ObjectInputStream and ObjectOutputStream in Java
In Java, the classes ObjectInputStream and ObjectOutputStream are used for object serialization and deserialization. Serialization refers to the process of converting an object into a byte stream so that it can be saved to a file, transmitted over a network, or stored in memory for later use. Deserialization is the reverse process, where a byte stream is converted back into an object.
ObjectOutputStream: Serializing Objects
The ObjectOutputStream class is used to write (serialize) Java objects to an output stream, typically to a file. It allows you to save objects in a form that can be restored later.
Basic Syntax for ObjectOutputStream:
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("data.ser"));
Key Methods:
writeObject(Object obj): Serializes the specified object and writes it to the underlying output stream.
Code Example
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// Example: Writing an Object to a Fileimport java.io.FileOutputStream;import java.io.ObjectOutputStream;import java.io.Serializable;class Student implements Serializable { private static final long serialVersionUID = 1L; String name; int age; public Student(String name, int age) { this.name = name; this.age = age; }}public class SerializeExample { public static void main(String[] args) { try { // Create an instance of Student Student student = new Student("John Doe", 20); // Create an ObjectOutputStream FileOutputStream fileOut = new FileOutputStream("student.ser"); ObjectOutputStream out = new ObjectOutputStream(fileOut); // Serialize the object out.writeObject(student); // Close the stream out.close(); fileOut.close(); System.out.println("Serialized data is saved in student.ser"); } catch (Exception e) { e.printStackTrace(); } }}Explanation:
- We create an instance of the
Studentclass and serialize it usingObjectOutputStream. - The serialized object is saved to a file named
student.ser.
ObjectInputStream: Deserializing Objects
The ObjectInputStream class is used to read (deserialize) objects from an input stream, such as a file or a network connection. It reconstructs an object from its byte stream form.
Basic Syntax for ObjectInputStream:
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("data.ser"));
Key Methods:
Object readObject(): Reads an object from the input stream and deserializes it.
Code Example
xxxxxxxxxx// Example: Reading an Object from a Fileimport java.io.FileInputStream;import java.io.ObjectInputStream;public class DeserializeExample { public static void main(String[] args) { try { // Create an ObjectInputStream FileInputStream fileIn = new FileInputStream("student.ser"); ObjectInputStream in = new ObjectInputStream(fileIn); // Deserialize the object Student student = (Student) in.readObject(); // Close the stream in.close(); fileIn.close(); // Display the object data System.out.println("Deserialized Student..."); System.out.println("Name: " + student.name); System.out.println("Age: " + student.age); } catch (Exception e) { e.printStackTrace(); } }}Explanation:
- We deserialize the
Studentobject previously serialized and saved instudent.ser. - The
readObject()method reads the object from the file and reconstructs it as aStudentobject.
Important Points to Understand
Serialization and Deserialization Process
- Serialization: Convert an object to a byte stream for storage or transmission.
- This process includes saving all fields of the object.
- Deserialization: Convert a byte stream back to an object.
The Serializable Interface
- Serializable: A marker interface in Java that a class must implement for its objects to be serialized.
serialVersionUID: A unique identifier for each class that is used during deserialization to ensure that a loaded class matches the serialized object.
private static final long serialVersionUID = 1L;
Transient Fields
- The
transientkeyword is used for fields that you don't want to serialize. - Fields marked as
transientare not included in the serialization process.
Externalizable Interface
- While
Serializableis used for default serialization, you can also implementExternalizableto control the serialization process manually.
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