从输入流里读取字节数据

read()方法要么返回下一次从流里读取的字节数（0到255，包括0和255），要么在达到流的末端时返回-1。

InputStream in = (...);
try {
  while (true) {
    int b = in.read();
    if (b == -1)
      break;
    (... process b ...)
  }
} finally {
  in.close();
}

从输入流里读取块数据

read()方法不一定会填满整个buf，所以你必须在处理逻辑中考虑返回的长度。

InputStream in = (...);
try {
  byte[] buf = new byte[100];
  while (true) {
    int n = in.read(buf);
    if (n == -1)
      break;
    (... process buf with offset=0 and length=n ...)
  }
} finally {
  in.close();
}

从文件里读取文本

BufferedReader in = new BufferedReader(
    new InputStreamReader(new FileInputStream(...), "UTF-8"));
try {
  while (true) {
    String line = in.readLine();
    if (line == null)
      break;
    (... process line ...)
  }
} finally {
  in.close();
}

向文件里写文本

PrintWriter out = new PrintWriter(
    new OutputStreamWriter(new FileOutputStream(...), "UTF-8"));
try {
  out.print("Hello ");
  out.print(42);
  out.println(" world!");
} finally {
  out.close();
}

参考