14. Java Object Serialization

Java Object Serialization

In this section, you will learn how to use Java's built-in serialization mechanism.

What is Serialization?

Serialization is the process of converting an object into a data format that can later be deserialized back into the original object.

To serialize the Java object, create an ObjectOutputStream, and pass the object to the streams writeObject() method. The ObjectOutputStream writes a sequence of bytes, and its constructor takes another stream as an argument.

To recreate the original Java object from the serialized bytes, read the bytes back into a ObjectInputStream.

Example

Here's a really bare-bones example demonstrating the basic procedure to serialize and deserialize a Java object:

import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;

public final class Main {
  public static void main(String[] args) throws Exception {
    Path path = Path.of("list.bin");
    try (var out = new ObjectOutputStream(Files.newOutputStream(path))) {
      out.writeObject(List.of("Hello", " ", "World!"));
    }
    try (var in = new ObjectInputStream(Files.newInputStream(path))) {
      List<String> deserialized = (List<String>) in.readObject();
      System.out.println(deserialized);
    }
  }
}

This program prints the following:

[Hello,  , World!]

This was kind of a silly example, though, because you would never serialize a list of strings like this — instead, you would probably write the strings to a regular text file with one line per string.

The Java Object Serialization Exercise on the next page has a slightly more realistic example for you to try out.

Further Reading

• serial JavaDoc
• ObjectOutputStream JavaDoc
• ObjectInputStream JavaDoc