Executing Mongo like Query (JSON)through Java

问题:

I was wondering if there is a way to execute mongo like query directly through Java i.e. we give mongoDB like query as a String to a function in Java driver for mongoDB as a String Object and an DBCursor Object is returned. Something like:

import com.mongodb.*;
import java.net.UnknownHostException;
public class ExecuteQuery {
public static void main(String args[]){
    try{
          Mongo m = new Mongo();
          DB db = m.getDB("test");
          DBCollection coll = db.getCollection("first");
          DBObject doc = new BasicDBObject();
          DBCursor cur =coll.executeQuery("db.first.find({"username":"joe"})");
       }
       catch(UnknownHostException e){
          System.out.println(e);
       }
       catch (MongoException.DuplicateKey e) {
          System.out.println("Exception Caught" + e);
       }
}
}

Note: executeQuery() is not a built in function. It is just used for demonstration purposes. So, Is there a function in the java api which converts a json string to a BasicDBObject instance? Thanks.

回答1:

What you showed here is not JSON, it's Javascript code for embedded MongoDB Shell. If you need for some reason to execute the code inside Java environment you will have to embed Javascript engine (like Rhino) and implement compatible API.

Otherwise you just need to convert JSON to DBObject and you can do this with JSON.parse() method or any other JSON-mapping library like Jackson. Note that MongoDB uses extended set of data types that are not present in JSON: http://www.mongodb.org/display/DOCS/Data+Types+and+Conventions

UPD: Scott Hernandez pointed out about JSON.parse.

回答2:

Yes, there is way, by passing the filter as a string. Example:

BasicDBObject query = BasicDBObject.parse("{userId: {$gt: \"1\"}}");
FindIterable<Document> dumps = crapCollection.find(query);

You can Also use com.mongodb.util.JSON, but I don't recommend it. It's less descriptive.

DBObject dbObject = (DBObject)JSON.parse("{userId: {$gt: \"1\"}}");

Please notice that this might be vulnerable to SQL injections because you parse/build the filter yourself.

I recommend using Jongo's parameterized query.

回答3:

Take a look at the Jongo library - it will allow you to run even pretty advanced queries using the command-line syntax.

It also uses a very fast GSON mapper to return your own objects back to you as the result of the query, instead of a list of BasicDBObjects.

回答4:

I would recommend to use mongo-shell-like-query utility (jar). It allows you to write mongo queries in java (or scala) code using the same syntax as that of mongo command shell. To be more specific, you can write mongo queries in string format. It also supports advance features such as aggregation pipeline. Have a look at https://github.com/EqualExperts/mongo-shell-like-query

回答5:

You can follow the example in the tutorial:

http://www.mongodb.org/display/DOCS/Java+Tutorial#JavaTutorial-GettingASetofDocumentsWithaQuery

Note their use a of (Basic)DBObject to create the query, not a string.