关于mybatis入门及一些注意点

mybatis入门程序分为几步：

1.引入依赖

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.4.5</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.6</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
    <dependency>
        <groupId>commons-dbcp</groupId>
        <artifactId>commons-dbcp</artifactId>
        <version>1.4</version>
    </dependency>
</dependencies>

2 编写配置文件sqlmapconfig.xml（模板可以提前在idea中准备）

<?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 resource="jdbc.properties"></properties> <!--引用外部配置文件 即jdbc.propertioes-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <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.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers><!-- 在引用注解是注意在mappers标签中的引用  从mapper--》变为package-->
        <package name="cn.kgc.dao"/>
    </mappers>
</configuration>

3 编写实体类

package cn.kgc.domain;

/**
 * @Date:Create in 2019/8/4 19:37
 */
public class Users {
    private Integer id;
    private String username;
    private String password;
    private String sex;
    private String address;

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

4 编写dao层

package cn.kgc.dao;

import cn.kgc.domain.Users;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import java.util.List;

/**
 * @Date:Create in 2019/8/4 19:41
 */
public interface UserDao {
    //查询全部
    @Select("select * from users")
    public List<Users> findAll();
    //根据id查询
    @Select("select * from users where id=#{id}")
    public Users findById(Integer id);
    //增加一条数据
    @Insert("insert into users values(null,#{username},#{password},#{sex},#{address})")
    public void save(Users user);
    //根据id删除一条数据
    @Delete("delete from users where id=#{id}")
    public void delete(Integer id);
    //修改数据
    @Update("update users set username=#{username} where id=#{id}")
    public void update(Users user);
}
5 编写测试类

import cn.kgc.dao.UserDao;
import cn.kgc.domain.Users;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

/**
 * @Date:Create in 2019/8/4 20:27
 */
public class TestMybatis {
    @Test
    public void test(){
        //创建SqlSessionFactory工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(this.getClass().getClassLoader().getResourceAsStream("SqlMapConfig.xml"));
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
//        System.out.println(userDao.findAll());
//        System.out.println(userDao.findById(8));
        Users users = new Users();
        users.setSex("女");
        users.setUsername("万字");
        users.setPassword("11111");
        users.setAddress("杭州");
        users.setId(12);
//        userDao.save(users);
//        userDao.update(users);
        userDao.delete(12);
        sqlSession.commit();
        sqlSession.close();
    }
}

另外：
   在编写sqlmapconfig.xml文件时一定要注意，小心，因为一个字母一个符号就可能导致整个项目报错，而一般小原因导致的错误是极其难找的，只要编写时注意点就ok。