Bson pretty print using Java MongoDb driver

问题:

I am using the Mongo Aggregation Framework using the Java MongoDB driver, version 3.3. I have an aggregagtion pipeline, that is merely collection of type List<Bson>. I am trying to find a way to pretty print each stage of the pipeline.

Calling the toString method on each element is not sufficient, because each stages is an instance of a simple implementation of the Bson interface, which is SimplePipelineStage. This stupid class has not any override of the toString method.

The pipeline is created using factory methods of mongo java driver Aggregates class, like the following:

Aggregates.match(/* ... */)
Aggregates.project(/* ... */)
// And so on...

Javadoc can be found here.

How can I pretty print such objects? I know for sure that the type BasicDbObject has a smart toString implementation, but I cannot find a way to convert from Bson to BasicDbObject.

Thanks a lot in advance.

回答1:

Googling a bit harder, I found a solution to pretty print a Bson instance. The trick is to convert it into an instance of BsonDocument, which has an implementation of the toString method that returns the string representation of the corresponding JSON.

Bson bson = Filters.gt("a", 10);
BsonDocument bsonDocument = bson.toBsonDocument(BsonDocument.class, MongoClient.DEFAULT_CODEC_REGISTRY);
System.out.println(bsonDocument);

The original link is the following: Converting Bson object to BsonDocument.

回答2:

For mongodb-java API 3.4, the constant MongoClient.DEFAULT_CODEC_REGISTRY is no more accessible directly, it's a private member. There is a static method CodecRegistry getDefaultCodecRegistry() which returns the same constant.

Another point, BsonDocument.toString() internally does a toJson() with default JsonWriterSettings. In order to see the Shell equivalent of Query, use it like below:

public void logQuery(Bson filter) {
    if (LOGGER.isDebugEnabled()) {

        LOGGER.debug(
                "filter query: " + filter.toBsonDocument(BsonDocument.class, MongoClient.getDefaultCodecRegistry())
                        .toJson(new JsonWriterSettings(JsonMode.SHELL)));
    }
}

回答3:

This is a rather old question, however I put my suggestion (for mongodb-driver 3.6.4) here as this is the most relevant post when googling on "mongodb java driver pretty print":

BsonDocument bsonDocument = bson.toBsonDocument(BsonDocument.class, MongoClient.getDefaultCodecRegistry());
JsonWriterSettings.Builder settingsBuilder = JsonWriterSettings.builder().indent(true);
System.out.println(bsonDocument.toJson(settingsBuilder.build());