Tomcat server absolute file access in war webapp

Question

I have a Spring webapp whose `.war` file has been uploaded to a Tomcat server. Most of the basic functions are working as intended - page views and form submission. My problem now is that my webapp needs to read and write files and I am clueless as to how I can achieve this (the file I/O returns `java.lang.NullPointerException`). I used the following code to get the absolute path of a given file suggested by Titi Wangsa Bin Damhore to know the path relative to the server: ``` HttpSession session = request.getSession(); ServletContext sc = session.getServletContext(); String file = sc.getRealPath("src/test.arff"); logger.info("File path: " + file); ``` Here is the output path: ``` /home/username/tomcat/webapps/appname/src/test.arff ``` But when I checked the file directory via WinSCP, the file's actual path is: ``` /home/username/tomcat/webapps/appname/WEB-INF/classes/test.arff ``` Here are my questions: - How do I transform these paths into something like `C:/Users/Workspace/appname/s…

Accepted Answer

To read files:

```
ServletContext application = ...;
InputStream in = null;

try {
  in = application.getResourceAtStream("/WEB-INF/web.xml"); // example

// read your file
} finally {
  if(null != in) try { in.close(); }
   catch (IOException ioe) { /* log this */ }
}
```

To write files:

```
ServletContext application = ...;
File tmpdir = (File)application.getAttribute("javax.servlet.context.tempdir");

if(null == tmpdir)
  throw new IllegalStateException("Container does not provide a temp dir"); // Or handle otherwise

File targetFile = new File(tmpDir, "my-temp-filename.txt");
BufferedWriter out = null;

try {
  out = new BufferedWriter(new FileWriter(targetFile));

// write to output stream
} finally {
  if(null != out) try { out.close(); }
  catch (IOException ioe) { /* log this */ }
}
```

If you don't want to use the tmpdir provided by the servlet container, then you should use someplace that is entirely outside of the servlet context's purvue, like `/path/to/temporary/files` or something like that. You definitely don't want to use the container's temporary directory for anything other than truly temporary files which are okay to delete on re-deployment, etc.

Tomcat server absolute file access in war webapp

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