Getting a NoClassDefFoundError after installing Vaadin

问题

I want to do a project using Vaadin and am facing some issues. Here's what I did.

I downloaded Eclipse and installed the Vaadin for Eclipse plugin. Then, I created a new Vaadin 7 project. It downloaded some Ivy dependencies but then, when I pressed Run, I get this error: java.lang.NoClassDefFoundError:com/vaadin/server/VaadinServlet.

I searched a bit on the Internet but to no avail. One thing is that in the web-app's WEB-INF/lib folder, there are no jars. I have attached a screenshot of the error and also web.xml and 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>

Please help. I am basically stuck without even starting to code. I am on Windows 8.1 Pro x64 with Java 7u45, Eclipse Kepler SR1 and Vaadin 7.1.7

回答1:

On stackoverflow there are many questions and more answers about this error exception.

Have a look at this good webpage: 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.

This is a good point to start.

In eclipse have a look at your project properties. There is a point called "Deployment Assembly" which should contain at least these two entries:

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

Moreover you must add your project to the tomcat server instance.

回答2:

https://vaadin.com/forum/message/2534863

What you can do is

1) Right-Click the project and Select properties 2) Select Deployment Assembly 3) Click Add 4) Choose the Java Build Path Entries 5) Adde the ivy library.

来源：https://stackoverflow.com/questions/19626808/getting-a-noclassdeffounderror-after-installing-vaadin