Java Application not recognizing my collections in my MongoDB databases.

Question

I am creating a simple web application and I am attempting to connect the application to MongoDB. Here is the class where I am establishing the connection.

public class JavaMongoDBConnection {

public static void main(String[] args) {
    try {
    MongoClient mongoClient = null;

        mongoClient = new MongoClient();

    List<String> databases = mongoClient.getDatabaseNames();

    for(String dbName: databases) {
        System.out.println("Databases: " + dbName);

        DB db  = mongoClient.getDB(dbName);

        Set<String> collections = db.getCollectionNames();

        for(String colName : collections) {
            System.out.println("\t + Collection: "+colName);

        }

    }
    mongoClient.close();


    } catch (UnknownHostException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

} }

When I run this class as a Java application, this is my result

Databases: admin Databases: budget Databases: config Databases: db Databases: local Databases: myTestDB

However, when I go to terminal and I run the following commands, here are my results.

show dbs

Response: admin 0.000GB budget 0.000GB config 0.000GB db 0.000GB local 0.000GB myTestDB 0.000GB

use myTestDB
show collections

Response: Budget budget myCollection

So, why are Budget, budget, and myCollection not showing up when I run this java application??

score 0 · Accepted Answer · answered May 23 '18 at 23:55

If you're using the current version of the MongoDB Java Driver (currently 3.7), use MongoDatabase instead of DB:

MongoClient mongoClient = new MongoClient();

for(String databaseName : mongoClient.listDatabaseNames()) {
    System.out.println("Database: " + databaseName);

    MongoDatabase db = mongoClient.getDatabase(databaseName);

    for(String colName : db.listCollectionNames()) {
        System.out.println("\t + Collection: " + colName);
    }
}

mongoClient.close();

The above code should have an output similar to the following:

Database: admin
         + Collection: system.version
Database: config
         + Collection: system.sessions
Database: local
         + Collection: startup_log
Database: test
         + Collection: testcoll1
         + Collection: testcoll2

Java Application not recognizing my collections in my MongoDB databases.

1 Answers1