Serialize and DeSerialize object by implementing Externalizable interface- override writeExternal() and readExternal() methods in java



For serializing object by implementing Externalizable interface, we need to override writeExternal() and readExternal() for serialization process to happen.

For Serialization process override writeExternal()  method & for DeSerialization process by override readExternal() method.



Let’s customize Serialization process by overriding writeExternal() method :

  public void writeExternal(ObjectOutput oo) throws IOException {
          System.out.println("in writeExternal()");
          oo.writeInt(id);
          oo.writeObject(name);
  }
We have serialized id and name manually by writing them in file.
  
Let’s customize DeSerialization process by overriding readExternal()  method :

  public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
          System.out.println("in readExternal()");
          this.id=in.readInt();
          this.name=(String)in.readObject();
  }
We have DeSerialized id and name manually by reading them from file.

Full Program/SourceCode to Serialize Object by calling writeExternal() method of Externalizable interface>
package SerDeser3ImplementExternalizable;
import java.io.Externalizable;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
/*Author : AnkitMittal  Copyright- contents must not be reproduced in any form*/
class Employee implements Externalizable {
  
   private static final long serialVersionUID = 1L;
   private Integer id;
   private String name;
   public Employee(){}  //This constructor is called during deSerializaition process, as we have implemented Externalizable.
  
   public Employee(Integer id, String name) {
      this.id = id;
          this.name = name;
   }
   @Override
   public String toString() {
          return "Employee [id=" + id + ", name=" + name + "]";
   }
  
   /*
   * define how Serialization process will write objects.  
   */
   @Override
   public void writeExternal(ObjectOutput oo) throws IOException {
          System.out.println("in writeExternal()");
          oo.writeInt(id);
          oo.writeObject(name);
   }
  
   /*
   * define how deSerialization process will read objects.  
   */
   @Override
   public void readExternal(ObjectInput in) throws IOException,  ClassNotFoundException {
          System.out.println("in readExternal()");
          this.id=in.readInt();
          this.name=(String)in.readObject();
   }
         
}
public class SerializeEmployee {
   public static void main(String[] args) {
          Employee object1 = new Employee(1, "amy");
          Employee object2 = new Employee(2, "ankit");
         
          try {
                 OutputStream fout = new FileOutputStream("ser.txt");
                 ObjectOutput oout = new ObjectOutputStream(fout);
                
                 System.out.println("Serialization process has started, serializing employee objects...");
                 oout.writeObject(object1);
                 oout.writeObject(object2);
                 fout.close();
        oout.close();
                 System.out.println("Object Serialization completed.");
                
          } catch (IOException ioe) {
                 ioe.printStackTrace();
          }
         
         
         
   }
}
/*OUTPUT
Serialization process has started, serializing employee objects...
in writeExternal()
in writeExternal()
Object Serialization completed.
*/


Full Program/SourceCode to DeSerialize object by calling readExternal() method of Externalizable interface>
package SerDeser3ImplementExternalizable;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
/*Author : AnkitMittal  Copyright- contents must not be reproduced in any form*/
public class DeSerializeEmployee {
  
   public static void main(String[] args){
          try{
                 InputStream fin=new FileInputStream("ser.txt");
                 ObjectInput oin=new ObjectInputStream(fin);
                
                 System.out.println("DeSerialization process has started, displaying deSerialized employee objects...");
                 //while( oin.readObject()!=null );
                 Employee emp;
                 while( (emp=(Employee)oin.readObject())!=null ){
                       System.out.println(emp);
                 }
                 fin.close();
       oin.close();
                
          }catch(IOException | ClassNotFoundException e){
                 //e.printStackTrace();
          }
          System.out.println("Object DeSerialization completed.");
         
  
   }
}
/*OUTPUT
DeSerialization process has started, displaying deSerialized employee objects...
in readExternal()
Employee [id=1, name=amy]
in readExternal()
Employee [id=2, name=ankit]
Object DeSerialization completed.
*/



RELATED LINKS>

Customizing  Serialization process >



Serializing and DeSerializing Singleton >


Interviews >

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