Return multiple documents from MongoDB using Java

Question

I have been searching through the world wide web for hours and I can't find a viable solution to my problem:

It is simple: I want to search through a collection of items from my MongoDB and return all the documents.

From a RESTFul API perspective : GET /items - Returns all items in the collection. Not sorted

// NOT WORKING - STILL TRYING  
    public static String getItems() {

        StringBuilder items = new StringBuilder();
    MongoCursor<Document> cursor = itemCollection.find().iterator();
    try {

        while (cursor.hasNext()) {
            items.append(cursor.next().toJson());

        }

    } finally {
        cursor.close();
    }

    return items.toString();
    }

As you can see I return a StringBuilder, since I want to concatenate every document into one big bulk. But this returns as TEXT and not JSON. See below:

This is when the read type is set as JSON

The below is when the read type is set to TEXT, which creates the output I need, but it is not the correct format.

I can't return it as a Document and then use the method: toJson(), since it will only return the last entry. I've tried with Lists, but it can't be converted into JSON documents. The above is the closest I get to what I need.

I hope someone in here has been through the same issue as me and can give a quick tip to solve the issue I'm having :-).

janos · Accepted Answer · 2017-10-30 18:56:03Z

2

You could collect the JSON strings in a List, and format that list as a JSON array string:

public static String getItems() {
    List<String> items = new ArrayList<>();
    MongoCursor<Document> cursor = itemCollection.find().iterator();
    try {
        while (cursor.hasNext()) {
            items.add(cursor.next().toJson());
        }
    } finally {
        cursor.close();
    }

    return "[" + String.join(", ", items) + "]";
}

edited Oct 30, 2017 at 18:56

answered Oct 30, 2017 at 18:17

janos

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Comments

Aleh Maksimovich · Accepted Answer · 2017-10-30 18:10:12Z

1

You have to modify your code to properly form a collection of JSON objects

    while (cursor.hasNext()) {
        items.append(cursor.next().toJson());

    }

Is building for you the next output:

{json object1}{json object2}...{json objectN}

While you need

[{json object1},{json object2}, ... {json objectN}]

While concatenating JSONs you have missed [, , and ]

answered Oct 30, 2017 at 18:10

Aleh Maksimovich

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1 Comment

Alexander Falk Over a year ago

I've been blind staring the forgettable comma, and the surrounding with array brackets. Well, I will just post my solution below this! But thank you for the notice. Sometimes another set of eyes is helpful ;)

Alexander Falk · Accepted Answer · 2017-10-30 18:20:41Z

Based on the answer from Aleh Maksimovich, I can tell you that I fixed the issue by correcting it a comma between each document and wrap it all in in array of documents.

Here is the code for the solution:

/**
 * This method is used to retrieve all the items in the item collection
 * @return - A String which contains all the documents. 
 */
public static String getItems() {

    StringBuilder items = new StringBuilder();
    MongoCursor<Document> cursor = itemCollection.find().iterator();
    try {

        items.append("[");
        while (cursor.hasNext()) {

            items.append(cursor.next().toJson());
            if(cursor.hasNext()) {
                items.append(",");
            }
        }
        items.append("]");
    } finally {
        cursor.close();
    }

    return items.toString();
}

Thank you for your contribution and have a nice evening.

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