Java/File Input Output/ObjectOutputStream

A program that serializes and deserializes an Employee array

   <source lang="java">
 

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

* A program that serializes and deserializes an Employee array.
*/

public class SerializeEmployeeTester {

 public static void main(String[] args) throws IOException,
     ClassNotFoundException {
   Employee[] staff = new Employee[2];
   staff[0] = new Employee("Fred Flintstone", 50000);
   staff[1] = new Employee("Barney Rubble", 60000);
   staff[0].setBuddy(staff[1]);
   staff[1].setBuddy(staff[0]);
   ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(
       "staff.dat"));
   out.writeObject(staff);
   out.close();
   ObjectInputStream in = new ObjectInputStream(new FileInputStream(
       "staff.dat"));
   Employee[] staff2 = (Employee[]) in.readObject();
   in.close();
   for (Employee e : staff2)
     System.out.println(e);
 }

} class Employee implements Serializable {

 public Employee(String name, double salary) {
   this.name = name;
   this.salary = salary;
   this.buddy = this;
 }
 public void setBuddy(Employee buddy) {
   this.buddy = buddy;
 }
 public String toString() {
   return getClass().getName() + "[name=" + name + ",salary=" + salary
       + ",buddy=" + buddy.name + "]";
 }
 private String name;
 private double salary;
 private Employee buddy;

}

 </source>
   
  
 
  

Create ObjectOutputStream out of FileOutputStream

   <source lang="java">
 

/*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*
*   - Neither the name of Sun Microsystems nor the names of its
*     contributors may be used to endorse or promote products derived
*     from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.io.FileOutputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class CardWriter {

 public static void main(String[] args) {
   Card3 card = new Card3(12, Card3.SPADES);
   System.out.println("Card to write is: " + card);
   try {
     FileOutputStream out = new FileOutputStream("card.out");
     ObjectOutputStream oos = new ObjectOutputStream(out);
     oos.writeObject(card);
     oos.flush();
   } catch (Exception e) {
     System.out.println("Problem serializing: " + e);
   }
 }

} /*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
* 
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met: -
* Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer. - Redistributions in binary
* form must reproduce the above copyright notice, this list of conditions and
* the following disclaimer in the documentation and/or other materials provided
* with the distribution. - Neither the name of Sun Microsystems nor the names
* of its contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
* 
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

class Card3 implements Serializable {

 private int suit = UNASSIGNED;
 private int number = UNASSIGNED;
 public final static int UNASSIGNED = -1;
 public final static int DIAMONDS = 1;
 public final static int CLUBS = 2;
 public final static int HEARTS = 3;
 public final static int SPADES = 4;
 public final static int ACE = 1;
 public final static int KING = 13;
 public Card3(int number, int suit) {
   if (isValidNumber(number)) {
     this.number = number;
   } else {
     // Error
   }
   if (isValidSuit(suit)) {
     this.suit = suit;
   } else {
     // Error
   }
 }
 public int getSuit() {
   return suit;
 }
 public int getNumber() {
   return number;
 }
 public static boolean isValidNumber(int number) {
   if (number >= ACE && number <= KING) {
     return true;
   } else {
     return false;
   }
 }
 public static boolean isValidSuit(int suit) {
   if (suit >= DIAMONDS && suit <= SPADES) {
     return true;
   } else {
     return false;
   }
 }
 public boolean equals(Object obj) {
   if (obj instanceof Card3) {
     Card3 card = (Card3) obj;
     if (card.getNumber() == this.number && card.getSuit() == this.suit) {
       return true;
     } else {
       return false;
     }
   } else {
     return false;
   }
 }
 public int hashCode() {
   return number * suit;
 }
 public String toString() {
   return numberToString(this.number) + " of " + suitToString(this.suit);
 }
 public static String numberToString(int number) {
   String result = "";
   switch (number) {
   case ACE:
     result = "Ace";
     break;
   case 2:
     result = "Two";
     break;
   case 3:
     result = "Three";
     break;
   case 4:
     result = "Four";
     break;
   case 5:
     result = "Five";
     break;
   case 6:
     result = "Six";
     break;
   case 7:
     result = "Seven";
     break;
   case 8:
     result = "Eight";
     break;
   case 9:
     result = "Nine";
     break;
   case 10:
     result = "Ten";
     break;
   case 11:
     result = "Jack";
     break;
   case 12:
     result = "Queen";
     break;
   case KING:
     result = "King";
     break;
   case UNASSIGNED:
     result = "Invalid Number";
     break;
   }
   return result;
 }
 public static String suitToString(int suit) {
   String result = "";
   switch (suit) {
   case DIAMONDS:
     result = "Diamonds";
     break;
   case CLUBS:
     result = "Clubs";
     break;
   case HEARTS:
     result = "Hearts";
     break;
   case SPADES:
     result = "Spades";
     break;
   case UNASSIGNED:
     result = "Invalid Suit";
     break;
   }
   return result;
 }

}

 </source>
   
  
 
  

implements Externalizable

   <source lang="java">
 

import java.io.Externalizable; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInput; import java.io.ObjectInputStream; import java.io.ObjectOutput; import java.io.ObjectOutputStream; class Engine implements Externalizable {

 private int numCylinders;
 public Engine() {
 }
 Engine(int numCylinders) {
   this.numCylinders = numCylinders;
 }
 int getNumCylinders() {
   return numCylinders;
 }
 public void readExternal(ObjectInput in) throws IOException, ClassCastException {
   System.out.println("READ-Engine");
   numCylinders = in.readInt();
 }
 public void writeExternal(ObjectOutput out) throws IOException {
   System.out.println("WRITE-Engine");
   out.writeInt(numCylinders);
 }

} class Car implements Externalizable {

 private int numTires;
 private Engine e;
 private String name;
 public Car() {
 }
 Car(String name, int numTires, Engine e) {
   this.name = name;
   this.numTires = numTires;
   this.e = e;
 }
 int getNumTires() {
   return numTires;
 }
 Engine getEngine() {
   return e;
 }
 String getName() {
   return name;
 }
 public void readExternal(ObjectInput in) throws IOException, ClassCastException {
   System.out.println("READ-Car");
   numTires = in.readInt();
   name = in.readUTF();
   try {
     e = (Engine) in.readObject();
   } catch (ClassNotFoundException e) {
   }
 }
 public void writeExternal(ObjectOutput out) throws IOException {
   System.out.println("WRITE-Car");
   out.writeInt(numTires);
   out.writeUTF(name);
   out.writeObject(e);
 }

} class EDemo {

 public static void main(String[] args) throws Exception {
   Car c1 = new Car("Some car", 4, new Engine(6));
   ObjectOutputStream oos = null;
   FileOutputStream fos = new FileOutputStream("car.ser");
   oos = new ObjectOutputStream(fos);
   oos.writeObject(c1);
   ObjectInputStream ois = null;
   FileInputStream fis = new FileInputStream("car.ser");
   ois = new ObjectInputStream(fis);
   Car c2 = (Car) ois.readObject();
   System.out.println("Number of tires = " + c2.getNumTires());
   System.out.println("Number of cylinders = " + c2.getEngine().getNumCylinders());
   System.out.println("Name = " + c2.getName());
 }

}

 </source>
   
  
 
  

new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(StringFileName)));

   <source lang="java">
 

/*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*
*   - Neither the name of Sun Microsystems nor the names of its
*     contributors may be used to endorse or promote products derived
*     from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.io.BufferedInputStream; import java.io.BufferedOutputStream; import java.io.EOFException; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.math.BigDecimal; import java.util.Calendar; public class ObjectStreams {

 static final String dataFile = "invoicedata";
 static final BigDecimal[] prices = { new BigDecimal("19.99"),
     new BigDecimal("9.99"), new BigDecimal("15.99"), new BigDecimal("3.99"),
     new BigDecimal("4.99") };
 static final int[] units = { 12, 8, 13, 29, 50 };
 static final String[] descs = { "Java T-shirt", "Java Mug",
     "Duke Juggling Dolls", "Java Pin", "Java Key Chain" };
 public static void main(String[] args) throws IOException,
     ClassNotFoundException {
   ObjectOutputStream out = null;
   try {
     out = new ObjectOutputStream(new BufferedOutputStream(
         new FileOutputStream(dataFile)));
     out.writeObject(Calendar.getInstance());
     for (int i = 0; i < prices.length; i++) {
       out.writeObject(prices[i]);
       out.writeInt(units[i]);
       out.writeUTF(descs[i]);
     }
   } finally {
     out.close();
   }
   ObjectInputStream in = null;
   try {
     in = new ObjectInputStream(new BufferedInputStream(new FileInputStream(
         dataFile)));
     Calendar date = null;
     BigDecimal price;
     int unit;
     String desc;
     BigDecimal total = new BigDecimal(0);
     date = (Calendar) in.readObject();
     System.out.format("On %tA, %<tB %<te, %<tY:%n", date);
     try {
       while (true) {
         price = (BigDecimal) in.readObject();
         unit = in.readInt();
         desc = in.readUTF();
         System.out.format("You ordered %d units of %s at $%.2f%n", unit,
             desc, price);
         total = total.add(price.multiply(new BigDecimal(unit)));
       }
     } catch (EOFException e) {
     }
     System.out.format("For a TOTAL of: $%.2f%n", total);
   } finally {
     in.close();
   }
 }

}

 </source>
   
  
 
  

Override writeObject(ObjectOutputStream oos) and readObject(ObjectInputStream ois)

   <source lang="java">
 

import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; class Employee implements Serializable {

 private String name;
 private double salary;
 Employee(String name, double salary) {
   this.name = name;
   this.salary = salary;
 }
 String getName() {
   return name;
 }
 double getSalary() {
   return salary;
 }
 private void writeObject(ObjectOutputStream oos) throws IOException {
   oos.defaultWriteObject();
   System.out.println("Serializing Employee object\n");
 }
 private void readObject(ObjectInputStream ois) throws Exception {
   ois.defaultReadObject();
   salary += 100;
   System.out.println("Deserializing Employee object");
 }

} class Main {

 public static void main(String[] args) throws Exception {
   Employee e1 = new Employee("A", 45000.0);
   System.out.println(e1.getName() + " " + e1.getSalary());
   FileOutputStream fos = new FileOutputStream("employee.ser");
   ObjectOutputStream  oos = new ObjectOutputStream(fos);
   oos.writeObject(e1);
   FileInputStream fis = new FileInputStream("employee.ser");
   ObjectInputStream  ois = new ObjectInputStream(fis);
   Employee e2 = (Employee) ois.readObject();
   System.out.println(e2.getName() + " " + e2.getSalary());
 }

}

 </source>
   
  
 
  

Returns a byte array from the given object.

   <source lang="java">

/*

* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
* 
*      http://www.apache.org/licenses/LICENSE-2.0
* 
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectOutputStream;

public class Main {

 /**
  * Returns a byte array from the given object.
  * 
  * @param object
  *            to convert
  * @return byte array from the object
  */
 public static byte[] objectToBytes(Object object) throws IOException {
     ByteArrayOutputStream baos = new ByteArrayOutputStream();
     ObjectOutputStream os = new ObjectOutputStream(baos);
     os.writeObject(object);
     return baos.toByteArray();
 }

}

 </source>
   
  
 
  

Serializing an Object (JButton)

   <source lang="java">
 

import java.io.ByteArrayOutputStream; import java.io.FileOutputStream; import java.io.ObjectOutput; import java.io.ObjectOutputStream; import javax.swing.JButton; public class Main {

 public static void main(String[] argv) throws Exception {
   Object object = new JButton("push me");
   ObjectOutput out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
   out.writeObject(object);
   out.close();
   // Serialize to a byte array
   ByteArrayOutputStream bos = new ByteArrayOutputStream();
   out = new ObjectOutputStream(bos);
   out.writeObject(object);
   out.close();
   // Get the bytes of the serialized object
   byte[] buf = bos.toByteArray();
   System.out.println(new String(buf));
 }

}

 </source>
   
  
 
  

Write different data types with ObjectOutputStream

   <source lang="java">
 

/*

* Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*
*   - Neither the name of Sun Microsystems nor the names of its
*     contributors may be used to endorse or promote products derived
*     from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

import java.io.BufferedInputStream; import java.io.BufferedOutputStream; import java.io.EOFException; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.math.BigDecimal; import java.util.Calendar; public class ObjectStreams {

 static final String dataFile = "invoicedata";
 static final BigDecimal[] prices = { new BigDecimal("19.99"),
     new BigDecimal("9.99"), new BigDecimal("15.99"), new BigDecimal("3.99"),
     new BigDecimal("4.99") };
 static final int[] units = { 12, 8, 13, 29, 50 };
 static final String[] descs = { "Java T-shirt", "Java Mug",
     "Duke Juggling Dolls", "Java Pin", "Java Key Chain" };
 public static void main(String[] args) throws IOException,
     ClassNotFoundException {
   ObjectOutputStream out = null;
   try {
     out = new ObjectOutputStream(new BufferedOutputStream(
         new FileOutputStream(dataFile)));
     out.writeObject(Calendar.getInstance());
     for (int i = 0; i < prices.length; i++) {
       out.writeObject(prices[i]);
       out.writeInt(units[i]);
       out.writeUTF(descs[i]);
     }
   } finally {
     out.close();
   }
   ObjectInputStream in = null;
   try {
     in = new ObjectInputStream(new BufferedInputStream(new FileInputStream(
         dataFile)));
     Calendar date = null;
     BigDecimal price;
     int unit;
     String desc;
     BigDecimal total = new BigDecimal(0);
     date = (Calendar) in.readObject();
     System.out.format("On %tA, %<tB %<te, %<tY:%n", date);
     try {
       while (true) {
         price = (BigDecimal) in.readObject();
         unit = in.readInt();
         desc = in.readUTF();
         System.out.format("You ordered %d units of %s at $%.2f%n", unit,
             desc, price);
         total = total.add(price.multiply(new BigDecimal(unit)));
       }
     } catch (EOFException e) {
     }
     System.out.format("For a TOTAL of: $%.2f%n", total);
   } finally {
     in.close();
   }
 }

}

 </source>
   
  
 
  

Writing objects to file with ObjectOutputStream

   <source lang="java">
 

import java.io.FileOutputStream; import java.io.ObjectOutputStream; import java.io.Serializable; class Person implements Serializable {

 private String firstName;
 private String lastName;
 private int age;
 public Person() {
 }
 public String getFirstName() {
   return firstName;
 }
 public void setFirstName(String firstName) {
   this.firstName = firstName;
 }
 public String getLastName() {
   return lastName;
 }
 public void setLastName(String lastName) {
   this.lastName = lastName;
 }
 public int getAge() {
   return age;
 }
 public void setAge(int age) {
   this.age = age;
 }
 public String toString() {
   StringBuffer buffer = new StringBuffer();
   buffer.append(firstName);
   buffer.append("\n");
   buffer.append(lastName);
   buffer.append("\n");
   buffer.append(age);
   buffer.append("\n");
   return buffer.toString();
 }

} public class Main {

 public static void main(String[] args) throws Exception {
   ObjectOutputStream outputStream = null;
   outputStream = new ObjectOutputStream(new FileOutputStream("yourFile.dat"));
   Person person = new Person();
   person.setFirstName("A");
   person.setLastName("B");
   person.setAge(38);
   outputStream.writeObject(person);
   person = new Person();
   person.setFirstName("C");
   person.setLastName("D");
   person.setAge(22);
   outputStream.writeObject(person);
 }

}

 </source>