Java Tutorial/File/ObjectInputStream

Create ObjectInputStream from FileInputStream

   <source lang="java">

import java.io.FileInputStream; import java.io.ObjectInputStream; import java.io.Serializable; import java.util.Date; public class ObjectReader {

 public static void main(String[] arguments) {
   try {
     FileInputStream fi = new FileInputStream("message.obj");
     ObjectInputStream oi = new ObjectInputStream(fi);
     Message mess = (Message) oi.readObject();
     System.out.println("Message:\n");
     System.out.println("From: " + mess.from);
     System.out.println("To: " + mess.to);
     System.out.println("Date: " + mess.when + "\n");
     for (int i = 0; i < mess.lineCount; i++)
       System.out.println(mess.text[i]);
     oi.close();
   } catch (Exception e) {
     System.out.println("Error " + e.toString());
   }
 }

} class Message implements Serializable {

 int lineCount;
 String from, to;
 Date when;
 String[] text;
 void writeMessage(String inFrom, String inTo, Date inWhen, String[] inText) {
   text = new String[inText.length];
   for (int i = 0; i < inText.length; i++)
     text[i] = inText[i];
   lineCount = inText.length;
   to = inTo;
   from = inFrom;
   when = inWhen;
 }

}</source>

Object serialization with Serializable interface, ObjectOutputStream and ObjectInputStream.

   <source lang="java">

import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; class MyClass implements Serializable {

 String str;
 double[] vals;
 File fn;
 public MyClass(String s, double[] nums, String fname) {
   str = s;
   vals = nums;
   fn = new File(fname);
 }
 public String toString() {
   String data = "  str: " + str + "\n  vals: ";
   for (double d : vals)
     data += d + " ";
   data += "\n  fn: " + fn.getName();
   return data;
 }

} public class Main {

 public static void main(String[] argv) throws Exception {
   double v[] = { 1.1, 2.2, 3.3 };
   double v2[] = { 9.0, 8.0, 7.7 };
   MyClass obj1 = new MyClass("This is a test", v, "Test.txt");
   MyClass obj2 = new MyClass("Alpha Beta Gamma", v2, "Sample.dat");
   ObjectOutputStream fout = new ObjectOutputStream(new FileOutputStream("obj.dat"));
   System.out.println("obj1:\n" + obj1);
   fout.writeObject(obj1);
   System.out.println("obj2:\n" + obj2);
   fout.writeObject(obj2);
   fout.close();
   ObjectInputStream fin = new ObjectInputStream(new FileInputStream("obj.dat"));
   MyClass inputObj;
   inputObj = (MyClass) fin.readObject();
   System.out.println("First object:\n" + inputObj);
   inputObj = (MyClass) fin.readObject();
   System.out.println("Second object:\n" + inputObj);
   fin.close();
 }

}</source>

Reading objects from file using ObjectInputStream

   <source lang="java">

import java.io.FileInputStream; import java.io.ObjectInputStream; import java.io.Serializable; public class Main {

 public static void main(String[] args) throws Exception {
   ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream("yourFile.dat"));
   Object obj = null;
   while ((obj = inputStream.readObject()) != null) {
     if (obj instanceof Person) {
       System.out.println(((Person) obj).toString());
     }
   }
   inputStream.close();
 }

} 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();
 }

}</source>

Store objects in file

   <source lang="java">

import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class Main {

 public static void main(String[] args) throws Exception {
   FileOutputStream fos = new FileOutputStream("books.dat");
   ObjectOutputStream oos = new ObjectOutputStream(fos);
   Book book = new Book("1", "Java", "A");
   oos.writeObject(book);
   oos.flush();
   oos.close();
   FileInputStream fis = new FileInputStream("books.dat");
   ObjectInputStream ois = new ObjectInputStream(fis);
   book = (Book) ois.readObject();
   System.out.println(book.toString());
   ois.close();
 }

} class Book implements Serializable {

 private String isbn;
 private String title;
 private String author;
 public Book(String isbn, String title, String author) {
   this.isbn = isbn;
   this.title = title;
   this.author = author;
 }
 public String toString() {
   return "[Book: " + isbn + ", " + title + ", " + author + "]";
 }

}</source>