springboot sql不用limit语句实现分页查询，很方便！！！

1、涉及内容：

①springboot

②java分页查询

③bootstrap前端框架 表单

④FreeMarker的<#if><#else>、<#list>标签使用

1.1建表：

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) NOT NULL,
  `password` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=14 DEFAULT CHARSET=utf8;

 1.2、我的springboot目录：

 

1.3、maven依赖：

对于springboot框架 以及FreeMarker模板等

 

 
        org.springframework.boot
        spring-boot-starter-parent
        
        1.5.6.RELEASE
         
    

    
        UTF-8
        UTF-8
        1.7
    



    
        org.springframework.boot
        spring-boot-starter
        
            
                org.springframework.boot
                spring-boot-starter-logging
            
        
    

    
        org.springframework.boot
        spring-boot-starter-web
        
            
                org.springframework.boot
                spring-boot-starter-logging
            
        
    

    
        org.springframework.boot
        spring-boot-legacy
        1.1.0.RELEASE
    
    
    
        org.springframework.boot
        spring-boot-starter-freemarker
    

    
    
        org.springframework.boot
        spring-boot-starter-log4j
        1.3.8.RELEASE
    

    
        c3p0
        c3p0
        0.9.0
    

    
        commons-dbutils
        commons-dbutils
        1.7
    

    
        com.sinocontact
        sinocontact-dbutils
        0.0.1
    

    
        mysql
        mysql-connector-java
        5.1.21
    

    
        com.alibaba
        fastjson
        1.2.15
    


    
        com.aliyun.oss
        aliyun-sdk-oss
        2.8.2
    


    
        org.apache.commons
        commons-lang3
        3.5
    

    
        org.springframework.boot
        spring-boot-starter-data-redis
    

    
        org.springframework.session
        spring-session-data-redis
    
    
    
        javax.mail
        mail
        1.4.7
    


    
    
        org.apache.poi
        poi-ooxml
        3.17
    

    
    
        net.sf.barcode4j
        barcode4j-light
        2.0
    

    
        
        org.jsoup
        jsoup
        1.11.3
    

    
        com.sinocontact
        aspectjweaver
        1.9.1
    


    
        com.sinocontact
        aspose-words
        14.9.0
    





    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

 2、实现效果：

3、具体实现：

 

3.1、User实体类：

package com.lemon.pojo;

public class User {

    private Integer id;
    private String username;
    private String password;

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

3.2、UserDao

springboot可以整合mybatis、hobernate等，用于数据库查询（熟练那个就用哪个）

package com.lemon.dao;

import com.lemon.pojo.User;
import com.lemon.utils.Page;
import com.lemon.utils.PageUtils;
import com.sinocontact.dbutils.DBControl;
import org.apache.log4j.Logger;
import org.omg.PortableInterceptor.INACTIVE;


import java.util.List;

public class UserDao {

    private static final Logger logger = Logger.getLogger(UserDao.class);

    //查询所有用户
    public Page queryAllUser(Integer pageNo){

        String sql = "select * from user";
        try {

            List userList = DBControl.getMainDbOperator().queryBeanList(sql, User.class);

            Page page = PageUtils.doPage(userList, pageNo);

            return page;
        }catch (Exception e){
            logger.error("查询user错误：",e);
        }

        return null;
    }

}

 3.3、userService：

package com.lemon.service;

import com.lemon.dao.UserDao;
import com.lemon.pojo.User;
import com.lemon.utils.Page;
import org.apache.commons.lang3.StringUtils;
import org.apache.log4j.Logger;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserService {
    private static final Logger logger = Logger.getLogger(UserService.class);

    private UserDao userDao = new UserDao();

    //查询所有用户
    public Page queryAllUser(String pageNo){

        Integer realPageNo = getRealPageNo(pageNo);

        Page page = userDao.queryAllUser(realPageNo);




        return page;
    }

    /**
     * 真实页码
     * @author lemon
     * @since 2019/10/28 0028
     */
    private Integer getRealPageNo(String pageNo) {
        Integer realPageNo = 1;

        try {
            if (!StringUtils.isEmpty(pageNo)) {
                realPageNo = Integer.parseInt(pageNo);
            }
        }catch (Exception e){
            logger.error("真实页码转换错误",e);
        }

        return realPageNo;
    }

}

 3.4、Page.java

分页实体类

package com.lemon.utils;

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

import org.apache.log4j.Logger;



/**
 * 分页实体类
 * 页码从第一页开始。
 * @author lemon
 * @since 2019/10/28 0028
 */
public class Page {
    private static final Logger logger = Logger.getLogger(Page.class);

    //返回的一页数据
    private List list = new ArrayList();

    //符合条件的总记录数
    private Integer totalElements = 0;

    //符合条件的总页数
    private Integer totalPages = 0;

    //一页多少条记录
    private Integer pageSize = 3;

    //当前页码
    private Integer currentPageNo = 1;

    //上一页的页码（如果为0，表示不同显示或不可点击）
    private Integer prevPageNo = 0;

    //下一页的页码（如果为0，表示不用显示或不可点击）
    private Integer nextPageNo = 0;

    //可点击的页码列表（其中页码为零表示不可点击）
    private List pageNoList = new ArrayList<>();

    @Override
    public String toString() {
        return "Page{" +
                "list=" + list +
                ", Page一页数据输出：totalElement=" + totalElements +
                ", totalPages=" + totalPages +
                ", pageSize=" + pageSize +
                ", currentPageNo=" + currentPageNo +
                ", prevPageNo=" + prevPageNo +
                ", nextPageNo=" + nextPageNo +
                ", pageNoList=" + pageNoList +
                '}';
    }

    public Integer getTotalElements() {
        return totalElements;
    }

    public void setTotalElements(Integer totalElements) {
        this.totalElements = totalElements;
    }

    public static Logger getLogger() {
        return logger;
    }

    public List getList() {
        return list;
    }

    public void setList(List list) {
        this.list = list;
    }


    public Integer getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(Integer totalPages) {
        this.totalPages = totalPages;
    }

    public Integer getPageSize() {
        return pageSize;
    }

    public void setPageSize(Integer pageSize) {
        this.pageSize = pageSize;
    }

    public Integer getCurrentPageNo() {
        return currentPageNo;
    }

    public void setCurrentPageNo(Integer currentPageNo) {
        this.currentPageNo = currentPageNo;
    }

    public Integer getPrevPageNo() {
        return prevPageNo;
    }

    public void setPrevPageNo(Integer prevPageNo) {
        this.prevPageNo = prevPageNo;
    }

    public Integer getNextPageNo() {
        return nextPageNo;
    }

    public void setNextPageNo(Integer nextPageNo) {
        this.nextPageNo = nextPageNo;
    }

    public List getPageNoList() {
        return pageNoList;
    }

    public void setPageNoList(List pageNoList) {
        this.pageNoList = pageNoList;
    }
}

 3.5、PageUtils.java

分页工具类

package com.lemon.utils;

import org.apache.log4j.Logger;

import java.util.ArrayList;
import java.util.List;
/**
 * 分页工具类
 * @author: lemon
 * @since: 2019/10/29 0029
 */
public class PageUtils {

    private static final Logger logger = Logger.getLogger(PageUtils.class);

    //一页最多显示多少条记录
    private static final Integer pageSize = 3;

    //页码最多显示多少个
    private static final Integer maxCountPageNo = 3;

    /**
     * 进行指定页数据获取
     * @author lemon
     * @since 2019/10/28 0028
     */
    public static Page doPage(List elementList, Integer pageNo){
        Page page = new Page();

        //设置一页多少条记录
        page.setPageSize(pageSize);
        //数据为空 则返回Page默认设置
        if(elementList == null || elementList.size() == 0){
            return page;
        }
        //设置总的页码数
        Integer totalPages = getTotalPageNo(elementList);
        page.setTotalPages(totalPages);

        //设置总的记录数
        page.setTotalElements(elementList.size());

        //设置当前的页码
        Integer realPageNo = getCurrentPageNo(pageNo,totalPages);
        page.setCurrentPageNo(pageNo);

        //设置上一页的页码
        Integer prevPageNo = getPrevPageNo(pageNo);
        page.setPrevPageNo(prevPageNo);

        //设置下一页的页码
        Integer nextPageNo = getNextPageNo(pageNo,totalPages);
        page.setNextPageNo(nextPageNo);

        //得到可点击的list
        List pageNoList = getPageNoList(pageNo, totalPages);
        page.setPageNoList(pageNoList);

        //得到指定页的一页数据
        List currentPageElementList = getCurrentPageElementList(elementList, pageNo);
        page.setList(currentPageElementList);

        return page;
    }




    /**
     * 获得总页码数
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static Integer getTotalPageNo(List elementList) {
        //计算总页数
        int totalPages = elementList.size()/pageSize;

        if((elementList.size()/pageSize) != 0){
            totalPages = totalPages + 1;
        }

        return totalPages;
    }

    /**
     * 得到当前正确页码
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static Integer getCurrentPageNo(Integer pageNo, Integer totalPages) {

        if(pageNo < 1){ // 页码小于1 则设为第一页
            pageNo = 1;
        }
        if(pageNo > totalPages){ // 页码大于最大页 则设为最后一页
            pageNo = totalPages;
        }

        return pageNo;
    }

    /**
     * 得到当前页面的上一页
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static Integer getPrevPageNo(Integer pagaNo){
        Integer pervPageNo = pagaNo - 1;

        if(pervPageNo < 0){
            pervPageNo = 0;
        }

        return pervPageNo;
    }

    /**
     * 得到当前页面的上一页
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static Integer getNextPageNo(Integer pagaNo, Integer totalPage){
        Integer nextPageNo = pagaNo + 1;

        if(nextPageNo < 2){
            nextPageNo = 2;
        }

        if(nextPageNo > totalPage){ //超过总页码，设置为0 ， 表示没有下一页
            nextPageNo = 0;
        }
        return nextPageNo;
        }

    /**
     * 得到可点击页码
     * @param pageNo 当前页码
     * @param totalPages 总的页码
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static List getPageNoList(Integer pageNo, Integer totalPages) {
        List pageNoList = new ArrayList<>();

        //只有一页的情况
        if(totalPages < 2){
            pageNoList.add(1);
            return pageNoList;
        }

        //总页码数小于最大显示页码数
        if(totalPages < maxCountPageNo){
            for (int i = 1; i <= totalPages; i++) {
                pageNoList.add(i);
            }
            return pageNoList;
        }

        //当前页数小于等于最大显示页数
        if(pageNo <= maxCountPageNo){
            for (int i = 1; i <= pageSize; i++) {
                pageNoList.add(i);
            }
            return pageNoList;
        }

        //当前页数大于最大显示页数
        if(pageNo > maxCountPageNo){
            for (int i = 0; i < 3; i++) {
                pageNoList.add(pageNo - pageSize + i + 1);

                if (i == pageSize){
                    break;
                }
            }
            return pageNoList;
        }

        return pageNoList;
    }


    /**
     * 得到指定页的一页数据
     * @param elementList
     * @param pageNo
     * @return List
     * @author lemon
     * @since 2019/10/28 0028
     */
    private static List getCurrentPageElementList(List elementList, Integer pageNo) {
        ArrayList onePageElementList = new ArrayList();

        int startIndex = (pageNo - 1) * pageSize;
        for(int i = startIndex; i < elementList.size(); i++){//从指定页的记录数开始取，如果不满一页的数据，则全部取得
            Object ob = elementList.get(i);
            onePageElementList.add(ob);
            if(onePageElementList.size() >= pageSize) {//如果取慢一页数据 则不再取
                break;
            }
        }
        return onePageElementList;
    }




}

 3.6、list.html

页面显示（这里使用FreeMarker语句 if list等）

    
    
    
    
    




    
        <#list page.list as user>
        

        

        

            
ID
            
用户名
            
密码
        
        
        

            
${user.id}
            
${user.username}
            
${user.password}
        
        
        
    

    
        

            <#if page.totalPages gt 1 >
            

                



                    <#if page.prevPageNo gt 0>
                    
«
                    <#else>
                    
«
                     


                <#list page.pageNoList as pageNo>
                     <#if page.currentPageNo == pageNo>
                
${pageNo}
                <#else>
                
${pageNo}
            
            




            <#if page.nextPageNo gt 0>
                
»
                <#else>
                 
»
                
                
            
            

            

                每页${page.pageSize}条 共${page.totalElements}条 共${page.totalPages}页