software engineering Software engineering is a branch of both computer science and engineering focused on designing, developing, testing, and maintaining Application software, software applications. It involves applying engineering design process, engineering principl ...

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

Jakarta Server 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 ...

, Jakarta Servlets,

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

es,

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

files, tag libraries, static web pages (

HTML Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

and related files) and other resources that together constitute a

web application A web application (or web app) is application software that is created with web technologies and runs via a web browser. Web applications emerged during the late 1990s and allowed for the server to dynamically build a response to the request, ...

Content and structure

A WAR file may be digitally signed 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 (software development), artifact that is deployed to some Web container, container/engine. In the Java Platform, Enterprise Edition, a deployment descriptor describes how ...

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 applicat ...

URL A uniform resource locator (URL), colloquially known as an address on the Web, is a reference to a resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identi ...

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 Jakarta 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 class loader's

classpath Classpath is a parameter in the Java Virtual Machine or the Java compiler that specifies the location of user-defined classes and packages. The parameter may be set either on the command-line, or through an environment variable. Overview and ...

. (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 class loader's classpath.

References

External links