455 lines
12 KiB
Markdown
455 lines
12 KiB
Markdown
# 第6章：MyBatis
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Spring: 负责实现业务层的逻辑
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MyBatis：主要和数据库打交道
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Spring MVC：主要负责前端页面
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## 6.1 MyBatis
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1.持久层框架： 负责数据库开发
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2.ORM框架：Object/Relational Mapping
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3.POJO(Plain Old Java Object)：普通的Java对象
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PO(Persisent Object):持久化对象
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## 6.2
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## 6.3
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## 6.4 MyBatis的入门程序
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基于MyBatis的客户管理系统的设计与实现
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### 系统功能：
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```java
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1. 根据id查询客户
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2. 根据姓名模糊查询
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3. 添加客户
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4. 更新客户
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5. 删除客户
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```
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### 程序准备：
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#### （1）mysql中创建数据库mybatis,表t_customer,插入数据。
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```mysql
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create database mybatis;
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```
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```mysql
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create table t_customer(
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id int (32) primary key auto_increment,
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username varchar(50),
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jobs varchar(50),
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phone varchar(16)
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);
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```
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```mysql
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insert into t_customer values
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('1','joy','doctor','13745874578'),
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('2','jack','teacher','13521210112'),
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('3','tom','worker','15179405961');
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```
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#### （2）创建项目，导2个包：mybatis mysql-connector-java
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```java
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<dependencies>
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<dependency>
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<groupId>org.mybatis</groupId>
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<artifactId>mybatis</artifactId>
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<version>3.4.2</version>
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</dependency>
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<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
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<dependency>
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<groupId>mysql</groupId>
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<artifactId>mysql-connector-java</artifactId>
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<version>8.0.28</version>
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<!-- 版本号与自己mysql版本一致-->
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</dependency>
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```
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#### （3）创建持久化类（实体类）
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作用：和表进行数据转换
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-- 增：实体类对象 转换 表中的记录
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-- 查：表中的记录 转换 实体类对象
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注意：成员变量的名字、数据类型 需要和 表中字段的名字、数据类型 保持一致
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生成setter、getter 和 toString()方法
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```java
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package com.gzh.po;
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public class Customer {
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private int id;
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private String username;
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private String jobs;
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private String phone;
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public int getId() {
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return id;
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}
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public void setId(int id) {
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this.id = id;
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}
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public String getUsername() {
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return username;
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}
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public void setUsername(String username) {
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this.username = username;
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}
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public String getJobs() {
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return jobs;
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}
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public void setJobs(String jobs) {
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this.jobs = jobs;
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}
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public String getPhone() {
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return phone;
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}
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public void setPhone(String phone) {
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this.phone = phone;
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}
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@Override
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public String toString() {
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return "Customer{" +
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"id=" + id +
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", username='" + username + '\'' +
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", jobs='" + jobs + '\'' +
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", phone='" + phone + '\'' +
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'}';
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}
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}
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```
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#### （4）在resources文件夹下创建CustomerMapper.xml文件，用来写sql语句
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##### 1.首先创建模板
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在 file （文件）中的 setting （设置）中搜索 File and Code Templates （文件和代码模板），在其中首页 Files （文件）下创建文件 Mapper.xml，然后在下面填入以下代码，选择 OK （确定） 退出
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```java
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
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<mapper namespace="">
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</mapper>
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```
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##### 2.创建CustomerMapper.xml文件
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在 resources 文件夹右击选择 new（新建）Mapper
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##### 3.写sql语句
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```java
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1.namespace属性的值：copy path（复制路径/引用）中 file name(文件名),去掉.xml
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<mapper namespace="CustomerMapper">
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2.#{id}占位符
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3.parameterType是来设置占位符对应的参数的数据类型
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4.resultType用来设置接收查询结果的持久化类，注意的是resultType属性值是全类名（全限定名）
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<select id="findCustomerById" parameterType="int"resultType="com.gzh.po.Customer">
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select * from t_customer where id=#{id}
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</select>
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```
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#### （5）在resources文件夹下创建mybatis-config.xml文件，该文件是MyBatis框架的配置文件
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##### 1.首先创建模板
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在 file （文件）中的 setting （设置）中搜索 File and Code Templates （文件和代码模板），在其中首页 Files （文件）下创建文件 mybatis-config.xml，然后在下面填入以下代码，选择 OK （确定） 退出
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```java
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
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"http://mybatis.org/dtd/mybatis-3-config.dtd" >
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<configuration>
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</configuration>
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```
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##### 2.创建mybatis-config.xml文件
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在 resources 文件夹右击选择 new（新建）mybatis-config
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##### 3.配置MyBatis框架
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```java
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<configuration>
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<!-- 1.连接数据库-->
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<environments default="mysql">
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<environment id="mysql">
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<transactionManager type="JDBC"></transactionManager>
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<dataSource type="POOLED">
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<!-- 四个成员变量不能错-->
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<property name="driver" value="com.mysql.jdbc.Driver"/>
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<property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
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<property name="username" value="root"/>
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<property name="password" value="8520"/>
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</dataSource>
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</environment>
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</environments>
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<!-- 2.加载Mapper文件-->
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<mappers>
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<!-- resource 从 copy path（复制路径/引用）中 file name(文件名)-->
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<mapper resource="CustomerMapper.xml"/>
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</mappers>
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</configuration>
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```
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#### （6）单元测试：查询
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在 com.gzh.po 包下创建测试类MybatisTest
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1.加载配置文件和 Mapper 文件
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通过 CustomerMapper.xml 文件中的 select 的 id 的值来命名测试类
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在输入 **Resources** 时通过提示导入名为 org 开头的包
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在此输入完此行代码后 getResourceAsStream 会爆红，不用管后续处理
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```java
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InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
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```
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##### 2.构建会话工厂
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```java
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SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
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```
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##### 3.构建会话 SqlSession
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```java
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SqlSession sqlSession = sqlSessionFactory.openSession();
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```
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因为要测试多个方法，所以将以上构造剪切到**成员变量**
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##### 4.处理爆红错误
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将鼠标放置到爆红的 resourceAsStream 处 Alt+回车 处理问题，选择添加类默认构造函数签名的异常
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##### 5.导包 Test ，并写完查询类
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selectOne（）中的参数 = CustomerMapper.xml文件中 namespace + select id
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MybatisTest.java 总体代码如下：
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```java
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package com.gzh.po;
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import org.apache.ibatis.io.Resources;
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import org.apache.ibatis.session.SqlSession;
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import org.apache.ibatis.session.SqlSessionFactory;
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import org.apache.ibatis.session.SqlSessionFactoryBuilder;
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import org.junit.Test;
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import java.io.IOException;
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import java.io.InputStream;
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public class MybatisTest {
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InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
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SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
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SqlSession sqlSession = sqlSessionFactory.openSession();
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public MybatisTest() throws IOException {
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}
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@Test
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public void findCustomerById(){
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// s: = CustomerMapper.xml文件中 namespace + select id
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Customer o = sqlSession.selectOne("CustomerMapper.findCustomerById", 1);
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System.out.println(o);
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}
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}
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```
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运行结果如下：
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### 1.根据id查询客户
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```java
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<select id="findCustomerById" parameterType="int" resultType="com.gzh.po.Customer">
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select * from t_customer where id=#{id}
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</select>
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```
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```java
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@Test
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public void findCustomerById() {
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Customer o = sqlSession.selectOne("com.CustomerMapper.findCustomerById", 1);
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System.out.println(o);
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}
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```
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### 2.根据姓名模糊查询
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```java
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<select id="findCustomerByName" parameterType="String" resultType="com.gzh.po.Customer">
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select * from t_customer where username like '%${value}%'
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</select>
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```
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```java
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@Test
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public void findCustomerByName() {
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List<Customer> o = sqlSession.selectList("CustomerMapper.findCustomerByName", "j");
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for (Customer customer : o){
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System.out.println(customer);
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}
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}
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```
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### 3.添加客户
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```java
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<insert id="addCustomer" parameterType="com.gzh.po.Customer">
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insert into t_customer values (#{id},#{username},#{jobs},#{phone})
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</insert>
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```
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```java
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@Test
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public void addCustomer(){
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Customer customer = new Customer();
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customer.setId(1);
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customer.setUsername("zhangsan");
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customer.setJobs("student");
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customer.setPhone("110");
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sqlSession.insert("CustomerMapper.addCustomer",customer);
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sqlSession.commit();//只要更改数据库中的数据，就需要调用该方法完成数据的
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sqlSession.close();//关闭数据库的连接
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}
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```
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### 4.更新客户
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```java
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<update id="updateCustomer" parameterType="com.gzh.po.Customer">
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update t_customer set username = #{username},jobs = #{jobs},phone = #{phone} where id = #{id}
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</update>
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```
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```java
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@Test
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public void updateCustomer() {
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Customer customer = new Customer();
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customer.setId(4);
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customer.setUsername("zhangsan");
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customer.setJobs("teacher");
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customer.setPhone("18888888888");
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sqlSession.update("CustomerMapper.updateCustomer", customer);
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sqlSession.commit();
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sqlSession.close();
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}
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```
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### 5.删除客户
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```java
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<delete id="deleteCustomer" parameterType="int">
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delete from t_customer where id = #{id}
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</delete>
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```
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```java
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@Test
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public void deleteCustomer() {
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sqlSession.delete("CustomerMapper.deleteCustomer", 1);
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sqlSession.commit();
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sqlSession.close();
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}
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```
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### 如何在控制台输入SQL语句？
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(1) 导包 log4j
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```java
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<dependency>
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<groupId>log4j</groupId>
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<artifactId>log4j</artifactId>
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<version>1.2.17</version>
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</dependency>
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```
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(2) 复制log4j.properties文件到resources.文件夹下
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(3) resources下新建directory,名为com
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(4) 将CustomerMapper.xml文件复制到com下
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(5) 复制后的CustomerMapper.Xml中的namespacel的值修改：com.CustomerMapper
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(6) 修改mybatis-config.xml文件中resource属性的值：
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(7) 修改测试方法中的值：
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运行测试结果如下：
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