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I just read this question and the answer claims:

"Lets assume db connection object is singleton in my application"

This is a must not. Your database connection MUST NEVER BE (yes, bolded and with capitals to make sure you and every reader never make this mistake) a singleton object. Your Connection con MUST NOT be part of a singleton to keep it open all the time. Instead, use a proper database connection pool that will take care of opening the necessary physical database connections and keep them alive through the live of your application.

We of course use a connection pool to take care of our, well, connections. Still, we store this pool in a singleton. How else would one ensure that it lives throughout the application? Ist his bad practice?

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    A connection pool might be one of the only valid use cases for a singleton pattern (which you usually want to avoid). I would be fine with it.
    – f1sh
    Feb 1, 2017 at 10:29
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    I think the answer means what you have done. Connections themselves should not be singletons, but CAN be managed by a singleton.
    – jr593
    Feb 1, 2017 at 10:30
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    Like jr593, I think you just misread the answer. Your implementation of Connection must not be designed as singleton, but your Connection Pool may be a singleton.
    – SME_Dev
    Feb 1, 2017 at 10:48
  • I too misread the text, I think is not a bad practice connections are a limited resource and are both expensive to initially create and then maintain over time. If not a singleton your system must still have access to a single instance of this pool but not a single instance to the connection.
    – Omar Ayala
    Feb 1, 2017 at 11:30

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I think the quoted answer is mainly stating an opinion.

The one fact in that answer is about the "per classloader" aspect.

In other words: unless you are in a situation, where that "multiple classloaders" part comes in there are no technical reasons to not use a singleton.

Of course, the key element would be to implement a "correct" singleton; for example by using a Java enum for that.

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What the author of the quote says is that the connection must never be a singleton, not stored in a singleton. I can't imagine a connection as a singleton with status like "connected", "available", etc... Pools are made for this.

On an application I do the same thing as you, the connections are stored in a pool held by a singleton, so that any thread can use them.

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