MongoDB Extended JSON

As discussed earlier, the Java driver supports reading and writing BSON documents represented as
MongoDB Extended JSON. Both variants are supported:

• Strict Mode: representations of BSON types that conform to the JSON RFC. This is the format that mongoexport produces and mongoimport consumes.
• Shell Mode: a superset of JSON that the MongoDB shell can parse.

Furthermore, the Document class provides two sets of convenience methods for this purpose:

• toJson(): a set of overloaded methods that convert a Document instance to a JSON string
• parse(): a set of overloaded static factory methods that convert a JSON string to a Document instance

Writing JSON

Consider the task of implementing a mongoexport-like tool using the Java driver.

String outputFilename;                 // initialize to the path of the file to write to
MongoCollection<Document> collection;  // initialize to the collection from which you want to query

BufferedWriter writer = new BufferedWriter(new FileWriter(outputFilename));

try {
    for (Document doc : collection.find()) {
        writer.write(doc.toJson());
        writer.newLine();
} finally {
   writer.close();
}

The Document.toJson() method constructs an instance of a JsonWriter with its default settings, which will write in strict mode with no new lines or indentation.

You can override this default behavior by using one of the overloads of toJson(). As an example, consider the task of writing a JSON string that can be copied and pasted into the MongoDB shell:

SimpleDateFormat fmt = new SimpleDateFormat("dd/MM/yy");
Date first = fmt.parse("01/01/2014");
Date second = fmt.parse("01/01/2015");
Document doc = new Document("startDate", new Document("$gt", first).append("$lt", second)); 
System.out.println(doc.toJson(new JsonWriterSettings(JsonMode.SHELL))); 

This code snippet will print out MongoDB shell-compatible JSON, which can then be pasted into the shell:

{ "startDate" : { "$gt" : ISODate("2014-01-01T05:00:00.000Z"), "$lt" : ISODate("2015-01-01T05:00:00.000Z") } }

Reading JSON

Consider the task of implementing a mongoimport-like tool using the Java driver.

String inputFilename;                  // initialize to the path of the file to read from
MongoCollection<Document> collection;  // initialize to the collection to which you want to write

BufferedReader reader = new BufferedReader(new FileReader(inputFilename));

try {
    String json;

    while ((json = reader.readLine()) != null) {
        collection.insertOne(Document.parse(json));
    } 
} finally {
    reader.close();
}

The Document.parse() static factory method constructs an instance of a JsonReader with the given string and returns an instance of an equivalent Document instance. JsonReader automatically detects the JSON flavor in the string, so you do not need to specify it.