How to connect client to mongodb using java plugin?

This appears to currentOpbe a command on the shell, but not a first-class mongodb command supported by all drivers . You will need to use to query the $cmd.sys.inprogcollection findOne(). Using the javadriver, you can do the following ( currentOpunder the hood, to be precise):

DB db = mongoclient.getDB("local");
DBObject currentOp = db.getCollection("$cmd.sys.inprog").findOne();

If you know what's going on behind the scenes when you call, currentOpyou'll understand:

> db.currentOp
function ( arg ){
    var q = {}
    if ( arg ) {
        if ( typeof( arg ) == "object" )
            Object.extend( q , arg );
        else if ( arg )
            q["$all"] = true;
    }
    return this.$cmd.sys.inprog.findOne( q );
}
>