将一个 Java 对象复制到另一个对象

Question

What's the best way to copy one Java object of a class to another object of the same class? I tried BeanUtil.copyProperties but it didn't work for some reason. The class is a complex class. (class contains another class objects etc)

My aim is to populate values in order through hibernate function

Public Response getOrder(Order order, Ticket ticket) {

order = OrderManager.getOrderByTicket(ticket); //Hibernate function This doesn't work, order object gets a new reference

}

Tried doing this

Public Response getOrder(Order order, Ticket ticket) {

Order temp = OrderManager.getOrderbByTicket(ticket);

//Now I want to copy temp to order

}

Answer 1

If all the fields are serializable then you can use ObjectOutputStream and ObjectInputStream .

If You need special handling during the serialization and deserialization process then implement special methods writeObject() and readObject() .

Please have a look at IO: Custom Reading and Writing with Serializable .

---

Sample code:

    class MyClass implements Serializable {
        private static final long serialVersionUID = 1L;
        String str;
        List<Integer> list = new ArrayList<Integer>();

        public MyClass(String str) {
            this.str = str;
        }
    }

    MyClass obj1 = new MyClass("abc");
    obj1.list.add(1);

    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(buffer);
    oos.writeObject(obj1);
    oos.close();

    byte[] rawData = buffer.toByteArray();
    ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(rawData));
    MyClass obj2 = (MyClass) ois.readObject();

    System.out.println(obj2.str);
    System.out.println(obj2.list.get(0));

Answer 2

To do a deep copy using Serialize / DeSerialize, you can use the code like below,

public Object deepCopy(Object input) {

    Object output = null;
    try {
        // Writes the object
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
        objectOutputStream.writeObject(input);

        // Reads the object
        ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
        ObjectInputStream objectInputStream = new ObjectInputStream(byteArrayInputStream);
        output = objectInputStream.readObject();

    } catch (Exception e) {
        e.printStackTrace();
    }
    return output;
}

Answer 3

I suppose you could use reflection if it was REALLY important or time consuming, but as I see it, there are two main choices

• One If you have access to the class, just implement Clonable and have the clone method produce a deep copy of the object and all its subobjects.

• Two Code it by hand. It may be time consuming and boring, but it works in all cases.

Answer 4

I believe you are talking about a 'deep' copy.

A similar question and various solutions are detailed here:

How do you make a deep copy of an object in Java?

The easiest way seems to be serialising the object and then deserialising it.

Answer 5

Better do it like this:

Public Response getOrder(Request request) {

Order temp = OrderManager.getOrderbByTicket(request.getTicket());
request.setOrder(temp);


//process the response

}

This will solve the problem of getting back the Order to the caller of the function. If you want that the caller gets a deep copy than serialize and deserialize it before seting it to the request