Mybatis实现数据表查询

1.配置pom.xml文件

向maven项目中导入依赖：
导入数据库jdbc驱动

 <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>

导入Junit

  <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

导入mybatis

 <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>

又因为在Mybatis中存在resources的资源过滤问题，有时候我们没有将所有的资源都放在/main/resources文件夹中，这样会导致无法获取指定的资源，因此我们需要使用resources标签来将这些资源打包
其中build标签下的filtering标签，用来决定是否进行过滤

 <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>

<?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>org.example</groupId>
    <artifactId>Mybatis-Study-test</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>Mybatis-Study-Test01</module>
    </modules>
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                    <include>**/*.properties</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>
</project>

创建mybatis的配置文件 mybatis-config.xml文件

<?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"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;allowPublicKeyRetrieval=true&amp;characterEncoding=UTF-8&amp;useSSL=false&amp;serverTimezone=Asia/Shanghai&amp;zeroDateTimeBehavior=CONVERT_TO_NULL"/>
                <property name="username" value="root"/>
                <property name="password" value="123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="dao/UserDaoMapper.xml"/>
    </mappers>
</configuration>

transactionManager 中的type属性用来指定连接的方式
mappers标签用来绑定资源，如果不进行资源的绑定，在使用sqlSession对象获取Mapper时，会出现无法识别的错误

创建数据库连接工具

每个基于 MyBatis 的应用都是以一个 SqlSessionFactory 的实例为核心的。SqlSessionFactory 的实例可以通过 SqlSessionFactoryBuilder 获得。而 SqlSessionFactoryBuilder 则可以从 XML 配置文件或一个预先配置的 Configuration 实例来构建出 SqlSessionFactory 实例。

从 XML 文件中构建 SqlSessionFactory 的实例非常简单，建议使用类路径下的资源文件进行配置。 但也可以使用任意的输入流（InputStream）实例，比如用文件路径字符串或 file:// URL 构造的输入流。MyBatis 包含一个名叫 Resources 的工具类，它包含一些实用方法，使得从类路径或其它位置加载资源文件更加容易。
创建过程：SqlSessionFactoryBuilder -->SqlSessionFactory—>SqlSesssion
在SqlSession对象中封装了所有的数据库操作方法，可以通过SqlSession实例来进行所有已经实现映射的sql语句

package 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;

public class DatabaseUtils {
    private  static SqlSessionFactory sqlSessionFactory;
    static {
        String resource="mybatis-config.xml";
        try {
            InputStream inputStream=Resources.getResourceAsStream(resource);
              sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
    public static SqlSession getSqlSession(){
        return  sqlSessionFactory.openSession();
    }

}

创建持久化对象（po）

 package 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 String getName() {
        return name;
    }

    public int getId() {
        return id;
    }

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

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + ''' +
                ", pwd='" + pwd + ''' +
                '}';
    }
}

mapper动态代理创建dao层

创建接口UserDao

package dao;

import pojo.User;

import java.util.List;

public interface UserDao {
      List<User>getUserList();
}

创建UserDaoMapper.xml映射文件

<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 配置文件的根元素 -->
<!--namespace //命名空间绑定接口-->
<mapper namespace="dao.UserDao">
    <select id="getUserList" resultType="pojo.User">
        select  * from  mybatis.user
    </select>
</mapper>

创建测试类

package UserDaoTest;

import dao.UserDao;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.DatabaseUtils;

import java.util.List;

public class UserDaoTest1 {

    @Test
    public  void  Test(){
        SqlSession sqlSession= DatabaseUtils.getSqlSession();//获取SqlSession对象的实例
        UserDao userDao=sqlSession.getMapper(UserDao.class);
        List <User> userList=userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

}

最后

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