example.java

// some kind of web app
class WebApp extends HttpWebApp {
  WebApp() {
    // creating new file object for composing with read and write handlers
    this(new File("/tmp/1"));
  }
  
  // composition?
  WebApp(File file) {
    super(
      // routes only PUT requests
      new HttpPut(
        new FileSave(file)
      ),
      // routes only GET requests
      new HttpGet(
        new FileRead(file)
      )
    )
  }
}
   

// file definition
interface File {
  void write(byte[] data);
  byte[] read();
}

// http endpoint to save content to file
class FileSave {
  File file;
  
  Response response(Request req) {
    file.write(req.data());
  }
}

// http endpoint to read content from file to response
class FileRead {
   File file;
  
   Response response(Request req) {
     return file.read();
   }
}