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Как читать файл в Java - BufferedReader

Как читать файл в Java - BufferedReader

В этой статье мы покажем вам, как использоватьjava.io.BufferedReader для чтения содержимого из файла.

Note
Прочтите этоdifferent ways read a file

1. Files.newBufferedReader (Java 8)

В Java 8 есть новый методFiles.newBufferedReader(Paths.get("file")) для возвратаBufferedReader

filename.txt

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FileExample1.java

package com.example;

import java.io.BufferedReader;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

public class FileExample1 {

    public static void main(String[] args) {

        StringBuilder sb = new StringBuilder();

        try (BufferedReader br = Files.newBufferedReader(Paths.get("filename.txt"))) {

            // read line by line
            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line).append("\n");
            }

        } catch (IOException e) {
            System.err.format("IOException: %s%n", e);
        }

        System.out.println(sb);

    }

}

Выход 

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2. BufferedReader

2.1 A classic BufferedReader with JDK 1.7 try-with-resources to auto close the resources.

FileExample2.java

package com.example;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileExample2 {

    public static void main(String[] args) {

        try (FileReader reader = new FileReader("filename.txt");
             BufferedReader br = new BufferedReader(reader)) {

            // read line by line
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }

        } catch (IOException e) {
            System.err.format("IOException: %s%n", e);
        }
    }

}

2.2 In the old days, we have to close everything manually.

FileExample3.java

package com.example.calculator;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileExample3 {

    public static void main(String[] args) {

        BufferedReader br = null;
        FileReader fr = null;

        try {

            fr = new FileReader("filename.txt");
            br = new BufferedReader(fr);

            // read line by line
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }

        } catch (IOException e) {
            System.err.format("IOException: %s%n", e);
        } finally {
            try {
                if (br != null)
                    br.close();

                if (fr != null)
                    fr.close();
            } catch (IOException ex) {
                System.err.format("IOException: %s%n", ex);
            }
        }

    }

}

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