[memo] Accessing files in a web application

Sometimes the easiest things are also the easiest to miss (or to forget :-) ). Therefore, in order to have this once and for all in one place - the quickest guide how to access files in a servlet environment (Spring Boot application in my case).

1. Classpath resource

A file that is present in a classpath (typically /WEB-INF/classes, /WEB-INF/lib).
Can be anything, most probably a configuration file that is packed with WAR during package preparation stage. In case of good old Maven - all of the resources (by default src/main/resources) will end up in the classpath. Access - via context class loader.
For example:

	ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
	InputStream inputStream = classLoader.getResourceAsStream("class/path/relative/file");

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2. Web resource 

All of the web application files - including static content (images, styles, html, ...) and files that are loaded into classpath (JARs from /WEB-INF/lib etc.) can be accessed this way. The only requirement is the presence of a ServletContext. 

PRO TIP: In a Spring application, the ServletContext can be simply autowired into a service requiring it. 

For example: 

	@Autowired private ServletContext context;
	...
	InputStream inputStream = context.getResourceAsStream("/app/content/index.html");

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As a last word - be __very__ cautious when planning to use ServletContext.getRealPath(). Why? Just take a look here: http://stackoverflow.com/questions/12160639/what-does-servletcontext-getrealpath-mean-and-when-should-i-use-it