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

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

/**
 * @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();
  }
}

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 {
}

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;
  }
}

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

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
    ]
  }
}