# How to read an Object from a File in Java

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Dec 11, 2019. Topics: Java.
Canonical URL: https://attacomsian.com/blog/java-read-object-from-file

> A quick tutorial to learn how to read an object from a file using Java. 

In an earlier article, we looked at how to [write an object to a file](https://attacomsian.com/blog/java-write-object-to-file) using Java. In this short article, you'll learn **how to read a Java Object from a file** or how to deserialize the serialized object saved in a file. 

The deserialization process is quite similar to the serialization process. Basically, to read an object from a file, you need to follow the below steps:

* Open the file that has the Java Object stored using `FileInputStream`.
* Create an instance of `ObjectInputStream` and pass `FileInputStream` as an argument to its constructor.
* Use `ObjectInputStream.readObject()` method to read the object from the file.
* The above method will return a generic object of type `Object`. You need to cast this object to its original type to properly use it.

## Create Java Class

Here is how our  `User.java` class looks like that we used to write an object to a file in the previous article:

```java
public class User implements Serializable {

    public String name;
    public String email;
    private String[] roles;
    private boolean admin;

    public User() {
    }

    public User(String name, String email, String[] roles, boolean admin) {
        this.name = name;
        this.email = email;
        this.roles = roles;
        this.admin = admin;
    }

    // getters and setters, toString() .... (omitted for brevity)
}
```

## Read Object from File

The following example shows how you can deserialize the `object.dat` file and convert it back to a `User` object in Java 7 or higher:

```javaread
try (FileInputStream fis = new FileInputStream("object.dat");
     ObjectInputStream ois = new ObjectInputStream(fis)) {

    // read object from file
    User user = (User) ois.readObject();

    // print object
    System.out.println(user);

} catch (IOException | ClassNotFoundException ex) {
    ex.printStackTrace();
}
```

The above code will print the following on the console:

```bash
User{name='John Doe', email='john.doe@example.com', roles=[Member, Admin], admin=true}
```

If you are using an older Java version (Java 6 or below), you have to manually close `ObjectInputStream` as shown below:

```java
try {
    FileInputStream fis = new FileInputStream("object.dat");
    ObjectInputStream ois = new ObjectInputStream(fis);

    // read object from file
    User user = (User) ois.readObject();

    // print object
    System.out.println(user);
    
    // close reader
    ois.close();

} catch (IOException | ClassNotFoundException ex) {
    ex.printStackTrace();
}
```

## Further Reading

You may be interested in other Java I/O articles:

* [Reading and Writing Files in Java](https://attacomsian.com/blog/java-read-write-files)
* [How to Read and Write Text Files in Java](https://attacomsian.com/blog/java-read-write-text-files)
* [How to Read and Write Binary Files in Java](https://attacomsian.com/blog/java-read-write-binary-files)
* [Reading and Writing Files using Java NIO API](https://attacomsian.com/blog/java-read-write-files-nio-api)
* [How to read a file line by line in Java](https://attacomsian.com/blog/how-to-read-a-file-line-by-line-in-java)