Java读取文本文件 - 我叫涛哥

Java读取文本文件

java.nio.file.Files

只有在处理小文件并且需要内存中的所有文件内容时，才应使用此方法。

    private static void readUsingFiles(String fileName) throws IOException {
        Path path = Paths.get(fileName);
        //read file to byte array
        byte[] bytes = Files.readAllBytes(path);
        System.out.println("Read text file using Files class");
        //read file to String list
        @SuppressWarnings("unused")
        List<String> allLines = Files.readAllLines(path, StandardCharsets.UTF_8);
        System.out.println(new String(bytes));
    }

 

java.io.FileReader

FileReader不支持编码并且使用系统默认编码，因此它不是非常有效的在java中读取文件的方式。

 private static void readUsingFileReader(String fileName) throws IOException {
        File file = new File(fileName);
        FileReader fr = new FileReader(file);
        BufferedReader br = new BufferedReader(fr);
        String line;
        System.out.println("Reading text file using FileReader");
        while((line = br.readLine()) != null){
            //process the line
            System.out.println(line);
        }
        br.close();
        fr.close();
        
    }

 

java.io.BufferedReader

适合处理大文件，它也支持编码。BufferedReader是同步的，因此对BufferedReader的读取操作可以安全地从多个线程完成。 BufferedReader的默认缓冲区大小为8KB。

    private static void readUsingBufferedReader(String fileName, Charset cs) throws IOException {
        File file = new File(fileName);
        FileInputStream fis = new FileInputStream(file);
        InputStreamReader isr = new InputStreamReader(fis, cs);
        BufferedReader br = new BufferedReader(isr);
        String line;
        System.out.println("Read text file using InputStreamReader");
        while((line = br.readLine()) != null){
            //process the line
            System.out.println(line);
        }
        br.close();
        
    }

private static void readUsingBufferedReaderJava7(String fileName, Charset cs) throws IOException {
        Path path = Paths.get(fileName);
        BufferedReader br = Files.newBufferedReader(path, cs);
        String line;
        System.out.println("Read text file using BufferedReader Java 7 improvement");
        while((line = br.readLine()) != null){
            //process the line
            System.out.println(line);
        }
        br.close();
    }

 private static void readUsingBufferedReader(String fileName) throws IOException {
        File file = new File(fileName);
        FileReader fr = new FileReader(file);
        BufferedReader br = new BufferedReader(fr);
        String line;
        System.out.println("Read text file using BufferedReader");
        while((line = br.readLine()) != null){
            //process the line
            System.out.println(line);
        }
        //close resources
        br.close();
        fr.close();
    }

 

java.util.Scanner

如果要逐行读取文件或基于一些Java正则表达式，Scanner是要使用的类。不是线程安全。

  private static void readUsingScanner(String fileName) throws IOException {
        Path path = Paths.get(fileName);
        Scanner scanner = new Scanner(path);
        System.out.println("Read text file using Scanner");
        //read line by line
        while(scanner.hasNextLine()){
            //process each line
            String line = scanner.nextLine();
            System.out.println(line);
        }
        scanner.close();
    }