public static OutputStream nullOutputStream() {
        return new OutputStream() {
            private volatile boolean closed;

            private void ensureOpen() throws IOException {
                if (closed) {
                    throw new IOException("Stream closed");
                }
            }

            @Override
            public void write(int b) throws IOException {
                ensureOpen();
            }

            @Override
            public void write(byte b[], int off, int len) throws IOException {
                Objects.checkFromIndexSize(off, len, b.length);
                ensureOpen();
            }

            @Override
            public void close() {
                closed = true;
            }老师close方法里没有回收资源啊只是返回true，真的回收在哪里啊？

        };
    }