构建一个Vaadin Flow web应用程序，用Java编写。

package com.example;

import com.vaadin.flow.component.Key;
import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.button.ButtonVariant;
import com.vaadin.flow.component.checkbox.Checkbox;
import com.vaadin.flow.component.dependency.CssImport;
import com.vaadin.flow.component.html.H1;
import com.vaadin.flow.component.orderedlayout.HorizontalLayout;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.component.textfield.TextField;
import com.vaadin.flow.router.Route;

@Route
public class MainView extends VerticalLayout 
{

  public MainView() 
  {
    Button button = new Button( "Do something" ); 
    addButton.addClickListener(
      click -> {
        … your Java code goes here, to execute server-side, in JVM.
      }
    );
    this.add(
      button 
    );
  }
}