java io读书笔记(7) Closing Output Streams

输出完毕后，需要close这个stream，从而使操作系统释放相关的资源。举例：

public void close( ) throws IOException

并不是所有的stream都需要close，可是，诸如file或者network，打开后，需要关闭。

try {
  OutputStream out = new FileOutputStream("numbers.dat");
  // Write to the stream...
  out.close( );
}
catch (IOException ex) {
  System.err.println(ex);
}

However, this code fragment has a potential leak. If an IOException is thrown while writing, the stream won't be closed. It's more reliable to close the stream in a finally block so that it's closed whether or not an exception is thrown. To do this you need to declare the OutputStream variable outside the try block. For example:

// Initialize this to null to keep the compiler from complaining
// about uninitialized variables
OutputStream out = null;
try {
  out = new FileOutputStream("numbers.dat");
  // Write to the stream...
}
catch (IOException ex) {
  System.err.println(ex);
}
finally {
  if (out != null) {
    try {
      out.close( );
    }
    catch (IOException ex) {
      System.err.println(ex);
    }
  }
}