In the previous tutorial we saw how to write an Object to a file in Java. In this example we are going to see how to read an Object from the file that we’ve stored it earlier.
Basically, to read an Object from a file, one should follow these steps:
- Open a
FileInputStreamto the file that you’ve stored the Object to. - Open a
ObjectInputStreamto the aboveFileInpoutStream. - Use
readObjectmethod ofObjectInputStreamclass to read the Object from the file. - The above method returns an Object of type
Object. So you have to cast it to the original type to use it properly.
Let’s see the code snippets that follow:
Student.java
package com.javacodegeeks.java.core;
import java.io.Serializable;
public class Student implements Serializable {
//default serialVersion id
private static final long serialVersionUID = 1L;
private String first_name;
private String last_name;
private int age;
public Student(String fname, String lname, int age){
this.first_name = fname;
this.last_name = lname;
this.age = age;
}
public void setFirstName(String fname) {
this.first_name = fname;
}
public String getFirstName() {
return this.first_name;
}
public void setLastName(String lname) {
this.first_name = lname;
}
public String getLastName() {
return this.last_name;
}
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return this.age;
}
@Override
public String toString() {
return new StringBuffer(" First Name : ").append(this.first_name)
.append(", Last Name : ").append(this.last_name).append(", Age : ").append(this.age).toString();
}
}ObjectIOExample.java
package com.javacodegeeks.java.core;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class ObjectIOExample {
private static final String filepath="C:\\Users\\nikos7\\Desktop\\obj";
public static void main(String args[]) {
ObjectIOExample objectIO = new ObjectIOExample();
//Read object from file
Student st = (Student) objectIO.ReadObjectFromFile(filepath);
System.out.println(st);
}
public Object ReadObjectFromFile(String filepath) {
try {
FileInputStream fileIn = new FileInputStream(filepath);
ObjectInputStream objectIn = new ObjectInputStream(fileIn);
Object obj = objectIn.readObject();
System.out.println("The Object has been read from the file");
objectIn.close();
return obj;
} catch (Exception ex) {
ex.printStackTrace();
return null;
}
}
}Output
The Object has been read from the file
First Name : John, Last Name : Frost, Age : 22
Here is the code of the complete Read/Write Object From/To File interface in Java:
Student.java
package com.javacodegeeks.java.core;
import java.io.Serializable;
public class Student implements Serializable {
//default serialVersion id
private static final long serialVersionUID = 1L;
private String first_name;
private String last_name;
private int age;
public Student(String fname, String lname, int age){
this.first_name = fname;
this.last_name = lname;
this.age = age;
}
public void setFirstName(String fname) {
this.first_name = fname;
}
public String getFirstName() {
return this.first_name;
}
public void setLastName(String lname) {
this.first_name = lname;
}
public String getLastName() {
return this.last_name;
}
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return this.age;
}
@Override
public String toString() {
return new StringBuffer(" First Name : ").append(this.first_name)
.append(", Last Name : ").append(this.last_name).append(", Age : ").append(this.age).toString();
}
}ObjectIOExample.java
package com.javacodegeeks.java.core;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class ObjectIOExample {
private static final String filepath="C:\\Users\\nikos7\\Desktop\\obj";
public static void main(String args[]) {
ObjectIOExample objectIO = new ObjectIOExample();
Student student = new Student("John","Frost",22);
objectIO.WriteObjectToFile(filepath, student);
//Read object from file
Student st = (Student) objectIO.ReadObjectFromFile(filepath);
System.out.println(st);
}
public void WriteObjectToFile(String filepath,Object serObj) {
try {
FileOutputStream fileOut = new FileOutputStream(filepath);
ObjectOutputStream objectOut = new ObjectOutputStream(fileOut);
objectOut.writeObject(serObj);
objectOut.close();
System.out.println("The Object was succesfully written to a file");
} catch (Exception ex) {
ex.printStackTrace();
}
}
public Object ReadObjectFromFile(String filepath) {
try {
FileInputStream fileIn = new FileInputStream(filepath);
ObjectInputStream objectIn = new ObjectInputStream(fileIn);
Object obj = objectIn.readObject();
System.out.println("The Object has been read from the file");
objectIn.close();
return obj;
} catch (Exception ex) {
ex.printStackTrace();
return null;
}
}
}Output
The Object was succesfully written to a file
The Object has been read from the file
First Name : John, Last Name : Frost, Age : 22
This was an example on how to Read an Object from File in Java
it always says “invalid stream header” :(
privatestaticfinallongserialVersionUID = 1L; can you please explain the purpose of this statement