How to Reset a BufferedReader Buffer in Java?

What are the methods to reset a BufferedReader in Java?

BufferedReader br = new BufferedReader(new FileReader("file.txt"));
// Read some data
String line = br.readLine();
// Reset buffer if marked
br.reset(); // This requires mark to have been called beforehand

In Java, the BufferedReader class can be used to read text from an input stream efficiently. However, if you need to reset the buffer to re-read data, it’s essential to understand how `mark` and `reset` methods work in BufferedReader. This article will walk you through resetting a BufferedReader’s buffer correctly.

BufferedReader br = new BufferedReader(new FileReader("file.txt"));
// Set a mark with a read-ahead limit of 100 characters
br.mark(100);
String line1 = br.readLine();
System.out.println(line1); // Print the first line
// Reset to marked position
br.reset();
String line2 = br.readLine();
System.out.println(line2); // Print the first line again

Causes

• BufferedReader does not reset to the previous position if 'mark()' was not called before reaching 'reset()'.
• The default buffer size may not be sufficient for larger data sets, which can lead to unexpected behavior.

Solutions

• Always call `mark(int readAheadLimit)` before calling `readLine()` or other read methods to set a position you can reset to later.
• Use the `reset()` method directly after reading to revert back to the last marked position.
• If you need to read data multiple times, consider copying it into a list or another structure instead of relying solely on BufferedReader.

Mistake: Forgetting to call mark() before read(), leading to failure in calling reset().

Solution: Always call mark(int) method to set a mark when you want to reset later.

Mistake: Using reset() without checking if the mark was set beforehand.

Solution: Check if mark() has been called before attempting to reset.