扩展tk.mybatis的流式查询功能实现

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);
});

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