Saving Arduino output to a text file in append mode

Question

I used the code below to save output from an Arduino Uno to a text file.

The problem is whenever I run the code the old data in the text file is deleted.

I don't want the old data to be deleted, what should I change?

import processing.serial.*;
Serial mySerial;
PrintWriter output;
void setup() {
   mySerial = new Serial( this, Serial.list()[0], 9600 );
   output = createWriter( "data.txt" );
}
void draw() {
    if (mySerial.available() > 0 ) {
         String value = mySerial.readString();
         if ( value != null ) {
              output.println( value );
         }
    }
}

void keyPressed() {
    output.flush();  // Writes the remaining data to the file
    output.close();  // Finishes the file
    exit();  // Stops the program
}

Answer 1

There are a couple of ways to append to a text file.

1. You can either read the entire file in a temporary variable, then append the new data to it and then write to file.

2. you can implement using printWriter instead like mentioned here: https://processing.org/discourse/beta/num_1267767630.html

Let me know if it works.

Answer 2

Load configuration data from the SPIFF file, return 0 if OK

• SPIFFS open function needs path and mode:
• mode = "r", "w", "a", "r+", "w+", "a+" (text file) or "rb", "wb", "ab", "rb+", "wb+", "ab+" (binary)
• where r = read, w = write, `a = append
• • means file is open for update (read and write)
• b means the file os open for binary operations
• Returns 0 if OK else:
• -1 = No SPIFFS file system
• -2 = File does not exist
• -3 = File too short
• -4 = Checksum does not compare