Why Does Getrealpath() Return Null When Deployed with a .War File

Properly load file packaged inside .war file

You should be using ServletContext#getResourceAsStream which would load your files with designed path based on root level of war package:

InputStream inputStream = ctx.getResourceAsStream("/WEB-INF/rules/rules.fcl");

Then, it is up to you to use that stream and chain it to load your file content. It should be something like the follwoing if there a FIS#load method that accept InputStream as paramter:

boolean verbose = true; //Just choose your suitable value (verbose mode or not)
FIS fis = FIS.load(inputStream, verbose);

^{Just caught the method signature from this svn repo.}

What does servletcontext.getRealPath(/) mean and when should I use it

Introduction

The ServletContext#getRealPath() is intented to convert a web content path (the path in the expanded WAR folder structure on the server's disk file system) to an absolute disk file system path.

The "/" represents the web content root. I.e. it represents the web folder as in the below project structure:

YourWebProject
 |-- src
 |    :
 |
 |-- web
 |    |-- META-INF
 |    |    `-- MANIFEST.MF
 |    |-- WEB-INF
 |    |    `-- web.xml
 |    |-- index.jsp
 |    `-- login.jsp
 :    

So, passing the "/" to getRealPath() would return you the absolute disk file system path of the /web folder of the expanded WAR file of the project. Something like /path/to/server/work/folder/some.war/ which you should be able to further use in File or FileInputStream.

Note that most starters don't seem to see/realize that you can actually pass the whole web content path to it and that they often use

String absolutePathToIndexJSP = servletContext.getRealPath("/") + "index.jsp"; // Wrong!

or even

String absolutePathToIndexJSP = servletContext.getRealPath("") + "index.jsp"; // Wronger!

instead of

String absolutePathToIndexJSP = servletContext.getRealPath("/index.jsp"); // Right!

Don't ever write files in there

Also note that even though you can write new files into it using FileOutputStream, all changes (e.g. new files or edited files) will get lost whenever the WAR is redeployed; with the simple reason that all those changes are not contained in the original WAR file. So all starters who are attempting to save uploaded files in there are doing it wrong.

Moreover, getRealPath() will always return null or a completely unexpected path when the server isn't configured to expand the WAR file into the disk file system, but instead into e.g. memory as a virtual file system.

getRealPath() is unportable; you'd better never use it

Use getRealPath() carefully. There are actually no sensible real world use cases for it. Based on my 20 years of Java EE experience, there has always been another way which is much better and more portable than getRealPath().

If all you actually need is to get an InputStream of the web resource, better use ServletContext#getResourceAsStream() instead, this will work regardless of the way how the WAR is expanded. So, if you for example want an InputStream of index.jsp, then do not do:

InputStream input = new FileInputStream(servletContext.getRealPath("/index.jsp")); // Wrong!

But instead do:

InputStream input = servletContext.getResourceAsStream("/index.jsp"); // Right!

Or if you intend to obtain a list of all available web resource paths, use ServletContext#getResourcePaths() instead.

Set<String> resourcePaths = servletContext.getResourcePaths("/");

You can obtain an individual resource as URL via ServletContext#getResource(). This will return null when the resource does not exist.

URL resource = servletContext.getResource(path);

Or if you intend to save an uploaded file, or create a temporary file, then see the below "See also" links.

See also:

• getResourceAsStream() vs FileInputStream
• Recommended way to save uploaded files in a servlet application
• Simple ways to keep data on redeployment of Java EE 7 web application

ServletContext().getRealPath() returns path not ending with /

I Fixed the issue.

The issue was, I didn't put '/' before "resources".

ServletContext.getRealPath("")+"/resources"

getServletContext().getRealPath() doesn't work in controller (NPE), but works in jsp

I was missing this:

ServletContext servletContext = request.getSession().getServletContext();

now it works from controller.

ServletContext servletContext = request.getSession().getServletContext();
String relativeWebPath = "img/image.png";
String absoluteDiskPath = servletContext.getRealPath(relativeWebPath);

Loading a file image in a war project

Use

File file = getRequest().getServletContext().getRealPath("/img/logoCorporativo.jpg");

getRealPath convert a URL root relative path (using slashes "/") to a File.
If the war does not unpack itself on deployment, getRealPath returns null.

System.getProperty(mode) returns null

You have to load mode.properties first, like this way

private Properties mode=null;
mode = new Properties();
mode.load(new FileInputStream(pathtoMODE));

String mode = mode.getProperty("mode");

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