MongoDB connection instantly closes - Java

Question

I am using the mongodb-driver-sync-4.1.0-rc0 dependency and whenever I connect to the database I can use it within the same method but as soon as i store it as a static var and try accessing it from another class it says "state should be: open". My connection instantly closes after establishing a connection.

public static void initializeClient(){
        String uri = "mongodb+srv://myusername:mypassword@userstats.9vs4b.mongodb.net/izzi?retryWrites=true&w=majority";

        try ( MongoClient mongoClient = MongoClients.create(uri)) {

            client = mongoClient;
            izzi = client.getDatabase("izzi").getCollection("userStats");

            System.out.println(getOverallLikes());
            System.out.println(getWinnersLastMonth());
            //after this it closes the connection

        }
    }

I get this message when it disconnects: [main] INFO org.mongodb.driver.connection - Closed connection [connectionId{localValue:4, serverValue:14654}] to userstats-shard-00-02.9vs4b.mongodb.net:27017 because the pool has been closed.

Here is an example code about creating `MongoClient` and using it in a Java application. When a `MongoClient` is created, by default, it is configured with a _connection pool_ of size 100 (this is specific for Java driver). So, a `MongoClient` can be created and used across the application from a Singleton class. See: [Managing Mongodb connections in Java as Object Oriented](https://stackoverflow.com/questions/60180119/managing-mongodb-connections-in-java-as-object-oriented/60337641#60337641). — prasad_, Jul 30 '20 at 01:54

aran · Answer 1 · 2020-08-10T20:06:58.813

Its behaviour is the normal one; This is a try-with-resources:

try ( MongoClient mongoClient = MongoClients.create(uri)) 
{
       client = mongoClient;
       izzi = client.getDatabase("izzi").getCollection("userStats");
       System.out.println(getOverallLikes());
       System.out.println(getWinnersLastMonth());
       //after this it closes the connection
}

From the documentation:

The try-with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement

Your resource is the MongoClient instance, which will be automatically closed after the last operation inside the try clause. As you assigned the mongoClient value to your client variable, once the try-clause is finished and the mongoClient closed, client will reference a closed session.

hello. in my case this worked. i've copied the code blindly from https://developer.mongodb.com/quickstart/java-mapping-pojos and didn't think about try-with-resource there. thank you very much! — morwed, Aug 10 '20 at 13:25

Gopinath · Answer 2 · 2020-07-29T22:40:28.890

The above observation of connection being closed is as per the intended functionality of the 'try with resources' feature of Java.

The desired requirement of keeping the connection active can be achieved by using a regular try ... catch ... finally block with mongoClient.close() called explicitly for closing the connection.

Moreover, if the requirement is to call the method from a different class, then the code for closing the connection need to be placed in a different method.

Working code snippets:

(a) Connect to MongoDB, fetch data and close connection:

    public void myMongoDBClient() {
        MongoClient mongoClient;
        String uri = "mongodb-connection-uri";
        try {
             mongoClient = new MongoClient(uri)

             // Fetch data from mongodb
             // Other statements


        } catch (Exception ex) {
           // Error handling

        } finally {
           // Close the conection
           mongoClient.close();
        }
    }

(b) Call mongodb client from other classes:

public class MyMongoDBClient {

    private static MongoClient mongoClient = null;
    private static String uri = "mongodb-connection-uri";

    public static void initializeClient() {
        try {
             mongoClient = new MongoClient(uri)

        } catch (Exception ex) {
           // Error handling

        } finally {
           // Close the conection
           mongoClient.close();
        }
    }

   public static void fetchData() throws Exception {
       // Code for fetching data
       // Can be called multiple times from external classes
   }

  public static void close() throws Exception {
      // Close connection.
      // Can be called once from an external class
      mongoClient.close();
  }


}

MongoDB connection instantly closes - Java

2 Answers2