JAVA高级面试进阶训练营视频教程

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由于数据库运用的MySQL，采用分页机制是满足MySQL需求的

废话少说，上代码

1、不采用Pageable对象分页，实际原理运用 MySQL中的limit分页功能

　　　　 Long userid = requestInfo.getQuery();
        Integer currentPage = requestInfo.getCurrentPage();
        Integer pageSize = requestInfo.getPageSize();
　　　　 currentPage = currentPage * pageSize;//由于MySQL中的limit分页机制：比如“limit 1， 5” ，意思从第一条 往后推算 5 条，所以currentPage页码需要乘上每页条数
        StringBuffer buffer = new StringBuffer("");
        System.out.println("获取用户ID信息：" + userid);
        buffer.append("select * from Rungrouppush r where r.userid = ? and readflag<>'S' order by pushdate desc,pushtime desc");
        Query query = this.entityManager.createNativeQuery(buffer.toString());
        //设置请求参数
        query.setParameter(1, userid);
        //将查询结果集转为Map
        query.unwrap(SQLQuery.class).setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);
        //设置分页
        query.setFirstResult(currentPage);
        query.setMaxResults(pageSize);
        //获取查询结果集
        List<Map<String, Object>> rungroupInfo = query.getResultList();
        List<Rungrouppush> rungrouppushList = EntityAndDTO.mapConvertToBean(rungroupInfo, Rungrouppush.class);

2、将查询结果map转换为实体类对象

package com.sinosoft.common;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.BeanUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * 快速的 domain 转换为DTO,
 * 将所有Enity 中和DTO中相同属性的值进行转换。
 */
public class EntityAndDTO {
    /**
     * 泛型的转换接口需要传入需要被转换的对象和转换后的对象的Class
     *
     * @param t
     * @param eClass
     * @param <E>
     * @param <T>
     * @return E
     */
    public static <E, T> E convert(T t, Class<E> eClass) {
        E e = null;
        try {
            e = eClass.newInstance();
            BeanUtils.copyProperties(t, e);

        } catch (InstantiationException e1) {
            e1.printStackTrace();
        } catch (IllegalAccessException e1) {
            e1.printStackTrace();
        }
        return e;
    }

    public static <E, T> List<E> convert(List<T> tList, Class<E> eClass) {

        List<E> eList = new ArrayList<E>();
        for (T t : tList) {
            eList.add(convert(t, eClass));
        }
        return eList;
    }

    /**
     * 将map结果集转换为POJO对象
     * @param tList source
     * @param eClass class
     * @param <E> e
     * @param <T> t
     * @return t
     */
    public static <E, T> List<E> mapConvertToBean(List<T> tList, Class<E> eClass) {
        List<E> eList = new ArrayList<E>();
        try {
            for (T t : tList) {
                Map<String, Object> map = (Map<String, Object>) t;
                eList.add((E) mapConvertToObject(map, eClass));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return eList;
    }

    /**
     * 将map转换为POJO对象
     * @param map map
     * @param beanClass class
     * @return r
     */
    public static Object mapConvertToObject(Map<String, Object> map, Class beanClass) {
        ObjectMapper mapper = new ObjectMapper();
        Object pojo = mapper.convertValue(map, beanClass);
        return pojo;
    }

}