springboot结合mysql主从来实现读写分离的方法示例

1.实现的功能

基于springboot框架，application.yml配置多个数据源，使用AOP以及AbstractRootingDataSource、ThreadLocal来实现多数据源切换，以实现读写分离。mysql的主从数据库需要进行设置数据之间的同步。

2.代码实现

application.properties中的配置

spring.datasource.druid.master.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.druid.master.url=jdbc:mysql://127.0.0.1:3306/node2?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&autoReconnect=true&useSSL=false
spring.datasource.druid.master.username=root
spring.datasource.druid.master.password=123456

spring.datasource.druid.slave.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.druid.slave.url=jdbc:mysql://127.0.0.1:3306/node1?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&autoReconnect=true&useSSL=false
spring.datasource.druid.slave.username=root
spring.datasource.druid.slave.password=123456

写一个DataSourceConfig.java来注入两个bean

 @Bean
    @ConfigurationProperties("spring.datasource.druid.master")
    public DataSource masterDataSource() {
        logger.info("select master data source");
        return DruidDataSourceBuilder.create().build();
    }

    @Bean
    @ConfigurationProperties("spring.datasource.druid.slave")
    public DataSource slaveDataSource() {
        logger.info("select slave data source");
        return DruidDataSourceBuilder.create().build();
    }

写一个enum来标识有哪些数据源

public enum DBTypeEnum {
    MASTER, SLAVE;
}

然后写一个ThreadLocal本地线程的管理类,用于设置当前线程是那一个数据源

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

    private static final ThreadLocal<DBTypeEnum> contextHolder2 = ThreadLocal.withInitial(() -> DBTypeEnum.MASTER);

    public static void set(DBTypeEnum dbType) {
        contextHolder.set(dbType);
    }

    public static DBTypeEnum get() {
        return contextHolder.get();
    }

    public static void master() {
        set(DBTypeEnum.MASTER);
        logger.info("切换到master数据源");
    }

    public static void slave() {
        set(DBTypeEnum.SLAVE);
        logger.info("切换到slave数据源");
    }

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

然后写一个DynamicDataSource继承AbstractRootingDataSource,重写它的determineCurrentLookupKey方法。

public class DynamicDataSource extends AbstractRoutingDataSource {
    private Logger logger = LogManager.getLogger(DynamicDataSource.class);

    @Override
    protected Object determineCurrentLookupKey() {
        logger.info("此时数据源为{}", DBContextHolder.get());
        return DBContextHolder.get();
    }
}

最后写一个AOP来实现数据源切换

@Aspect
@Order(1)
@Component
public class DataSourceAop {

    private Logger logger = LogManager.getLogger(DataSourceAop.class);

    @Pointcut("(execution(* com.springboot.demo.service..*.select*(..)) " +
            "|| execution(* com.springboot.demo.service..*.find*(..)) " +
            "|| execution(* com.springboot.demo.service..*.get*(..)))")
    public void readPointcut() {
        logger.info("read only operate ,into slave db");
    }

    @Pointcut("execution(* com.springboot.demo.service..*.insert*(..)) " +
            "|| execution(* com.springboot.demo.service..*.update*(..)) " +
            "|| execution(* com.springboot.demo.service..*.delete*(..)) ")
    public void writePointcut() {
        logger.info("read or write operate ,into master db");
    }

    @Before("readPointcut()")
    public void read() {
        logger.info("read operate");
        DBContextHolder.slave();
    }

    @Before("writePointcut()")
    public void write() {
        logger.info("write operate");
        DBContextHolder.master();
    }

    @After("writePointcut(),readPointcut()")
    public void clean() {
        logger.info("dataSource cleanAll");
        DBContextHolder.cleanAll();
    }
}

注意：这里只是使用了偷懒的方法，对于service里面的select、get、find前缀的方法都使用从库，对于insert、update和delete方法都使用主库。

可以使用注解如下来进行优化:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DataSource {

    @AliasFor("dataSource")
    DBTypeEnum value() default DBTypeEnum.MASTER;

    DBTypeEnum dataSource() default DBTypeEnum.MASTER;

}

使用此注解来放入到service方法上，

@DataSource(DBTypeEnum.SLAVE)

然后AOP方法修改为：

private static final String POINT = "execution (* com.springboot.demo.service.*.*(..))";

 @Around(POINT)
    public Object dataSourceAround(ProceedingJoinPoint joinPoint) throws Throwable {
        Object[] args = joinPoint.getArgs();
        Object obj;
        Object target = joinPoint.getTarget();
        String methodName = joinPoint.getSignature().getName();
        Class clazz = target.getClass();
        Class<?>[] parameterTypes = ((MethodSignature) joinPoint.getSignature()).getMethod().getParameterTypes();
        boolean isDynamicDataSourceMethod = false;
        try {
            Method method = clazz.getMethod(methodName, parameterTypes);
            DataSources currentDataSource = null;
            if (method != null && method.isAnnotationPresent(DataSource.class)) {
                isDynamicDataSourceMethod = true;
                currentDataSource = method.getAnnotation(DataSource.class).value();
                DataSourceTypeManager.set(currentDataSource);
                log.info("DataSourceInterceptor Switch DataSource To {}",currentDataSource);
            }
            obj = joinPoint.proceed(args);
            if (isDynamicDataSourceMethod) {
                log.info("DataSourceInterceptor DataSource {} proceed",currentDataSource);
            }
        } finally {
            if (isDynamicDataSourceMethod) {
                DataSourceTypeManager.reset();
                log.info("DataSourceInterceptor Reset DataSource To {}",DataSourceTypeManager.get());
            }
        }
        return obj;
    }

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