Use Arduino for reading accelerometer data & save to raspi

Question

I want to use Arduino to read data from ADXL345 accelerometer and use raspberry pi with Processing to save the data into a txt file in pi. I used the code from https://www.researchgate.net/post/How_can_I_save_data_directly_in_the_pc_using_an_Arduino_UNO

And my Arduino code is shown as follows:

#include <Wire.h>
#define DEVICE (0x53)    //ADXL345 device address
#define TO_READ (6)        //num of bytes we are going to read each time (two bytes for each axis)

byte buff[TO_READ] ;    //6 bytes buffer for saving data read from the device
char str[512];                      //string buffer to transform data before sending it to the serial port

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output

  //Turning on the ADXL345
  writeTo(DEVICE, 0x2D, 0);      
  writeTo(DEVICE, 0x2D, 16);
  writeTo(DEVICE, 0x2D, 8);
}

void loop()
{
  int regAddress = 0x32;    //first axis-acceleration-data register on the ADXL345
  int x, y, z;

  readFrom(DEVICE, regAddress, TO_READ, buff); //read the acceleration data from the ADXL345

   //each axis reading comes in 10 bit resolution, ie 2 bytes.  Least Significat Byte first!!
   //thus we are converting both bytes in to one int
  x = (((int)buff[1]) << 8) | buff[0];   
  y = (((int)buff[3])<< 8) | buff[2];
  z = (((int)buff[5]) << 8) | buff[4];

  //we send the x y z values as a string to the serial port
  sprintf(str, "%d %d %d", x, y, z);  
  Serial.print(str);
  Serial.write(10);

  //It appears that delay is needed in order not to clog the port
  delay(15);
}



void writeTo(int device, byte address, byte val) {
   Wire.beginTransmission(device); //start transmission to device 
   Wire.write(address);        // send register address
   Wire.write(val);        // send value to write
   Wire.endTransmission(); //end transmission
}

void readFrom(int device, byte address, int num, byte buff[]) {
  Wire.beginTransmission(device); //start transmission to device 
  Wire.write(address);        //sends address to read from
  Wire.endTransmission(); //end transmission

  Wire.beginTransmission(device); //start transmission to device (initiate again)
  Wire.requestFrom(device, num);    // request 6 bytes from device

  int i = 0;
  while(Wire.available())    //device may send less than requested (abnormal)
  { 
    buff[i] = Wire.read(); // receive a byte
    i++;
  }
  Wire.endTransmission(); //end transmission
}

Processing code is shown as follows:

    import processing.serial.*;
Serial mySerial;
PrintWriter output;
void setup() {
mySerial = new Serial( this, Serial.list()[0], 9600 );
output = createWriter( "/home/pi/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
}

When only use serial monitor window to show x, y, z values, it looks well, but when using Processing to get data while Arduino serial monitor window is running, the data format changes, e.x. wrong format

Please help me.