运行 jdbc 时出错

Question

遵循的步骤

mysqlworkbench安装

Connector-J 下载并解压到程序文件中的 Mysql 文件夹已复制

import java.sql.*;
public class FirstExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
static final String DB_URL = "jdbc:mysql://localhost/EMP";

 //  Database credentials
static final String USER = "username";
static final String PASS = "password";

public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
   //STEP 2: Register JDBC driver
   Class.forName("com.mysql.jdbc.Driver");

   //STEP 3: Open a connection
   System.out.println("Connecting to database...");
   conn = DriverManager.getConnection(DB_URL,USER,PASS);

   //STEP 4: Execute a query
   System.out.println("Creating statement...");
   stmt = conn.createStatement();
   String sql;
   sql = "SELECT id, first, last, age FROM Employees";
   ResultSet rs = stmt.executeQuery(sql);

   //STEP 5: Extract data from result set
   while(rs.next()){
      //Retrieve by column name
      int id  = rs.getInt("id");
      int age = rs.getInt("age");
      String first = rs.getString("first");
      String last = rs.getString("last");

      //Display values
      System.out.print("ID: " + id);
      System.out.print(", Age: " + age);
      System.out.print(", First: " + first);
      System.out.println(", Last: " + last);
   }
       //STEP 6: Clean-up environment
   rs.close();
   stmt.close();
   conn.close();
}catch(SQLException se){
   //Handle errors for JDBC
   se.printStackTrace();
}catch(Exception e){
   //Handle errors for Class.forName
   e.printStackTrace();
}finally{
   //finally block used to close resources
        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
  }//end FirstExample

此代码到eclipse 中的新项目。当我运行它发生这个错误时

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
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 FirstExample.main(FirstExample.java:17)
  Goodbye!

然后尝试了这个 cmd 命令

set classpath=C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-   
 connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar;

还是一样的错误该怎么做，请给出一些解释以及您宝贵的解决方案谢谢

Answer 1

You will have to copy the JDBC connector jar file into library folder of your project

or in library folder of server

Both works fine...

Runtime variables are not getting it from these two locations

Answer 2

在您的 pom.xml

中添加以下依赖项

<!-- http://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.6</version>
</dependency>

如果您不使用 maven，则将此 jar com.mysql.jdbc_5.1.5.jar 添加到您的 eclipse build path rightclick on project--> build path-->configure build path-->libraries-->add external jar

Answer 3

您的类路径包含 space，因此 java.exe 将无法正确拾取它。
使用脱字符 ^ 转义 space:

set classpath=C:\Program^ Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar;

（并仔细检查路径是否正确！）。

运行 jdbc 时出错

Error while running jdbc

java

mysql

eclipse

jdbc

classpath