今天完成的事：学习mybaits 链接数据方法

练习mybatisdemo

创建User.java

package Dao;

public class User {
    private int id;
    private String userName;
    private String userAge;
    private String userAddress;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public String getUserAge() {
        return userAge;
    }
    public void setUserAge(String userAge) {
        this.userAge = userAge;
    }
    public String getUserAddress() {
        return userAddress;
    }
    public void setUserAddress(String userAddress) {
        this.userAddress = userAddress;
    }
}

创建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="Dao.UserMapper">
    <select id="selectUserByID" parameterType="int" resultType="User">
        select * from `user` where id = #{id}
    </select>
</mapper>

创建db_conf.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="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true" />
                <property name="username" value="root" />
                <property name="password" value="deng796443" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="Dao/UserMapper.xml" />
    </mappers>

</configuration>

创建Test.java

package  Dao;

import java.io.Reader;
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 Test {
        private static SqlSessionFactory sqlSessionFactory;
        private static Reader reader;

        static{
            try{
                reader    = Resources.getResourceAsReader("Dao/UserMapper.xml");
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            }catch(Exception e){
                e.printStackTrace();
            }
        }

        public static SqlSessionFactory getSession(){
            return sqlSessionFactory;
        }

        public static void main(String[] args) {
            SqlSession session = sqlSessionFactory.openSession();
            try {
                User user = (User) session.selectOne("Dao.UserMapper.selectUserByID", 1);
                System.out.println(user.getUserAddress());
                System.out.println(user.getUserName());
            } finally {
                session.close();
            }
}
运行结果报错：
/Library/Java/JavaVirtualMachines/jdk-17.0.1.jdk/Contents/Home/bin/java -javaagent:/Applications/IntelliJ IDEA CE.app/Contents/lib/idea_rt.jar=54068:/Applications/IntelliJ IDEA CE.app/Contents/bin -Dfile.encoding=UTF-8 -classpath /var/root/IdeaProjects/Mydatis/target/classes:/Users/kiven/App/repository/mysql/mysql-connector-java/8.0.11/mysql-connector-java-8.0.11.jar:/Users/kiven/App/repository/com/google/protobuf/protobuf-java/2.6.0/protobuf-java-2.6.0.jar:/Users/kiven/App/repository/org/mybatis/mybatis/3.5.6/mybatis-3.5.6.jar:/Users/kiven/App/repository/log4j/log4j/1.2.12/log4j-1.2.12.jar Dao.Test
java.io.IOException: Could not find resource Dao/UserMapper.xml
	at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:114)
	at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:100)
	at org.apache.ibatis.io.Resources.getResourceAsReader(Resources.java:160)
	at Dao.Test.<clinit>(Test.java:15)
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "org.apache.ibatis.session.SqlSessionFactory.openSession()" because "Dao.Test.sqlSessionFactory" is null
	at Dao.Test.main(Test.java:27)