java - 使用字符串在 Java 中创建 Mongo 查询

Question

Mongo Java 驱动程序提供了JSON.parse(String query)一种将查询转换为DBObject.

public void find() {
    DBObject query = JSON.parse("{name:{$exists:true}}");
    DBCursor cursor = collection.find(query);
}

使用Jackson对象可以以相同的方式取消/编组：

DBCollection collection = new Mongo().getDB("db").getCollection("friends");

public void save() {
    DBObject document = jsonMarshall(new Friend("John", 24));
    collection.save(document);
    // db.peoples.save({name: 'John', age: 24})
}

ObjectMapper jsonMapper = new ObjectMapper();

public DBObject jsonMarshall(Object obj) throws Exception {
    Writer writer = new StringWriter();
    jsonMapper.writer().writeValue(writer, obj);
    return (DBObject) JSON.parse(writer.toString());
}

幸运的是，库bson4jackson允许使用 Jackson 对对象进行 un/marshalled，而无需JSON.parse(String)：

public void save() {
    DBObject document = bsonMarshall(new Friend("John", 24));
    collection.save(document);
    // db.peoples.save({name: 'John', age: 24})
}

ObjectMapper bsonMapper = new ObjectMapper(new BsonFactory());

public DBObject bsonMarshall(Object obj) throws Exception {
    ByteArrayOutputStream output = new ByteArrayOutputStream();
    bsonMapper.writer().writeValue(output, obj);
    return new LazyWriteableDBObject(output.toByteArray(), new LazyBSONCallback());
}

但是，不幸的是，这种技术似乎不适用于查询。有没有办法使用 bson4jackson 将字符串编组到 DBObject？喜欢：

public void find() {
    DBObject query = bsonMarshall("{name:{$exists:true}}");
    DBCursor cursor = collection.find(query);
}

非常感谢。