【JDBC】JDBC学习（一）

1、引入依赖

<?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>com.sheep</groupId>
    <artifactId>jdbc-study</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>jdbc-study</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.22</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

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

 2、resources目录下编写jdbc.properties文件

mysql.driver=com.mysql.cj.jdbc.Driver
mysql.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=CTT
mysql.userName=root
mysql.password=root

3、编写DButils工具类

package com.sheep.utils;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class DBUtils {
    // 公共的两部分：1建立连接、2资源释放
    // 想要程序一运行就能建立连接，连接需要的东西都写成static静态的，最先执行的。
    private static String driver;
    private static String url;
    private static String userName;
    private static String password;

    static {
        Properties p = new Properties();
        try {
            InputStream inputStream = DBUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
            p.load(inputStream);
            driver = p.getProperty("mysql.driver");
            url = p.getProperty("mysql.url");
            userName = p.getProperty("mysql.userName");
            password = p.getProperty("mysql.password");
            // 加载驱动
            Class.forName(driver);

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    // 建立连接
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, userName, password);
    }

    // 2.释放资源
    public static void close(ResultSet rs, PreparedStatement pst, Connection con) throws SQLException {
        close(rs);
        close(pst);
        close(con);
    }

    private static void close(Connection con) throws SQLException {
        if (con != null) {
            con.close();
        }
    }

    private static void close(PreparedStatement pst) throws SQLException {
        if (pst != null) {
            pst.close();
        }
    }

    private static void close(ResultSet rs) throws SQLException {
        if (rs != null) {
            rs.close();
        }
    }

}

4、编写测试类

public class AppTest {

    @Test
    public void testB() throws Exception {
        // 建立连接
        Connection con = DBUtils.getConnection();
        // 预处理sql语句
        PreparedStatement pst = con.prepareStatement("select * from t_student limit 5");
        // 执行sql语句
        ResultSet rs = pst.executeQuery();
        while (rs.next()) {
            System.out.println(rs.getInt("age") + "==" + rs.getString("name"));
        }
        DBUtils.close(rs, pst, con);
    }
}

 5、编写BaseDao.java

public class BaseDao<T> {

    public List<T> executeQuery(String sql, Class clz) throws Exception {
        List<T> list = new ArrayList<T>();
        // 建立连接
        Connection con = DBUtils.getConnection();
        // 预处理sql语句
        PreparedStatement pst = con.prepareStatement(sql);
        // 执行sql语句
        ResultSet rs = pst.executeQuery();
        // 处理执行sql的结果
        T t;
        while (rs.next()) {
            // 反射
            t = (T) clz.newInstance();
            // 获取对象的所有属性
            Field[] fields = clz.getDeclaredFields();
            for (Field f : fields) {
                f.setAccessible(true);
                f.set(t, rs.getObject(f.getName()));
                f.setAccessible(false);
            }
            list.add(t);
        }
        DBUtils.close(rs, pst, con);
        return list;
    }
}

6、编写具体实现测试

package com.sheep.dao;

import com.sheep.domain.Student;
import com.sheep.utils.BaseDao;

import java.util.List;

public class StudentDao extends BaseDao<Student> {

    // 定义list()方法
    public List<Student> list() throws Exception {
        // 需要执行的sql语句，以及查询的所属对象
        // 返回 调用父类的executeQuery()方法 获得的返回值
        return super.executeQuery("select * from t_student limit 5", Student.class);
    }

    public static void main(String[] args) throws Exception {

        StudentDao studentDao = new StudentDao();
        List<Student> list = studentDao.list();
        for (Student s : list) {
            System.out.println(s);
        }
    }
}