Saving from textview data into file in android

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Android

Hi,

I want to save data into text file from TextView.
but before saving i want to manipulate the data.

data which i am getting is from serial port.
into textview.
I am able to save into file directly from textview.
but i want to manipulate the data.
like split,substring and adding some string to the textview data.

What I have tried:

btnSave5.setOnClickListener(new View.OnClickListener() {
	String fileName1 = "n1.txt";
	String fileName = "IT_"+formatter.format(now) + ".txt";

	@Override
	public void onClick(View v)
	{
		try
		{
			File root = new File(Environment.getExternalStorageDirectory(), "IT1");

			if (!root.exists()) {
				root.mkdirs();
				root.createNewFile();
			}
			File gpxfile = new File(root, fileName);
			FileWriter writer = new FileWriter(gpxfile,true);
			writer.write(tvTerminal.getText()+"\n\n");
			writer.flush();
			writer.close();

			//till this the code works good and file will be saved
			File gpxfile1 = new File(root, fileName1);
			FileWriter writer1 = new FileWriter(gpxfile1,true);
			String  r = "TIME         VOLTAGE        CURRENT           IR-VALUE";

			// The below code is not working 
			//when i try to save it is exiting
			String spdata = tvTerminal.getText().toString();
			String pdata = spdata.substring(78);

			String abc = heading + r;
			writer1.write(abc);
			writer1.flush();
			writer1.close();
			// clear.setVisibility(View.VISIBLE);
		}
		catch(IOException e)
		{
			e.printStackTrace();
		}
	}
});