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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

image-20220528181123512

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。


来源:https://www.cnblogs.com/0x3e-time/p/16324209.html
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