Java IO, Serialization, Externalization, and File Handling

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Java IO Steams
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01110001001100
01110001001100
Input stream
Output stream

2. Reading and Writing
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Leaf
Stone
Paper Computer

3. Data - 01110001001100
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•Image files
•Video files
•Audio files
•Doc files
•Other files
Binary Data
Text Data
•.txt
•.java
•.bat
110001001100
01110001001100
This is Ram
This is Ram
byte byte
char
1 byte = 8 bit

4. Text Data
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5. Sources and Targets
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Network
File
Hardware

6. IO package
Package java.io contains classes to read
and write the data.
Binary data is read by InputStream and
write by OutputStream classes and
their child classes
Text data is read by Reader and write by
Writer classes and their child classes
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7. InputStream and OutputStream hierarchy
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8. Reader and Writer hierarchy
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9. Read data from a Text File
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ABCD1234567890

10. Read text file - FileReader
1. import java.io.FileReader;
2. public class ReadTextFile {
3. public static void main(String[] args) throws IOException {
4. FileReader in = new FileReader("f:/test.txt");
5. int ch = in.read(); // reads a character
6. while (ch != -1) { // -1 is end of file
7. System.out.print( (char) ch );
8. ch = in.read();
9. }
10. in.close();
11. }
12.}
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Read a character
1010
Text Data
•.txt
•.java
•.bat
ABCD
FileReader
Char
Byte

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ASCII Table

13. try-with-resources
1. public static void main(String[] args) throws IOException {
2. try (FileReader in = new FileReader("f:/test.txt")) {
3. int ch = in.read();
4. while (ch != -1) { // -1 is end of file
5. System.out.print((char) ch);
6. ch = in.read();
7. }
8. }//try block end
9. }
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Read a file line by line
 public static void main(String[] args) throws IOException {
1. FileReader file= new FileReader("c:/test.txt");
2. BufferedReader in= new BufferedReader(file);
3. String line = in.readLine();
4. while (line != null) {
5. System.out.println(line);
6. line = in.readLine();
7. }
8. in.close();
 }
• New line character n

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Read file: line by line
1010
Text Data
•.txt
•.java
•.bat
ABCD This is Line
BufferedReader
FileReader
Char Line
Byte
Byte
Char
Line

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Read File By Scanner
 java.util.Scanner class is used to parse primitive data and
strings from a text stream. It does not throw checked
exceptions.
public static void main(String[] args) throws Exception{
FileReader reader = new FileReader("c:/newtest.txt");
Scanner sc = new Scanner(reader);
while(sc.hasNext()){
System.out.println(sc.nextLine());
}
reader.close();
}

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Write to a File
public static void main(String[] args) throws IOException {
FileWriter out = new FileWriter("f:/newtest.txt");
out.write('A');
out.write('n'); //new line character
out.write("This is line one");
out.write("This is line two");
out.close();
System.out.println("Check f:/newtest.txt");
}
FileWriter will always create a new file.
Old file will be overwritten

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Write data line by line : PrintWriter
public static void main(String[] args) throws IOException {
FileWriter out = new FileWriter(“f:/newtest.txt");
PrintWriter pw= new PrintWriter( out);
for (int i = 0; i < 5; i++) {
pw.println(i + " : Line");
}
pw.close();
out.close();
System.out.println("Check c:/newtest.txt ");
}

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Write to a File
1010
ABCD
•Text Data
•.txt
•.java
•.bat
This is Line
PrintWriter
FileWriter
Char
Line
Byte
Contains print and println methods
Line
Char
Byte

20. Copy a binary file
1. String source= "c:/baby1.jpg";
2. String target = "c:/baby2.jpg";
3. FileInputStream in= new FileInputStream(source);
4. FileOutputStream out= new FileOutputStream(target);
5. int ch = in.read() ;
6. while (ch != -1){
1. out.write(ch);
2. ch = in.read();
7. }
8. in.close();
9. out.close();
10. System.out.println(source + " is copied to "+ target);
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21. Append data to the File
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Append Text/Bytes in existing File
FileWriter/ FileOutputStream will always create a
new file. Old data is overwritten.
If you append new data in old file then pass second
parameter Boolean value ‘true’ to the constructor:
o new FileWriter(“c:a.txt”,true)
o new FileOutputStream (“c:a.jpg”,true)

23. Exception Handling
 Java throws IOException in case of abnormal condition during
o Opening file
o Reading file
o Writing file
o Closing the file
Exception can be handled by try-catch block
We have propagated exception from main method
o public static void main(String[] args) throws IOException
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24. Read from Keyboard
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25. Convert Binary to Text Stream
Class : InputStreamReader
Reads Data From Keyboard
o InputStreamReader ir= new InputStreamReader(System.in);
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1010
ABCD
Char
Byte
InputStreamReader

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Read from Keyboard (Hardware)
1. Reads data from keyboard and writes into a file
2. InputStreamReader isReader = new InputStreamReader(System.in);
3. BufferedReader in = new BufferedReader(isReader );
4. PrintWriter out = new PrintWriter(new FileWriter("c:/temp.txt"););
5. String line = in.readLine();
6. while (!line.equals("quit")) {
7. out.println(line);
8. line = in.readLine();
9. }
10. out.close();
11. in.close();

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Read file attributes
import java.io.File; java.util.Date;
public static void main(String[] args) {
File f = new File("c:/temp/a.txt”");
if(f.exists()){
System.out.println(“Name” + f.getName());
System.out.println(“Absolute path: “ + f.getAbsolutePath());
System.out.println(" Is writable: “ + f.canWrite());
System.out.println(" Is readable: “ + f.canRead());
System.out.println(" Is File“ + f.isFile());
System.out.println(" Is Directory“ + f.isDirectory());
System.out.println("Last Modified at " + new Date(f.lastModified()));
System.out.println(“Size " + f.length() + " bytes long.");
}
}
}

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Java Serialization
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01110001001100
01110001001100
Serialization
Deserialization
Object

29. Serialization / Deserialization
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Serialization
Deserialization

30. Serialization / Deserialization
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Serialization
Deserialization
Object
1010101010101000001111
Convert to byte stream
Convert to object

31. Everything is an Object
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Employee
RAM
Sharma
Manager
10 Lac
India
10001
10011
10010
10101
10111
Contiguous bytes to store => 1010101010101000001111

32. When?
When an object go out of JVM
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Network
File
JVM Data Out

33. Which classes?
 Class implements java.io.Serializable interface
 Serializable interface contains Zero methods, it is a marker
interface.
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Employee
Serializable
Marksheet
Serializable
Class
Serializable

34. How?
Java provides two classes to serialize and deserialize
an object:
o ObjectOutputStream: for serialization
o ObjectInputStream: for deserialization
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35. Marksheet
1. import java.io.Serializable;
2. public class Marksheet implements Serializable {
3. public String name = null;
4. public int maths = 0;
5. public int physics = 0;
6. public int chemistry = 0;
7. }
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36. WriteObject
1. public class WriteObject {
2. public static void main(String[] args) throws IOException {
3. FileOutputStream file = new FileOutputStream("f:/object.ser");
4. ObjectOutputStream out = new ObjectOutputStream(file);
5. Marksheet m = new Marksheet();
6. m.name = "Ram";
7. m.physics = 89;
8. m.chemistry = 99;
9. m.maths = 95;
10. out.writeObject(m);
11. out.close();
12. file.close();
13. }
14. }
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37. ReadObject
1. public class ReadObject {
2. public static void main(String[] args) throws Exception {
3. FileInputStream file = new FileInputStream("f:/object.ser");
4. ObjectInputStream in = new ObjectInputStream(file);
5. Marksheet m = (Marksheet) in.readObject();
6. System.out.println(m.name);
7. System.out.println(m.physics);
8. System.out.println(m.chemistry);
9. System.out.println(m.maths);
10. in.close();
11. file.close();
12. }
13. }
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38. Transient Attributes
1. import java.io.Serializable;
2. public class Marksheet implements Serializable {
3. public String name = null;
4. public int maths = 0;
5. public int physics = 0;
6. public int chemistry = 0;
7. private transient int total = 0;
8. private transient double percentage = 0;
9. }
10. Transient variables will be discarded during serialization
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39. Externalizable interface
1. Developers can use Externalizable
interface to write custom code to serialize and
deserialize an object.
2. Externalizable interface has two methods
1.readExternal() to read the object
2.writeExternal() to write the object
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40. Employee implements Externalizable
1. public class Employeeimplements Externalizable{
2. public String id = null;
3. public String firstName = null;
4. public String lastName = null;
5. public double salary = 0;
6. @Override
7. public void readExternal(ObjectInput in) throws Exception {
8. id = (String) in.readObject();
9. firstName = (String) in.readObject();
10. lastName = (String) in.readObject();
11. salary = in.readDouble();
12. }
13. @Override
14. public void writeExternal(ObjectOutput out) throws Exception {
15. out.writeObject(id);
16. out.writeObject(firstName);
17. out.writeObject(lastName);
18. out.writeDouble(salary);
19. }
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41. What we have learned?
 IO Streams
 Read and write text file
 Read and write binary file
 try-with-resources block
 Read from keyboard
 Read file attributes
 Serialization
 Deserialization
 Externalizable interface
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42. Thank You!
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