从src / main / resources读取会产生NullPointerException

Question

In my Maven project, I have a xls file in src/main/resources. When I read it like this:

 InputStream in = new
 FileInputStream("src/main/resources/WBU_template.xls");

everything is ok.

However I want to read it as InputStream with getResourceAsStream. When I do this, with or without the slash I always get a NPE.

     private static final String TEMPLATEFILE = "/WBU_template.xls";
     InputStream in = this.getClass.getResourceAsStream(TEMPLATEFILE);

No matter if the slash is there or not, or if I make use of the getClassLoader() method, I still get a NullPointer.

I also have tried this :

URL u = this.getClass().getResource(TEMPLATEFILE);
System.out.println(u.getPath());

the console says.../target/classes/WBU_template.xls and then get my NullPointer.

What am I doing wrong ?

Answer 1

FileInputStream will load a the file path you pass to the constructor as relative from the working directory of the Java process.

getResourceAsStream() will load a file path relative from your application's classpath.

When you use .getClass().getResource(fileName) it considers the location of the fileName is the same location of the of the calling class.

When you use .getClass().getClassLoader().getResource(fileName) it considers the location of the fileName is the root - in other words bin folder.

The file should be located in src/main/resources when loading using Class loader

In short, you have to use .getClass().getClassLoader().getResource(fileName) to load the file in your case.

Answer 2

我通常像这样从WEB-INF加载文件

session.getServletContext().getResourceAsStream("/WEB-INF/WBU_template.xls")