src/org/nutz/mvc/upload/util/BufferRing.java
public void skipMark() throws IOException {
        dump(new OutputStream() {
            public void write(int b) throws IOException {}

            public void close() throws IOException {}

            public void flush() throws IOException {}

            public void write(byte[] b, int off, int len) throws IOException {}

            public void write(byte[] b) throws IOException {}

        });
    }
public void skipMark() throws IOException {
        dump(new OutputStream() {
            public void write(int b) throws IOException {}

            public void close() throws IOException {}

            public void flush() throws IOException {}

            public void write(byte[] b, int off, int len) throws IOException {}

            public void write(byte[] b) throws IOException {}

        });
    }
不输出，直接跳过 Mark，相当于将当前的 Mark dump 到一个空的输出流

@throws IOException