03jdbc的crud练习

//添加

jdbc连接防止乱码
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/db1?characterEncoding=utf-8","root","");
package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**

• account表 添加一条记录 insert 语句

*/
public class JDBCDemo2 {

public static void main(String[] args) {
    Statement stmt = null;//放到try内部就是局部变量
    Connection conn = null;
    try {
        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2. 定义sql
        String sql = "insert into account values(null,'王五',3000)";
        //3.获取Connection对象
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
        //4.获取执行sql的对象 Statement
        stmt = conn.createStatement();
        //5.执行sql
        int count = stmt.executeUpdate(sql);//影响的行数
        //6.处理结果
        System.out.println(count);
        if(count > 0){
            System.out.println("添加成功！");
        }else{
            System.out.println("添加失败！");
        }

    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }finally {
        //stmt.close();
        //7. 释放资源
        //避免空指针异常
        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


}

}
package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**

• account表 修改记录

*/
public class JDBCDemo3 {

public static void main(String[] args) {
    Connection conn = null;
    Statement stmt = null;
    try {
        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接对象
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
        //3.定义sql
        String sql  = "update account set balance = 1500 where id = 3";
        //4.获取执行sql对象
        stmt = conn.createStatement();
        //5.执行sql
        int count = stmt.executeUpdate(sql);
        //6.处理结果
        System.out.println(count);
        if(count > 0){
            System.out.println("修改成功！");
        }else{
            System.out.println("修改失败");
        }

    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        //7.释放资源

        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }


}

}
package cn.itcast.jdbc;

import cn.itcast.util.JDBCUtils;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**

• account表 删除一条记录

*/
public class JDBCDemo4 {

public static void main(String[] args) {
    Connection conn = null;
    Statement stmt = null;
    try {
        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接对象
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
       //conn = JDBCUtils.getConnection("jdbc:mysql:///db3", "root", "root");
        //3.定义sql
        String sql  = "delete from account where id = 3";
        //4.获取执行sql对象
        stmt = conn.createStatement();
        //5.执行sql
        int count = stmt.executeUpdate(sql);
        //6.处理结果
        System.out.println(count);
        if(count > 0){
            System.out.println("删除成功！");
        }else{
            System.out.println("删除失败");
        }

    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        //7.释放资源

        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

}
package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

/**

• 执行DDL语句

*/
public class JDBCDemo5 {

public static void main(String[] args) {
    Connection conn = null;
    Statement stmt = null;
    try {
        //1. 注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接对象
        conn = DriverManager.getConnection("jdbc:mysql:///db3", "root", "root");
        //3.定义sql
        String sql  = "create table student (id int , name varchar(20))";
        //4.获取执行sql对象
        stmt = conn.createStatement();
        //5.执行sql
        int count = stmt.executeUpdate(sql);
        //6.处理结果
        System.out.println(count);

    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        //7.释放资源

        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

}