时间：2023-02-27 10:34:06 | 栏目：JAVA代码 | 点击：次
mybatis查询默认是一次获取全部， 有时候需要查询上万上百万数据时，如果一次性读取到内存中，会容易导致OOM问题。这时候需要采用流式查询。以下扩展了tk.mybatis的流式查询功能。 直接上干货：
@Options注解是关键
import org.apache.ibatis.annotations.Options;
import org.apache.ibatis.annotations.SelectProvider;
import org.apache.ibatis.mapping.ResultSetType;
import org.apache.ibatis.session.ResultHandler;
/**
* 通用Mapper接口,流式查询
*
* @param <T> 不能为空
* @author sunchangtan
*/
@tk.mybatis.mapper.annotation.RegisterMapper
public interface SelectStreamByExampleMapper<T> {
/**
* 根据example条件和RowBounds进行流式查询
*
* @param example
* @return
*/
@Options(resultSetType = ResultSetType.FORWARD_ONLY, fetchSize = 1000)
@SelectProvider(type = StreamExampleProvider.class, method = "dynamicSQL")
void selectStreamByExampleMapper(Object example, ResultHandler resultHandler);
}
带RowBounds的流式查询
import org.apache.ibatis.annotations.Options;
import org.apache.ibatis.annotations.SelectProvider;
import org.apache.ibatis.mapping.ResultSetType;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
/**
* 通用Mapper接口,流式查询
*
* @param <T> 不能为空
* @author sunchangtan
*/
@tk.mybatis.mapper.annotation.RegisterMapper
public interface SelectStreamByExampleRowBoundsMapper<T> {
/**
* 根据example条件和RowBounds进行流式查询
*
* @param example
* @return
*/
@Options(resultSetType = ResultSetType.FORWARD_ONLY, fetchSize = 1000)
@SelectProvider(type = StreamExampleProvider.class, method = "dynamicSQL")
void selectStreamByExampleRowBoundsMapper(Object example, RowBounds rowBounds, ResultHandler resultHandler);
}
流式ExampleProvider
import org.apache.ibatis.mapping.MappedStatement;
import tk.mybatis.mapper.mapperhelper.MapperHelper;
import tk.mybatis.mapper.provider.ExampleProvider;
/**
* 流式查询的SqlProvider
* @author sunchangtan
*/
public class StreamExampleProvider extends ExampleProvider {
public StreamExampleProvider(Class<?> mapperClass, MapperHelper mapperHelper) {
super(mapperClass, mapperHelper);
}
/**
* 根据Example流式查询
*
* @param ms
* @return
*/
public String selectStreamByExampleMapper(MappedStatement ms) {
return this.selectByExample(ms);
}
/**
* 根据Example和RowBounds流式查询
* @param ms
* @return
*/
public String selectStreamByExampleRowBoundsMapper(MappedStatement ms) {
return this.selectByExample(ms);
}
}
将SelectStreamByExampleMapper和SelectStreamByExampleRowBoundsMapper组合成一个接口
/**
* 流式查询接口
* @param <T>
* @author sunchangtan
*/
@tk.mybatis.mapper.annotation.RegisterMapper
public interface StreamMapper<T> extends
SelectStreamByExampleMapper<T>,
SelectStreamByExampleRowBoundsMapper<T> {
}
在BaseMapper中加入StreamMapper
/**
* Mapper的基类
* @author sunchangtan
* @param <T>
*/
public interface BaseMapper<T> extends Mapper<T>, MySqlMapper<T>, StreamMapper<T> {
}
使用例子：
this.userMapper.selectStreamByExampleRowBoundsMapper(example, new RowBounds(0, 1), resultContext -> {
User user= (User) resultContext.getResultObject();
System.out.println(user);
});
this.userMapper.selectStreamByExampleMapper(example, resultContext -> {
User user= (User) resultContext.getResultObject();
System.out.println(User);
});