Springboot使用JPA实现完整的增删改查（CRUD）和分页

步骤 1 : 可运行项目

首先下载一个简单的可运行项目作为演示 -> 网盘链接：https://www.90pan.com/b1869093

下载后解压，比如解压到 E:\project\springboot 目录下

步骤 2 : CategoryController

为 CategoryController 添加：增加、删除、获取、修改映射

@RequestMapping("/addCategory")
public String addCategory(Category c) throws Exception {
    categoryDAO.save(c);
    return "redirect:listCategory";
}
@RequestMapping("/deleteCategory")
public String deleteCategory(Category c) throws Exception {
    categoryDAO.delete(c);
    return "redirect:listCategory";
}
@RequestMapping("/updateCategory")
public String updateCategory(Category c) throws Exception {
    categoryDAO.save(c);
    return "redirect:listCategory";
}
@RequestMapping("/editCategory")
public String editCategory(int id,Model m) throws Exception {
    Category c= categoryDAO.getOne(id);
    m.addAttribute("c", c);
    return "editCategory";
}

值得注意：JPA 新增和修改用的都是 save. 它根据实体类的id是否为0来判断是进行增加还是修改

修改查询映射

@RequestMapping("/listCategory")
public String listCategory(Model m,@RequestParam(value = "start", defaultValue = "0") int start,@RequestParam(value = "size", defaultValue = "6") int size) throws Exception {
    start = start<0?0:start;
    Sort sort = new Sort(Sort.Direction.DESC, "id");
    Pageable pageable = new PageRequest(start, size, sort);
    Page<Category> page =categoryDAO.findAll(pageable);
    m.addAttribute("page", page);
    return "listCategory";
}

在参数里接受当前是第几页 start ，以及每页显示多少条数据 size。默认值分别是0和6。
(Model m,@RequestParam(value = "start", defaultValue = "0") int start,@RequestParam(value = "size", defaultValue = "6") int size)
如果 start 为负，那么修改为0. 这个事情会发生在当前是首页，并点击了上一页的时候
start = start<0?0:start;
设置倒排序
Sort sort = new Sort(Sort.Direction.DESC, "id");
根据start,size和sort创建分页对象
Pageable pageable = new PageRequest(start, size, sort);
CategoryDAO根据这个分页对象获取结果page.
Page<Category> page = categoryDAO.findAll(pageable);

在这个 page 对象里，不仅包含了分页信息，还包含了数据信息，即有哪些分类数据。这个可以通过 getContent() 获取出来。

把 page 放在 "page" 属性里，跳转到 listCategory.jsp
m.addAttribute("page", page);return "listCategory";

完整 CategoryController 类

package com.ryan.springboot.web;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

import com.ryan.springboot.dao.CategoryDAO;
import com.ryan.springboot.pojo.Category;
  
@Controller
public class CategoryController {
    @Autowired CategoryDAO categoryDAO;
     
    @RequestMapping("/listCategory")
     
    public String listCategory(Model m,@RequestParam(value = "start", defaultValue = "0") int start,@RequestParam(value = "size", defaultValue = "6") int size) throws Exception {
        start = start<0?0:start;
         
        Sort sort = new Sort(Sort.Direction.DESC, "id");
        Pageable pageable = new PageRequest(start, size, sort);
        Page<Category> page = categoryDAO.findAll(pageable);
         
        System.out.println(page.getNumber());
        System.out.println(page.getNumberOfElements());
        System.out.println(page.getSize());
        System.out.println(page.getTotalElements());
        System.out.println(page.getTotalPages());
         
        m.addAttribute("page", page);
         
        return "listCategory";
    }
 
    @RequestMapping("/addCategory")
    public String addCategory(Category c) throws Exception {
        categoryDAO.save(c);
        return "redirect:listCategory";
    }
    @RequestMapping("/deleteCategory")
    public String deleteCategory(Category c) throws Exception {
        categoryDAO.delete(c);
        return "redirect:listCategory";
    }
    @RequestMapping("/updateCategory")
    public String updateCategory(Category c) throws Exception {
        categoryDAO.save(c);
        return "redirect:listCategory";
    }
    @RequestMapping("/editCategory")
    public String ediitCategory(int id,Model m) throws Exception {
        Category c = categoryDAO.getOne(id);
        m.addAttribute("c", c);
        return "editCategory";
    }
}

步骤 3 : listCategory.jsp

通过 page.getContent 遍历当前页面的 Category 对象。
在分页的时候通过 page.number 获取当前页面，page.totalPages获取总页面数。
注：page.getContent会返回一个泛型是Category的集合。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
 
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
   
<div align="center">
 
</div>
 
<div style="width:500px;margin:20px auto;text-align: center">
    <table align='center' border='1' cellspacing='0'>
        <tr>
            <td>id</td>
            <td>name</td>
            <td>编辑</td>
            <td>删除</td>
        </tr>
        <c:forEach items="${page.content}" var="c" varStatus="st">
            <tr>
                <td>${c.id}</td>
                <td>${c.name}</td>
                <td><a href="editCategory?id=${c.id}">编辑</a></td>
                <td><a href="deleteCategory?id=${c.id}">删除</a></td>
            </tr>
        </c:forEach>
         
    </table>
    <br>
    <div>
                <a href="?start=0">[首  页]</a>
            <a href="?start=${page.number-1}">[上一页]</a>
            <a href="?start=${page.number+1}">[下一页]</a>
            <a href="?start=${page.totalPages-1}">[末  页]</a>
    </div>
    <br>
    <form action="addCategory" method="post">
     
    name: <input name="name"> <br>
    <button type="submit">提交</button>
     
    </form>
</div>

步骤 4 : editCategory.jsp

修改分类的页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
 pageEncoding="UTF-8" isELIgnored="false"%>
 
<div style="margin:0px auto; width:500px">
 
<form action="updateCategory" method="post">
 
name: <input name="name" value="${c.name}"> <br>
 
<input name="id" type="hidden" value="${c.id}">
<button type="submit">提交</button>
 
</form>
</div>

步骤 5 : 重启测试

因为在pom中增加了新jar的依赖，所以要手动重启，重启后访问测试地址：

http://127.0.0.1:8080/listCategory?start=0

注：启动方式是 Springboot 特有的，直接运行类：com.ryan.springboot.Application 的主方法。
看到如图所示的效果