How to read properties file in web application? [duplicate]

Question

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Where to place and how to read configuration resource files in servlet based application? (6 answers)

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Properties file location is WEB-INF/classes/auth.properties.

I cannot use JSF-specific ways (with ExternalContext) because I need properties file in a service module which doesn't have a dependency on a web-module.

I've already tried

MyService.class.getClassLoader().getResourceAsStream("/WEB-INF/classes/auth.properties");

but it returns null.

I've also tried to read it with FileInputStream but it requires the full path what is unacceptable.

Any ideas?

Answer 1

Several notes:

1. You should prefer the ClassLoader as returned by Thread#getContextClassLoader().

   ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
   

   This returns the parentmost classloader which has access to all resources. The Class#getClassLoader() will only return the (child) classloader of the class in question which may not per se have access to the desired resource. It will always work in environments with a single classloader, but not always in environments with a complex hierarchy of classloaders like webapps.

2. The /WEB-INF folder is not in the root of the classpath. The /WEB-INF/classes folder is. So you need to load the properties files relative to that.

   classLoader.getResourceAsStream("/auth.properties");
   

   If you opt for using the Thread#getContextClassLoader(), remove the leading /.

The JSF-specific ExternalContext#getResourceAsStream() which uses ServletContext#getResourceAsStream() "under the hoods" only returns resources from the webcontent (there where the /WEB-INF folder is sitting), not from the classpath.

Answer 2

Try this:

MyService.class.getClassLoader().getResourceAsStream("/auth.properties");

Reading files with getResourceAsStream looks on the classpath to find the resource to load. Since the classes directory is in the classpath for your webapp, referring to the file as /auth.properties should work.

Answer 3

ResourceBundle (http://download.oracle.com/javase/6/docs/api/java/util/ResourceBundle.html) resolve most of the problems with a relative/absotule path for Properties Files.

It uses the the Resource class and point it to a Dummy Class to make reference to a properties file.

For example:

1. You a have file called MAINProperties.properties and inside it there is a property: mail.host=foo.example.com
2. Create a Dummy Class called MAINProperties without nothing.

3. Use the following code:

   ResourceBundle.getBundle("com.example.com.MAINProperties").getProperty("mail.host")

And That's it. No InputStreams Required.

P.D. Apache Commons has a Library Called Apache Commons Configuration that has a lot of capabilities (reloadable files, multiple domain types) that could be used in combination of the above.