为什么我只能先关闭socket的输出流再关闭输入流？

Question

I wrap a socket.getInputStream() by an InputStreamReader, and wrap a socket.getOutputStream() by an OutputStreamWriter. I find that the closing order of these streams really matters but I didn't figure out why.

If I close the outputStream first and then close the inputStream, it works fine:

outputStreamWriter.close();
inputStreamReader.close();

However, if I close the inputStream first and then close the outputStream, it throws an error:

inputStreamReader.close();
outputStreamWriter.close();

The error is:

java.net.SocketException: Socket closed
    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:118)
    at java.net.SocketOutputStream.write(SocketOutputStream.java:155)
    at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
    at sun.nio.cs.StreamEncoder.implClose(StreamEncoder.java:316)
    at sun.nio.cs.StreamEncoder.close(StreamEncoder.java:149)
    at java.io.OutputStreamWriter.close(OutputStreamWriter.java:233)
    at http.HTTPServer.start(HTTPServer.java:69)
    at http.HTTPTest.main(HTTPTest.java:10)

Also, I want to ask do I still need to call socket.close() after closing the socket's inputstream and output stream? And if I close the socket first, do I still need to close these two streams?

Answer 1

From Socket.close()

Closing this socket will also close the socket's InputStream and OutputStream .

From Socket.getInputStream()

Closing the returned InputStream will close the associated socket.

From Socket.getOutputStream()

Closing the returned OutputStream will close the associated socket.

So you can't close just one stream intentionally or accidentally. If you're done with the socket, then Socket.close() is fine. Although if you're using try-with-resources then the streams may get closed automatically anyway. Depends on your design how to write the logic.

The reason for the exception here is OutputStreamWriter buffering bytes, so when you close() it writes out its buffer first (if buffer is not empty). If you close the writer first, the socket is still open and the bytes will be written, if you close the reader first the socket is closed and you get an exception.