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What is ear war?

Published in Java EE Packaging 6 mins read

The question "What is ear war?" appears to combine two distinct terms related to Java EE (now Jakarta EE) application packaging: EAR and WAR. These are critical components for deploying enterprise and web applications, respectively.

What are EAR and WAR Files?

EAR (Enterprise Archive) and WAR (Web Application Archive) files are standard Java EE packaging formats. While a WAR file specifically bundles a web application, an EAR file is designed to contain a complete enterprise application, often encompassing multiple WAR files along with other modules.

Understanding EAR Files

What is an EAR File?

An EAR file stands for Enterprise Archive. It is a JAR file with a .ear extension used for deploying Java EE applications onto an application server. EAR files are intended to contain complete enterprise applications.

In this context, an enterprise application is defined as:

  • A collection of .jar files (for business logic, utility classes, EJB modules).
  • Resources.
  • Classes.
  • Multiple Web applications (WARs).

This packaging allows for the deployment of complex, multi-module enterprise applications as a single, cohesive unit.

Structure and Contents of an EAR

A typical EAR file has a structured directory layout:

  • META-INF/application.xml: The deployment descriptor for the entire enterprise application, defining the modules contained within the EAR.
  • JAR Modules: Contains EJB (Enterprise JavaBeans) modules, utility JARs with shared business logic or libraries, and client application JARs.
  • WAR Modules: Contains one or more Web Application Archives, each representing a distinct web application.
  • RAR Modules: (Resource Adapter Archives) for connecting to enterprise information systems (EIS).
  • Other Resources: Any additional files or configurations needed by the application.

Benefits of Using EAR Files

  • Centralized Deployment: Simplifies the deployment of complex applications with multiple components (web, EJB, etc.) as a single unit.
  • Dependency Management: Allows sharing common libraries and resources among different modules (e.g., WARs and EJB JARs) within the same EAR.
  • Unified Lifecycle Management: The entire enterprise application can be started, stopped, and managed as one entity on the application server.
  • Security Configuration: Centralized security settings can be applied across all contained modules.

Understanding WAR Files

What is a WAR File?

A WAR file stands for Web Application Archive. It is a JAR file with a .war extension specifically designed to package a single web application. These web applications are typically built using technologies like Servlets, JavaServer Pages (JSPs), HTML, CSS, and JavaScript.

Structure and Contents of a WAR

A WAR file adheres to a well-defined structure:

  • WEB-INF/: This directory contains application-specific resources that are not directly exposed to the client.
    • WEB-INF/web.xml: The deployment descriptor for the web application, configuring servlets, filters, listeners, and other web components.
    • WEB-INF/classes/: Contains compiled Java servlet classes and other application-specific classes.
    • WEB-INF/lib/: Stores JAR files of third-party libraries or utility classes required by the web application.
  • Static Content: HTML files, CSS stylesheets, JavaScript files, images, and other static resources.
  • JSP Files: JavaServer Pages that generate dynamic web content.

When to Use WAR Files

  • Standalone Web Applications: Ideal for deploying a single web application that doesn't require complex enterprise services (like EJBs) or integration with other modules.
  • Web Containers: WARs can be deployed directly onto web containers like Apache Tomcat, which primarily handle HTTP requests and serve web content.

The Relationship Between EAR and WAR Files

The key relationship is that an EAR file acts as a container for one or more WAR files, along with other enterprise modules. This hierarchical structure is fundamental to Java EE application architecture.

EAR as a Container for WARs

An enterprise application, as defined by an EAR, can include several distinct web applications (each packaged as a WAR) that might share common business logic or data access layers packaged in separate JAR files within the same EAR. For example, a banking enterprise application might have:

  • One WAR file for the customer-facing online banking portal.
  • Another WAR file for an internal administration panel.
  • Shared JAR files containing the core business logic (e.g., account management) and persistence layers used by both web applications.

All these components would be bundled together in a single EAR file for deployment.

Deployment Scenarios

  • Standalone WAR Deployment: For simpler web applications, a WAR file can be deployed directly to a web server or servlet container (like Tomcat or Jetty).
  • Enterprise Application Deployment (using EAR): For larger, multi-module applications requiring transactional integrity, security services, or integration with Enterprise JavaBeans, deploying an EAR to a full-fledged application server (like WildFly, WebLogic, or WebSphere) provides a unified and managed environment.

Key Differences and Complementary Roles

Feature EAR (Enterprise Archive) WAR (Web Application Archive)
Full Name Enterprise Archive Web Application Archive
Primary Purpose Packages complete enterprise applications, potentially with multiple modules. Packages a single web application.
Contents JARs (EJB, utility), WARs, RARs, resources, classes. Servlets, JSPs, HTML, CSS, JavaScript, images, web.xml.
Scope Application level; manages various types of modules. Web module level; handles HTTP-related components.
Deployment Deployed on an application server (e.g., WildFly, WebLogic, WebSphere). Can be deployed directly on a web container (e.g., Tomcat) or within an EAR on an application server.
Contains WARs? Yes, can contain multiple WAR files. No, cannot contain other WARs or EARs.
Specification Java EE / Jakarta EE Application Specification Java EE / Jakarta EE Web Application Specification

Practical Insights and Examples

Consider a large-scale e-commerce platform. Such a system might be packaged as an EAR file containing:

  • Storefront.war: The customer-facing web application for browsing products, adding to cart, and checkout.
  • AdminPanel.war: An internal web application for managing products, orders, and customer data.
  • BusinessLogic.jar: An EJB JAR or a simple utility JAR containing core business logic for order processing, inventory management, and user authentication, shared by both web applications.
  • Persistence.jar: A JAR containing JPA entities and data access objects (DAOs) for database interaction.
  • PaymentGateway.rar: A resource adapter for integrating with an external payment processing system.

This structure allows the different components to be developed and managed somewhat independently while still being deployed and functioning as a single, coherent application. The EAR ensures all necessary dependencies are met and deployed together, simplifying the overall application lifecycle.

For more detailed information, refer to the Jakarta EE documentation.

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