private static List doSplitCollection()

in mongodbreader/src/main/java/com/alibaba/datax/plugin/reader/mongodbreader/util/CollectionSplitUtil.java [66:167]
92 lines of code
16 McCabe index (conditional complexity)

    private static List<Range> doSplitCollection(int adviceNumber, MongoClient mongoClient,
                                                 String dbName, String collName, boolean isObjectId) {

        MongoDatabase database = mongoClient.getDatabase(dbName);
        List<Range> rangeList = new ArrayList<Range>();
        if (adviceNumber == 1) {
            Range range = new Range();
            range.lowerBound = "min";
            range.upperBound = "max";
            return Arrays.asList(range);
        }

        Document result = database.runCommand(new Document("collStats", collName));
        int docCount = result.getInteger("count");
        if (docCount == 0) {
            return rangeList;
        }
        int avgObjSize = 1;
        Object avgObjSizeObj = result.get("avgObjSize");
        if (avgObjSizeObj instanceof Integer) {
            avgObjSize = ((Integer) avgObjSizeObj).intValue();
        } else if (avgObjSizeObj instanceof Double) {
            avgObjSize = ((Double) avgObjSizeObj).intValue();
        }
        int splitPointCount = adviceNumber - 1;
        int chunkDocCount = docCount / adviceNumber;
        ArrayList<Object> splitPoints = new ArrayList<Object>();

        // test if user has splitVector role(clusterManager)
        boolean supportSplitVector = true;
        try {
            database.runCommand(new Document("splitVector", dbName + "." + collName)
                .append("keyPattern", new Document(KeyConstant.MONGO_PRIMARY_ID, 1))
                .append("force", true));
        } catch (MongoCommandException e) {
            if (e.getErrorCode() == KeyConstant.MONGO_UNAUTHORIZED_ERR_CODE ||
                e.getErrorCode() == KeyConstant.MONGO_ILLEGALOP_ERR_CODE) {
                supportSplitVector = false;
            }
        }

        if (supportSplitVector) {
            boolean forceMedianSplit = false;
            int maxChunkSize = (docCount / splitPointCount - 1) * 2 * avgObjSize / (1024 * 1024);
            //int maxChunkSize = (chunkDocCount - 1) * 2 * avgObjSize / (1024 * 1024);
            if (maxChunkSize < 1) {
                forceMedianSplit = true;
            }
            if (!forceMedianSplit) {
                result = database.runCommand(new Document("splitVector", dbName + "." + collName)
                    .append("keyPattern", new Document(KeyConstant.MONGO_PRIMARY_ID, 1))
                    .append("maxChunkSize", maxChunkSize)
                    .append("maxSplitPoints", adviceNumber - 1));
            } else {
                result = database.runCommand(new Document("splitVector", dbName + "." + collName)
                    .append("keyPattern", new Document(KeyConstant.MONGO_PRIMARY_ID, 1))
                    .append("force", true));
            }
            ArrayList<Document> splitKeys = result.get("splitKeys", ArrayList.class);

            for (int i = 0; i < splitKeys.size(); i++) {
                Document splitKey = splitKeys.get(i);
                Object id = splitKey.get(KeyConstant.MONGO_PRIMARY_ID);
                if (isObjectId) {
                    ObjectId oid = (ObjectId)id;
                    splitPoints.add(oid.toHexString());
                } else {
                    splitPoints.add(id);
                }
            }
        } else {
            int skipCount = chunkDocCount;
            MongoCollection<Document> col = database.getCollection(collName);

            for (int i = 0; i < splitPointCount; i++) {
                Document doc = col.find().skip(skipCount).limit(chunkDocCount).first();
                Object id = doc.get(KeyConstant.MONGO_PRIMARY_ID);
                if (isObjectId) {
                    ObjectId oid = (ObjectId)id;
                    splitPoints.add(oid.toHexString());
                } else {
                    splitPoints.add(id);
                }
                skipCount += chunkDocCount;
            }
        }

        Object lastObjectId = "min";
        for (Object splitPoint : splitPoints) {
            Range range = new Range();
            range.lowerBound = lastObjectId;
            lastObjectId = splitPoint;
            range.upperBound = lastObjectId;
            rangeList.add(range);
        }
        Range range = new Range();
        range.lowerBound = lastObjectId;
        range.upperBound = "max";
        rangeList.add(range);

        return rangeList;
    }