software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term ' ...

, a WAR file (Web Application Resource or Web application ARchive) is a file used to distribute a collection of JAR-files,

JavaServer Pages Jakarta Server Pages (JSP; formerly JavaServer Pages) is a collection of technologies that helps software developers create dynamically generated web pages based on HTML, XML, SOAP, or other document types. Released in 1999 by Sun Microsystems, J ...

Java Servlet A Jakarta Servlet (formerly Java Servlet) is a Java software component that extends the capabilities of a server. Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applicatio ...

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

classes,

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. ...

files, tag libraries, static web pages (

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...

and related files) and other resources that together constitute a

web application A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection. History In earlier computing models like client-serve ...

Content and structure

A WAR file may be

digitally signed A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created b ...

in the same way as a JAR file in order to allow others to determine where the source code came from. There are special files and directories within a WAR file: * The /WEB-INF directory in the WAR file contains a file named

web.xml A deployment descriptor (DD) refers to a configuration file for an artifact that is deployed to some container/engine. In the Java Platform, Enterprise Edition, a deployment descriptor describes how a component, module or application (such as ...

which defines the structure of the web application. If the web application is only serving JSP files, the web.xml file is not strictly necessary. If the web application uses servlets, then the servlet container uses web.xml to ascertain to which

servlet A Jakarta Servlet (formerly Java Servlet) is a Java software component that extends the capabilities of a server. Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applicatio ...

URL A Uniform Resource Locator (URL), colloquially termed as a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifie ...

request will be routed. The web.xml file is also used to define context variables which can be referenced within the servlets and it is used to define environmental dependencies which the deployer is expected to set up. An example of this is a dependency on a mail session used to send email. The servlet container is responsible for providing this service.

Advantages of WAR files

* Easy testing and deployment of web applications * Easy identification of the version of the deployed application * All Java EE containers support WAR files * MVC structure supports WAR files. Assuming production environments do not promote a fix without sufficient testing prior to deployment, a WAR file has a distinct advantage when properties files are used to identify environment specific variables. For example, an LDAP server in a testing environment may be something like ldaps://testauth.example.com:636. The LDAP server in a production environment is ldaps://auth.example.com:636. An external properties file would define the link with some thing like: LINKED_PAGE=ldaps://testauth.example.com:636 The source code reads the property file to determine the target LDAP server. In this way, developers can be certain that the WAR file tested and verified is exactly the same as that which is being promoted to production.

Disadvantages of WAR files

Some consider web deployment using WAR files to be disadvantageous when minor changes to source code are required for dynamic environments. Each change to source code must be repackaged and deployed in development. This does not require stopping the web server if configured for runtime deployment.

Example

The following sample ''web.xml'' file demonstrates the declaration and association of a

HelloServlet

mypackage.HelloServlet

HelloServlet

/HelloServlet

Resource reference to a factory for javax.mail.Session instances that may be used for sending electronic mail messages, preconfigured to connect to the appropriate SMTP server.

mail/Session

javax.mail.Session

Container

The /WEB-INF/classes directory is on the ClassLoader's classpath. (The classpath consists of a list of locations from which .class files can be loaded and executed by the JVM.) The /WEB-INF/classes directory contains the classes associated with the web application itself. Any JAR files placed in the /WEB-INF/lib directory will also be placed on the ClassLoader's classpath.

References

External links