今天完成的事 实现mybatis查询数据库

用Navicat 创建数库mybatis

创建表单user

设计设置列表格式

用IDEA新建项目

目录结构为

编辑pom.xml

<?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>mybatistast</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>RELEASE</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>RELEASE</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>

</project>

创建SqlMapConfig.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration >
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>
    <!-- 和Spring整合后envirnmentss 配置将被移除-->
    <environments default="mysql">
        <environment id="mysql">
            <!-- 使用jdbc事务管理-->
            <transactionManager type="JDBC"/>
            <!-- 数据库连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="deng796443"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 写完SQL映射文件后为了能让mybatis资源文件加载类解析Mapper文件-->
    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>

创建SQL映射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="test">
    <select id="usersId" parameterType="int" resultType="Dao.User">
        select * from user where id =#{id}
    </select>
</mapper>

创建实体类User.java

package Dao;
import java.io.Serializable;
import java.util.Date;
public class User implements Serializable{
    private int id;
    public  User(int id, String username, String password, String gender,
                 String email, String province, String city, Date birthday)
    {
        super();
        this.id=id;
        this.username=username;
        this.gender=gender;
        this.email=email;
        this.province=province;
        this.password=password;
        this.city=city;
        this.birthday=birthday;
    }
    public void setProvince(String province) {
        this.province = province;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    private String username;
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    private String password;
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    private String gender;
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    private String email;
    private String province;
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    private String city;
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    private Date    birthday;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
}

创建数据库交互DataConnection.java

package Dao;
import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class DataConnection {
    private String resource= "SqlMapConfig.xml";
    private SqlSessionFactory sqlSessionFactory;
    private SqlSession sqlSession;
    public SqlSession getSqlSession() throws IOException{
        InputStream inputStream= Resources.getResourceAsStream(resource);
        //创建会话工厂，传入MyBatis配置文件信息
        sqlSessionFactory =new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession=sqlSessionFactory.openSession();
        return sqlSession;
    }
}

创建测试用例

import  java.io.IOException;
import  java.text.SimpleDateFormat;
import Dao.DataConnection;
import Dao.User;
import  org.apache.ibatis.session.SqlSession;
import org.junit.jupiter.api.Test;

public class MyBatisTest {
    public DataConnection dataConnection=new DataConnection();
    @Test
    public void TestSelect() throws IOException{
        SqlSession sqlSession=dataConnection.getSqlSession();
            //最终结果与映射文件中所匹配的resultType类型
        User user=sqlSession.selectOne("test.usersId",1);
        System.out.println("姓名："+user.getUsername());
        System.out.println("性别："+user.getGender());
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
        System.out.println("生日："+sdf.format(user.getBirthday()));
        System.out.println("所在地:"+user.getCity());
        sqlSession.close();


    }
}

最终输出结果

 明天的任务：学习一对多查询

今天遇到的问题：

运行报错
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database.  Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for test.usersId
### Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for test.usersId 

mybatis.xml 找不到映射地址

添加下mapper 源地址后查询终于跑起来了
<mappers>
    <mapper resource="UserMapper.xml" />
</mappers> 

今天的收获

知道了找bug的方法与测试程序的方法

知道了

User user=sqlSession.selectOne("test.usersId",1);

sqlSession的selectOne方法有两个参数，第一个参数是SQL映射文件UserMapper.xml中的namespace加上statement配置的id

第二个参数是SQL映射文件中所匹配parameterType类型的参数。执行selectOne之后的结果为SQL映射文件中所匹配的resultType类型。

test.userId中的test对应的是namespace值，usersId 对应的是id

<mapper namespace="test">
   <select id="usersId" parameterType="int" resultType="Dao.User">
       select * from user where id =#{id}
</select>