在其他对象之间共享JDBC连接对象 [英] sharing a JDBC Connection object between other objects

问题描述

我创建了一个Database类，该类使用静态连接对象，以便在其自身的实例之间共同使用.我的问题是这种方法是否存在问题?

I have created a Database class which uses a static connection object in order to be used in common between instances of itself. my question is that is there any problem with this approach or not?

class Database {
    private static Connection connection = null;

    public Database() {
        if(connection == null){
            ...
            connection = DriverManager.getConnection(...);
            ...
        }
    }
}

推荐答案

如果您每秒要进行许多(数百个)查询，那么实现连接池是您的最佳选择.有关更多详细信息，请参见此问题的答案.但是，如果您是Java的新手(我们都是一天！)，那么我不认为您会需要此要求，并且可能很难实现它.

If you are going to have many (hundreds) of queries per second then implementing a connection pool is the way to go. See the answer to this question for more details. However, if you a Java novice (we all were one day!) then I don't imagine you will be needing this requirement, and probably will struggle to implement it.

相反，如果需要的话，创建一个新连接，然后在完成后将其关闭的简单模式将是您前进的最佳方法.下面是您的 Database 类的修改版本，我认为这是前进的好方法.

Instead, the simple pattern of creating a new connection if required, and then closing it when finished will be the best way to go forward for you. Below is a modified version of your Database class which I think is a good way to move forward.

class Database {
    private Connection con = null;
    private final String connectionString;

    public Database(String connectionString) {
        this.connectionString = connectionString;
    }

    public void connect() throws SQLException {
        if (con != null // if the connection exists
             && !con.isClosed() // and has not been closed 
             && con.isValid(0)) { // and appears to be functioning (with a test timeout of 0ms)
             return; // skip connection creation
        }

        // create the connection
        con = DriverManager.getConnection(connectionString);        
    }

    public void testFunction() {
        try {
            connect();
            // .. do some stuff with the connection ..
        } catch (Exception e) {
            // log or otherwise deal with the error
        } finally {
            try {
                con.close();
            } catch (Exception e) {
                System.err.println("Failed to close connection: " + e.toString());
            }
        }

    }
}

有关此解决方案的一些注意事项:

Some things to note about this solution:

• 效率不是很高-与使用现有连接相比，创建新连接总是要花费更多时间
• 如果不是线程安全的此类-如果您需要此要求，建议使用线程池.但是，如果您为每个线程创建此类的新实例，则它 将是线程安全的(因为无需担心静态连接！)
• 它确实可以完成工作-当然，对于简单的情况也是如此.我将该模型用于相对较低的数据库，该数据库每分钟建立/关闭约50-100个连接，并且不会增加明显的延迟
• 它非常坚固[em] -没有什么比打开和关闭每个查询连接更安全的了.您一定可以处理每个查询的连接失败，并且连接将始终关闭(除非已经关闭).

• It is not very efficient - creating a new connection always takes more time than using an existing one
• This class if not thread safe - if you need this requirement, I recommend using a thread pool. However, if you create a new instance of this class per thread then it will be thread safe (as there is not static connection to worry about!)
• It does do the job - certainly for simple cases. I use the model for a relatively low volume database which has approx 50-100 connections made/closed per minute and it does not add a noticeable lag
• It is very robust - nothing is safer than opening and closing a connection per query. You are guaranteed to be able to handle a connection failure per query, and the connection will always be closed (unless it already has been).

免责声明上面的解决方案并不是特别出色的解决方案.但是，我相信它的实现很简单，并且是Java新手在进入外部库之前先了解绳索的好方法.

Disclaimer The solution above is not a particularly amazing solution. However, I believe it is simple to implement and a good way for a Java novice to get to know the ropes before jumping into external libraries.

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