[Netty] brief talk about Non-Blocking I/O ref: http://qiita.com/SHUAI/items/bea4b8621380b642f116

file0.java

// sample code:
read(file, tmp_buf, len);
write(socket, tmp_buf, len);

file1.java

// sample code:
tmp_buf = mmap(file, len);
write(socket, tmp_buf, len);

file2.java

// sample code:
sendfile(socket, file, len);

file3.java

public class Example {
  public static void main(String... args) throws Exception {
    ExecResult<String> result = ExecHarness.yieldSingle(c ->
      Promise.value("foo")
        .transform(up -> down ->
          up.connect(down.<String>onSuccess(value -> {
            try {
              down.success(value.toUpperCase());
            } catch (Throwable e) {
              down.error(e);
            }
          }))
        )
    );

    assertEquals("FOO", result.getValue());
  }
}