bucket used

b-used.java

Bson a=Aggregates.match( new Document("year", 5));

BucketOptions o=new BucketOptions();

o.output(
        new BsonField("student_ids", new Document("$push","$student_id")),
        new BsonField("attended_class",new Document("$sum",
                new Document("$cond",
                        Arrays.asList(
                                new Document("$gte",Arrays.asList("$attn",8)),
                                1,
                                0
                        )
                )
        )
        ),
        new BsonField("students_total", new Document("$sum",1))
);
        
Bson b=Aggregates.bucket("$final_grade", Arrays.asList(0,45,55,70,85,100),o);

//LIST for the pipeline
List<Bson> l=new ArrayList<>();

l.add(a);
l.add(b);

//STUDENTS_COLLECTION mongodb collection assumed to be provided
MongoCursor cur=STUDENTS_COLLECTION.aggregate(l).iterator();

//print as JSON
while(cur.hasNext())
    System.out.println(((Document) cur.next()).toJson());