eclipse中的数据库连接 - ClassNotFoundException [英] Database connection in eclipse - ClassNotFoundException

问题描述

我已经在Eclipse中创建了MySQL的连接配置文件。我编写了这个代码：

  public static void main（String [ ] args）{
 
 Connection conn; 
 
 try {
 Class.forName（com.mysql.jdbc.Driver）; 
 
 String url =jdbc：mysql：// localhost：3306 / test1; 
 conn = DriverManager.getConnection（url，root，swathi）; 
 
声明stmt = conn.createStatement（）; 
 String query =select * from sample; 
 
 System.out.println（stmt.executeQuery（query））; 
 
} catch（ClassNotFoundException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} catch（SQLException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} 
 
} 
  

我设置了

  classpath = C：\Program Files\MySQL\MySQL Connector J\mysql-connector-java-5.1.26-bin .jar 
  

当我运行程序时，我收到此错误：

  java.lang.NoClassDefFoundError：C：\Users\swathi\workspace\project1; C：\Program 
引起的：java .lang.ClassNotFoundException：C：\Users\swathi\workspace\project1; C：\Program 
在java.net.URLClassLoader $ 1.run（URLClassLoader.java:202）
 at java.security.AccessController.doPrivileged（Native Method）
在java.net.URLClassLoader.findClass（URLClassLoader.java:190）
在java.lang.ClassLoader.loadClass（ClassLoader.java:306）
 at sun.misc.Launcher $ AppClassLoader.loadClass（Launcher.java:301）
在java.lang.ClassLoader.loadClass（ClassLoader.java:247）
线程main$中的异常
  

解决方案

扩展项目类路径的正确方法是编辑设置对于该项目：

 右键单击您的项目>构建路径>配置构建路径... 
  

转到选项卡库然后

单击添加外部JAR ... ，找到jdbc驱动程序，然后单击打开然后确定。

或

点击添加库... 然后用户库和ckick 下一个> 。单击用户库，然后单击新建... 。输入您的lib的名称，例如 JDBC_DRIVER_MYSQL_5 然后单击添加外部JAR ... 。

我建议尽量将您的项目转换为 maven 项目，并将其添加为依赖关系：

 < dependency> 
< groupId> mysql< / groupId> 
< artifactId> mysql-connector-java< / artifactId> 
< version> 5.1.6< / version> 
< / dependency> 
  

I have created connection profile of MySQL in Eclipse.I have written this code:

public static void main(String[] args) {

        Connection conn;

        try {
            Class.forName("com.mysql.jdbc.Driver");

            String url="jdbc:mysql://localhost:3306/test1";
            conn= DriverManager.getConnection(url,"root","swathi");

            Statement stmt= conn.createStatement();
            String query="select * from sample";

            System.out.println(stmt.executeQuery(query));

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

i have set the

classpath=C:\Program Files\MySQL\MySQL Connector J\mysql-connector-java-5.1.26-bin.jar

When i run the program i am getting this error:

java.lang.NoClassDefFoundError: C:\Users\swathi\workspace\project1;C:\Program
Caused by: java.lang.ClassNotFoundException: C:\Users\swathi\workspace\project1;C:\Program
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Exception in thread "main" 

解决方案

The proper way to extend your project's class path is to edit the setting for that project:

Right click on your project > Build Path > Configure Build Path...

Go to the tab Libraries then

click Add External JARs..., locate the jdbc driver and click open then OK.

Or

click Add Library... then User Library and ckick Next >. Click User Libraries and then click New.... enter a name for your lib, for example JDBC_DRIVER_MYSQL_5 then click Add External JARs....

I would recomend though to convert your project into a maven project and add it as a dependency:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.6</version>
</dependency>

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