Upgrade to Mongo 4 java driver

Currently the Mongo DB instrumentation references legacy classes in the Mongo 3 java driver. Spring Boot requires the Mongo 4 driver starting with 2.3.0.RELEASE.

There are 2 Mongo listeners that provide metrics:

• MongoMetricsCommandListener
• MongoMetricsConnectionPoolListener

They both reference com.mongo.MongoClient (only for a Javadoc @link tag) which still exists in the Mongo 4 java driver, but its in the mongodb-driver-legacy lib. The connection pool listener, however, actually references event classes that have been removed in Mongo 4 driver.

Suggested plan:

• Upgrade the Mongo dependency to mongodb-driver-sync
• Replace the @link tag w/ {@code } therefore removing the dependency on any MongoClient (its not used anyways)
• Replace the usage of the deleted event classes in the connection pool listener w/ their Mongo 4 equivalent events

Concerns:

• This will force Mongo 4 on consumers of the instrumentation. It would have to be in a minor version release. There may be a way to use an lowest common denominator of Mongo 3 and 4 for the connection pool listener events so as to be usable by both Mongo 3 and 4.

[jonatan-ivanov]

@bono007 Fyi, this is in progress (see the draft PR), after this is done, I will take a look at the extra tags.

[jonatan-ivanov]

@bono007 Makes sense, thank you for the info. I really encourage upgrading dependencies, I just would like to figure out what this upgrade would mean for micrometer users (last time I used the mongo-driver in prod was 2013 I guess, so I need to keep up).

Micrometer is not really a Spring library, it is used outside of Spring too so an upgrade in Spring Data does not necessarily triggers an upgrade in Micrometer but you made a great point, I’m going to ask the Spring Data Team about the background of dropping 3.x.