PageHelper · 随堂笔记-Java105班

[TOC] # PageHelper ## 步骤 1 : 基于前面的知识点本知识点基于SSM 分页进行，SSM 分页进行是采用手动SQL方式进行，本知识点将采用PageHelper插件进行。 PageHelper是一款犀利的Mybatis分页插件，使用了这个插件之后，分页开发起来更加简单容易。 ## 步骤 2 : 先运行，看到效果，再学习先将完整的项目（向老师要相关资料），配置运行起来，确认可用之后，再学习做了哪些步骤以达到这样的效果。 ## 步骤 3 : 模仿和排错在确保可运行项目能够正确无误地运行之后，再严格照着教程的步骤，对代码模仿一遍。模仿过程难免代码有出入，导致无法得到期望的运行结果，此时此刻通过比较**正确答案** ( 可运行项目 ) 和自己的代码，来定位问题所在。采用这种方式，**学习有效果，排错有效率**，可以较为明显地提升学习速度，跨过学习路上的各个槛。 ## 步骤 4 : 效果访问页面看到如图所示效果 ## 步骤 5 : jar包因为是第三方插件，所以需要额外的jar包（向老师要相关资料）：pagehelper-5.1.0-beta2.jar，jsqlparser-1.0.jar ，将包放在WEB-INF/lib下 ## 步骤 6 : 修改applicationContext.xml 增加PageHelper插件配置 ~~~ <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation=" http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd">   <context:annotation-config />  <context:component-scan base-package="com.dodoke.service" />  <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName"> <value>com.mysql.jdbc.Driver</value> </property> <property name="url"> <value>jdbc:mysql://localhost:3306/ssm_integration?characterEncoding=UTF-8 </value> </property> <property name="username"> <value>root</value> </property> <property name="password"> <value></value> </property> </bean>   <bean id="sqlSession" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="typeAliasesPackage" value="com.dodoke.pojo" /> <property name="dataSource" ref="dataSource" /> <property name="mapperLocations" value="classpath:com/dodoke/mapper/*.xml" />  <property name="plugins"> <array> <bean class="com.github.pagehelper.PageInterceptor"> <property name="properties"> <value> </value> </property> </bean> </array> </property> </bean>  <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="com.dodoke.mapper" /> </bean> </beans> ~~~ ## 步骤 7 : CategoryService CategoryService去掉total方法和list(Page) 方法 ~~~ package com.dodoke.service; import java.util.List; import com.dodoke.pojo.Category; public interface CategoryService { List<Category> list(); } ~~~ ## 步骤 8 : CategoryServiceImpl CategoryServiceImpl去掉total方法和list(Page) 方法 ~~~ package com.dodoke.service.impl; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import com.dodoke.mapper.CategoryMapper; import com.dodoke.pojo.Category; import com.dodoke.service.CategoryService; @Service public class CategoryServiceImpl implements CategoryService { @Autowired CategoryMapper categoryMapper; @Override public List<Category> list() { return categoryMapper.list(); } } ~~~ ## 步骤 9 : CategoryMapper CategoryMapper去掉total方法和list(Page) 方法 ~~~ package com.dodoke.mapper; import java.util.List; import com.dodoke.pojo.Category; public interface CategoryMapper { public int add(Category category); public void delete(int id); public int update(Category category); public Category get(int id); public List<Category> list(); } ~~~ ## 步骤 10 : Category.xml Category.xml去掉total对应的sql语句，list也去掉limit ~~~ <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.dodoke.mapper.CategoryMapper"> <insert id="add" parameterType="Category"> insert into category(name) values(#{name}) </insert> <delete id="delete" parameterType="Category"> delete from category where id=#{id} </delete> <update id="update" parameterType="Category"> update category set name=#{name} where id=#{id} </update> <select id="get" parameterType="int" resultType="Category"> select * from category where id=#{id} </select> <select id="list" resultType="Category"> select * from category </select> </mapper> ~~~ ## 步骤 11 : CategoryController CategoryController在调用categoryService.list(); 之前，执行： `PageHelper.offsetPage(page.getStart(),5);` 并通过`int total = (int) new PageInfo<>(cs).getTotal();`获取总数。其他都不变 ~~~ package com.dodoke.controller; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.servlet.ModelAndView; import com.dodoke.pojo.Category; import com.dodoke.service.CategoryService; import com.dodoke.util.Page; import com.github.pagehelper.PageHelper; import com.github.pagehelper.PageInfo; //告诉spring mvc这是一个控制器类 @Controller @RequestMapping("") public class CategoryController { @Autowired CategoryService categoryService; @RequestMapping("listCategory") public ModelAndView listCategory(Page page) { ModelAndView mav = new ModelAndView(); PageHelper.offsetPage(page.getStart(), 5); List<Category> cs = categoryService.list(); int total = (int)new PageInfo<>(cs).getTotal(); page.calculateLast(total); // 放入转发参数 mav.addObject("cs",cs); // 放入jsp路径 mav.setViewName("listCategory"); return mav; } } ~~~ ## 步骤 12 : MybatisTest MybatisTest 类注释掉用旧方式分页的代码 ~~~ package com.dodoke.test; import java.util.List; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import com.dodoke.mapper.CategoryMapper; import com.dodoke.pojo.Category; import com.dodoke.util.Page; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration("classpath:applicationContext.xml") public class MybatisTest { @Autowired private CategoryMapper categoryMapper; @Test public void testAdd() { for (int i = 0; i < 100; i++) { Category category = new Category(); category.setName("new Category"); categoryMapper.add(category); } } // @Test // public void testTotal() { // int total = categoryMapper.total(); // System.out.println(total); // } // // @Test // public void testList() { // Page p = new Page(); // p.setStart(2); // p.setLast(3); // List<Category> cs = categoryMapper.list(p); // for (Category c : cs) { // System.out.println(c.getName()); // } // } } ~~~ ## 步骤 13 : listCategory.jsp 增加分页临界判断 ~~~ <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Insert title here</title> </head> <body> <table border='1' cellspacing='0'> <tr> <td>id</td> <td>name</td> </tr> <c:forEach items="${cs}" var="c" varStatus="st"> <tr> <td>${c.id}</td> <td>${c.name}</td> </tr> </c:forEach> </table> <div style=""> <a href="?start=0">首页</a> <c:if test="${page.start-page.count>=0}"> <a href="?start=${page.start-page.count}">上一页</a> </c:if> <c:if test="${page.start-page.count<0}"> <a href="javascript:void(0)">上一页</a> </c:if> <c:if test="${page.start+page.count<=page.last}"> <a href="?start=${page.start+page.count}">下一页</a> </c:if> <c:if test="${page.start+page.count>page.last}"> <a href="javascript:void(0)">下一页</a> </c:if> <a href="?start=${page.last}">末页</a> </div> </body> </html> ~~~ ## 步骤 14 : 重启tomcat,测试重启tomcat,访问地址： `http://127.0.0.1:8080/ssm/listCategory` ![](https://box.kancloud.cn/fd23d423c2ed83ec27c773854b7f8f20_542x370.png)