SpringCloud（4）—— EntityManage 分頁解決方案

由於數據庫運用的MySQL，采用分頁機制是滿足MySQL需求的

廢話少說，上代碼

1、不采用Pageable對象分頁，實際原理運用 MySQL中的limit分頁功能

　　　　 Long userid = requestInfo.getQuery();
        Integer currentPage = requestInfo.getCurrentPage();
        Integer pageSize = requestInfo.getPageSize();
　　　　 currentPage = currentPage * pageSize;//由於MySQL中的limit分頁機制：比如“limit 1， 5” ，意思從第一條 往后推算 5 條，所以currentPage頁碼需要乘上每頁條數
        StringBuffer buffer = new StringBuffer("");
        System.out.println("獲取用戶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());
        //設置請求參數
        query.setParameter(1, userid);
        //將查詢結果集轉為Map
        query.unwrap(SQLQuery.class).setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);
        //設置分頁
        query.setFirstResult(currentPage);
        query.setMaxResults(pageSize);
        //獲取查詢結果集
        List<Map<String, Object>> rungroupInfo = query.getResultList();
        List<Rungrouppush> rungrouppushList = EntityAndDTO.mapConvertToBean(rungroupInfo, Rungrouppush.class);

2、將查詢結果map轉換為實體類對象

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 轉換為DTO,
 * 將所有Enity 中和DTO中相同屬性的值進行轉換。
 */
public class EntityAndDTO {
    /**
     * 泛型的轉換接口需要傳入需要被轉換的對象和轉換后的對象的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;
    }

    /**
     * 將map結果集轉換為POJO對象
     * @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;
    }

    /**
     * 將map轉換為POJO對象
     * @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;
    }

}