Java 如何在整个应用程序中使用一个数据库连接对象？

How can I use one database connection object in whole application?

提问by Dhruv Kapatel

I have created this class which returns connection object. I have used MySQL database.

我创建了这个返回连接对象的类。我用过 MySQL 数据库。

public class Connect_db {        
    public Connection getConnection(String db_name,String user_name,String password)
    {
        Connection con=null;
        try
        {
        Class.forName("com.mysql.jdbc.Driver");
        con=DriverManager.getConnection("jdbc:mysql://localhost/"+db_name+"?user="+user_name+"&password="+password);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

        return con;        
    }
}  

Now all I want to do is instantiate this class once and get connection object. And I want to use this same object in entire application. Another solution will also be appreciated.

现在我想要做的就是实例化这个类一次并获取连接对象。我想在整个应用程序中使用这个相同的对象。另一种解决方案也将受到赞赏。

采纳答案by I?ya Bursov

I suppose you need singleton pattern, here is quick example:

我想你需要单例模式，这是一个简单的例子：

public class Connect_db {        
    static Connection con=null;
    public static Connection getConnection()
    {
        if (con != null) return con;
        // get db, user, pass from settings file
        return getConnection(db, user, pass);
    }

    private static Connection getConnection(String db_name,String user_name,String password)
    {
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            con=DriverManager.getConnection("jdbc:mysql://localhost/"+db_name+"?user="+user_name+"&password="+password);
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

        return con;        
    }
} 

then you will be able to use connection like this:

那么您将能够使用这样的连接：

Connect_db.getConnection().somemethods();

but, you should think - how this will work in multi-threaded environment, when several threads are trying to make requests to database.

但是，您应该考虑 - 当多个线程试图向数据库发出请求时，这将如何在多线程环境中工作。

回答by JosefN

very primitive way, you can get a Connection instance by

非常原始的方式，您可以通过以下方式获取 Connection 实例

Connect_db.getConnection(dbName,userName,passwd);

Connect_db.getConnection(dbName,userName,passwd);

in any class because it is static method.

在任何类中，因为它是静态方法。

public class Connect_db {   
static {
     try {
        Class.forName("com.mysql.jdbc.Driver");
    } catch (ClassNotFoundException e) {
        throw new IllegalArgumentException("MySQL db driver isnot on classpath");
    }
}
public static Connection getConnection(String db_name,String user_name,String password) throws SQLException
{
    return DriverManager.getConnection("jdbc:mysql://localhost/"+db_name+"?user="+user_name+"&password="+password);    
}

}

}

if your applicaiton is mutlithreaded and should perfom well use a pool

如果您的应用程序是多线程的并且应该很好地使用池

回答by Dmitry Buslaev

I really liked Lashane's response, I used the code to create a DataSourcesolution. I also redesigned it to only store DataSourceand not the Connection, in case you do want to open multiple ones.

我真的很喜欢 Lashane 的回应，我使用代码创建了一个DataSource解决方案。我还将它重新设计为仅存储DataSource而不是Connection，以防您确实想打开多个。

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;

public class SignalDB {

    private static MysqlDataSource ds = null;

    public static MysqlDataSource getDataSource(String db_name) {
        if (ds == null) {
            // db variables set here
            getDataSource(db_url, db_user, db_password, db_port);
        }
        ds.setDatabaseName(db_name);
        return ds;
    }

    private static void getDataSource(String db_url, String db_user, String db_password, int db_port) {
        try {
            ds = new MysqlDataSource();
            ds.setServerName(db_url);
            ds.setUser(db_user);
            ds.setPassword(db_password);
            ds.setPort(db_port);
        } catch (Exception e) {
            System.out.println("MysqlDataSource err: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

Then you could create connections using:

然后您可以使用以下方法创建连接：

con = SignalDB.getDataSource("database_name").getConnection();

con = SignalDB.getDataSource("database_name").getConnection();

I added ability to connect to a different database every time, in some cases, like ours, it's what you need to do on the fly.

我增加了每次连接到不同数据库的能力，在某些情况下，就像我们的一样，这是您需要即时执行的操作。

Hope this helps.

希望这可以帮助。