385 lines
10 KiB
Markdown
385 lines
10 KiB
Markdown
# 第七章：MyBatis核心配置
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## 7.1 核心对象
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### 1.复制第6章的代码
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#### （1）导包 mybatis mysql
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```java
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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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</dependency>
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```
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#### （2）准备数据
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沿用上一章节数据
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#### （3）复制实体类
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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）复制两个xml文件
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mybatis-config.xml：
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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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<!--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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<!--
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transactionManager：设置事务管理方式
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属性：
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type：设置事务管理方式，type="JDBC|MANAGED"
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type="JDBC"：设置当前环境的事务管理都必须手动处理
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type="MANAGED"：设置事务被管理，例如spring中的AOP
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-->
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<dataSource type="POOLED">
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<!--
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dataSource：设置数据源
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属性：
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type：设置数据源的类型，type="POOLED|UNPOOLED|JNDI"
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type="POOLED"：使用数据库连接池，即会将创建的连接进行缓存，下次使用可以从缓存中直接获取，不需要重新创建
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type="UNPOOLED"：不使用数据库连接池，即每次使用连接都需要重新创建
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type="JNDI"：调用上下文中的数据源
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-->
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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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<!--
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以包为单位，将包下所有的映射文件引入核心配置文件
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注意：
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1. 此方式必须保证mapper接口和mapper映射文件必须在相同的包下
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2. mapper接口要和mapper映射文件的名字一致
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-->
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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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CustomerMapper.xml：
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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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<!-- namespace属性的值：copy path 中 file name(复制引用中的文件名),去掉.xml-->
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<mapper namespace="CustomerMapper">
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<!-- 1.根据id查询客户信息-->
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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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<!-- 2.根据客户名进项模糊搜索-->
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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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<!-- 3.添加客户-->
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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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<!-- 4.更新客户-->
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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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<!-- 5.删除客户-->
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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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</mapper>
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```
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#### （5）测试类
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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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import java.util.List;
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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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Customer o = sqlSession.selectOne("CustomerMapper.findCustomerById", 2);
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System.out.println(o);
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}
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```
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运行结果如下：
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### 2.创建工具类，对外提供SqlSession对象
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在 main 下创建一个新的包 com.gzh.utils （通常为工具包），并创建类 MyBatisUtil
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```java
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package com.gzh;
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import com.gzh.po.Customer;
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import com.gzh.utils.MyBatisUtil;
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import org.apache.ibatis.session.SqlSession;
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import org.junit.Test;
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public class MyBatisTest {
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SqlSession sqlSession=MyBatisUtil.getSession();
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@Test
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public void findCustomerByIdTest(){
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Customer o = sqlSession.selectOne("CustomerMapper.findCustomerById", 2);
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System.out.println(o);
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}
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}
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```
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将 Test 测试类转移到 com.gzh 包下，代码如下：
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```java
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public class MyBatisTest {
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SqlSession sqlSession=MyBatisUtil.getSession();
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@Test
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public void findCustomerByIdTest(){
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Customer o = sqlSession.selectOne("CustomerMapper.findCustomerById", 2);
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System.out.println(o);
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}
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}
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```
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运行截图：
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## 7.2 配置文件
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### 1.properties 元素
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连接数据库，通过该元素进行内部配置外在化。
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(1) 在resources下创建db.properties
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```java
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jdbc.driver=com.mysql.cj.jdbc.Driver
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jdbc.url=jdbc:mysql://localhost:3306/mybatis
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jdbc.username=root
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jdbc.password=8520
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```
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(2) 修改配置文件 2处
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1.在<configuration>文件下添加<properties>
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```java
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<properties resource="db.properties"/>
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```
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2.在<dataSource>标签中<property>的 value 属性修改如下：
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```java
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<property name="driver" value="${jdbc.driver}"/>
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<property name="url" value="${jdbc.url}"/>
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<property name="username" value="${jdbc.username}"/>
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<property name="password" value="${jdbc.password}"/>
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```
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（3）测试运行截图
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### 2.typeAliases元素 给实体类起别名
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（1）修改CustomerMapper.xml中的：（修改resultType属性）
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```java
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<select id="findCustomerById" parameterType="int" resultType="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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（2）在mybatis-config.xml文件中起别名（添加）
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```java
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<properties resource="db.properties"/>
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<typeAliases>
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<typeAlias type="com.wqx.po.Customer" alias="customer"/>
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</typeAliases>
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```
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（3）测试截图如下：
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## 7.3 映射文件
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### 1.resultMap元素:将表中字段和实体类成员变量进行对应
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（1）修改实体类 username->name
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重写getter and setter 以及 toString()
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（2）测试结果：当实体类中的成员变量名和表中字段名字不一致时，导致字段值不能被赋值给成员变量
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Customer{id=2, name='null', jobs='teacher', phone='13521210112'}
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（3）如何解决当实体类中的成员变量名和表中字段名字不一致时，还可以将字段值赋值给成员变量？
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resultMap
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（4）修改CustomerMapper.xml
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添加 resultMap 和 修改 select 中主键的 resultType 属性改为 resultMap
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```java
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<resultMap id="a" type="customer">
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<id property="id" column="id"/>
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<result property="name" column="username"/>
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<result property="jobs" column="jobs"/>
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<result property="phone" column="phone"/>
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</resultMap>
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<select id="findCustomerById" parameterType="int" resultMap="a">
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select * from t_customer where id=#{id}
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</select>
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```
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---如何将sql语句显示到控制台？
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（1）log4j.properties
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```java
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#Global logging configuration
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log4j.rootLogger=ERROR,stdout
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#MyBatis logging configuration...
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log4j.logger.com=DEBUG
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#Console output...
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log4j.appender.stdout=org.apache.log4j.ConsoleAppender
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log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
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log4j.appender.stdout.layout.ConversionPattern=%5p [%t]-%m%n
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```
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（2）导包
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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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（3）resources 下 创建com,把CustomerMapper.xml文件移动到com下
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（4）修改两个xml文件
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CustomerMapper.xml
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```java
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namespace="com.CustomerMapper"
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```
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mybatis-config.xml
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```java
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resource="com/CustomerMapper.xml"
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```
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（5）修改测试方法
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```java
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Customer o = sqlSession.selectOne("com.CustomerMapper.findCustomerById", 2);
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```
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（6）运行截图
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