FileInputStream class extracts input bytes from a file in a file system. FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader. It should be used to read byte-oriented data for example to read audio, video, images, etc. The hierarchy of classes to deal with Input streams is as follows:
Hierarchy of classes to deal with Input streams
Example 1:
Java
// Java program to demonstrate Use of FileInputStream class// Importing the desired classimport java.io.FileInputStream;// Importing input output class from java.io packageimport java.io.IOException;// Main classclass FileInputStreamGFG { // Method 1 // To read from the file private void readFile() throws IOException { // Creating an object of FileInputStream FileInputStream fileInputStream = null; // Try block to check for exceptions try { // Now, creating a FileInputStream by // opening a connection to an actual file // The file named by the path name in the // file system // Here customly we have taken // gfg.txt contains fileInputStream = new FileInputStream("gfg.txt"); // data - "Java was called // Oak at the beginning." int i; // Reads a byte of data from this input stream // using read() method // Till condition holds true while ((i = fileInputStream.read()) != -1) { // Print the stream System.out.print((char)i); } } // If there is any exception encountered // then execute this block finally { // Stream is not there in file if (fileInputStream != null) { // Then close this file input stream and // releases any system resources associated // with the stream using close() method fileInputStream.close(); } } } // Method 2 // Main driver method public static void main(String[] args) throws IOException { // Constructor of this class FileInputStreamGFG fileInputStreamGfg = new FileInputStreamGFG(); // Calling the readFile() method // in the main() method fileInputStreamGfg.readFile(); }} |
Output :
Java was called Oak at the beginning.
Now dwelling onto the output stream that is ObjectInputStream is used for deserializing primitive data and objects previously written using an ObjectOutputStream. Only objects that support the java.io.Externalizable interface can be read from streams. The Java ObjectInputStream class enables you to read Java objects from an InputStream instead of just raw bytes. You wrap an InputStream in an ObjectInputStream and so that you can read objects from it. Of course, the bytes read must represent a valid, serialized Java object. Otherwise, reading objects will fail. Normally we will use the ObjectInputStream to read data objects written(serialized) by a Java ObjectOutputStream.
Example 2:
Java
// Java program to demonstrate Use of ObjectInputStream// class// Importing required input output classesimport java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.ObjectInputStream;import java.io.Serializable;// Before serialization and de-serialization of objects the// class of the object must implement java.io.Serializable// Class 1// Helper class implementing Serializable interfaceclass Student implements Serializable { // Private class member variables private static final long serialVersionUID = -1438960132000208485L; private String name; private int age; // Constructor of this class public Student(String name, int age) { // super keyword refers to parent class super(); // this keyword refers to current object instance this.name = name; this.age = age; } // Getters and Setter for class public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } // Override toString method @Override public String toString() { // Simply return the name and age return "Student [name=" + name + ", age=" + age + "]"; }}// Class 2// Main classpublic class ObjectInputStreamDemo { // Main driver method public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException { // Creating an object of above class // in the main() method ObjectInputStreamDemo objectInputStreamDemo = new ObjectInputStreamDemo(); // Readfile function call objectInputStreamDemo.readStudentObject(); } // Member method of main class private void readStudentObject() throws IOException, FileNotFoundException, ClassNotFoundException { // Initially null is set to both streams // read and write streams FileInputStream fileInputStream = null; ObjectInputStream objectInputStream = null; // Try block to check for exceptions try { // Input stream directory fileInputStream = new FileInputStream("student.txt"); // Input stream object objectInputStream = new ObjectInputStream(fileInputStream); // Creating an object of above class to // read an object from the ObjectInputStream Student student = (Student)objectInputStream.readObject(); // Display message when input stream is // completely read System.out.println( "Successfully read student object from the file."); // Print an display commands System.out.println(student); System.out.println("Name = " + student.getName()); System.out.println("Age = " + student.getAge()); } // When an exception is encountered execute the // block finally { // If there is nothing to be read if (objectInputStream != null) { // Then close a ObjectInputStream will // the InputStream instance from which // the ObjectInputStream is reading // isong the close() method objectInputStream.close(); } } }} |
Output:
Successfully read student object from the file. Student [name=John, age=25] Name = John Age = 25
The only difference between FileInputStream and ObjectInputStream is :
| FileInputStream | ObjectInputStream |
|---|---|
| The Java FileInputStream class, in java.io.FileInputStream, makes it possible to read the contents of a file as a stream of bytes, hence FileInputStream can be used for Serialization. | ObjectInputStream in Java can be used to convert InputStream to object. This process of conversion of the input stream to an object is called deserialization. |
| The Java FileInputStream class obtains input bytes from a file. | It can also be used to pass the objects between hosts by using a SocketStream. |
| It is used for reading byte-oriented data. | It is mainly used to deserialize the primitive data and objects which are written by using ObjectOutputStream. |
| The FileInputStream class contains 9 methods. | The ObjectInputStrean class contains 27 methods. |
