NoClassDefFoundError：org / aspectj / lang / Sign

Question

我一直在尝试一个简单的程序来将MYSQL连接到我的Java应用程序。我正在使用Windows操作系统。我使用了在线教程并在记事本中尝试了以下程序：

import java.sql.*;

public class Database1{
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
static final String DB_URL = "jdbc:mysql://localhost/EMP";

static final String USER = "root";
static final String PASS = "admin";

public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;

try{
   Class.forName("com.mysql.jdbc.Driver");
   System.out.println("Connecting to database...");

    conn = DriverManager.getConnection(DB_URL,USER,PASS);

    System.out.println("Creating statement...");
    stmt = conn.createStatement();
    ResultSet rs = stmt.executeQuery("SELECT * FROM Employees");

    System.out.println("ID             NAME         ");

    while(rs.next()){
      String id=rs.getString("ID");
      String name=rs.getString("NAME");
      System.out.print(id);
      System.out.println(name);

      }

      rs.close();
      stmt.close();
      conn.close();
     } //close try block
    catch(SQLException s){ s.printStackTrace();}
    catch(Exception e){e.printStackTrace();}

    finally{

  try{
     if(stmt!=null)
        stmt.close();
   }catch(SQLException se2){
   }// nothing we can do
  try{
     if(conn!=null)
        conn.close();
   }catch(SQLException se){
     se.printStackTrace();
   }//end finally try
   }//end try
   System.out.println("Goodbye!");

   }//end main
}

我收到了错误：

  C:\JavaP>java -cp .;C:\JavaP\mysql-connector-java-3.1.14-bin-g Database1
  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 Database1.main(Database1.java:17)
   Goodbye!

经过数小时的谷歌搜索和在线搜索后，我终于能够解决我的问题了（ - 在我的情况下，java lib文件夹（C：\ Program Files \ Java \ jdk1.8.0_05 \ lib）的位置是在环境变量中维护的，没有任何java程序可以执行。）

但现在我遇到了另一个问题：

 C:\JavaP>java -cp .;C:\JavaP\mysql-connector-java-3.1.14-bin-g.jar Database1
 Exception in thread "main" java.lang.NoClassDefFoundError: org/aspectj/lang/Signature
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at Database1.main(Database1.java:17)
Caused by: java.lang.ClassNotFoundException: org.aspectj.lang.Signature
    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)
    ... 3 more

Answer 1

您需要add jar包含课程org.aspectj.lang.Signature的{​​{1}}文件的位置classpath

等。

java -cp .;C:\JavaP\mysql-connector-java-3.1.14-bin-g.jar;C:\JavaP\aspectj.jar Database1

Answer 2

这里是JAR的清单：

Manifest-Version: 1.0

Name: org/aspectj/lang/
Specification-Title: AspectJ Runtime Classes 
Specification-Version: 1.8
Specification-Vendor: aspectj.org
Implementation-Title: org.aspectj.tools
Implementation-Version: 1.8.7
Implementation-Vendor: aspectj.org
Bundle-Name: AspectJ Runtime
Bundle-Version: 1.8.7
Bundle-Copyright: (C) Copyright 1999-2001 Xerox Corporation, 2002 Palo 
  Alto Research Center, Incorporated (PARC), 2003-2009 Contributors. 
  All Rights Reserved.

Answer 3

事实上，我认为你为jdbc驱动程序选择调试版jar，当我下载MySQL SQL driver jar并解压缩zip文件时，它看起来如下：

您应该在调试文件夹中选择名称为mysql-connector-java-5.0.8-bin.jar但不是mysql-connector-java-5.0.8-bin**-g**.jar的jar。