Difference between .JAR and .WAR packaging in JAVA

Eya Filali — Fri, 21 Nov 2025 12:38:30 +0000

1. JAR packaging
A JAR (Java ARchive) file is a compressed archive that can contain compiled .class files, resources, libraries, and metadata.
It is used to package Java applications or libraries into a single file.
2. WAR packaging
A WAR (Web Application Archive) file is used to package Java web applications.
It contains everything needed to deploy a web app on a Servlet/JSP container (such as Apache Tomcat, Jetty, or GlassFish).
WAR files are specifically designed for web application deployments.

3. Key differences
The key difference is their purpose and the way they function. JAR files allow us to package multiple files in order to use them as a library, plugin, or any kind of application. On the other hand, WAR files are only used for web applications.
The structure of the archives is also different. We can create a JAR with any desired structure. In contrast, WAR has a predefined structure.
Finally, we can run a JAR from the command line if we build it as an executable JAR without using additional software, or we can use it as a library. In contrast, we need a server to execute a WAR.

Understanding JDK, JRE, and JVM (Clear & Simple Explanation)

Eya Filali — Fri, 21 Nov 2025 12:19:01 +0000

1. What is the JDK?
The Java Development Kit (JDK) is a collection of software tools used to develop, compile, and run Java programs.
It includes:

JRE (for running Java programs)
Development tools such as: [ javac : java compiler / jdb: java debuggr] and other utilities used during the development.

2. What is the JRE?
The Java Runtime Environment (JRE) is needed only to run Java applications.
You don’t need the JDK unless you want to compile code.
The JRE contains:

JVM (Java Virtual Machine)
Java class libraries (e.g., networking, collections, I/O)
Other runtime components

3. What is the JVM?
The Java Virtual Machine (JVM) is the core execution engine of java. It is responsible for compiling your Java code (.java file) to bytecode (.class file) and then into native machine code.

DEV Community: Eya Filali

Difference between .JAR and .WAR packaging in JAVA

Understanding JDK, JRE, and JVM (Clear & Simple Explanation)