java.lang.NoClassDefFoundError when using MongoDB

问题:

I am trying to connect to a MongoDB database hosted on mlab using the Java driver on a servlet.

import org.bson.Document; 
import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;

public class MongoConnection {

    protected void connectToMongo(String loc){

        String dbName = "readings";
        String collection = "data";

        MongoClientURI uri = new MongoClientURI("mongodb://user:[e-mail]:43109/readings");
        MongoClient client = new MongoClient(uri);
        MongoDatabase db = client.getDatabase(dbName);

        MongoCollection<Document> readings = db.getCollection(collection);

        Document doc = Document.parse(loc);

        readings.insertOne(doc);

        client.close();
    }
}

The problem is I am getting the following error: java.lang.NoClassDefFoundError: com/mongodb/MongoClientURI

I looked at one answer (How to resolve ClassNotFoundException: com.mongodb.connection.BufferProvider?) that highlighted to me that I need other jars, I have since downloaded them however I am still getting this error.

I am using Eclipse and adding the three jars to the build path, navigating through the menu by right clicking on the project then following Build Path -> Configure build path -> Java build path -> libraries -> add external JARs.

Is this the right way to do it? Is there something else I am supposed to do as well/instead?

回答1:

You have java.lang.NoClassDefFoundError - that means your class is missed during runtime (not during build/compile time). So you should open your "Run Configurations" dialog for the project (project context menu -> "Run As" -> "Run Configurations...") and make sure you have bson-xxx.jar, mongodb-driver-xxx.jar, and mongodb-driver-core-xxx.jar somehow listed in Classpath tab. And yes, like Xavier Bouclet said - if you run it under application server - this jars should be added to your server's classpath.

回答2:

You have to make sure that the mongodb jars are exported to server if your call to the database are made from the servlet.

Check how you deploy your app on your local server dans make sure the jars are there.