[FIXED] How to save generated file temporarily in servlet based web application

Issue

I am trying to generate a XML file and save it in /WEB-INF/pages/.

Below is my code which uses a relative path:

File folder = new File("src/main/webapp/WEB-INF/pages/");
StreamResult result = new StreamResult(new File(folder, fileName));

It's working fine when running as an application on my local machine (C:\Users\userName\Desktop\Source\MyProject\src\main\webapp\WEB-INF\pages\myFile.xml).

But when deploying and running on server machine, it throws the below exception:

javax.xml.transform.TransformerException: java.io.FileNotFoundException C:\project\eclipse-jee-luna-R-win32-x86_64\eclipse\src\main\webapp\WEB INF\pages\myFile.xml

I tried getServletContext().getRealPath() as well, but it's returning null on my server. Can someone help?

Solution

Never use relative local disk file system paths in a Java EE web application such as new File("filename.xml"). For an in depth explanation, see also getResourceAsStream() vs FileInputStream.

Never use getRealPath() with the purpose to obtain a location to write files. For an in depth explanation, see also What does servletcontext.getRealPath("/") mean and when should I use it.

Never write files to deploy folder anyway. For an in depth explanation, see also Recommended way to save uploaded files in a servlet application.

Always write them to an external folder on a predefined absolute path.

• Either hardcoded:

    File folder = new File("/absolute/path/to/web/files");
    File result = new File(folder, "filename.xml");
    // ...
  

• Or configured in one of many ways:

    File folder = new File(System.getProperty("xml.location"));
    File result = new File(folder, "filename.xml");
    // ...
  

• Or making use of container-managed temp folder:

    File folder = (File) getServletContext().getAttribute(ServletContext.TEMPDIR);
    File result = new File(folder, "filename.xml");
    // ...
  

• Or making use of OS-managed temp folder:

    File result = File.createTempFile("filename-", ".xml");
    // ...
  

The alternative is to use a (embedded) database or a CDN host (e.g. S3).

See also:

• Recommended way to save uploaded files in a servlet application
• Where to place and how to read configuration resource files in servlet based application?
• Simple ways to keep data on redeployment of Java EE 7 web application
• Store PDF for a limited time on app server and make it available for download
• What does servletcontext.getRealPath("/") mean and when should I use it
• getResourceAsStream() vs FileInputStream

Answered By - BalusC
Answer Checked By - Candace Johnson (JavaFixing Volunteer)