Munging Text Files

To process a text file line-by-line, we can use BufferedReader and PrintWriter:

BufferedReader

+ BufferedReader(Reader)
+ readLine() : String

PrintWriter

+ BufferedReader(OutputStream)
+ print(Object or primitive)
+ println(Object or primitive)

BufferedReader.readLine() returns null at the EOF.
PrintWriter's print() and println() are overloaded to handle all primitive types, as well as String and arbitrary Object types:
boolean char char[] double float int long String Object
(PrintWriter prints Objects by calling their toString() method)

import java.io.*;

public class MungeTest {
    static final String INFILE  = "index.html";
    static final String OUTFILE = "index.txt";

    public static void main(String[] args) {
        try {
            munge();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void munge() throws IOException {
        BufferedReader reader = new BufferedReader(
                                new FileReader(INFILE));
        PrintWriter    writer = new PrintWriter(
                                new FileWriter(OUTFILE));
        
        String line;
        while ((line = reader.readLine()) != null) {
            line = mungeLine(line);
            writer.println(line);
        }

        reader.close();
        writer.close();
    }

    private static String mungeLine(String line) {
        return line.toUpperCase();
    }
}