目录
报错解决:java.lang.ExceptionInInitializerError
报错解决:ibatis.binding.MapperRegistry.getMapper
建表
我们先建立一个数据库和一张user表,插点数据
新建父子工程
结构如下
父工程导入jar包
导入jar包没什么好说的。注意,最后的两个<filter>标签里要写false,其实很好理解的。我不让maven把自己配置的文件路径过滤掉,所以设置false
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.lt</groupId>
<artifactId>Mybatis-Study</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
<module>Mybatis-01</module>
</modules>
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
</dependencies>
<!--在build中配置resources,防止配置文件编译时失败-->
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>false</filtering>
</resource>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.properties</include>
<include>**/*.xml</include>
</includes>
<filtering>false</filtering>
</resource>
</resources>
</build>
</project>
新建配置文件连接数据库
这个是项目的配置文件mybatis-config.xml,数据库用户名密码别写错了
<?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核心配置文件-->
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/lt/dao/UserMapper.xml"/>
</mappers>
</configuration>
注意我们的<mapper>标签,这里面我把UserMapper.xml文件注册到mybatis中了。但如果有多个xml文件呢,你可以使用通配符
<mapper resource="com/lt/dao/*Mapper.xml"/>
新建Mybatis工具类得到sqlsession
mybatis的使用需要通过SqlSessionFactoryBuilder===》SqlSessionFactory==》SqlSession。
实际上帮助我们增删改查数据的就是SqlSession,工具类的目的就是new出SqlSession对象
package com.lt.utils;
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;
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static{
try {
//使用Mybatis第一步:获取sqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
//既然有了 SqlSessionFactory,顾名思义,我们就可以从中获得 SqlSession 的实例了。
// SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession();
}
}
新建实体类
package com.lt.pojo;
public class User {
private int id;
private String name;
private String pwd;
public User() {
}
public User(int id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public String getPwd() {
return pwd;
}
public void setId(int id) {
this.id = id;
}
public void setName(String name) {
this.name = name;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
Dao层新建接口
public interface UserDao {
List<User> getUserList();
}
新建mapper.xml文件
写SQL语句用
<?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">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.lt.dao.UserDao">
<!--select查询语句-->
<select id="getUserList" resultType="com.lt.pojo.User">
select * from mybatis.user
</select>
</mapper>
新建测试类
package com.lt.dao;
import com.lt.pojo.User;
import com.lt.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@Test
public void test(){
//第一步:获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> userList = userDao.getUserList();
for (User user : userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSession.close();
}
}
报错解决:java.lang.ExceptionInInitializerError
如果你在pom文件中只导入依赖,最后没加build标签会报错。原因是maven默认不会再程序编译时编译自定义的xml文件。所以你需要在<build>标签中设置让它编译这部分xml文件
报错解决:ibatis.binding.MapperRegistry.getMapper
这是啥意思?
这个错误是说,只要你使用配置好的mabtis文件,你就必须在整个项目的配置文件中注册这个mybatis文件