Java基础之JDBC的数据库连接与基本操作

Class.forName(“com.mysql.jdbc.Driver”);

DriverManager.registerDriver(com.mysql.jdbc.Driver);

jdbc:子协议:子名称
协议：JDBC URL中的协议总是jdbc 
子协议：子协议用于标识一个数据库驱动程序
子名称：一种标识数据库的方法。子名称可以依不同的子协议而变化，用子名称的目的是为了定位数据库提供足够的信息。包含主机名(对应服务端的ip地址)，端口号，数据库名

// 对于 Oracle 数据库连接，采用如下形式： 
jdbc:oracle:thin:@localhost:1521:DatabaseName
// 对于 SQLServer 数据库连接，采用如下形式：
jdbc:microsoft:sqlserver//localhost:1433; DatabaseName=sid
// 对于 MYSQL 数据库连接，采用如下形式：   
jdbc:mysql://localhost:3306/DatabaseName
// 插入中文的时候，这个url要写成这个
jdbc:mysql://localhost:3306/数据库名称?useUnicode=true&characterEncoding=UTF-8

package com.company;
// 导入依赖包
import org.junit.Test;
import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class Demo1 {

    public static void main(String[] args) {
        System.out.println("JDBC Test...");
    }
	
	// 使用Driver来实现数据库连接
    @Test
    public void test1() throws SQLException {
		// 
        Driver driver=new com.mysql.jdbc.Driver();
        Properties p1 = new Properties();
        p1.setProperty("user", "root");
        p1.setProperty("password", "mysql123");
        Connection connect = driver.connect("jdbc:mysql://localhost:3306/myemployees", p1);
        System.out.println("connect = " + connect);

    }
	
	// 使用DriverManager来实现数据库连接
    @Test
    public void test2() throws SQLException {
        com.mysql.jdbc.Driver driver = new com.mysql.jdbc.Driver();
        Properties p1 = new Properties();
        p1.setProperty("user", "root");
        p1.setProperty("password", "mysql123");
        DriverManager.registerDriver(driver);
        Connection connection = DriverManager.getConnection
                ("jdbc:mysql://localhost:3306/myemployees", p1);

        System.out.println("connection = " + connection);

    }
	// 将账号密码抽出到配置文件中，并使用IO流读取配置文件的方式连接数据库
    @Test
    public void test3() throws Exception {
        Properties p = new Properties();

        FileInputStream fis = new FileInputStream("p.properties");
        p.load(fis);
        fis.close();
        Class.forName(p.getProperty("driverClass"));
        Connection connection = DriverManager.getConnection(p.getProperty("url"),
                p.getProperty("user"), p.getProperty("password"));
        System.out.println("connection = " + connection);

    }
}

url=jdbc:mysql://localhost:3306/myemployees
user=root
password=mysql123
driverClass=com.mysql.jdbc.Driver

// 使用PreparedStatement来完成数据的增删改查操作
package com.company.jdbc;

import org.junit.Test;

import java.io.FileInputStream;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;


public class CRUDDemo {

    
    @Test
    public void test() throws SQLException {
        //1.获取数据库连接对象
        Connection connection = JDBCUtils.getConnection();
        //2.预编译
        // ? : 占位符（只能是设置数据的地方可以写成占位符）
        String sql = "insert into student(sid,sname,sage) values(?,?,?)";
        PreparedStatement ps = connection.prepareStatement(sql);
        //3.给占位符赋值
        
        ps.setInt(1,100);
        //数据设置成中文可不可以取决于表的编码集
        ps.setString(2,"longge");
        ps.setInt(3,20);
        //4.执行sql
        //返回值 ： 有几条数据受到影响
        int result = ps.executeUpdate();//增，删，改的语句使用该方法
        System.out.println("有"+result+"条数据受到影响");
        //5.关资源
        JDBCUtils.close(ps,connection);
    }

    
    @Test
    public void test2() throws SQLException {
        //1.获取数据库连接对象
        Connection connection = JDBCUtils.getConnection();
        //2.预编译
        String sql = "update student set sid=? where sid=?";
        PreparedStatement ps = connection.prepareStatement(sql);
        //3.给占位符赋值
        ps.setInt(1,10);
        ps.setInt(2,100);
        //4.执行sql语句
        int result = ps.executeUpdate();
        System.out.println("有"+result+"条数据受到影响");
        //5.关闭资源
        JDBCUtils.close(ps,connection);
    }

    
    @Test
    public void test3() throws SQLException {
        //1.获取数据库连接对象
        Connection connection = JDBCUtils.getConnection();
        //2.预编译
        String sql = "delete from student where sid=?";
        PreparedStatement ps = connection.prepareStatement(sql);
        //3.给占位符赋值
        ps.setInt(1,10);
        //4.执行sql语句
        int i = ps.executeUpdate();
        System.out.println("有"+i+"条数据受到影响");
        //5.关闭资源
        JDBCUtils.close(ps,connection);
    }

    
    @Test
    public void test4() throws Exception {
        List<Student> students = getStudent();
        for (Student s : students) {
            System.out.println(s);
        }

    }

    public List<Student> getStudent() throws Exception {
        //1.获取数据库连接对象
        Connection connection = JDBCUtils.getConnection();
        //2.预编译
        PreparedStatement ps = connection.prepareStatement("select sid,sname,sage from student");
        //3.执行sql语句
        ResultSet resultSet = ps.executeQuery();//查询语必须执行此方法

        List<Student> list =  new ArrayList<>();
        //4.遍历ResultSet
        while(resultSet.next()){//是否有数据
            
            int sid = resultSet.getInt("sid");
            String sname = resultSet.getString("sname");
            int sage = resultSet.getInt("sage");

            //System.out.println(sid + " " + sname + " " + sage);
            list.add(new Student(sid,sname,sage));
        }
        //5.关闭资源
        JDBCUtils.close(ps,connection,resultSet);

        return list;
    }

}

//JDBCUtils类，专门实现数据库的连接与资源释放操作
package com.company.jdbc;

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

public class JDBCUtils {
    private static String driverClass;
    private static String url;
    private static String username;
    private static String password;

    static{
        FileInputStream fis = null;
        try {
            //1.获取数据库连接对象
            //通过Properties读取内容
            //1.创建Properties对象
            Properties p = new Properties();
            //2.加载流
            fis = new FileInputStream("jdbc.properties");
            p.load(fis);
            driverClass = p.getProperty("driverClass");
            url = p.getProperty("url");
            username = p.getProperty("username");
            password = p.getProperty("password");
        }catch (Exception e){
            //终止程序的运行
            e.printStackTrace();
            //将编译时异常转换成运行时异常
            throw new RuntimeException("xxxxxxxx");
        }finally {
            if (fis != null){
                //3.关资源
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    
    public static Connection getConnection(){
        try {
            Class.forName(driverClass);
            //获取数据库连接对象
            Connection connection = DriverManager.getConnection(url, username, password);
            return connection;
        }catch (Exception e){
            e.printStackTrace();
            throw new RuntimeException("获取连接失败");
        }
    }

    
    public static void close(PreparedStatement ps, Connection connection) {
        if (ps != null){
            try {
                ps.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }

        if (connection != null){
            try {
                connection.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }

    public static void close(PreparedStatement ps, Connection connection, ResultSet resultSet) {
        close(ps,connection);
        if (resultSet != null){
            try {
                resultSet.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}