java 对象序列化

/*对象序列化： * 将那些实现了Serializable接口的对象转换成一个字节序列，并能够将这个字节完全恢复为原来的对象。*/class Data implements Serializable{private int n;public Data(int n){this.n=n;}public String toString(){return Integer.toString(n);}}public class Worm implements Serializable{   private static Random rand=new Random(47);   private Data[] d={   new Data(rand.nextInt(10)),   new Data(rand.nextInt(10)),   new Data(rand.nextInt(10))   };   private Worm next;   private char c;   public Worm(int i,char x){   print("Worm constructor: "+i);   c=x;   if(--i>0)   next=new Worm(i,(char)(x+1));   }   public Worm(){   print("Default constructor");   }   public String toString(){   StringBuilder result=new StringBuilder(":");   result.append(c);   result.append("(");   for(Data dat:d)   result.append(dat);   result.append(")");   if(next!=null)   result.append(next);   return result.toString();   }   public static void main(String[]args)throws ClassNotFoundException,IOException{   Worm w=new Worm(6,'a');   print("w= "+w);   ObjectOutputStream out=new ObjectOutputStream(new FileOutputStream("worm.out"));   out.writeObject("Worm storage\n");   out.writeObject(w);   out.close();   ObjectInputStream in=new ObjectInputStream(new FileInputStream("worm.out"));   String s=(String)in.readObject();   Worm w2=(Worm)in.readObject();   print(s+"w2= "+w2);   ByteArrayOutputStream bout=new ByteArrayOutputStream();   ObjectOutputStream out2=new ObjectOutputStream(bout);   out2.writeObject("Worm storage\n");   out2.writeObject(w);   out2.flush();   ObjectInputStream in2=new ObjectInputStream(new ByteArrayInputStream(bout.toByteArray()));   s=(String)in2.readObject();   Worm w3=(Worm)in2.readObject();   print(s+"w3 = "+w3);   }   }

序列化的控制：

例如不希望对象的某一部分被序列化，或者一个对象被还原后，某个子对象需要重新创建，从而不必将子对象序列化。

/*序列化控制。实现Externalizable接口，增加两个方法，这两个方法会在序列化还原的过程中被自动调用。 * 默认构造器必须是public,对于一个Externalizable对象，所有普通的默认构造器都会被调用（包括在字段定义时的初始化）， * 然后调用readExternal（）。*/public class Blip3 implements Externalizable{   private int i;   private String s;   public Blip3(){   print("Blip3 Constructor");   }   public Blip3(String x,int a){   print("Blip3(String x,int a)");   s=x;   i=a;   }   public String toString(){return s+i;}   public void writeExternal(ObjectOutput out)throws IOException{   print("Blip3.writeExternal");   out.writeObject(s);   out.writeInt(i);   }   public void readExternal(ObjectInput in)throws IOException,ClassNotFoundException{   print("Blip3.readExternal");   s=(String)in.readObject();   i=in.readInt();   }   public static void main(String[]args)throws IOException,ClassNotFoundException{   print("Constructing objects:");   Blip3 b3=new Blip3("A String ",47);   print(b3);      ObjectOutputStream o=new ObjectOutputStream(new FileOutputStream("Blip3.out"));   print("Saving object:");   o.writeObject(b3);   o.close();   ObjectInputStream in=new ObjectInputStream(new FileInputStream("Blip3.out"));   print("Recovering b3:");   b3=(Blip3)in.readObject();   print(b3);   }}

transient(关键字)

/*transient(瞬时) 关键字 * 如果正在操作的是一个Serializable对象，那么所有的序列化操作都会自动进行，为了能够控制， * 可以用transient(瞬时)关键字逐个字段地关闭序列化，他的意思是"不用麻烦你保存或恢复数据——我们会处理"*/public class Logon implements Serializable{   private Date date=new Date();   private String username;   private transient String password;   public Logon(String name,String pwd){   username=name;   password=pwd;   }   public String toString(){   return "logon info: \n username: "+username+"\n date: "+date+"\n password: "+password;   }   public static void main(String[]args)throws Exception{   Logon a=new Logon("Mulk","MyLittlePony");   print("logon a= "+a);   ObjectOutputStream o=new ObjectOutputStream(new FileOutputStream("Logon.out"));   o.writeObject(a);   o.close();   TimeUnit.SECONDS.sleep(1);   ObjectInputStream in=new ObjectInputStream(new FileInputStream("Logon.out"));   print("Recovering object at "+new Date());   a=(Logon)in.readObject();   print("logon a= "+a);   }}