Google App Engine的Vaadin应用程序问题

Question

我自动生成的Vaadin 8应用程序在Google App Engine本地主机上运行良好，但是当部署在Google Cloud / Google App Engine上时，它显示UI，但我收到消息通信错误，请注意...。演示模板不起作用（单击按钮无效）。

我创建Vaadin 8项目，然后在Eclipse中将其转换为Google App Engine项目。

这是我的appengine-web.xml

<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">

  <threadsafe>true</threadsafe>
  <sessions-enabled>true</sessions-enabled>
  <runtime>java8</runtime>

  <system-properties>
    <property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
  </system-properties>

</appengine-web-app>

这是我的pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.example</groupId>
	<artifactId>OMABusinessAPI</artifactId>
	<packaging>war</packaging>
	<version>1.0-SNAPSHOT</version>
	<name>OMABusinessAPI</name>

	<prerequisites>
		<maven>3</maven>
	</prerequisites>

	<properties>
		<vaadin.version>8.7.0</vaadin.version>
		<vaadin.plugin.version>8.7.0</vaadin.plugin.version>
		<jetty.plugin.version>9.3.9.v20160517</jetty.plugin.version>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
		<!-- If there are no local customizations, this can also be "fetch" or "cdn" -->
		<vaadin.widgetset.mode>local</vaadin.widgetset.mode>
	</properties>

	<repositories>
		<repository>
			<id>vaadin-addons</id>
			<url>http://maven.vaadin.com/vaadin-addons</url>
		</repository>
	</repositories>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>com.vaadin</groupId>
				<artifactId>vaadin-bom</artifactId>
				<version>${vaadin.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>3.0.1</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>com.vaadin</groupId>
			<artifactId>vaadin-server</artifactId>
		</dependency>
		<dependency>
			<groupId>com.vaadin</groupId>
			<artifactId>vaadin-push</artifactId>
		</dependency>
		<dependency>
			<groupId>com.vaadin</groupId>
			<artifactId>vaadin-client-compiled</artifactId>
		</dependency>
		<dependency>
			<groupId>com.vaadin</groupId>
			<artifactId>vaadin-themes</artifactId>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-war-plugin</artifactId>
				<version>3.2.0</version>
				<configuration>
					<failOnMissingWebXml>false</failOnMissingWebXml>
					<!-- Exclude an unnecessary file generated by the GWT compiler. -->
					<packagingExcludes>WEB-INF/classes/VAADIN/widgetsets/WEB-INF/**</packagingExcludes>
				</configuration>
			</plugin>
			<plugin>
				<groupId>com.vaadin</groupId>
				<artifactId>vaadin-maven-plugin</artifactId>
				<version>${vaadin.plugin.version}</version>
				<executions>
					<execution>
						<goals>
							<goal>update-theme</goal>
							<goal>update-widgetset</goal>
							<goal>compile</goal>
							<!-- Comment out compile-theme goal to use on-the-fly theme compilation -->
							<goal>compile-theme</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-clean-plugin</artifactId>
				<version>3.0.0</version>
				<!-- Clean up also any pre-compiled themes -->
				<configuration>
					<filesets>
						<fileset>
							<directory>src/main/webapp/VAADIN/themes</directory>
							<includes>
								<include>**/styles.css</include>
								<include>**/styles.scss.cache</include>
							</includes>
						</fileset>
					</filesets>
				</configuration>
			</plugin>

			<!-- The Jetty plugin allows us to easily test the development build by
				running jetty:run on the command line. -->
			<plugin>
				<groupId>org.eclipse.jetty</groupId>
				<artifactId>jetty-maven-plugin</artifactId>
				<version>${jetty.plugin.version}</version>
				<configuration>
					<scanIntervalSeconds>2</scanIntervalSeconds>
				</configuration>
			</plugin>
		</plugins>
	</build>

	<profiles>
		<profile>
			<!-- Vaadin pre-release repositories -->
			<id>vaadin-prerelease</id>
			<activation>
				<activeByDefault>false</activeByDefault>
			</activation>

			<repositories>
				<repository>
					<id>vaadin-prereleases</id>
					<url>http://maven.vaadin.com/vaadin-prereleases</url>
				</repository>
				<repository>
					<id>vaadin-snapshots</id>
					<url>https://oss.sonatype.org/content/repositories/vaadin-snapshots/</url>
					<releases>
						<enabled>false</enabled>
					</releases>
					<snapshots>
						<enabled>true</enabled>
					</snapshots>
				</repository>
			</repositories>
			<pluginRepositories>
				<pluginRepository>
					<id>vaadin-prereleases</id>
					<url>http://maven.vaadin.com/vaadin-prereleases</url>
				</pluginRepository>
				<pluginRepository>
					<id>vaadin-snapshots</id>
					<url>https://oss.sonatype.org/content/repositories/vaadin-snapshots/</url>
					<releases>
						<enabled>false</enabled>
					</releases>
					<snapshots>
						<enabled>true</enabled>
					</snapshots>
				</pluginRepository>
			</pluginRepositories>
		</profile>
	</profiles>

</project>

这是自动生成的Vaadin UI：

package com.example.OMABusinessAPI;

import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.ui.Button;
import com.vaadin.ui.Label;
import com.vaadin.ui.TextField;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

/**
 * This UI is the application entry point. A UI may either represent a browser window 
 * (or tab) or some part of an HTML page where a Vaadin application is embedded.
 * <p>
 * The UI is initialized using {@link #init(VaadinRequest)}. This method is intended to be 
 * overridden to add component to the user interface and initialize non-component functionality.
 */
@Theme("mytheme")
public class MyUI extends UI {

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        final VerticalLayout layout = new VerticalLayout();
        
        final TextField name = new TextField();
        name.setCaption("Type your name here:");

        Button button = new Button("Click Me");
        button.addClickListener(e -> {
            layout.addComponent(new Label("Thanks " + name.getValue() 
                    + ", it works!"));
        });
        
        layout.addComponents(name, button);
        
        setContent(layout);
    }

    @WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false)
    public static class MyUIServlet extends VaadinServlet {
    }
}

结果是：