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场景复现

采用Maven构建非Spring项目，在开发阶段能够正常开发（采用IDEA直接run，是可以运行的），通过maven打包后，通过java -jar 运行项目报错：Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError， 查看网上各种办法不得行，后面捣鼓半天明白原来是在打包时候出现的问题。

问题描述

Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: org/apache/poi/ss/usermodel/Workbook
        at gui.MainGUI.<init>(MainGUI.java:19)
        at Application$1.run(Application.java:15)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
        at java.awt.EventQueue.access$500(EventQueue.java:97)
        at java.awt.EventQueue$3.run(EventQueue.java:709)
        at java.awt.EventQueue$3.run(EventQueue.java:703)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
Caused by: java.lang.ClassNotFoundException: org.apache.poi.ss.usermodel.Workbook
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)

问题原因

在某些第三发包的引入下，采用以下maven构建时会将第三方jar忽略掉，也就是没有进行打包，导致项目无法运行

原来打包的maven文件为：

...
...
...

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <mainClass>Application</mainClass>
                            <!--  此处为主入口 -->
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

解决方式

采用将依赖jar打包到项目中，修改maven文件
pom.xml

...
...
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.5.5</version>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>Application</mainClass>
                        </manifest>
                    </archive>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
                <!-- 添加此项后，可直接使用mvn package | mvn install -->
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>