原因：jar包里面META-INF/MANIFEST.MF文件缺了“Main-Class”的鍵值對
解決辦法：
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>com.u1w2.sla.App</mainClass>
</manifest>
</archive>
</configuration>
</plugin>