSources.forEach((key, value) -> {			Object lookupKey = resolveSpecifiedLookupKey(key);			DataSource dataSource = resolveSpecifiedDataSource(value);			this.resolvedDataSources.put(lookupKey, dataSource);		});		if (this.defaultTargetDataSource != null) {			this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);		}	}    /**     *获取jdbc链接时，调用determineTargetDataSource，获取指定的数据     */    @Override	public Connection getConnection() throws SQLException {		return determineTargetDataSource().getConnection();	}    /**     *determineCurrentLookupKey方法通过子类自定义实现，获取lookupKey，然后从resolvedDefaultDataSource map对象中获取数据源     */    protected DataSource determineTargetDataSource() {		Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");		Object lookupKey = determineCurrentLookupKey();		DataSource dataSource = this.resolvedDataSources.get(lookupKey);		if (dataSource == null && (this.lenientFallback || lookupKey == null)) {			dataSource = this.resolvedDefaultDataSource;		}		if (dataSource == null) {			throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");		}		return dataSource;	}    /**     *子类必须实现的获取lookupKey的方法     */    protected abstract Object determineCurrentLookupKey();}
   

创建DataSourceAddressEnum枚举类，定义MASTER与SLAVE，路由名称。代码如下：

public enum DataSourceAddressEnum {    /**     * 主数据库     */    MASTER,    /**     * 从数据库     */    SLAVE;}

创建DataSourceContextHolder，使用ThreadLocal，定义每次操作的类型枚举，代码如下：

public class DataSourceContextHolder {    private static final ThreadLocal
   
     CONTEXT_HOLDER = ThreadLocal.withInitial(() -> DataSourceAddressEnum.MASTER);    public static void setCurrentDataSource(DataSourceAddressEnum dataSourceAddressEnum) {        CONTEXT_HOLDER.set(dataSourceAddressEnum);    }    public static DataSourceAddressEnum getCurrentDataSource() {        return CONTEXT_HOLDER.get();    }    public static void removeDataSource() {        CONTEXT_HOLDER.remove();    }}
   

创建RoutingDataSourceWithAddress，继承AbstractRoutingDataSource，实现determineCurrentLookupKey，即实现了可以根据DataSourceAddressEnum枚举类实现数据源的动态路由，代码如下：

public class RoutingDataSourceWithAddress extends AbstractRoutingDataSource {    /**     * @param defaultTargetDataSource 默认的 DataSource     * @param targetDataSources       配置的所有 DataSource     */    public RoutingDataSourceWithAddress(DataSource defaultTargetDataSource, Map
   
     targetDataSources) {        super.setDefaultTargetDataSource(defaultTargetDataSource);        super.setTargetDataSources(targetDataSources);    }    /**     *配置的数据源     */    @Override    protected Object determineCurrentLookupKey() {        DataSourceAddressEnum routingDataSourceAddressEnum = DataSourceContextHolder.getCurrentDataSource();        if (log.isDebugEnabled()) {            log.debug("routing data source address is {}", routingDataSourceAddressEnum.name());        }        return routingDataSourceAddressEnum;    }}
   

使用AOP+注解的方式，对指定的方法进行数据源动态切换的控制。创建RoutingDataSource注解，定义需要路由的数据源，创建RoutingDataSourceAOP定义数据源路由的切面操作，代码如下：

/** * DataSource路由注解 **/@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)public @interface RoutingDataSource {    /**     * 路由的DataSource地址，默认为MASTER     */    DataSourceAddressEnum value() default DataSourceAddressEnum.MASTER;}/** * RoutingDataSource 的aop拦截 **/@Aspect@Component@Order(10000)@Slf4jpublic class RoutingDataSourceAOP {    @Pointcut("@annotation(com.kuqi.mall.demo.conmon.datasource.RoutingDataSource)|| @within(com.kuqi.mall.demo.conmon.datasource.RoutingDataSource)")    public void routingDataSourcePointcut() {    }    @Around("routingDataSourcePointcut()")    public Object around(ProceedingJoinPoint joinPoint) throws Throwable {        MethodSignature signature = (MethodSignature) joinPoint.getSignature();        Method method = signature.getMethod();        RoutingDataSource routerDataSource = method.getAnnotation(RoutingDataSource.class);        // 如果没有设置则默认为 MASTER        DataSourceAddressEnum dataSourceAddressEnum = Objects.isNull(routerDataSource) ? DataSourceAddressEnum.MASTER : routerDataSource.value();        DataSourceContextHolder.setCurrentDataSource(dataSourceAddressEnum);        try {            return joinPoint.proceed();        } finally {            DataSourceContextHolder.removeDataSource();        }    }}

创建基于Springboot的自动配置类RoutingDataSourceAutoConfiguration，只要配置了master和slave的属性文件，和mybatis属性文件，就可以自动启动配置。RoutingDataSourceAutoConfiguration源码如下：

@Configuration@ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class, DruidDataSource.class})@EnableConfigurationProperties(MybatisProperties.class)public class RoutingDataSourceAutoConfiguration {    /**     * 配置master数据源     */    @Bean(name = "masterDataSource", initMethod = "init", destroyMethod = "close")    @Primary    @ConfigurationProperties(prefix = "spring.datasource.druid.master")    public DataSource masterDataSource() {        DataSource dataSource = DataSourceBuilder.create(this.getClass().getClassLoader())                .type(com.alibaba.druid.pool.DruidDataSource.class).build();        return dataSource;    }    /**     * 配置slave数据源     */    @Bean(name = "slaveDataSource", initMethod = "init", destroyMethod = "close")    @ConfigurationProperties(prefix = "spring.datasource.druid.slave")    public DataSource slaveDataSource() {        DataSource dataSource = DataSourceBuilder.create(this.getClass().getClassLoader())                .type(com.alibaba.druid.pool.DruidDataSource.class).build();        return dataSource;    }    /**     * 初始化路由DataSource     */    @Bean(name = "routingDataSourceWithAddress")    public DataSource dataSource(            @Autowired @Qualifier("masterDataSource") DataSource masterDataSource,            @Autowired @Qualifier("slaveDataSource") DataSource slaveDataSource) {        DataSource defaultTargetDataSource;        Map
   
     targetDataSources = ImmutableMap.of(                DataSourceAddressEnum.MASTER, defaultTargetDataSource = masterDataSource,                DataSourceAddressEnum.SLAVE, slaveDataSource);        return new RoutingDataSourceWithAddress(defaultTargetDataSource, targetDataSources);    }    /**     * 使用SqlSessionFactoryBean配置MyBatis的SqlSessionFactory     **/    @Bean    @ConditionalOnMissingBean    public SqlSessionFactory sqlSessionFactory(            @Autowired @Qualifier("routingDataSourceWithAddress") DataSource routingDataSourceWithAddress,            @Autowired MybatisProperties mybatisProperties,            @Autowired ResourceLoader resourceLoader) throws Exception {        SqlSessionFactoryBean factory = new SqlSessionFactoryBean();        factory.setDataSource(routingDataSourceWithAddress);        // 设置configuration        org.apache.ibatis.session.Configuration configuration = mybatisProperties.getConfiguration();        factory.setConfiguration(configuration);        // 设置SqlSessionFactory属性        String configLocation;        if (StringUtils.isNotBlank(configLocation = mybatisProperties.getConfigLocation())) {            factory.setConfigLocation(resourceLoader.getResource(configLocation));        }        Resource[] resolveMapperLocations;        if (ArrayUtils.isNotEmpty(resolveMapperLocations = mybatisProperties.resolveMapperLocations())) {            factory.setMapperLocations(resolveMapperLocations);        }        String typeHandlersPackage;        if (StringUtils.isNotBlank(typeHandlersPackage = mybatisProperties.getTypeHandlersPackage())) {            factory.setTypeHandlersPackage(typeHandlersPackage);        }        String typeAliasesPackage;        if (StringUtils.isNotBlank(typeAliasesPackage = mybatisProperties.getTypeAliasesPackage())) {            factory.setTypeAliasesPackage(typeAliasesPackage);        }        return factory.getObject();    }    /**     * 使用routingDataSourceWithAddress配置数据库事务     */    @Bean    @ConditionalOnMissingBean    public DataSourceTransactionManager dataSourceTransactionManager(            @Autowired @Qualifier("routingDataSourceWithAddress") DataSource routingDataSourceWithAddress) {        return new DataSourceTransactionManager(routingDataSourceWithAddress);    }    /**     * 编程式事务     */    @Bean    public TransactionTemplate transactionTemplate(            @Autowired @Qualifier("dataSourceTransactionManager") PlatformTransactionManager platformTransactionManager) {        return new TransactionTemplate(platformTransactionManager);    }    @Bean    @ConditionalOnMissingBean(RoutingDataSourceAOP.class)    public RoutingDataSourceAOP rRoutingDataSourceAOP() {        return new RoutingDataSourceAOP();    }}
   

数据源使用DruidDataSource，详细的配置文件，master和slave数据源，可以配置不同的数据库用来测试，实际开发中，配置为满足数据库主从复制的配置，配置代码如下：

spring:  datasource:    type: com.alibaba.druid.pool.DruidDataSource    druid:      master:        driver-class-name: com.mysql.jdbc.Driver        url: jdbc:mysql://127.0.0.1:3306/kuqi_mall?autoReconnectForPools=true&useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai        username: root        password: root      slave:        driver-class-name: com.mysql.jdbc.Driver        url: jdbc:mysql://127.0.0.1:3306/kuqi_mall?autoReconnectForPools=true&useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai        username: root        password: root

在springboot的启动类中，屏蔽DruidDataSourceAutoConfigure自动配置类，就能启动。启动类代码，以及操作示例代码如下：

/** * springboot启动类exclude DruidDataSourceAutoConfigure */@SpringBootApplication(exclude = DruidDataSourceAutoConfigure.class)@MapperScan(basePackages = {"com.kuqi.mall.demo.dao"})public class DemoApplication {    public static void main(String[] args) {        SpringApplication.run(DemoApplication.class, args);    }}         /**     * 注解定义动态数据源操作     */    @Override    @RoutingDataSource(DataSourceAddressEnum.SLAVE)    public CouponBo getFromSlave(Long id) {        return get(id);    }

完整示例代码，可以参考链接spring-boot-mall项目

转载地址：http://ewyc.baihongyu.com/