mybatis查询默认是一次获取全部,如果数据过于庞大,就会导致OOM问题,本文就介绍了tk.mybatis 流式查询,具有一定的参考价值,感兴趣的可以了解一下
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不能为空 * @author sunchangtan */ @tk.mybatis.mapper.annotation.RegisterMapper public interface SelectStreamByExampleMapper { /** * 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不能为空 * @author sunchangtan */ @tk.mybatis.mapper.annotation.RegisterMapper public interface SelectStreamByExampleRowBoundsMapper { /** * 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* @author sunchangtan */ @tk.mybatis.mapper.annotation.RegisterMapper public interface StreamMapper extends SelectStreamByExampleMapper , SelectStreamByExampleRowBoundsMapper { }
在BaseMapper中加入StreamMapper
/** * Mapper的基类 * @author sunchangtan * @param*/ public interface BaseMapper extends Mapper , MySqlMapper , StreamMapper { }
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); });
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