如何将两个Java序列化对象重新链接在一起？

Question

有时候(实际上很多)我们在Java中得到一个情况,其中两个对象指向同一个东西.现在,如果我们将这些单独序列化,则序列化表单具有对象的单独副本是非常合适的,因为它应该可以打开而不使用另一个.但是,如果我们现在对它们进行反序列化,我们发现它们仍然是分开的.有什么方法可以将它们联系在一起吗？

示例如下.

public class Example {

 private static class ContainerClass implements java.io.Serializable {
  private ReferencedClass obj;
  public ReferencedClass get() {
   return obj;
  }
  public void set(ReferencedClass obj) {
   this.obj = obj;
  }
 }

 private static class ReferencedClass implements java.io.Serializable {
  private int i = 0;
  public int get() {
   return i;
  }
  public void set(int i) {
   this.i = i;
  }
 }

 public static void main(String[] args) throws Exception {
  //Initialise the classes
  ContainerClass test1 = new ContainerClass();
  ContainerClass test2 = new ContainerClass();
  ReferencedClass ref = new ReferencedClass();

  //Make both container class point to the same reference
  test1.set(ref);
  test2.set(ref);

  //This does what we expect: setting the integer in one (way of accessing the) referenced class sets it in the other one
  test1.get().set(1234);
  System.out.println(Integer.toString(test2.get().get()));

  //Now serialise the container classes
  java.io.ObjectOutputStream os = new java.io.ObjectOutputStream(new java.io.FileOutputStream("C:\\Users\\Public\\test1.ser"));
  os.writeObject(test1);
  os.close();
  os = new java.io.ObjectOutputStream(new java.io.FileOutputStream("C:\\Users\\Public\\test2.ser"));
  os.writeObject(test2);
  os.close();

  //And deserialise them
  java.io.ObjectInputStream is = new java.io.ObjectInputStream(new java.io.FileInputStream("C:\\Users\\Public\\test1.ser"));
  ContainerClass test3 = (ContainerClass)is.readObject();
  is.close();
  is = new java.io.ObjectInputStream(new java.io.FileInputStream("C:\\Users\\Public\\test2.ser"));
  ContainerClass test4 = (ContainerClass)is.readObject();
  is.close();

  //We expect the same thing as before, and would expect a result of 4321, but this doesn't happen as the referenced objects are now separate instances
  test3.get().set(4321);
  System.out.println(Integer.toString(test4.get().get()));
 }

}

Answer 1

该readResolve()方法允许这样做（当然，首先您必须定义如何决定哪些对象应该是“相同的”）。但将两个对象序列化到同一个文件中会更容易 - ObjectOut/InputStream 保留其已序列化/反序列化的所有对象的记录，并且仅存储和返回对其已见过的对象的引用。