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 ] } }
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