学习Mybatis遇到的错误

学习mybatis错误集合

1.空指针

搭建完环境，编写完代码后，编写测试类测试代码时，报以下信息的错误

 查看代码，测试类的etSqlSeeion有问题

 

 

 继续找getSqlSeeion方法的问题，发现蓝色返回的Session有问题，而蓝色是从红色部分得到的，发现红色部分有灰色，这水说明有没有使用的地方，而红色部分应该是同一个变量

 

 

 

 

 

发现是图中又重新给Session定义了类型，导致编程新的变量

 

 

2.没有注册Mapper

rg.apache.ibatis.binding.BindingException: Type interface com.dao.StudentDao is not known to the MapperRegistry.的错误

 

 发现是没有在mybatis的配置文件中注册Mapper

 

3.找不到Mapper的配置

 

 添加以下配置文件

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

修改程序后，刷新以下Maven，继续运行

4.没有找到postgresql驱动，这里应该是驱动的路径问题，

这里卡了好久，找不到解决办法，有大咖知道的吗？？？

 

 

 项目代码

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>untitled</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>untitled1</module>
    </modules>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <dependencies>
       <!-- mysql驱动-->
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.3.6</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <!-- mybatis驱动-->
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <resources >
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

<?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">
    <parent>
        <artifactId>untitled</artifactId>
        <groupId>org.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>untitled1</artifactId>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <dependencies>
        <!-- mysql驱动-->
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.3.6</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <!-- mybatis驱动-->
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <resources >
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

Mybatisutils

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 MybatisUtils {
    private   static   SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //获取mybatis第一步
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
              sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        }catch (IOException e){
            e.printStackTrace();
        }
   }
    public static SqlSession getSqlSeeion(){
        SqlSession  sqlSession= sqlSessionFactory.openSession();
        return sqlSession;
    }
}

mybatis-config.xml

<?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="org.postgresql.Driver "/>
                <property name="url" value="jdbc:postgresql://localhost:5432/postgres?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="postgres"/>
                <property name="password" value="hap"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/dao/StudentMapper.xml"/>
    </mappers>
</configuration>

Pojo

import java.util.Date;

public class Student {
    private int id;
    private Date creat_time;
    private String name;
    private int score;

    public Student() {
    }

    public Student(int id, Date creat_time, String name, int score) {
        this.id = id;
        this.creat_time = creat_time;
        this.name = name;
        this.score = score;
    }

    public int getId() {
        return id;
    }

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

    public Date getCreat_time() {
        return creat_time;
    }

    public void setCreat_time(Date creat_time) {
        this.creat_time = creat_time;
    }

    public String getName() {
        return name;
    }

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

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
}

StudentDao

import com.pojo.Student;

import java.util.List;

public interface StudentDao {
  List <Student> getStudentList();

}

StudentMapper.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.dao.StudentDao">
    <select id="getStudentList" resultType="com.pojo.Student">
        select * from postgres.study_student
    </select>
</mapper>

StudentTest

import java.util.List;

public class StudentTest {
    @Test
    public void test(){

        //第一步，获取sqlSessiond对象
       SqlSession sqlsession= MybatisUtils.getSqlSeeion();
      StudentDao studentdao= sqlsession.getMapper(StudentDao.class);
      List<Student> studentlist= studentdao.getStudentList();
        for (Student student : studentlist) {
            System.out.println(student);
        }
        sqlsession.close();
    }
}