PageHelper · 隨堂筆記-Java105班

[TOC] # PageHelper ## 步驟 1 : 基于前面的知識點本知識點基于SSM 分頁進行，SSM 分頁進行是采用手動SQL方式進行，本知識點將采用PageHelper插件進行。 PageHelper是一款犀利的Mybatis分頁插件，使用了這個插件之后，分頁開發起來更加簡單容易。 ## 步驟 2 : 先運行，看到效果，再學習先將完整的項目（向老師要相關資料），配置運行起來，確認可用之后，再學習做了哪些步驟以達到這樣的效果。 ## 步驟 3 : 模仿和排錯在確保可運行項目能夠正確無誤地運行之后，再嚴格照著教程的步驟，對代碼模仿一遍。模仿過程難免代碼有出入，導致無法得到期望的運行結果，此時此刻通過比較**正確答案** ( 可運行項目 ) 和自己的代碼，來定位問題所在。采用這種方式，**學習有效果，排錯有效率**，可以較為明顯地提升學習速度，跨過學習路上的各個檻。 ## 步驟 4 : 效果訪問頁面看到如圖所示效果 ## 步驟 5 : jar包因為是第三方插件，所以需要額外的jar包（向老師要相關資料）：pagehelper-5.1.0-beta2.jar，jsqlparser-1.0.jar ，將包放在WEB-INF/lib下 ## 步驟 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> ~~~ ## 步驟 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(); } ~~~ ## 步驟 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(); } } ~~~ ## 步驟 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(); } ~~~ ## 步驟 10 : Category.xml Category.xml去掉total對應的sql語句，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> ~~~ ## 步驟 11 : CategoryController CategoryController在調用categoryService.list(); 之前，執行： `PageHelper.offsetPage(page.getStart(),5);` 并通過`int total = (int) new PageInfo<>(cs).getTotal();`獲取總數。其他都不變 ~~~ 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; //告訴spring mvc這是一個控制器類 @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); // 放入轉發參數 mav.addObject("cs",cs); // 放入jsp路徑 mav.setViewName("listCategory"); return mav; } } ~~~ ## 步驟 12 : MybatisTest MybatisTest 類注釋掉用舊方式分頁的代碼 ~~~ 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()); // } // } } ~~~ ## 步驟 13 : listCategory.jsp 增加分頁臨界判斷 ~~~ <%@ 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>${c.name}</td> </tr> </c:forEach> </table> <div style=""> <a href="?start=0">首頁</a> <c:if test="${page.start-page.count>=0}"> <a href="?start=${page.start-page.count}">上一頁</a> </c:if> <c:if test="${page.start-page.count<0}"> <a href="javascript:void(0)">上一頁</a> </c:if> <c:if test="${page.start+page.count<=page.last}"> <a href="?start=${page.start+page.count}">下一頁</a> </c:if> <c:if test="${page.start+page.count>page.last}"> <a href="javascript:void(0)">下一頁</a> </c:if> <a href="?start=${page.last}">末頁</a> </div> </body> </html> ~~~ ## 步驟 14 : 重啟tomcat,測試重啟tomcat,訪問地址： `http://127.0.0.1:8080/ssm/listCategory` ![](https://box.kancloud.cn/fd23d423c2ed83ec27c773854b7f8f20_542x370.png)