Spring boot实现数据库读写分离

背景

数据库配置主从之后，如何在代码层面实现读写分离？

用户自定义设置数据库路由

Spring boot提供了AbstractRoutingDataSource根据用户定义的规则选择当前的数据库，这样我们可以在执行查询之前，设置读取从库，在执行完成后，恢复到主库。

实现可动态路由的数据源，在每次数据库查询操作前执行

ReadWriteSplitRoutingDataSource.java

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

/**
 * @author songrgg
 * @since 1.0
 */
public class ReadWriteSplitRoutingDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return DbContextHolder.getDbType();
    }
}

线程私有路由配置，用于ReadWriteSplitRoutingDataSource动态读取配置

DbContextHolder.java

/**
 * @author songrgg
 * @since 1.0
 */
public class DbContextHolder {
    public enum DbType {
        MASTER,
        SLAVE
    }

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

    public static void setDbType(DbType dbType) {
        if(dbType == null){
            throw new NullPointerException();
        }
        contextHolder.set(dbType);
    }

    public static DbType getDbType() {
        return contextHolder.get() == null ? DbType.MASTER : contextHolder.get();
    }

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

AOP优化代码

利用AOP将设置数据库的操作从代码中抽离，这里的粒度控制在方法级别，所以利用注解的形式标注这个方法涉及的数据库事务只读，走从库。

只读注解，用于标注方法的数据库操作只走从库。

ReadOnlyConnection.java

package com.wallstreetcn.hatano.config;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Indicates the database operations is bound to the slave database.
 * AOP interceptor will set the database to the slave with this interface.
 * @author songrgg
 * @since 1.0
 */
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ReadOnlyConnection {
}

ReadOnlyConnectionInterceptor.java

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;

/**
 * Intercept the database operations, bind database to read-only database as this annotation
 * is applied.
 * @author songrgg
 * @since 1.0
 */
@Aspect
@Component
public class ReadOnlyConnectionInterceptor implements Ordered {

    private static final Logger logger = LoggerFactory.getLogger(ReadOnlyConnectionInterceptor.class);

    @Around("@annotation(readOnlyConnection)")
    public Object proceed(ProceedingJoinPoint proceedingJoinPoint, ReadOnlyConnection readOnlyConnection) throws Throwable {
        try {
            logger.info("set database connection to read only");
            DbContextHolder.setDbType(DbContextHolder.DbType.SLAVE);
            Object result = proceedingJoinPoint.proceed();
            return result;
        } finally {
            DbContextHolder.clearDbType();
            logger.info("restore database connection");
        }
    }

    @Override
    public int getOrder() {
        return 0;
    }
}

UserService.java

@ReadOnlyConnection
public List<User> getUsers(Integer page, Integer limit) {
    return repository.findAll(new PageRequest(page, limit));
}

配置Druid数据库连接池

build.gradle

compile("com.alibaba:druid:1.0.18")

groovy依赖注入

配置dataSource为可路由数据源

context.groovy

import com.alibaba.druid.pool.DruidDataSource
import DbContextHolder
import ReadWriteSplitRoutingDataSource

** SOME INITIALIZED CODE LOAD PROPERTIES **
def dataSourceMaster = new DruidDataSource()
dataSourceMaster.url = properties.get('datasource.master.url')
println("master set to " + dataSourceMaster.url)
dataSourceMaster.username = properties.get('datasource.master.username')
dataSourceMaster.password = properties.get('datasource.master.password')

def dataSourceSlave = new DruidDataSource()
dataSourceSlave.url = properties.get('datasource.slave.url')
println("slave set to " + dataSourceSlave.url)
dataSourceSlave.username = properties.get('datasource.slave.username')
dataSourceSlave.password = properties.get('datasource.slave.password')  
beans {
    dataSource(ReadWriteSplitRoutingDataSource) { bean ->
        targetDataSources = [
                (DbContextHolder.DbType.MASTER): dataSourceMaster,
                (DbContextHolder.DbType.SLAVE): dataSourceSlave
        ]
    }
}

参考资料

1. Dynamic DataSource Routing with Spring @Transactional
2. Alibaba Druid

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