错误-无法找到或加载主类

Question

我想连接我的Java程序以连接数据库并检索数据。它可以完美编译但运行时我正在获取此Error : Could not find or load main class

我已经安装了Java SQL驱动程序，并将jar路径作为CLASSPATH添加到环境变量中>

import java.sql.*;
public class Java2Sql{
    public static void main(String args[]){
        String url = "jdbc:mysql://localhost:80/";
        String dbName = "test";
        String driver = "com.mysql.jdbc.Driver";
        String userName = "root";
        String password = "root";

        try{
            Class.forName(driver).newInstance();
            Connection conn = DriverManager.getConnection(url+dbName,userName,password);

            Statement stmt = conn.createStatement();
            String strsql = "SELECT * FROM student";

            ResultSet res = stmt.executeQuery(strsql);

            while(res.next()){
                System.out.println("ID :"+res.getString(1));
                System.out.println("Name :"+res.getString(2));
                System.out.println("Tel :"+res.getString(3));
                System.out.println("City :"+res.getString(4));
            }
            res.close();
            conn.close();
        }catch(Exception e){
            e.printStackTrace();
        }

    }
}
    

我想连接我的Java程序以连接数据库并检索数据。它可以完美编译，但是运行时出现此错误：找不到或加载主类，我已经安装了Java ...

Answer 1

您应该从HERE下载驱动程序

Answer 2

假设您的Java2Sql位于test包中。

Answer 3

清单清单Main-class条目中命名的类在您的JAR文件中不存在，或者清单中可能没有Main-class：条目。

Answer 4

MySQL连接的默认端口为3306。因此更改此行

Answer 5

    `
import java.sql.*;
    import java.util.Scanner;
    class MySql
    {
            public static void main(String arg[])
            {
               String name,branch;
               Scanner sc=new Scanner(System.in);
               System.out.println("enter the name:");
               name=sc.nextLine();
               System.out.println("enter the branch:");
               branch=sc.nextLine();
              try
    {
    Class.forName("com.mysql.cj.jdbc.Driver");
    Connection con=DriverManager.getConnection("jdbc:mysql://localhost::3306/java","root","");
    Statement stmt=con.createStatement();
    stmt.execute("insert into detail values('"+name+"','"+branch+"')");
    System.out.print("insert successful");
    }
    catch(Exception e){e.printStackTrace();}
    }
    }
`

    enter code here