Java - Packaging, Archive, Library (JAR, WAR, EAR File)

For deployment purpose, J2EE applications are delivered and reside in Archive files (or unit).

A RAR, WAR or EAR file is a standard JAR (.jar) file with a .war or .ear extension. Each archive extension file denotes its purpose. A JAR (Java ARchive) file format is based on the standard ZIP file format with an optional manifest file.

A J2EE archive is composed of:

• one or more modules
• and a deployment descriptor

Using modules and JAR, WAR, EAR files makes it possible to assemble a number of different J2EE applications using some of the same components. No extra coding is needed; it is just a matter of assembling various J2EE modules into Java EE JAR, WAR, or EAR files.

You can create/archiving JAR files, either:

• by using the JAR utility directly,
• through an IDE such as Oracle JDeveloper, Eclipse, …
• or by using the ant utility and a build.xml file.

Creating a jar-file is not very difficult. But creating a startable jar-file needs more steps:

• create a manifest-file containing the start class,
• creating the target directory
• and archiving the files

echo Main-Class: com.gerardnico.HelloWorld>myManifest
md build\jar
jar cfm build\jar\HelloWorld.jar myManifest -C build\classes

The following command will unpack the archive in the current directory

jar xvf myArchive.ear

The following command will unpack all ear archive in the current directory

jar xvf *.ear

java -jar myJAR.jar

See The System class contains a means of loading files and libraries with the methods (load and loadlibrary). For a class, see Java - Class (Definition)

• See jar search

• https://creadur.apache.org/tentacles/ - Apache Tentacles™ will download all the archives from a staging repo, unpack them and create a little report of what is there.

An EAR file contains:

• Java EE modules
• and, optionally, deployment descriptors.

where:

• the directory META-INF contains the configuration files (deployment descriptors, manifest). <note tip>META-INF is WEB-INF for a Web module.</note>

A Java EE module consists of:

• one or more Java EE components for the same container type (Ejb, Web component, …)
• and, optionally, one component deployment descriptor of that type.

A Java EE module can be deployed as a stand-alone module.

Java EE modules are of the following types:

An EJB modules contain:

• class files for enterprise beans
• and an EJB deployment descriptor.

EJB modules are packaged as JAR files with a .jar extension.

Java - Web Application (Web Module) - War

Application client modules contain:

• class files
• and an application client deployment descriptor.

Application client modules are packaged as JAR files with a .jar extension.

Resource adapter modules contain:

• all Java interfaces,
• classes,
• native libraries,
• and other documentation,
• along with the resource adapter deployment descriptor.

Together, these implement the Connector architecture for a particular EIS.

Resource adapter modules are packaged as JAR files with an .rar (resource adapter archive) extension.

• The J2EE Tutorial - Packaging
• The j2EE tutorial
• Find a class somewhere inside dozens of JAR files?