Question

我正在尝试连接到数据库。早先它工作正常。但是现在有些罐子已被删除或者我不知道的东西（红十字会出现在他们身上）。但是我再次下载了所有的jar（mysql-connector，commons-io-2.4），我仍然在Class.forName（“com.mysql.jdbc.Driver”）中得到classnotfound异常; 这是我的代码

    package abc;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;

     public class JDBC_oracle {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
    //step1 load the driver class  
    Class.forName("com.mysql.jdbc.Driver");
    //step2 create  the connection object  
    Connection  connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/database_name","user_name", "pswrd");
    //step3 create the statement object  
    Statement statement = connection.createStatement();
    statement.executeUpdate("sql_query"); 
    ResultSet rs=statement.executeQuery("sql_query");       
    while(rs.next())  
        System.out.println("I am triyng to print data");
//step5 close the connection object 
    connection.close();  
}
  }

这是错误

    java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at java.net.URLClassLoader$1.run(Unknown Source)
   at java.net.URLClassLoader$1.run(Unknown Source)
   at java.security.AccessController.doPrivileged(Native Method)
 at java.net.URLClassLoader.findClass(Unknown Source)
 at java.lang.ClassLoader.loadClass(Unknown Source)
 at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at deiniteguide.JDBC_example.main(JDBC_example.java:24)

我尝试过使用try catch也不适合我。

Answer 1

如果您使用的是netbeans，则可以转到项目中的库文件夹。右键单击并添加库并选择mysql驱动程序。抱歉由于声誉较低而无法发表评论，如果您可以发布您收到的错误消息会更容易。还可以在程序中使用try catch，以便更容易找到错误。您的代码可以是这样的：

  public class JDBC_oracle {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
    //step1 load the driver class  
     try{
    Class.forName("com.mysql.jdbc.Driver");
       }catch(Exception e){
         System.out.println("Class not found" +e);
    //step2 create  the connection object  
     try{
    Connection  connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/database_name","user_name", "pswrd");
     }catch(Exception es){
     System.out.println("connection couldn't be made "+es);
      }
    //step3 create the statement object  
     try{
    Statement statement = connection.createStatement();
    statement.executeUpdate("sql_query"); 
    ResultSet rs=statement.executeQuery("sql_query");   }
     catch(Exception er){
      System.out.println("Query wasnot executed "+er);    
     }
    while(rs.next())  
        System.out.println("I am triyng to print data");
//step5 close the connection object 
    connection.close();  
}
  }

在java

1 个答案: