java - 运行jdbc时出错

Question

遵循的步骤

• mysql工作台安装

• 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
  

将此代码添加到 Eclipse 中的新项目中。当我运行它时，我发生了这个错误

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;

还是同样的错误该怎么办，请给出一些解释以及您有值(value)的解决方案谢谢

Answer 1

在 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>

如果您没有使用 maven，则将此 jar com.mysql.jdbc_5.1.5.jar 添加到您的 eclipse 构建路径右键单击项目-->构建路径-->配置构建路径-->库-->添加外部jar