Convert DBObject to a POJO using MongoDB Java Driver
题
MongoDB seems to return BSON/JSON objects.
I thought that surely you'd be able to retrieve values as Strings, ints etc. which can then be saved as POJO.
I have a DBObject (instantiated as a BasicDBObject) as a result of iterating over a list ... (cur.next()).
Is the only way (other than using some sort of persistence framework) to get the data into a POJO to use a JSON serlialiser/deserialiser?
My method looks like this:
public List<User> findByEmail(String email){
DBCollection userColl;
try {
userColl = Dao.getDB().getCollection("users"); } catch (UnknownHostException e) { e.printStackTrace(); } catch (MongoException e) { e.printStackTrace();}
DBCursor cur = userColl.find();
List<User> usersWithMatchEmail = new ArrayList<User>();
while(cur.hasNext()) {
// this is where I want to convert cur.next() into a <User> POJO
usersWithMatchEmail.add(cur.next());
}
return null;
}
EDIT: It's pretty obvious, just do something like this.
解决方案
There is a few java libs that can help you with it:
- Morhpia - http://code.google.com/p/morphia/
- Spring Data for MongoDB - http://www.springsource.org/spring-data/mongodb
其他提示
Let Spring do the heavy lifting with the stuff it already has built for this...
The real trick is: mongoTemplate.getConverter().read(Foo.class, obj);
For example, when using a DBCursor -
while (cursor.hasNext()) {
DBObject obj = cursor.next();
Foo foo = mongoTemplate.getConverter().read(Foo.class, obj);
returnList.add(foo);
}
http://revelfire.com/spring-data-mongodb-convert-from-raw-query-dbobject/
Though a late answer , someone might find this useful.
I use GSON to convert from BasicDBObject
to my own POJO which is TinyBlogDBObject
TinyBlogDBObject obj = convertJSONToPojo(cursor.next().toString());
private static TinyBlogDBObject convertJSONToPojo(String json){
Type type = new TypeToken< TinyBlogDBObject >(){}.getType();
return new Gson().fromJson(json, type);
}
1. Provide MongoDatabase bean with proper CodecRegistry
@Bean
public MongoClient mongoClient() {
ConnectionString connectionString = new ConnectionString("mongodb://username:password@127.0.0.1:27017/dbname");
ConnectionPoolSettings connectionPoolSettings = ConnectionPoolSettings.builder()
.minSize(2)
.maxSize(20)
.maxWaitQueueSize(100)
.maxConnectionIdleTime(60, TimeUnit.SECONDS)
.maxConnectionLifeTime(300, TimeUnit.SECONDS)
.build();
SocketSettings socketSettings = SocketSettings.builder()
.connectTimeout(5, TimeUnit.SECONDS)
.readTimeout(5, TimeUnit.SECONDS)
.build();
MongoClientSettings clientSettings = MongoClientSettings.builder()
.applyConnectionString(connectionString)
.applyToConnectionPoolSettings(builder -> builder.applySettings(connectionPoolSettings))
.applyToSocketSettings(builder -> builder.applySettings(socketSettings))
.build();
return MongoClients.create(clientSettings);
}
@Bean
public MongoDatabase mongoDatabase(MongoClient mongoClient) {
CodecRegistry defaultCodecRegistry = MongoClientSettings.getDefaultCodecRegistry();
CodecRegistry fromProvider = CodecRegistries.fromProviders(PojoCodecProvider.builder().automatic(true).build());
CodecRegistry pojoCodecRegistry = CodecRegistries.fromRegistries(defaultCodecRegistry, fromProvider);
return mongoClient.getDatabase("dbname").withCodecRegistry(pojoCodecRegistry);
}
2. Annotate POJOS
public class ProductEntity {
@BsonProperty("name") public final String name;
@BsonProperty("description") public final String description;
@BsonProperty("thumb") public final ThumbEntity thumbEntity;
@BsonCreator
public ProductEntity(
@BsonProperty("name") String name,
@BsonProperty("description") String description,
@BsonProperty("thumb") ThumbEntity thumbEntity) {
this.name = name;
this.description = description;
this.thumbEntity = thumbEntity;
}
}
public class ThumbEntity {
@BsonProperty("width") public final Integer width;
@BsonProperty("height") public final Integer height;
@BsonProperty("url") public final String url;
@BsonCreator
public ThumbEntity(
@BsonProperty("width") Integer width,
@BsonProperty("height") Integer height,
@BsonProperty("url") String url) {
this.width = width;
this.height = height;
this.url = url;
}
}
3. Query mongoDB and obtain POJOS
MongoCollection<Document> collection = mongoDatabase.getCollection("product");
Document query = new Document();
List<ProductEntity> products = collection.find(query, ProductEntity.class).into(new ArrayList<>());
Please check my answer in other post
POJO to org.bson.Document and Vice Versa