Serialization and deserialization of Java 21-13 IO streams

serialized Stream : The object is stored in the same way as a stream in a text file or transmitted over a Network. Object-stream Data (objectoutputstream)

Construction Method: ObjectInputStream (inputstream In) creates objectinputstream read from the specified InputStream

deserialization Stream : Restores the Stream object data in the text file or the stream object data in the network to an Object. Stream Data--object (objectinputstream)

Construction Method: ObjectInputStream (inputstream In) creates objectinputstream read from the specified InputStream

Because the operands that are serialized and deserialized are classes, a class is created First:

1  packagezl_copy;2 3 Importjava.io.Serializable;4 5 /*6 //notserializableexception: class is not serialized exception, so the class to be serialized is to implement the Serializable interface7      8  */9  public classAnimalImplements Serializable{Ten  one      private static final long serialversionuid = 6425500536266476858L;  a         PrivateString name; -//Private intage ;
* private transient int age;  -          the          -          publicAnimal () { -             Super(); -             //TODO auto-generated Constructor stub +         } -  +  a          publicAnimal (String name,intage ) { at             Super(); -              this. Name =name; -              this. Age =age ; -         } -  -  in          publicString getName () { -             returnname; to         } +  -  the          public voidsetName (String Name) { *              this. Name =name; $         }Panax Notoginseng  -  the          public intgetage () { +             returnage ; a         } the  +  -          public voidSetage (intage ) { $              this. Age =age ; $         } -  -  the @Override -          publicString toString () {Wuyi             return"Animal [name=" + name + ", age=" + age + "]"; the         } -          wu          -}

Implementation Class:　

1  public classObjectstreamdemo {2 3      public Static voidMain (string[] Args)throwsioexception, classnotfoundexception {4         //because the serialized object is a class, you first create a class5         //Serialization Methods6         //Write ();7         //deserialization8 Read (); 9     }Ten  one     Private Static voidRead ()throwsioexception, ioexception, classnotfoundexception { a         //  Create a deserialization object  -         //ObjectInputStream (inputstream In) creates a ObjectInputStream read from the specified InputStream -ObjectInputStream Ois =NewObjectInputStream (NewFileInputStream ("test.txt")); the          -         //restores the serialized object, regardless of class, anyway it's the parent class is Object -Object o =Ois.readobject (); -          +         //Freeing Resources - ois.close (); +         //output results to the console look a System.out.println (o); at         //Animal [name= samoyed, age=2] -          -     } -  -     Private Static voidWrite ()throwsIOException { -          // Create a serialized object  in         //ObjectOutputStream (outputstream Out) creates objectoutputstream written to the specified Outputstream.  -ObjectOutputStream Oos =NewObjectOutputStream (NewFileOutputStream ("test.txt")); to          +         //create an object of the class you want to serialize -Animal A =NewAnimal ("samoyed", 2); the          *         //write to the serialized object, note that the class is written $ Oos.writeobject (a);Panax Notoginseng          -         //Freeing Resources the oos.close (); +          a         //java.io.NotSerializableException the         //Notserializableexception: class is not serialized exception, so the class to be serialized is to implement the Serializable interface +     } -  $}

Attention:

Private static final Long Serialversionuid = 6425500536266476858L;:
Why did you write this? If you do not write this, change the variables inside the class, such as:

1 Private int age ; 2 instead: 3 int age;

If this changes, it must be serialized again, or an error will occur:

java.io.InvalidClassException:cn.itcast_07.Person; Local class Incompatible: stream Classdesc serialversionuid = -2071565876962058344, Local class Serialversionuid = -8345153069362641443

Why is there a problem?
The person class implements the serialization interface, so it should also have a tag Value.
Let's assume that this tag value is 100.
At the Beginning:
person.class--id=100
Wirte Data: oos.txt--id=100
Read Data: oos.txt--id=100

After you change the age:
person.class--id=200
Wirte Data: oos.txt--id=100
Read Data: oos.txt--id=100
We may also need to use previously written data in Real-world development, but we cannot write again.
so, Let's set this ID value to a fixed value in the Java file so that the ID value will not change when the file is Modified.
The method is: see the class name at the yellow alarm line, click the Mouse.

private transient int age;

There may be a lot of member variables in a class, but some variables do not want to be serialized.
Method: Use the Transient keyword to declare member variables that do not require serialization

Serialization and deserialization of Java 21-13 IO streams