Where to place and how to read configuration resource files in servlet based application?

Question

It's your choice. There are basically three ways in a Java web application archive (WAR):

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1. Put it in classpath

So that you can load it by ClassLoader#getResourceAsStream() with a classpath-relative path:

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream input = classLoader.getResourceAsStream("foo.properties");
// ...
Properties properties = new Properties();
properties.load(input);

Here foo.properties is supposed to be placed in one of the roots which are covered by the default classpath of a webapp, e.g. webapp's /WEB-INF/lib and /WEB-INF/classes, server's /lib, or JDK/JRE's /lib. If the propertiesfile is webapp-specific, best is to place it in /WEB-INF/classes. If you're developing a standard WAR project in an IDE, drop it in src folder (the project's source folder). If you're using a Maven project, drop it in /main/resources folder.

You can alternatively also put it somewhere outside the default classpath and add its path to the classpath of the appserver. In for example Tomcat you can configure it as shared.loader property of Tomcat/conf/catalina.properties.

If you have placed the foo.properties it in a Java package structure like com.example, then you need to load it as below

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream input = classLoader.getResourceAsStream("com/example/foo.properties");
// ...

Note that this path of a context class loader should not start with a /. Only when you're using a "relative" class loader such as SomeClass.class.getClassLoader(), then you indeed need to start it with a /.

ClassLoader classLoader = getClass().getClassLoader();
InputStream input = classLoader.getResourceAsStream("/com/example/foo.properties");
// ...

However, the visibility of the properties file depends then on the class loader in question. It's only visible to the same class loader as the one which loaded the class. So, if the class is loaded by e.g. server common classloader instead of webapp classloader, and the properties file is inside webapp itself, then it's invisible. The context class loader is your safest bet so you can place the properties file "everywhere" in the classpath and/or you intend to be able to override a server-provided one from the webapp on.

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2. Put it in webcontent

So that you can load it by ServletContext#getResourceAsStream() with a webcontent-relative path:

InputStream input = getServletContext().getResourceAsStream("/WEB-INF/foo.properties");
// ...

Note that I have demonstrated to place the file in /WEB-INF folder, otherwise it would have been public accessible by any webbrowser. Also note that the ServletContext is in any HttpServlet class just accessible by the inherited GenericServlet#getServletContext() and in Filter by FilterConfig#getServletContext(). In case you're not in a servlet class, it's usually just injectable via @Inject.

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3. Put it in local disk file system

So that you can load it the usual java.io way with an absolute local disk file system path:

InputStream input = new FileInputStream("/absolute/path/to/foo.properties");
// ...

Note the importance of using an absolute path. Relative local disk file system paths are an absolute no-go in a Java EE web application. See also the first "See also" link below.

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Which to choose?

Just weigh the advantages/disadvantages in your own opinion of maintainability.

If the properties files are "static" and never needs to change during runtime, then you could keep them in the WAR.

If you prefer being able to edit properties files from outside the web application without the need to rebuild and redeploy the WAR every time, then put it in the classpath outside the project (if necessary add the directory to the classpath).

If you prefer being able to edit properties files programmatically from inside the web application using Properties#store() method, put it outside the web application. As the Properties#store() requires a Writer, you can't go around using a disk file system path. That path can in turn be passed to the web application as a VM argument or system property. As a precaution, never use getRealPath(). All changes in deploy folder will get lost on a redeploy for the simple reason that the changes are not reflected back in original WAR file.

See also:

• getResourceAsStream() vs FileInputStream
• Adding a directory to tomcat classpath
• Accessing properties file in a JSF application programmatically

Word of warning: if you put config files in your WEB-INF/classes folder, and your IDE, say Eclipse, does a clean/rebuild, it will nuke your conf files unless they were in the Java source directory. BalusC's great answer alludes to that in option 1 but I wanted to add emphasis.

I learned the hard way that if you "copy" a web project in Eclipse, it does a clean/rebuild from any source folders. In my case I had added a "linked source dir" from our POJO java library, it would compile to the WEB-INF/classes folder. Doing a clean/rebuild in that project (not the web app project) caused the same problem.

I thought about putting my confs in the POJO src folder, but these confs are all for 3rd party libs (like Quartz or URLRewrite) that are in the WEB-INF/lib folder, so that didn't make sense. I plan to test putting it in the web projects "src" folder when i get around to it, but that folder is currently empty and having conf files in it seems inelegant.

So I vote for putting conf files in WEB-INF/commonConfFolder/filename.properties, next to the classes folder, which is Balus option 2.

Ex: In web.xml file the tag

<context-param>
        <param-name>chatpropertyfile</param-name>
        <!--  Name of the chat properties file. It contains the name and description                   of rooms.-->     
        <param-value>chat.properties</param-value>
    </context-param>

And chat.properties you can declare your properties like this

For Ex :

Jsp = Discussion about JSP can be made here.
Java = Talk about java and related technologies like J2EE.
ASP = Discuss about Active Server Pages related technologies like VBScript and JScript etc.
Web_Designing = Any discussion related to HTML, JavaScript, DHTML etc.
StartUp = Startup chat room. Chatter is added to this after he logs in.

It just needs to be in the classpath (aka make sure it ends up under /WEB-INF/classes in the .war as part of the build).

You can you with your source folder so whenever you build, those files are automatically copied to the classes directory.

Instead of using properties file, use XML file.

If the data is too small, you can even use web.xml for accessing the properties.

Please note that any of these approach will require app server restart for changes to be reflected.