Showing posts with label Read File. Show all posts
Showing posts with label Read File. Show all posts

Friday, December 14, 2012

Java: Reading and writing text files

package pritom;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * User: pritom
 * Date: 14/12/12
 * Time: 9:28 AM
 * To change this template use File | Settings | File Templates.
 */
public class ReadWriteTextFileJDK7 {

    public static void main(String... aArgs) throws IOException {
        ReadWriteTextFileJDK7 text = new ReadWriteTextFileJDK7();

        //treat as a small file
        List<String> lines = text.readSmallTextFile(FILE_NAME);
        log(lines);
        lines.add("This is a line added in code.");
        text.writeSmallTextFile(lines, FILE_NAME);

        //treat as a large file - use some buffering
        text.readLargerTextFile(FILE_NAME);
        lines = Arrays.asList("Line added #1", "Line added #2");
        text.writeLargerTextFile(OUTPUT_FILE_NAME, lines);
    }

    final static String FILE_NAME = "C:/tmp/input.txt";
    final static String OUTPUT_FILE_NAME = "C:/tmp/output.txt";
    final static Charset ENCODING = StandardCharsets.UTF_8;

    //For smaller files

    List<String> readSmallTextFile(String aFileName) throws IOException {
        System.out.print("***** readSmallTextFile *****\n");
        Path path = Paths.get(aFileName);
        return Files.readAllLines(path, ENCODING);
    }

    void writeSmallTextFile(List<String> aLines, String aFileName) throws IOException {
        System.out.print("***** writeSmallTextFile *****\n");
        Path path = Paths.get(aFileName);
        Files.write(path, aLines, ENCODING);
    }

    //For larger files

    void readLargerTextFile(String aFileName) throws IOException {
        System.out.print("***** readLargerTextFile *****\n");
        Path path = Paths.get(aFileName);
        Scanner scanner =  new Scanner(path, ENCODING.name());
        while (scanner.hasNextLine()){
            //process each line in some way
            log(scanner.nextLine());
        }
    }

    void readLargerTextFileAlternate(String aFileName) throws IOException {
        System.out.print("***** readLargerTextFileAlternate *****\n");
        Path path = Paths.get(aFileName);
        BufferedReader reader = Files.newBufferedReader(path, ENCODING);
        String line = null;
        while ((line = reader.readLine()) != null) {
            //process each line in some way
            log(line);
        }
    }

    void writeLargerTextFile(String aFileName, List<String> aLines) throws IOException {
        System.out.print("***** writeLargerTextFile *****\n");
        Path path = Paths.get(aFileName);
        BufferedWriter writer = Files.newBufferedWriter(path, ENCODING);
        for(String line : aLines){
            writer.write(line);
            writer.newLine();
        }
        writer.flush();
    }

    private static void log(Object aMsg){
        System.out.println(String.valueOf(aMsg));
    }

}
http://www.javapractices.com/topic/TopicAction.do?Id=42