Question

我正在使用MySQL 5.5和mysql-connector-java-5.1.15。（两者都是新安装的）

我使用记事本和命令提示符尝试了JDBC程序。

我的JDBC程序：

import java.sql.*;
import java.io.*;


public class MysqlConnect{
  public static void main(String[] args) {

    System.out.println("MySQL Connect Example.");
    Connection conn = null;
    String url = "jdbc:mysql://localhost:3306/";
    String dbName = "employement";
    String driver = "com.mysql.jdbc.Driver";
    String userName = "root"; 
    String password = "12345";
    try {
      Class.forName(driver).newInstance();
      conn = DriverManager.getConnection(url+dbName,userName,password);
      System.out.println("Connected to the database");
      conn.close();
      System.out.println("Disconnected from database");
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

我在mysql ....中创建了一个名为employement的数据库。

我尝试运行此程序......

C:\Users\Innodea\Desktop>javac MysqlConnect.java

C:\Users\Innodea\Desktop>java MysqlConnect
Exception in thread "main" java.lang.NoClassDefFoundError: MysqlConnect
Caused by: java.lang.ClassNotFoundException: MysqlConnect
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: MysqlConnect.  Program will exit.

如何清除此错误？

我也尝试过如下，

C:\Users\Innodea\Desktop>set classpath=C:\Program Files\MySQL\mysql-connector-ja
va-5.1.15\mysql-connector-java-5.1.15.jar

C:\Users\Innodea\Desktop>javac MysqlConnect.java

C:\Users\Innodea\Desktop>java MysqlConnect
Exception in thread "main" java.lang.NoClassDefFoundError: MysqlConnect
Caused by: java.lang.ClassNotFoundException: MysqlConnect
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: MysqlConnect.  Program will exit.

同样也会发生同样的错误请帮我清除此错误并运行JDBC程序....

Answer 1

java -cp .;C:\Program Files\MySQL\mysql-connector-java-5.1.15\mysql-connector-java-5.1.15.jar MysqlConnect

Answer 2

尝试使用这个 -

java -cp %CLASSPATH%;.; MysqlConnect.java

或者添加。到你的类路径阅读它像

set classpath=C:\Program Files\MySQL\mysql-connector-ja va-5.1.15\mysql-connector-java-5.1.15.jar;.;

你当前的类也需要在classpath上，因此也就是dot-current目录。

Answer 3

使用-cp开关应该可以正常工作

java -cp=.;C:\Program Files\MySQL\mysql-connector-java-5.1.15\mysql-connector-java-5.1.15.jar MysqlConnect

几乎不需要设置CLASSPATH环境变量

运行JDBC程序时出错

3 个答案: