[zz]Do not create multiple buffered wrappers on a single InputStream

https://www.securecoding.cert.org/confluence/display/java/FIO06-J.+Do+not+create+multiple+buffered+wrappers+on+a+single+InputStream

 

多次对System.in进行包装，每次重新生成一个BufferedInputStream，原来的buffer里面的内容会被清空

public final class InputLibrary {
  public static char getChar() throws EOFException, IOException {
    BufferedInputStream in = new BufferedInputStream(System.in); // wrapper
    int input = in.read();
    if (input == -1) {
      throw new EOFException();
    }
    // Down casting is permitted because InputStream guarantees read() in range
    // 0..255 if it is not -1
    return (char) input;
  }
 
  public static void main(String[] args) {
    try {
      // Either redirect input from the console or use
      // System.setIn(new FileInputStream("input.dat"));
      System.out.print("Enter first initial: ");
      char first = getChar();
      System.out.println("Your first initial is " + first);
      System.out.print("Enter last initial: ");
      char last = getChar();
      System.out.println("Your last initial is " + last);
    } catch (EOFException e) {
      System.err.println("ERROR");
      // Forward to handler
    } catch (IOException e) {
      System.err.println("ERROR");
      // Forward to handler
    }
  }
}

 

When compiled under Java 1.6.0 and run from the command line, this program successfully takes two characters as input and prints them out. However, when run with a file redirected to standard input, the program throws EOFException because the second call to getChar() finds no characters to read upon encountering the end of the stream.

 

It may appear that the mark() and reset() methods of BufferedInputStream could be used to replace the read bytes. However, these methods provide look-ahead by operating on the internal buffers of the BufferedInputStream rather than by operating directly on the underlying stream. Because the example code creates a new BufferedInputStream on each call to getchar(), the internal buffers of the previous BufferedInputStream are lost.

正确处理方法

public final class InputLibrary {
  private static BufferedInputStream in =
      new BufferedInputStream(System.in);
 
  public static char getChar() throws EOFException, IOException {
    int input = in.read();
    if (input == -1) {
      throw new EOFException();
    }
    in.skip(1); // This statement is to advance to the next line
                // The noncompliant code example deceptively
                // appeared to work without it (in some cases)
    return (char) input;
  }
 
  public static void main(String[] args) {
    try {
      System.out.print("Enter first initial: ");
      char first = getChar();
      System.out.println("Your first initial is " + first);
      System.out.print("Enter last initial: ");
      char last = getChar();
      System.out.println("Your last initial is " + last);
    } catch (EOFException e) {
      System.err.println("ERROR");
      // Forward to handler
    } catch (IOException e) {
       System.err.println("ERROR");
       // Forward to handler
    }
  }
}