java学习之MybBaits

0x00前言

我前面使用的jdbc和jdbc的工具类集成的但是它们在少部分代码的情况下会会简单，但是以后如果项目较大jdbc的固定代码会很难维护，如果使用框架会简单很多，也标志着java学习正式进入到框架阶段

0x01配置MyBaits

0x1创建模块，导入坐标

在maven的配置文件中pom.xml中加入所需要的jar包

<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>4.11</version>
        <scope>test</scope>
    </dependency>

0x2配置数据库连接文件

修改自己的数据库地址和密码；

<?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>
    <!--    别名-->
    <typeAliases>
        <package name="com.it.pojo"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--                数据库连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/tese"/>
                <property name="username" value="root"/>
                <property name="password" value="zhonglin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
                <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

0x3编写sql映射文件

这个文件存在的意义是为了以后的开发，查询那个表那个表的语句就写一个这样的映射表，方便管理和维护

<?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="test">
    <select id="findAll" resultType="com.test.domain.User">
        select * from user;
    </select>
</mapper>

在数据库配置文件中要加入，文件名就是你的sql映射文件

<mappers>
            <mapper resource="UserMapper.xml"/>
</mappers>

0x02入门使用

0x1定义实体类

实体类的内容为你数据库查询的内容

public class User {
    private String name;
    private String password;
    private String gender;
    private int id;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", password='" + password + '\'' +
                ", gender='" + gender + '\'' +
                ", id=" + id +
                '}';
    }

0x2基础使用

1. 加载核心配置文件

2. 获取sqlSession对象，执行SQL语句

3. 释放资源

   public class demo1 {
       public static void main(String[] args) throws IOException {
           //1.加载mybatis配置文件，获取SqlSessionFactory,sql语句工厂
           InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");//输出流获取配置文件地址
           SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();//获取bulid对象然后获取Factory对象
           SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
           SqlSession sqlSession = build.openSession();
           List<User> users = sqlSession.selectList("test.findAll");//通过sql语句的映射文件去查询
           System.out.println(users);
           sqlSession.close();
       }
   }
   

0x03代理开发

0x1配置映射文件和接口

定义sql映射文件相同名字的Mapper文件，且文件路径要一致，就是要在同一个文件夹下面

UserMapper文件：

public interface UserMapper {
   List<User> findAll();
}

映射文件是在resources下面的所以我们要给它新的一个文件夹他的命名方式是com/test而接口的命名方式是com.test这点是要注意的，随后需要修改

0x2配置核心文件

<mappers>
            <mapper resource="com/test/UserMapper.xml"/>
</mappers>

需要把在mybatis-config中的映射声明改成新的文件路径

0x3使用Mapper开发

1. 还是先获取配置文件，然后用sqlSession对象获取userMapper.class文件，mapper就是UserMapper的代理对象了
2. 用代理对象去实现UserMapper中的方法

public class demo2 {
    public static void main(String[] args) throws IOException {
        //1.加载mybatis配置文件，获取SqlSessionFactory,sql语句工厂
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
        SqlSession sqlSession = build.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> all = mapper.findAll();
        System.out.println(all);

0x04MyBatis的增删改查

0x1条件查询

如果是对同一个表进行的操作就写在一个接口里面

public interface UserMapper {
   List<User> findAll();
   User selectbyID(int id);
}

在对于的xml文件里面写入对应的sql语句

<mapper namespace="com.test.domain.com.test.UserMapper">
    <select id="findAll" resultType="com.test.domain.User">
        select * from user;
    </select>
    <select id="selectbyID" resultType="com.test.domain.User">
        select * from user where id =#{id}
    </select>
</mapper>

还是用代理的方式进行开发和查询

public class dmo3 {
    public static void main(String[] args) throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
        SqlSession sqlSession = build.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.selectbyID(5);
        System.out.println(user);
        sqlSession.close();
    }
}

0x2resultMap标签

<resultMap id="paswwrod" type="com.test.domain.User">
    <result column="paswword" property="password"></result>
</resultMap>

这个标签的作用可以用于当你的pojo(实体)对象的属性和你的数据的表明对不上的时候可以做一个属性的映射

• id=唯一表示符合
• type=pojo对象
• property:实体类的属性名

0x3增删改查

学习完这些基础的以后剩下的就是sql代码的问题了列如；模糊查询应该怎么做

1.在对应表的接口写出方法

public interface UserMapper {
   List<User> findlike(String name);
}

写出对于的sql语句，模糊查询select *（需要的属性名） from user(对应的表名) where name like #{name}(条件)

<select id="findlike" resultMap="paswwrod">
    select * from  user where name like #{mame}
</select>

对应的删除方法

public interface UserMapper {
   void delById(int id );
}

<delete id="delById">
    delete * from user where id=#{id}
</delete>

对应修改方法

void updateId(User user);

<update id="updateId">
    UPDATE user set
                    name =#{name},
                    gender=#{gender},
                    password=#{password}
    where id=#{id}
    </update>

public static void main(String[] args) throws IOException {
        User user = new User();
        user.setGender("男");
        user.setName("小小");
        user.setPassword("123452");
        user.setId(14);
        InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
        SqlSession sqlSession = build.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.updateId(user);

对应修改方法

void add(User user);

<insert id="add">
    insert into user (name,password,gender)
    values (#{name},#{password},#{gender})
</insert>

public static void main(String[] args) throws IOException {
    User user = new User();
    user.setPassword("root");
    user.setName("hellopw");
    user.setGender("女");
    InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
    SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
    SqlSessionFactory build = sqlSessionFactoryBuilder.build(resourceAsStream);
    SqlSession sqlSession = build.openSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.add(user);
    sqlSession.close();

#0x05总结

其实现在的MyBatis还有一些负责当它和spring一起使用的时候会更简单，需要记住的是sql语句的语法。