IOException Example in Java

In this tutorial I am going to explain one of the most common Java exception that is well known by all the Java developers. IOExceptions are thrown when there is any input / output file operation issues while application performing certain tasks accessing the files. IOException is a checked exception and application developer has to handle in correct way.

IOException has many sub classes that are specific in nature. That means, when your application searching to read a file, if the file is not found that there is a ileNotFoundException to be thrown. FileNotFoundException is a subclass of IOException. Like this there are many subclasses defined in exception packages for handling the specific scenarios.

Java IOException — This figure shows key facts about IOException in Java application

Few of the well known classes are:

FileNotFoundException
EOFException
SSLException
UnSupportedEncodingException
SocketException

IOException Example

Here is simple example for IOException:

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class ExceptionExample {
public FileInputStream testMethod1(){
File file = new File("test.txt");
FileInputStream fileInputStream = null;
try{
fileInputStream = new FileInputStream(file);
fileInputStream.read();
}catch (IOException e){
e.printStackTrace();
}
finally{
try{
if (fileInputStream != null){
fileInputStream.close();
}
}catch (IOException e){
e.printStackTrace();
}
}
return fileInputStream;
}
public static void main(String[] args){
ExceptionExample instance1 = new ExceptionExample();
instance1.testMethod1();
}
}

When you run the above program where there is no file present in the file system, you would get the following exception:

java.io.FileNotFoundException: test.txt (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at logging.simple.ExceptionExample.testMethod1(ExceptionExample.java:12)
at logging.simple.ExceptionExample.main(ExceptionExample.java:30)

This is one of the IOException, but depends on the different problems in reading the file, your application may throw some other IOExceptions.

If you look at the above code:

The above code tries to read the file test.txt from the file system.
It throws the FileNotFoundException, that is a subclass of IOException
IOException and all the subclasses are checked exceptions
If you create a file names test.txt in the correct path and run the above program, you will not get any exception.