您如何在 Java 中外部化列表

Question

我有一个 class 实现了 Externalizable，它包含三个对象和这三种对象类型之一的列表。我假设您将简单地在子 classes 中实现 externalizable，然后为成员对象定义外部读写，但是否也可以包含 List，如果可以的话如何？

public class AuthSuccessPacket extends Packet implements Externalizable {

public static final long serialVersionUID = 10003L;
Contact contact;
Network network;
Account account;
List<Contact> contacts;

public AuthSuccessPacket(){
    super(Type.AUTH_SUCCESS);
}

public AuthSuccessPacket(Contact contact, Network network, Account account, List<Contact> contacts){
    super(Type.AUTH_SUCCESS);
    this.contact = contact;
    this.network = network;
    this.account = account;
    this.contacts = contacts;
}

@Override
public void writeExternal(ObjectOutput out) {
  out.writeObject(account);
  out.writeObject(network);
  out.writeObject(contact);
// ??? write list
}

@Override
public void readExternal(ObjectInput in)  {
}
contact = (Contact) in.readObject();
network = (Network) in.readObject();
account = (Account) in.readObject();
// ??? read list
}

Answer 1

我会尝试类似的方法：

@Override
public void writeExternal(ObjectOutput out) throws IOException {
  out.writeObject(account);
  out.writeObject(network);
  out.writeObject(contact);
  // ??? write list
  out.writeInt(contacts.size());
  for (Contact cntct : contacts) {
    out.writeObject(cntct);
  }
}

@Override
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {

  contact = (Contact) in.readObject();
  network = (Network) in.readObject();
  account = (Account) in.readObject();
  // ??? read list
  contacts = new ArrayList<>();
  int contactsNo = (int) in.readInt();
  for (int i = 0; i < contactsNo; i++) {
    Contact cntct = (Contact) in.readObject();
    contacts.add(cntct);
  }
}

Answer 2

public static class Person implements Externalizable{
    private String firstName;
    private String lastName;
    private int age;
    private Person mother;
    private Person father;
    private List<Person> children;

    public Person(){
    }

    public Person(String firstName, String lastName, int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    public void setMother(Person mother) {
        this.mother = mother;
    }

    public void setFather(Person father) {
        this.father = father;
    }

    public void setChildren(List<Person> children) {
        this.children = children;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeObject(mother);
        out.writeObject(father);
        out.writeObject(firstName);
        out.writeObject(lastName);
        out.writeInt(age);
        out.writeObject(children);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        mother = (Person) in.readObject();
        father = (Person) in.readObject();
        firstName = (String)in.readObject();
        lastName = (String) in.readObject();
        age = in.readInt();
        children = (List<Person>) in.readObject();
    }
}

您如何在 Java 中外部化列表

How do you Externalize a List in Java

java

externalizable