public static void writeObjectToFile(Object obj)
  {
    File file =new File("test.dat");
    FileOutputStream out;
    try {
      out = new FileOutputStream(file);
      ObjectOutputStream objOut=new ObjectOutputStream(out);
      objOut.writeObject(obj);
      objOut.flush();
      objOut.close();
      System.out.println("write object success!");
    } catch (IOException e) {
      System.out.println("write object failed");
      e.printStackTrace();
    }
  }

Object obj=new Object();
    //failed,the object in map does not implement Serializable interface
    HashMap<String, Object> objMap=new HashMap<String,Object>();
    objMap.put("test", obj);
    writeObjectToFile(objMap);

public static Object readObjectFromFile()
  {
    Object temp=null;
    File file =new File("test.dat");
    FileInputStream in;
    try {
      in = new FileInputStream(file);
      ObjectInputStream objIn=new ObjectInputStream(in);
      temp=objIn.readObject();
      objIn.close();
      System.out.println("read object success!");
    } catch (IOException e) {
      System.out.println("read object failed");
      e.printStackTrace();
    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    }
    return temp;
  }