由于某种原因，“请求的资源不可用”

Question

我的代码是：

package com.example.upravnik_dokumenata;

import java.io.File;

import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.data.util.FilesystemContainer;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.ui.Button;
import com.vaadin.ui.Button.ClickEvent;
import com.vaadin.ui.ComboBox;
import com.vaadin.ui.Label;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

@SuppressWarnings("serial")
@Theme("upravnik_dokumenata")
public class UprUI extends UI {

    FilesystemContainer dokumenta = new FilesystemContainer(new File("C:\\Users\\x\\Desktop\\Informatika"));
    ComboBox combo = new ComboBox("Documents", dokumenta);

    @Override
    protected void init(VaadinRequest request) {
        setContent(combo);

    }

}

很简单，但不起作用。顺便说一下，我正在使用Eclipse Luna 4.4.1，Tomcat 8.0v。