从MongoDB检索值时将DBObject转换为Java对象

在我的Java应用程序中，我已将值存储在ArrayList（Java对象集）中的mongoDB中。 如何从DBObject检索数据

我将数据存储在mongoDB中，如下所示：

{ "students" : [{"firstName" : "Jesse", "lastName" : "Varnell", "age" : "15", "gender" : "M" }, { "firstName" : "John", "lastName" : "Doe", "age" : "13", "gender" : "F"}] } 

我正在为学生提供Java对象：

 public class Student { public String firstName; public String lastName; public String age; public String gender; // M, F } 

我正在从mongoDB中检索数据，如：

 BasicDBObject query = new BasicDBObject(); query.put("user", username); DBCursor cursor = theCollection.find(query); while (cursor.hasNext()) { DBObject theObj = cursor.next(); //How to get the DBObject value to ArrayList of Java Object? } 

Answer 1

你可以这样做：

 List students = new ArrayList(); BasicDBObject query = new BasicDBObject(); query.put("user", username); DBCursor cursor = theCollection.find(query); while (cursor.hasNext()) { DBObject theObj = cursor.next(); //How to get the DBObject value to ArrayList of Java Object? BasicDBList studentsList = (BasicDBList) theObj.get("students"); for (int i = 0; i < studentsList.size(); i++) { BasicDBObject studentObj = (BasicDBObject) studentsList.get(i); String firstName = studentObj.getString("firstName"); String lastName = studentObj.getString("lastName"); String age = studentObj.getString("age"); String gender = studentObj.getString("gender"); Student student = new Student(); student.setFirstName(firstName); student.setLastName(lastName); student.setAge(age); student.setGender(gender); students.add(student); } } 

Answer 2

您通常使用ORM工具（尽管在非关系数据库的情况下将其称为ORM没有意义）。

有几个这样的工具。 我喜欢spring-data，它为你隐藏了很多样板代码，并为你提供了一个简单，干净的语法。 像这样的东西：

 @Repository public class UserRepositoryImpl implements UserRepository { private MongoTemplate mongoTemplate; @Autowired public UserRepositoryImpl(MongoTemplate mongoTemplate) { this.mongoTemplate = mongoTemplate; } @Override public User findsUserByUsernameAndPassword(String userName, String encodedPassword) { return mongoTemplate.findOne(query(where("userName").is(userName).and("encodedPassword").is(encodedPassword)), User.class); } } 

将User类定义为：

 @Document(collection = "users") public class User { private String userName; private String encodedPassword; // snip getters and setters }