Java - ObjectInputStream.GetField get(String name, Short val) method

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Description

The Java ObjectInputStream.getField get(String name, Short val) method gets the value of the named short field from the persistent field.

Declaration

Following is the declaration for java.io.ObjectInputStream.getField.get() method.

public abstract Object get(String name, Short val)

Parameters

• name − The name of the field.

• val − The default value to use if name does not have a value.

Return Value

This method returns the value of the named short field.

Exception

• IOException − If there are I/O errors while reading from the underlying InputStream.

• IllegalArgumentException − If type of name is not serializable or if the field type is incorrect.

Example - Usage of ObjectInputStream.getField get(String name, Short val) method

The following example shows the usage of ObjectInputStream.getField get(String name, Short val) method.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamField;
import java.io.Serializable;

public class ObjectInputStreamDemo implements Serializable {
   public static void main(String[] args) {
      try {
         // create a new file with an ObjectOutputStream
         FileOutputStream out = new FileOutputStream("test.txt");
         ObjectOutputStream oout = new ObjectOutputStream(out);

         // write something in the file
         oout.writeObject(new Example());
         oout.flush();
         oout.close();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // read an object from the stream and cast it to Example
         Example a = (Example) ois.readObject();

         // print var of a
         System.out.println("" + a.var);
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }

   static public class Example implements Serializable {
      static short var = 5;
      
      // assign a new serialPersistentFields 
      private static final ObjectStreamField[] serialPersistentFields = {
         new ObjectStreamField("var", Short.TYPE)
      };

      private void readObject(ObjectInputStream in)
         throws IOException, ClassNotFoundException {

         // get the field and assign it at var
         ObjectInputStream.GetField fields = in.readFields();

         // get var
         short d = 87;
         var = fields.get("var", d);
      }

      private void writeObject(ObjectOutputStream out) throws IOException {

         // write into the ObjectStreamField array the variable string
         ObjectOutputStream.PutField fields = out.putFields();
         fields.put("var", var);
         out.writeFields();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result −

5

Example - Read a Serialized short Field when Field is Present

The following example shows the usage of ObjectInputStream.getField get(String name, short val) method. This example demonstrates reading a short field that was properly serialized.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class ObjectInputStreamDemo {
   public static void main(String[] args) throws Exception {
      String file = "short_example1.bin";

      // Serialize object with 'level'
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file))) {
         Player p = new Player((short) 42);
         oos.writeObject(p);
      }

      // Deserialize
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file))) {
         Player p = (Player) ois.readObject();
      }
   }

   static class Player implements Serializable {
      private static final long serialVersionUID = 1L;
      short level;

      public Player(short level) {
         this.level = level;
      }

      private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
         ObjectInputStream.GetField fields = ois.readFields();
         short lvl = fields.get("level", (short) -1);
         System.out.println("Deserialized level: " + lvl);
         if (fields.defaulted("level")) {
            System.out.println("Field 'level' was defaulted.");
         } else {
            System.out.println("Field 'level' was present.");
         }
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Deserialized level: 42
Field 'level' was present.

Explanation

• We serialize a class with a short field called level, then read it using GetField.get("level", (short) -1).

• Since the field exists in the stream, the actual value is returned.

Example - Handling a Missing short Field

The following example shows the usage of ObjectInputStream.getField get(String name, short val) method. In this example, we don't write the temperature field, so during deserialization, the default value is returned.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class ObjectInputStreamDemo {
   public static void main(String[] args) throws Exception {
      String filename = "person_fixed.ser";

      // Serialize object (simulating older version with missing 'age' field)
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         Person person = new Person("Bob");
         oos.writeObject(person); // writeObject will exclude 'age'
         System.out.println("Serialized without 'age' field.");
      }

      // Deserialize (simulating newer version expecting 'age')
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         Person p = (Person) ois.readObject();
      }
   }

   static class Person implements Serializable {
      private static final long serialVersionUID = 1L;

      String name;
      short age = 25; // default in new version

      Person(String name) {
         this.name = name;
      }

      // Custom serialization - omit 'age'
      private void writeObject(ObjectOutputStream oos) throws IOException {
         ObjectOutputStream.PutField putFields = oos.putFields();
         putFields.put("name", name);
         // 'age' is intentionally left out
         oos.writeFields();
      }

      // Custom deserialization - try reading 'age'
      private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
         ObjectInputStream.GetField fields = ois.readFields();
         name = (String) fields.get("name", "Unknown");
         age = fields.get("age", (short)-1);

         if (fields.defaulted("age")) {
            System.out.println("Field 'age' was defaulted (not present in stream).");
         } else {
            System.out.println("Field 'age' was found: " + age);
         }
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Serialized without 'age' field.
Field 'age' was found: 0

Explanation

• We simulate an old version by not serializing the age field.

• On deserialization, field age gets a default value of 0.