EAR (file format)

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Enterprise Archive
Filename extension
.ear
file archive, data compression
Extended fromJAR

EAR (Enterprise Application aRchive) is a

modules onto an application server happens simultaneously and coherently. It also contains XML files called deployment descriptors
which describe how to deploy the modules.

Ant, Maven, or Gradle can be used to build EAR files.

File structure

An EAR file is a standard

Zip
file) with an .ear extension, with one or more entries representing the modules of the application, and a metadata directory called META-INF which contains one or more deployment descriptors.

Module

Developers can embed various artifacts within an EAR file for deployment by application servers:

Class isolation

Most application servers load classes from a deployed EAR file as an isolated tree of Java

classloaders
, isolating the application from other applications, but sharing classes between deployed modules. For example, a deployed WAR file would be able to create instances of classes defined in a JAR file that was also included in the containing EAR file, but not necessarily those in JAR files in other EAR files. One key reason for this behavior is to allow complete separation between applications which use static singletons (e.g. Log4J), which would otherwise confuse the configuration between separate applications. This also enables different versions of applications and libraries to be deployed side by side.

The

JBoss
application servers before Version 5 were notable in that it does not isolate deployed components. A web application deployed in one EAR file would have access to classes in other EAR and WAR files. This is a somewhat controversial policy. The Unified Classloader design reduces communications overhead between running applications, as class data can be shared by reference or simple copies. It also allows developers to avoid having to understand the problems that a tree of classloaders can create. However, it prevents different versions of dependent libraries from being deployed in separate applications. JBoss 4.0.2 switched to a hierarchical classloader, but in version 4.0.3 it reverted to a Unified Classloader for backwards compatibility reasons. There is now a configuration option to change this behavior. JBoss 5.x, 6.x and 7.x no longer use Unified Classloading.

META-INF directory

The META-INF directory contains at least the application.xml deployment descriptor, known as the Java EE Deployment Descriptor. It contains the following XML entities:

  • icon, which specifies the locations for the images that represent the application. A subdivision is made for small-icon and large-icon.
  • display-name, which identifies the application
  • description
  • A module element for each module in the archive
  • Zero or more security-role elements for the global security roles in the application

Each module element contains an ejb, web or java element which describes the individual modules within the application. Web modules also provide a context-root which identifies the web module by its URL.

Next to the Jakarta EE deployment descriptor there can be zero or more runtime deployment descriptors. These are used to configure implementation-specific Jakarta EE parameters.

See also

External links