Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to append data to a file in Java?
In most scenarios if you try to write contents to a file, using the classes of the java.io package, the file will be overwritten i.e. data existing in the file is erased and the new data is added to it.
But, in certain scenarios like logging exceptions into a file (without using logger frame works) you need to append data (message) in the next line of the file.
You can do this using the Files class of the java.nio package. This class provides a method named write() which accepts
- An object of the class Path, representing a file.
- A byte array holding the data to the file.
- A variable arguments of the type OpenOption (interface) as a value to it you can pass one of the elements of StandardOpenOption enumeration which contains 10 options namely, APPEND, CREATE, CREATE_NEW, DELETE_ON_CLOSE, DSYNC, READ, SPARSE, SYNC, TRUNCATE_EXISTING, WRITE.
You can invoke this method by passing the path of the file, byte array containing the data to be appended and, the option StandardOpenOption.APPEND.
Example
Following Java program has an array storing 5 integer values, we are letting the user to choose two elements from the array (indices of the elements) and performing division between them. We are wrapping this code in try block with three catch blocks catching ArithmeticException, InputMismatchException and, ArrayIndexOutOfBoundsException. In each of them we are invoking the writeToFile() method.
This method accepts an exception object, and appends it to a file using the write() method of the Files class.
public class LoggingToFile {
private static void writeToFile(Exception e) throws IOException {
//Retrieving the log file
Path logFile = Paths.get("ExceptionLog.txt");
//Preparing the data to be logged
byte bytes[] = ("\r
"+LocalDateTime.now()+": "+e.toString()).getBytes();
//Appending the exception to your file
Files.write(logFile, bytes, StandardOpenOption.APPEND);
System.out.println("Exception logged to your file");
}
public static void main(String [] args) throws IOException {
Scanner sc = new Scanner(System.in);
int[] arr = {10, 20, 30, 2, 0, 8};
System.out.println("Array: "+Arrays.toString(arr));
System.out.println("Choose numerator and denominator (not 0) from this array (enter positions 0 to 5)");
try {
int a = sc.nextInt();
int b = sc.nextInt();
int result = (arr[a])/(arr[b]);
System.out.println("Result of "+arr[a]+"/"+arr[b]+": "+result);
}catch(ArrayIndexOutOfBoundsException ex) {
System.out.println("Warning: You have chosen a position which is not in the array");
writeLogToFile(ex);
}catch(ArithmeticException ex) {
System.out.println("Warning: You cannot divide an number with 0");
writeLogToFile(ex);
}catch(InputMismatchException ex) {
System.out.println("Warning: You have entered invalid input");
writeLogToFile(ex);
}
}
}Output 1
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 2 4 Warning: You cannot divide an number with 0 Exception logged to your file
Output 2
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) 5 12 Warning: You have chosen a position which is not in the array Exception logged to your file
Output 3
Enter 3 integer values one by one: Array: [10, 20, 30, 2, 0, 8] Choose numerator and denominator(not 0) from this array (enter positions 0 to 5) hello Warning: You have entered invalid input Exception logged to your file
ExceptionLog.txt
2019-07-19T17:57:09.735: java.lang.ArithmeticException: / by zero 2019-07-19T17:57:39.025: java.lang.ArrayIndexOutOfBoundsException: 12 2019-07-19T18:00:23.374: java.util.InputMismatchException
534 Views
