Servlet容器和测试环境中ClassLoader.getSystemClassLoader().getResource()的不同行为 [英] Different behavior of ClassLoader.getSystemClassLoader().getResource() in servlet container and test environment

问题描述

我有一个Web应用程序，我的要求是读取一些文件并进行处理，并在应用程序启动时将文件内容保留在数据库中.

I have a web application my requirement is to read some files and process it and persist the file content in database when the application starts.

class MyUtil{
/**
*Read the files
*/
 public static void readFiles(){ 

  File file = new File(ClassLoader.getSystemClassLoader().getResource("MyFile").toURI()); //NullPointerException
  // ClassLoader.getSystemClassLoader().getResource("MyFile") is giving null in servlet.init() method.
  if (file.isDirectory()) {
        //Read all the files and persist.
   }
 }
}

MyFile 文件夹/目录在类路径中可用.在JUnit测试用例中调用MyUtil.readFiles()时，它可以正常工作.但是当在servelet.init()方法中调用它时，ClassLoader.getSystemClassLoader().getResource("MyFile")给出了空值.

MyFile folder/dir is available in class path. When MyUtil.readFiles() is called in JUnit test case it works fine. But when It's called in servelet.init() method ClassLoader.getSystemClassLoader().getResource("MyFile") gives the null.

推荐答案

您可以使用getClass().getClassLoader().getResource(...)替代ClassLoader.getSystemClassLoader().getResource(...)

之所以可行，是因为在Web服务器中有多个类加载器，并且您无法确定是哪个类加载了您的类.我猜ClassLoader类先于默认Java类加载器加载，然后MyUtil类与Web服务器一起加载不同的类加载器，因此导致不同的类路径.

The alternative works because in webserver there are more than one class loader, and you can't be sure whichone loaded your class. I guess ClassLoader class loaded before anything with default java class loader, and then MyUtil class loaded with different class loader with the webserver hence it resulted in different classpath.

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