how to serialize class?

Question

When I insert a List into mongodb, there is a problem:

Exception in thread "main" java.lang.IllegalArgumentException: can't serialize class mongodb.Person
    at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:234)
    at org.bson.BasicBSONEncoder.putIterable(BasicBSONEncoder.java:259)
    at org.bson.BasicBSONEncoder._putObjectField(BasicBSONEncoder.java:198)
    at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:140)
    at org.bson.BasicBSONEncoder.putObject(BasicBSONEncoder.java:86)
    at com.mongodb.DefaultDBEncoder.writeObject(DefaultDBEncoder.java:27)
    at com.mongodb.OutMessage.putObject(OutMessage.java:142)
    at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:252)
    at com.mongodb.DBApiLayer$MyCollection.insert(DBApiLayer.java:211)
    at com.mongodb.DBCollection.insert(DBCollection.java:57)
    at com.mongodb.DBCollection.insert(DBCollection.java:87)
    at com.mongodb.DBCollection.save(DBCollection.java:716)
    at com.mongodb.DBCollection.save(DBCollection.java:691)
    at mongodb.MongoDB.main(MongoDB.java:45)

the class Person is defined as follows:

class Person{
    private String name;
    public Person(String name){
        this.name = name;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

The program is :

        DBCollection coll = db.getCollection("test");
        DBObject record = new BasicDBObject();
        List<Person> persons= new ArrayList<Person>();
        persons.add(new Person("Jack"));
        record.put("person", persons);
        coll.save(record);

I can't find the answer from google, so please help me.

Answer 1

You can achieve this by using following code:

import com.google.gson.annotations.Expose;
import com.mongodb.ReflectionDBObject;

class PersonList extends ReflectionDBObject {
    // person property
    @Expose public java.util.List<Person> person;
}

Now in your mongodb code, you can serialise a Person list as follows

....
PersonList personList = new PersonList();
personList.person = new ArrayList<>();
// add persons to the list
....
....
record.put("personsList", personList);
....
// rest of your code

Answer 2

Here is the code example to make Employee object serialized:

public class Employee implements Serializable {

    private int empId;
    private String name;

    public int getEmpId() {
        return empId;
    }

    public String getName() {
        return name;
    }

    public void setEmpId(int empId) {
        this.empId = empId;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "EMployee id : " + empId + "  \nEmployee Name : " + name;
    }
}

//Another Main Class
public class Main{
    public static void main(String[] args) 
        throws FileNotFoundException, IOException, ClassNotFoundException {

        String filename = "data.txt";
        Employee e = new Employee();
        e.setEmpId(101);
        e.setName("Yasir Shabbir");

        FileOutputStream fos = null;
        ObjectOutputStream out = null;

        fos = new FileOutputStream(filename);
        out = new ObjectOutputStream(fos);
        out.writeObject(e);

        out.close();

        // Now to read the object from file
        // save the object to file
        FileInputStream fis = null;
        ObjectInputStream in = null;

        fis = new FileInputStream(filename);
        in = new ObjectInputStream(fis);
        e = (Employee) in.readObject();
        in.close();

        System.out.println(e.toString());
    }
}