Mybatis 查询数据库

以你之姓@ 2021-09-22 10:22 379阅读 0赞

**1、搭建项目环境**

a、 创建普通项目

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b、添加引用jar包

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c、创建 t\_user 表

DROP TABLE IF EXISTS t_user;
    CREATE TABLE t_user (
      userid int(11) NOT NULL AUTO_INCREMENT,
      username varchar(20) DEFAULT NULL,
      password varchar(20) DEFAULT NULL,
      name varchar(20) DEFAULT NULL,
      PRIMARY KEY (userid)
    );
    
    -- ----------------------------
    -- Records of t_user
    -- ----------------------------
    INSERT INTO t_user VALUES ('1', 'Sary', 'sl311', '赛丽') ;
    INSERT INTO t_user VALUES ('2', 'Luci', 'luci123', '露西');
    INSERT INTO t_user VALUES ('3', 'Peter', '1111', '皮特');
    INSERT INTO t_user VALUES ('4', 'Tom', '333', '汤姆');

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**2、Java程序&Mybatis配置**

a、定义实体类 User

创建 com.cheese.pojo 包，在该包下创建User.java

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package com.cheese.pojo;
    
    public class User
    {
    	private int userID;
        private String userName;//用户名
        private String password;
        private String name;//全名
    
    	public User()
        {
        }
    
    	
        public int getUserID() {
    		return userID;
    	}
        
    	public void setUserID(int userID) {
    		this.userID = userID;
    	}
    
    	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 getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}   
    }

b、创建com.cheese.mapping包，

在包中创建t\_user表的sql映射文件 userMapper.xml

<?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="com.cheese.mapping.userMapper">
          
        
        <select id="getUser" parameterType="int" resultType="com.cheese.pojo.User">
            select * from t_user where userid=#{userID}
        </select>
    </mapper>

在命名空间**com.cheese.mapping.userMapper**中定义了一个名为**getUser**的映射语句，这样它就允许你使用指定的完全限定名**com.cheese.mapping.userMapper.****getUser** 来调用映射语句，就像在下面的测试程序中那样

c、在 src 目录下添加 mybatis 配置文件 config.xml

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<?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>
        <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/base1"/>
                    <property name="username" value="btsuser" />
                    <property name="password" value="b111" />
                </dataSource>
            </environment>              
        </environments>
            
        <mappers>
            
            <mapper resource="com/cheese/mapping/userMapper.xml"/>
    
        </mappers>    
        
    </configuration>

d、测试类

使用 MyBatis 的主要 Java 接口就是 SqlSession。SqlSessions 是由 SqlSessionFactory 实例创建的。SqlSessionFactory 对 象 包 含 创 建 SqlSession 实 例 的 所 有 方 法 。 而 SqlSessionFactory 本 身 是 由 SqlSessionFactoryBuilder 创建的,它可以从 XML 配置,注解或手动配置 Java 来创建 SqlSessionFactory。

package com.cheese.test;
    
    import java.io.IOException;
    import java.io.InputStream;
    
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    
    import com.cheese.pojo.User;
    
    public class Test {
    	
        public static void main(String[] args) throws IOException {
            
            String resource = "config.xml";//mybatis配置文件        
            InputStream is = Test.class.getClassLoader().getResourceAsStream(resource);//加载mybatis配置文件
            //创建sqlSession工厂
            SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);     
            //创建sqlSession
            SqlSession session = sessionFactory.openSession();
            /**
             * 映射sql的标识字符串，
             * com.cheese.mapping.userMapper是userMapper.xml文件中mapper标签的namespace属性的值，
             * getUser是select标签的id属性值，select标签的id属性值就是SQL语句的别名
             */
            String queryStr = "com.cheese.mapping.userMapper.getUser";//映射sql的标识字符串
            //执行查询返回一个唯一user对象的sql
            User user = session.selectOne(queryStr, 4);
            System.out.println(user.getName());
        }
    }

测试程序运行结果

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[SouthEast]: /images/20210920/676c8809845245a8be53b1ec4a1853a0.png
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