URL url = this.getClass().getClassLoader().getResource("/" + packageName.replaceAll("\\.", "/"));

上面的结果返回为null

严重: StandardWrapper.Throwable
java.lang.NullPointerException
    at com.kaikai.servlet.MyDispatcherServlet.doScanner(MyDispatcherServlet.java:153)
    at com.kaikai.servlet.MyDispatcherServlet.init(MyDispatcherServlet.java:35)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1280)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1193)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1088)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:5176)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5460)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
    at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266)
    at java.util.concurrent.FutureTask.run(FutureTask.java)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

getResource方法要注意类路径

public class MyTest {   
    public static void main(String[] args) {        
        MyTest myTest = new MyTest();        
        // URL url = myTest.getClass().getClassLoader().getResource("/");       
        URL url = myTest.getClass().getClassLoader().getResource("");       
        System.out.println(url);    
    }
}

测试后发现方法参数为"",返回的url是类路径的。

maven工程编译后的class文件目录结构的类路径，不需要以/开头。

URL url = this.getClass().getClassLoader().getResource(packageName.replaceAll("\\.", "/"));

就正常了
```