With Java we generate .JAR files to bundle a set of resources. For J2EE web applications, we generate .WAR (Web Archive) files for deployments. Both of these are ways of archiving a set of files.Both these .jar or .war archives are in zip format. So there are plenty of ways to open those files to read the content. One way would be to use any tool that you use to open/extract a .zip file. Next will be to use the Jar command itself.
JAR Command
JAR (command) utility in Java can be used to open/extract these files as follows. Run following command from the folder where you need the content to be extracted by providing the path to the archive.
jar xf <path-to-file>
options:
x - extract the files
f - file to extract
jar xf myWebApp.war
jar xf myProject.jar
Related : Open and read a file inside a war file of a web application with Java