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步骤1:先运行，看到效果，再学习步骤2:模仿和排错步骤3:增加100条catgory数据步骤4:修改Category.xml步骤5:测试步骤6:注解方式

步骤 1 : 先运行，看到效果，再学习
老规矩，先下载下载区(点击进入)的可运行项目，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 2 : 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。
推荐使用diffmerge软件，进行文件夹比较。把你自己做的项目文件夹，和我的可运行项目文件夹进行比较。
这个软件很牛逼的，可以知道文件夹里哪两个文件不对，并且很明显地标记出来
这里提供了绿色安装和使用教程：diffmerge 下载和使用教程步骤 3 : 增加100条catgory数据
为了观察分页查询的效果，把分类表里的数据都删除掉，然后新增100个数据package com.how2java;import java.io.IOException;import java.io.InputStream;import java.util.List;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.how2java.pojo.Category;public class TestMybatis {public static void main(String[] args) throws IOException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(inputStream);SqlSession session = sqlSessionFactory.openSession();List<Category> cs = session.selectList("listCategory");for (Category c : cs) {session.delete("deleteCategory", c);}for (int i = 0; i < 100; i++) {Category c = new Category();c.setName("category name " + i);session.insert("addCategory", c);}List<Category> cs2 = session.selectList("listCategory");for (Category c : cs2) {System.out.println(c.getName());}session.commit();session.close();}}步骤 4 : 修改Category.xml
新增limit<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.how2java.pojo"><insert id="addCategory" parameterType="Category" >insert into category_ ( name ) values (#{name}) </insert><delete id="deleteCategory" parameterType="Category" >delete from category_ where id= #{id} </delete><select id="getCategory" parameterType="_int" resultType="Category">select * from category_ where id= #{id} </select><update id="updateCategory" parameterType="Category" >update category_ set name=#{name} where id=#{id} </update><select id="listCategory" resultType="Category">select * from category_ <if test="start!=null and count!=null">limit #{start},#{count}</if></select> </mapper>步骤 5 : 测试
用注解方式再做一遍注： start是指从第0个开始，如果是第二页，那么就是第5个开始。注： count参数是指每页有5条数据

• CategoryMapper.java
• TestMybatis.java

package com.how2java.mapper;import java.util.List;import org.apache.ibatis.annotations.Many;import org.apache.ibatis.annotations.Param;import org.apache.ibatis.annotations.Result;import org.apache.ibatis.annotations.Results;import org.apache.ibatis.annotations.Select;import com.how2java.pojo.Category;public interface CategoryMapper {public List<Category> list();public List<Category> listByPage(@Param("start") int start, @Param("count")int count);}package com.how2java;import java.io.IOException;import java.io.InputStream;import java.util.HashMap;import java.util.List;import java.util.Map;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.how2java.mapper.CategoryMapper;import com.how2java.pojo.Category;public class TestMybatis {public static void main(String[] args) throws IOException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(inputStream);SqlSession session = sqlSessionFactory.openSession();// xmlWay(session); annotationWay(session);session.commit();session.close();}private static void xmlWay(SqlSession session) {Map<String,Object> params = new HashMap<>();params.put("start", 0);params.put("count", 5);List<Category> cs =session.selectList("listCategory", params);for (Category c : cs) {System.out.println(c);}}private static void annotationWay(SqlSession session) {CategoryMapper mapper = session.getMapper(CategoryMapper.class);List<Category> cs =mapper.listByPage(0, 5);for (Category c : cs) {System.out.println(c);}}}步骤 6 : 注解方式

• CategoryMapper.java
• TestMybatis.java

package com.how2java.mapper;import java.util.List;import org.apache.ibatis.annotations.Many;import org.apache.ibatis.annotations.Param;import org.apache.ibatis.annotations.Result;import org.apache.ibatis.annotations.Results;import org.apache.ibatis.annotations.Select;import com.how2java.pojo.Category;public interface CategoryMapper {@Select(" select * from category_ ")@Results({@Result(property = "products", javaType = List.class, column = "id", many = @Many(select = "com.how2java.mapper.ProductMapper.listByCategory"))}) public List<Category> list();@Select(" select * from category_ limit #{start},#{count}")public List<Category> listByPage(@Param("start") int start, @Param("count")int count);}package com.how2java;import java.io.IOException;import java.io.InputStream;import java.util.List;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.how2java.mapper.CategoryMapper;import com.how2java.pojo.Category;public class TestMybatis {public static void main(String[] args) throws IOException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(inputStream);SqlSession session = sqlSessionFactory.openSession();CategoryMapper mapper = session.getMapper(CategoryMapper.class);List<Category> cs =mapper.listByPage(0, 5);for (Category c : cs) {System.out.println(c);}session.commit();session.close();}}
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