java - 安装 Vaadin 后出现 NoClassDefFoundError

Question

我想使用 Vaadin 做一个项目，但遇到了一些问题。这是我所做的。

我下载了 Eclipse 并安装了 Vaadin for Eclipse 插件。然后，我创建了一个新的 Vaadin 7 项目。它下载了一些 Ivy 依赖项，但随后，当我按下“运行”时，出现此错误:java.lang.NoClassDefFoundError:com/vaadin/server/VaadinServlet。

我在互联网上搜索了一下，但无济于事。一件事是在网络应用程序的 WEB-INF/lib 文件夹中，没有 jar 。我已附上错误的屏幕截图以及 web.xml 和 ivy.xml。

Ivy .xml:

<?xml version="1.0"?>
<!DOCTYPE ivy-module [
    <!ENTITY vaadin.version "7.1.7">
]>

<ivy-module version="2.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="http://ant.apache.org/ivy/schemas/ivy.xsd">
    <info organisation="com.example" module="v7proj" />
    <configurations>
        <!-- The default configuration, which should be deployed to the server -->
        <conf name="default" />
        <!-- A configuration only needed when compiling the widget set. Should 
            not be deployed to the server -->
        <conf name="widgetset-compile" />
        <!-- A configuration used in compilation of server side classes only.
            Should be deployed to the server -->
        <conf name="nodeploy" />
    </configurations>
    <dependencies defaultconf="default" defaultconfmapping="default->default">
        <!-- The core server part of Vaadin -->
        <dependency org="com.vaadin" name="vaadin-server" rev="&vaadin.version;" />

        <!-- Vaadin themes -->
        <dependency org="com.vaadin" name="vaadin-themes" rev="&vaadin.version;" />

        <!-- Push support -->
        <dependency org="com.vaadin" name="vaadin-push" rev="&vaadin.version;" />

        <!-- Servlet 3.0 API -->
        <dependency org="javax.servlet" name="javax.servlet-api" rev="3.0.1" conf="nodeploy->default" />

        <!-- Precompiled DefaultWidgetSet -->
        <dependency org="com.vaadin" name="vaadin-client-compiled"
            rev="&vaadin.version;" />

        <!-- Vaadin client side, needed for widget set compilation -->
        <dependency org="com.vaadin" name="vaadin-client" rev="&vaadin.version;"
             conf="widgetset-compile->default" />

        <!-- Compiler for custom widget sets. Should not be deployed -->
        <dependency org="com.vaadin" name="vaadin-client-compiler"
            rev="&vaadin.version;" conf="widgetset-compile->default" />
    </dependencies>
</ivy-module>

ivysettings.xml:

<?xml version="1.0" encoding="UTF-8"?>
<ivysettings>
    <settings defaultResolver="default" />
    <resolvers>
        <chain name="default">
            <!-- Public Maven repository -->
            <ibiblio name="public" m2compatible="true" />

            <!-- Vaadin Add-on repository -->
            <ibiblio name="vaadin-addons" usepoms="true" m2compatible="true"
                root="http://maven.vaadin.com/vaadin-addons" />

            <!-- Vaadin snapshots repository -->
            <ibiblio name="vaadin-snapshots" usepoms="true" m2compatible="true"
                root="https://oss.sonatype.org/content/repositories/vaadin-snapshots" />
            <!-- Repository used for Vaadin modified smartsprites library -->
            <dual name="custom-smartsprites">
                <filesystem name="smartsprites-ivy">
                    <ivy pattern="${basedir}/ivymodule/[module]-ivy-[revision].xml" />
                </filesystem>
                <url name="smartsprites-artifact">
                    <artifact
                        pattern="http://dev.vaadin.com/svn/versions/6.8/build/smartsprites/lib/[artifact](-[revision]).[ext]" />
                </url>
            </dual>
        </chain>
    </resolvers>
    <modules>
        <!-- Vaadin patched SmartSprites -->
        <module organisation="com.carrotsearch" name="smartsprites"
            revision="0.2.3-itmill" resolver="custom-smartsprites" />
    </modules>


</ivysettings>

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>ScanAir</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
</web-app>

请帮忙。我基本上没有开始编码就被卡住了。我在使用 Java 7u45、Eclipse Kepler SR1 和 Vaadin 7.1.7 的 Windows 8.1 Pro x64

Answer 1

在 stackoverflow 上有很多关于这个错误异常的问题和更多答案。

看看这个好网页:http://javareferencegv.blogspot.ch/2013/10/debugging-javalangnoclassdeffounderror.html

One thing is that in the web-app's WEB-INF/lib folder, there are no jars.

这是一个很好的起点。

在 Eclipse 中查看您的项目属性。有一个名为“Deployment Assembly”的点，它至少应该包含这两个条目:

/src          -> WEB-INF/classes
/WebContent   -> /

此外，您必须将项目添加到 tomcat 服务器实例。