JAR vs WAR | Generated by AI
In Java packaging, JAR (Java ARchive) and WAR (Web ARchive) are both archive file formats based on the ZIP structure, but they serve distinct purposes and have different characteristics. Below is a detailed explanation of their differences:
1. Purpose
- JAR: A JAR file is a general-purpose archive used to package Java classes, libraries, or standalone applications. It’s commonly employed to distribute reusable libraries (e.g., utility classes) or executable Java programs that can run on the Java Virtual Machine (JVM).
- WAR: A WAR file is specifically designed for web applications. It packages all components needed for a web app, such as servlets, JSPs (JavaServer Pages), HTML, CSS, JavaScript, and configuration files, into a single unit for deployment on a web server or application server (e.g., Apache Tomcat, JBoss).
2. Contents
- JAR: Contains Java class files (
.class), aMANIFEST.MFfile (under theMETA-INFdirectory) that provides metadata (e.g., the main class for executable JARs), and optional resources like configuration files, images, or property files. - WAR: Includes web-specific components with a defined structure:
- WEB-INF/: A mandatory directory containing:
web.xml(deployment descriptor for configuring servlets, mappings, etc.),classes/(compiled Java classes),lib/(JAR files used as dependencies by the web app).
- Static resources (e.g., HTML, CSS, JavaScript) typically reside in the root directory or subdirectories outside
WEB-INF, though JSPs may be placed insideWEB-INFto restrict direct access.
- WEB-INF/: A mandatory directory containing:
3. Structure
- JAR: Has a flat structure, primarily consisting of class files and resources, with the manifest file specifying metadata. Example:
myapp.jar ├── META-INF/ │ └── MANIFEST.MF ├── com/ │ └── example/ │ └── MyClass.class └── resources/ └── config.properties - WAR: Follows a hierarchical structure tailored for web applications. Example:
mywebapp.war ├── index.html ├── css/ │ └── style.css ├── WEB-INF/ │ ├── web.xml │ ├── classes/ │ │ └── com/ │ │ └── example/ │ │ └── MyServlet.class │ └── lib/ │ └── dependency.jar
4. Deployment and Usage
- JAR:
- Included in an application’s classpath to provide libraries or reusable code.
- If executable (with a
Main-Classspecified in the manifest), it can be run directly usingjava -jar myapp.jar.
- WAR:
- Deployed to a servlet container or application server (e.g., Tomcat), which unpacks it and makes the web application accessible at a specific URL (context path).
- Not executable standalone; it relies on the server to manage its lifecycle.
5. Dependency Handling
- JAR: Does not inherently contain other JARs; dependencies are managed externally (e.g., via the classpath or build tools like Maven).
- WAR: Can bundle dependent JARs inside the
WEB-INF/lib/directory, ensuring the web application uses specific versions of libraries, isolated from other applications on the same server.
6. Creation
Both JAR and WAR files can be created using the jar command-line tool from the JDK or modern build tools like Maven or Gradle:
- JAR Example:
jar cvf myapp.jar -C classes . - WAR Example:
jar cvf mywebapp.war .(assuming the directory is structured withWEB-INF, etc.). - In Maven, the packaging type is specified in the
pom.xml:<packaging>jar</packaging>for JAR.<packaging>war</packaging>for WAR.
Summary Table
| Feature | JAR | WAR |
|---|---|---|
| Full Name | Java ARchive | Web ARchive |
| Purpose | Libraries, standalone apps | Web applications |
| Contents | Classes, manifest, resources | Servlets, JSPs, HTML, WEB-INF, etc. |
| Structure | Flat | Hierarchical (WEB-INF, etc.) |
| Deployment | Classpath or java -jar |
Web server (e.g., Tomcat) |
| Dependencies | External | Bundled in WEB-INF/lib/ |
Key Takeaway
In essence, a JAR is a versatile archive for general Java code, while a WAR is a specialized archive for web applications, complete with a structure and components tailored for deployment on a web server. Understanding their distinct roles ensures proper use in Java development and deployment scenarios.