In this post we will going to take a look at FileNotFoundException in Java. This exception is thrown during a failed attempt to open the file denoted by a specified path-name. Also, this exception can be thrown when an application tries to open a file for writing, but the file is read only, or the permissions of the file do not allow the file to be read by any application.
This exception extends the IOException class, which is the general class of exceptions produced by failed or interrupted I/O operations. Also, it implements the Serializable interface and finally, theFileNotFoundException exists since the first version of Java (1.0).
The following snippet reads all the lines of a file, but if the file does not exist, a FileNotFoundException is thrown.
(FileNotFoundExceptionExample.java:30)
This exception extends the IOException class, which is the general class of exceptions produced by failed or interrupted I/O operations. Also, it implements the Serializable interface and finally, theFileNotFoundException exists since the first version of Java (1.0).
The FileNotFoundException in Java
The following constructors throw a FileNotFoundException when the specified filename does not exist: FileInputStream,FileOutputStream, and RandomAccessFile. These classes aim to obtain input bytes from a file in a file system, while the former class supports both reading and writing to a random access file.The following snippet reads all the lines of a file, but if the file does not exist, a FileNotFoundException is thrown.
FileNotFoundExceptionExample.java:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public class FileNotFoundExceptionExample {
private static final String filename = "input.txt";
public static void main(String[] args) {
BufferedReader rd = null;
try {
// Open the file for reading.
rd = new BufferedReader(new FileReader(new File(filename)));
// Read all contents of the file.
String inputLine = null;
while((inputLine = rd.readLine()) != null)
System.out.println(inputLine);
}
catch(IOException ex) {
System.err.println("An IOException was caught!");
ex.printStackTrace();
}
finally {
// Close the file.
try {
rd.close();
}
catch (IOException ex) {
System.err.println("An IOException was caught!");
ex.printStackTrace();
}
}
}
}
In case the file is missing, the following output is produced:
An IOException was caught!
java.io.FileNotFoundException: input.txt (No such file or directory) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.(FileInputStream.java:146) at java.io.FileReader.(FileReader.java:72) at main.java.FileNotFoundExceptionExample.main(FileNotFoundExceptionExample.java:16) Exception in thread "main" java.lang.NullPointerException at main.java.FileNotFoundExceptionExample.main
The following snippet tries to append a string at the end of a file. If the file does not exist, the application creates it. However, if the file cannot be created, is a directory, or the file already exists but its permissions are sufficient for changing its content, a FileNotFoundException is thrown.
FileNotFoundExceptionExample_v2.java:
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
public class FileNotFoundExceptionExample_v2 {
private static final String filename = "input.txt";
public static void main(String[] args) {
BufferedWriter wr = null;
try {
// Open the file for writing, without removing its current content.
wr = new BufferedWriter(new FileWriter(new File(filename), true));
// Write a sample string to the end of the file.
wr.write("A sample string to be written at the end of the file!\n");
}
catch(IOException ex) {
System.err.println("An IOException was caught!");
ex.printStackTrace();
}
finally {
// Close the file.
try {
wr.close();
}
catch (IOException ex) {
System.err.println("An IOException was caught!");
ex.printStackTrace();
}
}
}
}
If the file exists and is a directory, the following exception is thrown:
An IOException was caught!
java.io.FileNotFoundException: input.txt (Is a directory)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.(FileOutputStream.java:221)
at java.io.FileWriter.(FileWriter.java:107)
at main.java.FileNotFoundExceptionExample_v2.main
(FileNotFoundExceptionExample_v2.java:16)
Exception in thread "main" java.lang.NullPointerException
at main.java.FileNotFoundExceptionExample_v2.main
(FileNotFoundExceptionExample_v2.java:28)
If the file exists, but it doesn’t have the appropriate permissions for writing, the following exception is thrown:
An IOException was caught!
java.io.FileNotFoundException: input.txt (Permission denied)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.(FileOutputStream.java:221)
at java.io.FileWriter.(FileWriter.java:107)
at main.java.FileNotFoundExceptionExample_v2.main
(FileNotFoundExceptionExample_v2.java:16)
Exception in thread "main" java.lang.NullPointerException
at main.java.FileNotFoundExceptionExample_v2.main
(FileNotFoundExceptionExample_v2.java:28)
Finally, the aforementioned exception can occur when the requested file exists, but it is already opened by another application.
How to deal with the FileNotFoundException
- If the message of the exception claims that there is no such file or directory, then you must verify that the specified is correct and actually points to a file or directory that exists in your system.
- If the message of the exception claims that permission is denied then, you must first check if the permissions of the file are correct and second, if the file is currently being used by another application.
- If the message of the exception claims that the specified file is a directory, then you must either alter the name of the file or delete the existing directory (if the directory is not being used by an application).
