Question

因此，我正在使用Java Eclipse制作JDBC CRUD程序，并且为了防止数据泄漏，我无法确定何时以及如何关闭连接。在其他情况下，我想问一下我的程序是否在每个函数中都打开了连接，这使得连接不太理想。以下是我的代码，

_getConnection代码建立数据库连接，

package com.Database;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class _getConnection {

    static final String JDBC_Driver = "com.mysql.jdbc.Driver";
    static final String URL = "jdbc:mysql://localhost:3306/rubyrail?useSSL=false";
    static final String Username = "root";
    static final String Password = "root";
    static Connection connection = null;


    public Connection connect()
    {
        //Connection connection = null;

        try {
              Class.forName("com.mysql.jdbc.Driver");              
              connection = DriverManager.getConnection(URL, Username, Password); 
        }
        catch(Exception e)
        {}

        return connection;
    }

    public static Connection close()
    {
        if (connection!=null)
        {
            try {
                connection.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return connection;
    }
}

Database_Connection是CRUD应用程序，

package com.Database;

import java.sql.*;
import java.sql.Date;
import java.util.*;

public class Database_Connection
{
    static Scanner scanner = new Scanner(System.in);

    public static void Create()
    {
        _getConnection get_connect = new _getConnection();
        Connection conn = get_connect.connect();
        int item_no = 0;
        String item_name = null;
        int item_cost = 0;
        Statement stmt = null;
        System.out.println("\nEnter the following details,");
        System.out.println("\nItem Number: ");
        item_no = scanner.nextInt();
        scanner.nextLine();
        System.out.println("\nItem Name: ");
        item_name = scanner.nextLine();
        System.out.println("\nItem Cost: ");
        item_cost = scanner.nextInt();

        try 
        {
            String sql = "Insert into item (item_no, item_name, item_cost, last_update) values ("+item_no+",'"+item_name+"',"+item_cost+",CURDATE())";
            stmt = conn.prepareStatement(sql);
            stmt.executeUpdate(sql);
            //stmt.execute(sql);
        }
        catch(Exception e)
        {System.out.println(e);}


    }

    public static void Read()
    {
        _getConnection get_connect = new _getConnection();
        Connection conn = get_connect.connect();
        Statement stmt=null;

        try 
        {
            String sql = "Select * from item";
            stmt = conn.prepareStatement(sql);
            ResultSet resultset = stmt.executeQuery(sql);
            while (resultset.next())
            {
                int item_no = resultset.getInt("item_no");
                String item_name = resultset.getString("item_name");
                int item_cost = resultset.getInt("item_cost");
                Date last_update = resultset.getDate("last_update");

                System.out.print("Item Number: " + item_no);
                 System.out.print(", Item Name: " + item_name);
                 System.out.print(", Item Cost: " + item_cost);
                 System.out.println(", Last Updated: " + last_update);
            }
        }
        catch(Exception e)
        {System.out.println(e);}
    }

    public static void Update()
    {
        _getConnection get_connect = new _getConnection();
        Connection conn = get_connect.connect();
        Statement stmt=null;
        int item_no = 0;
        String item_name = null;
        int item_cost = 0;
        System.out.println("\nEnter the Item Number to be Updated,");
        System.out.println("\nItem Number: ");
        item_no = scanner.nextInt();
        scanner.nextLine();
        System.out.println("\nEnter the following details,");
        System.out.println("\nItem Name: ");
        item_name = scanner.nextLine();
        System.out.println("\nItem Cost: ");
        item_cost = scanner.nextInt();

        try 
        {
            String sql = "update item set item_name = '"+item_name+"',item_cost ="+item_cost+",last_update = CURDATE() where item_no = "+item_no;
            stmt = conn.prepareStatement(sql);
            stmt.executeUpdate(sql);
        }
        catch(Exception e)
        {System.out.println(e);}

    }

    public static void Delete()
    {
        _getConnection get_connect = new _getConnection();
        Connection conn = get_connect.connect();
        Statement stmt=null;
        int item_no = 0;
        System.out.println("\nEnter the Item Number to be Deleted,");
        System.out.println("\nItem Number: ");
        item_no = scanner.nextInt();

        try 
        {
            String sql = "delete from item where item_no = "+item_no;
            stmt = conn.prepareStatement(sql);
            stmt.executeUpdate(sql);
        }
        catch(Exception e)
        {System.out.println(e);}
    }

    public static void Close()
    {
        _getConnection.close();

        System.out.println("Closing Connection..");

        System.out.println("Connection Closed!");
    }

        public static void main (String args[])
        {
            _getConnection get_connect = new _getConnection();
            Connection conn = get_connect.connect();
            int choice= 0;
            try {
                  if(conn!=null)
                  while (choice < 6)
                  {
                      System.out.println("\n1. Create");
                      System.out.println("\n2. Read");
                      System.out.println("\n3. Update");
                      System.out.println("\n4. Delete");
                      System.out.println("\n5. Close");

                  choice = scanner.nextInt();
                  switch(choice)
                  {
                  case 1: Create();
                  break;

                  case 2: Read();
                  break;

                  case 3: Update();
                  break;

                  case 4: Delete();
                  break;

                  case 5: Close();
                  break;
                  }
                } 
            }
            catch (Exception e) {}
        }

}

我希望我的解决方案在程序的Close（）函数中具有结束位置。

Answer 1

关闭数据库连接始终是最佳实践。您可以添加一个finally块以关闭数据库连接。最佳做法是按以下顺序关闭连接 ResultSet, Statement, and Connection在程序末尾的finally块中。

请点击此链接以获取更多详细信息[接受的答案] https://stackoverflow.com/a/2225275/7719903

Answer 2

您可以将代码更改为：

public class DatabaseConnection {

    static final String URL = "jdbc:mysql://localhost:3306/rubyrail?useSSL=false";
    static final String Username = "root";
    static final String Password = "root";

    private static Connection createConnection() {
        return DriverManager.getConnection(URL, Username, Password);
    }

    public static void create() {
        try (Connection connection = createConnection()) {
            // do something with the connection
        } catch (SQLException e) {
            e.printStackTrace();
            // or something else to handle the error
        }
    }

    // same for the rest of your methods

    public static void main (String args[]) {
        int choice= 0;
        while (choice < 6) {
            System.out.println("\n1. Create");
            System.out.println("\n2. Read");
            System.out.println("\n3. Update");
            System.out.println("\n4. Delete");
            System.out.println("\n5. Close");

            choice = scanner.nextInt();
            switch(choice) {
            case 1: 
                create();
                break;
            // other cases
            }
        }
    }
}

这将为每个方法调用创建一个连接，这可能会降低效率，但会简化资源管理。如果性能至关重要，则应考虑使用提供连接池的数据源（例如HikariCP，Apache DBCP等）。使用连接池将允许连接的重用，而您的代码不必担心除了设置数据源配置之外的其他事情。

或者，在主连接中创建一次连接，并将其传递给您要调用的每个方法：

public static void create(Connection connection) {
    try {
        // do something with connection
    } catch (SQLException e) {
        e.printStackTrace();
        // or something else to handle the error
    }
}
public static void main (String args[]) {
    try (Connection connection = createConnection()) {
        int choice= 0;
        while (choice < 6) {
            System.out.println("\n1. Create");
            System.out.println("\n2. Read");
            System.out.println("\n3. Update");
            System.out.println("\n4. Delete");
            System.out.println("\n5. Close");

            choice = scanner.nextInt();
            switch(choice) {
            case 1: 
                create(connection);
                break;
            // other cases
            }
        }
    } catch (SQLException e) {
        e.printStackTrace();
        // or something else to handle the error
    }
}

如何以这种方式关闭数据库连接？

2 个答案: