java io - read and write java objects

8/11/2019 Java IO - Read and Write Java Objects

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Introduction

ObjectInputStream can be used to de-serialize and read

java objects that have been serialized and written using

ObjectOutputStream. In the example below the 'Course'

object is written to a persistent storage. The Course object

contains a list of Student objects. The object writing

preserves object references. We first create an object

output stream that stores the bytes to a file using a

FileOutputStream.

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The Course Class

Create an object output stream.

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ObjectOutputStream objectOutputStream = new ObjectOutputStream( new FileOutputStream("javaObjects.txt"));// write a dateobjectOutputStream.writeObject(new Date());// write a booleanobjectOutputStream.writeBoolean(true);// write a float

objectOutputStream.writeFloat(1.0f);// the other primitive types and objects can be saved as well

// create two students objects and add them in a list. create a course// object and add the list of students to a listStudent student1 = new Student();student1.setAge(30);student1.setName("Student1");

Student student2 = new Student();student2.setAge(31);student2.setName("Student2");

Course course = new Course();course.setName("Java IO");List students = new ArrayList();

students.add(student1);students.add(student2);course.setStudents(students);

// write the course object to the objectoutputstream. This writes the// object as well all objects that it referes to.// it writes only those objects that implement serializable

objectOutputStream.writeObject(course);objectOutputStream.flush();objectOutputStream.close();

// the object input stream reads the objects back from the file and// creates java objects out of them. It recreates all// references that were present when the objects were writtenObjectInputStream objectInputStream = new ObjectInputStream(

new FileInputStream("javaObjects.txt"));// start getting the objects out in the order in which they were writtenDate date = (Date) objectInputStream.readObject();System.out.println(date);System.out.println(objectInputStream.readBoolean());System.out.println(objectInputStream.readFloat());

// get the course objectCourse readCourse = (Course) objectInputStream.readObject();System.out.println(readCourse.getName());Student student1Read = readCourse.getStudents().get(0);System.out.println(student1Read.getAge());System.out.println(student1Read.getName());objectInputStream.close();

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The Student Class


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public class Student implements Serializable { private String name; private int age;

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; }}


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public class Course implements Serializable { String name; List students;

public void setName(String name) { this.name = name; }

public void setStudents(List students) { this.students = students; }

public String getName() { return name; }

public List getStudents() { return students; }}

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java io - read and write java objects

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