JDBC不工作

Question

我的JDBC代码什么也没做。它将打印出“连接到数据库”语句，但仅此而已。我引用了JDBC jar文件，所以我有点困惑为什么我的代码不能工作。下面是我一直在尝试运行的代码。

package exampleDatabase;


import java.sql.*; 


public class Main {

        // TODO Auto-generated method stub


        static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
           static final String DB_URL = "jdbc:mysql://localhost:81/companylist";

           //  Database credentials
           static final String USER = "root";
           static final String PASS = "";

           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, firstName, lastName,Email FROM Staff";
              ResultSet rs = stmt.executeQuery(sql);

              //STEP 5: Extract data from result set
              while(rs.next()){
                 //Retrieve by column name
                 int ID  = rs.getInt("ID");
                 String firstName = rs.getString("firstName");
                 String lastName = rs.getString("lastName");
                 String Email = rs.getString("Email");

                 //Display values
                 System.out.print("ID: " + ID);
                 System.out.print(", First: " + firstName);
                 System.out.println(", Last: " + lastName);
                 System.out.println(", Last: " + Email);

              }
              //STEP 6: Clean-up environment
              rs.close();
              stmt.close();
              conn.close();
           }catch(SQLException se){
              //Handle errors for JDBC
              se.printStackTrace();
           } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
           }
    }

Answer 1

数据库服务器的Port Address不是web服务器的端口。因此，要解决这个问题，您应该将连接URL更改为jdbc:mysql://localhost:3306/companylist，因为3306是MySQL数据库服务器的默认端口地址。

Answer 2

jdbc:mysql://localhost:81/companylist无效。

由于您使用的是mysql database，因此服务器的默认port编号为3306。

所以试试这个，jdbc:mysql://localhost:3306/companylist

它将运行..。