简介
MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以对配置和原生Map使用简单的 XML 或注解，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。[1]
本文将演示Mybatis的基本用法，通过XML或接口类对数据库的增删改查。
创建Mybatis项目
1、使用Idea创建一个maven项目，依赖包内容如下
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.4</version>
</dependency>
</dependencies>
2、创建Mybatis配置文件
使用Idea集成开发环境，可以下载Mybatis plugin，然后可更好的使用mybatis。关于mybatis的破解过程，参考附录的mybatis plugin 破解
新建Mybatis配置文件
项目文件内容
1、在resource目录下增加mybatis-config.xml文件，内容如下
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties>
<property name="jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="jdbc.user" value="aihe" />
<property name="jdbc.pass" value="123456" />
<property name="jdbc.url" value="jdbc:mysql://localhost:3306/test" />
</properties>
<settings>
<!-- Globally enables or disables any caches configured in any mapper under this configuration -->
<setting name="cacheEnabled" value="true"/>
<!-- Sets the number of seconds the driver will wait for a response from the database -->
<setting name="defaultStatementTimeout" value="3000"/>
<!-- Enables automatic mapping from classic database column names A_COLUMN to camel case classic Java property names aColumn -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
<!-- Allows JDBC support for generated keys. A compatible driver is required.
This setting forces generated keys to be used if set to true,
as some drivers deny compatibility but still work -->
<setting name="useGeneratedKeys" value="true"/>
</settings>
<!--便于后面解析对象-->
<typeAliases>
<package name="me.aihe" />
</typeAliases>
<!-- Continue going here -->
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.user}" />
<property name="password" value="${jdbc.pass}" />
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="BlogMapper.xml" />
</mappers>
</configuration>
2、在resource目录下增加BlogMapper.xml文件，内容如下
<?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="me.aihe.dao.BlogMapper">
<select id="selectBlog" resultType="me.aihe.Blog">
select * from Blog where id = #{id}
</select>
<insert id="insertBlog" parameterType="Blog">
insert into Blog (id,title) values (#{id},#{title})
</insert>
<update id="updateBlog" parameterType="Blog">
UPDATE Blog SET title=#{title} WHERE id=#{id}
</update>
<delete id="deleteBlog" parameterType="integer">
DELETE FROM BLOG WHERE id=#{id}
</delete>
</mapper>
3、新建Blog对象
package me.aihe;
public class Blog {
int id;
String title;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
@Override
public String toString() {
return "Blog{" +
"id=" + id +
", title='" + title + '\'' +
'}';
}
}
4、新建主文件，Tutorial.java，并进行测试。
当前我们的数据表内容如下
新建数据表
5、Tutorial.java文件内容如下
package me.aihe;
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 java.io.IOException;
import java.io.InputStream;
import java.util.Random;
public class Tutorial {
public static void main(String[] args) {
SqlSession sqlSession = null;
try {
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 查询数据库内容
sqlSession = sqlSessionFactory.openSession();
Blog blog = sqlSession.selectOne("me.aihe.dao.BlogMapper.selectBlog",1);
System.out.println(blog);
// 插入数据库内容
Blog b = new Blog();
b.setTitle("Insert Value" + new Random().nextInt(1000));
int row = sqlSession.insert("me.aihe.dao.BlogMapper.insertBlog",b);
System.out.println(row);
sqlSession.commit();
// 更新数据库内容
b.setId(2);
row = sqlSession.update("me.aihe.dao.BlogMapper.updateBlog",b);
System.out.println(row);
sqlSession.commit();
//删除数据库内容
row = sqlSession.delete("me.aihe.dao.BlogMapper.deleteBlog",1);
System.out.println(row);
sqlSession.commit();
} catch (IOException e) {
e.printStackTrace();
}finally {
if (sqlSession != null) {
sqlSession.close();
}
}
}
}
最终的项目结构如下
项目结构
6、运行结果
Blog{id=1, title='Hello Mybatis'}
1
1
1
查看当前数据表的内容，可见查询了id为1的数据，插入了一条心的数据，更新了id为2 的数据，删除了id为1的数据。
演示后数据表内容
总结
这篇文章主要简单的演示了通过xml配置Mybatis，对数据库的增删改查。使用接口注解的方式类似，可自行查阅。关于更多高级用法，请听下回分解。
可扩充部分
- 接口注解增删改查
- Mybatis配置属性详细介绍
- 更好的组织项目结构
错误汇总
1、mybatis-config.xml属性顺序错误
Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException:
### Error building SqlSession.
### Cause: org.apache.ibatis.builder.BuilderException: Error creating document instance. Cause: org.xml.sax.SAXParseException; lineNumber: 50; columnNumber: 17; 元素类型为 "configuration" 的内容必须匹配 "(properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,reflectorFactory?,plugins?,environments?,databaseIdProvider?,mappers?)"
解决方案：mybatis-config.xml文件按照(properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,reflectorFactory?,plugins?,environments?,databaseIdProvider?,mappers?)进行顺序排列。
mybatis配置顺序
2、不能找到某个类文件
Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException:
### Error building SqlSession.
### The error may exist in BlogMapper.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Blog'. Cause: java.lang.ClassNotFoundException: Cannot find class: Blog
解决方案：两者选其一即可
1、在Mapper文件的resultType中返回为全路径
解决方案1
2、添加TypeAlias
解决方案2
