getServletContext（）。getResource（file3）返回null url资源

Question

这是我的代码，它读取excelsheet文件。但是我可以看到我的其他函数工作正常但是当尝试获取资源作为url时它返回null。

    URL resource = null;
    try {
        System.out.println(file3);
        resource = getServletContext().getResource(file3);
        System.out.println("Problem with getting resource"+resource);
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    File file = null;
    try {
        System.out.println(resource.toURI());
        file = new File(resource.toURI());
    } catch (URISyntaxException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    FileInputStream input = null;
    try {
        input = new FileInputStream(file);
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

        Workbook w;
        w = Workbook.getWorkbook(input);
          // Get the first sheet
        Sheet sheet = w.getSheet(0);

     return sheet;