@Test
void testReadFile1() throws IOException {
   //文件內(nèi)容：Hello World|Hello Zimug
   String fileName = "D:\\data\\test\\newFile4.txt";

   try (Scanner sc = new Scanner(new FileReader(fileName))) {
      while (sc.hasNextLine()) {  //按行讀取字符串
         String line = sc.nextLine();
         System.out.println(line);
      }
   }

   try (Scanner sc = new Scanner(new FileReader(fileName))) {
      sc.useDelimiter("\\|");  //分隔符
      while (sc.hasNext()) {   //按分隔符讀取字符串
         String str = sc.next();
         System.out.println(str);
      }
   }

   //sc.hasNextInt() 、hasNextFloat() 、基礎(chǔ)數(shù)據(jù)類型等等等等。
   //文件內(nèi)容：1|2
   fileName = "D:\\data\\test\\newFile5.txt";
   try (Scanner sc = new Scanner(new FileReader(fileName))) {
      sc.useDelimiter("\\|");  //分隔符
      while (sc.hasNextInt()) {   //按分隔符讀取Int
          int intValue = sc.nextInt();
         System.out.println(intValue);
      }
   }
}

@Test
void testReadFile2() throws IOException {
   String fileName = "D:\\data\\test\\newFile.txt";

   // 讀取文件內(nèi)容到Stream流中，按行讀取
   Stream<String> lines = Files.lines(Paths.get(fileName));

   // 隨機(jī)行順序進(jìn)行數(shù)據(jù)處理
   lines.forEach(ele -> {
      System.out.println(ele);
   });
}

// 按文件行順序進(jìn)行處理
lines.forEachOrdered(System.out::println);

// 轉(zhuǎn)換成List<String>, 要注java.lang.OutOfMemoryError: Java heap space
List<String> collect = lines.collect(Collectors.toList()

@Test
void testReadFile3() throws IOException {
   String fileName = "D:\\data\\test\\newFile3.txt";

   // 轉(zhuǎn)換成List<String>, 要注意java.lang.OutOfMemoryError: Java heap space
   List<String> lines = Files.readAllLines(Paths.get(fileName),
               StandardCharsets.UTF_8);
   lines.forEach(System.out::println);

}

@Test
void testReadFile4() throws IOException {
   String fileName = "D:\\data\\test\\newFile3.txt";

   // java 11 開始提供的方法，讀取文件不能超過(guò)2G，與你的內(nèi)存息息相關(guān)
   //String s = Files.readString(Paths.get(fileName));
}

@Test
void testReadFile5() throws IOException {
   String fileName = "D:\\data\\test\\newFile3.txt";

   //如果是JDK11用上面的方法，如果不是用這個(gè)方法也很容易
   byte[] bytes = Files.readAllBytes(Paths.get(fileName));

   String content = new String(bytes, StandardCharsets.UTF_8);
   System.out.println(content);
}

@Test
void testReadFile6() throws IOException {
   String fileName = "D:\\data\\test\\newFile3.txt";

   // 帶緩沖的流讀取，默認(rèn)緩沖區(qū)8k
   try (BufferedReader br = new BufferedReader(new FileReader(fileName))){
      String line;
      while ((line = br.readLine()) != null) {
         System.out.println(line);
      }
   }

   //java 8中這樣寫也可以
   try (BufferedReader br = Files.newBufferedReader(Paths.get(fileName))){
      String line;
      while ((line = br.readLine()) != null) {
         System.out.println(line);
      }
   }
}

try (FileInputStream fis = new FileInputStream(fileName);
     ObjectInputStream ois = new ObjectInputStream(fis)){
   ois.readObject();
}