擴展tk.mybatis的流式查詢功能實現(xiàn)

更新時間：2021年12月01日 15:41:47 作者：sunct

mybatis查詢默認是一次獲取全部，如果數(shù)據(jù)過于龐大，就會導致OOM問題，本文就介紹了tk.mybatis 流式查詢，具有一定的參考價值，感興趣的可以了解一下

mybatis查詢默認是一次獲取全部，有時候需要查詢上萬上百萬數(shù)據(jù)時，如果一次性讀取到內(nèi)存中，會容易導致OOM問題。這時候需要采用流式查詢。以下擴展了tk.mybatis的流式查詢功能。直接上干貨：

@Options注解是關鍵

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,流式查詢
 *
 * @param <T> 不能為空
 * @author sunchangtan
 */
@tk.mybatis.mapper.annotation.RegisterMapper
public interface SelectStreamByExampleMapper<T> {

    /**
     * 根據(jù)example條件和RowBounds進行流式查詢
     *
     * @param example
     * @return
     */
    @Options(resultSetType = ResultSetType.FORWARD_ONLY, fetchSize = 1000)
    @SelectProvider(type = StreamExampleProvider.class, method = "dynamicSQL")
    void selectStreamByExampleMapper(Object example, ResultHandler resultHandler);

}

帶RowBounds的流式查詢

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,流式查詢
 *
 * @param <T> 不能為空
 * @author sunchangtan
 */
@tk.mybatis.mapper.annotation.RegisterMapper
public interface SelectStreamByExampleRowBoundsMapper<T> {

    /**
     * 根據(jù)example條件和RowBounds進行流式查詢
     *
     * @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;

/**
 * 流式查詢的SqlProvider
 * @author sunchangtan
 */

public class StreamExampleProvider extends ExampleProvider {

    public StreamExampleProvider(Class<?> mapperClass, MapperHelper mapperHelper) {
        super(mapperClass, mapperHelper);
    }


    /**
     * 根據(jù)Example流式查詢
     *
     * @param ms
     * @return
     */
    public String selectStreamByExampleMapper(MappedStatement ms) {
        return this.selectByExample(ms);
    }

    /**
     * 根據(jù)Example和RowBounds流式查詢
     * @param ms
     * @return
     */
    public String selectStreamByExampleRowBoundsMapper(MappedStatement ms) {
        return this.selectByExample(ms);
    }

}

將SelectStreamByExampleMapper和SelectStreamByExampleRowBoundsMapper組合成一個接口

/**
 * 流式查詢接口
 * @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的基類
 * @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);
});

到此這篇關于擴展tk.mybatis的流式查詢功能實現(xiàn)的文章就介紹到這了,更多相關tk.mybatis 流式查詢內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關文章希望大家以后多多支持腳本之家！?

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