SisendiLugemineFileist.rst

Sisendi lugemine failist

Javas võib sisend-väljud näha keeruline, kuid see pole halb. Sellega saavutatakse seda, et nii klaviatuurilt kui ka failist saab andmeid lugeda kõrgema kihi objektidega nagu BufferedReader või Scanner. Lisaks sellele on veel täiendav võimalus Files.readAllLines().

Kasutades Try with meetodit ei ole vaja manuaalselt lugemis meetodit kinni pannal. Juhul kui ei kasuta try with resources siis tuleb teha finally block kus pannakse lugemis meetod kinni. All pool on ka sellest näide.

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Stream;

public class ReadFile {
        // Filename to be read.
    public static final String FILENAME = "test.txt";
    public static final File FILE = new File(FILENAME);
    public static final Path path = Paths.get(FILENAME);

    public static void main(String[] args) {
        // Buffered reader with StrngBuilder.
        try (BufferedReader br = new BufferedReader(new FileReader(FILENAME))) {
            StringBuilder sb = new StringBuilder();
            String line = br.readLine();

            while (line != null) {
                sb.append(line);
                sb.append(System.lineSeparator());
                line = br.readLine();
            }
            String everything = sb.toString();
            System.out.println(everything);
        } catch (IOException e) {
        e.printStackTrace();
        }

      //  Try with reources
        try (InputStream inputStream = new FileInputStream(FILE)) {
            String fileContents = "";
            int intValueOfLetter;
            char letter;
            while ((intValueOfLetter = inputStream.read()) != -1) {
                letter = (char) intValueOfLetter;
                fileContents += letter;
            }
            System.out.println(fileContents);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Files.readAllLines
        try {
            Path path = Paths.get(FILENAME);
            List<String> lines = Files.readAllLines(path);
            for (String line : lines) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // BufferedReader with normal string.
        try (BufferedReader reader = Files.newBufferedReader(path)) {
            String finalString = "";
            String line;
            while ((line = reader.readLine()) != null) {
                finalString += line + "\n";
            }
            System.out.println(finalString);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Scanner
        try (Scanner scanner = new Scanner(path)) {
            String finalString = "";
            while (scanner.hasNextLine()) {
                finalString += scanner.nextLine() + "\n";
                System.out.println(finalString);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Lambda
        try (Stream<String> stream = Files.lines(path)) {
            stream.forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }
}
}

Siin on koodi näide kuidas readerit manuaalselt kinni panna.

try {
    BufferedReader reader = Files.newBufferedReader(path);
    try {
        String finalStringForBufferedReader = "";
        String line;
        while ((line = reader.readLine()) != null) {
            finalStringForBufferedReader += line + "\n";
        }
        System.out.println(finalStringForBufferedReader);
    } finally {
        reader.close();
    }
} catch (IOException e) {
    e.printStackTrace();
}