Apache Tomcat (called "Tomcat" for short) is a
free and open-source
Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...
implementation of the
Jakarta Servlet,
Jakarta Expression Language
The Jakarta Expression Language (EL; formerly Expression Language and Unified Expression Language) is a special purpose programming language mostly used in Jakarta EE web applications for embedding and evaluating expressions in web pages.
The s ...
, and
WebSocket technologies. It provides a "pure Java"
HTTP
The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...
web server
A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initia ...
environment in which
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 ...
code can also run. Thus it's a Java web application server, although not a full JEE application server.
Tomcat is developed and maintained by an open community of developers under the auspices of the
Apache Software Foundation
The Apache Software Foundation (ASF) is an American nonprofit corporation (classified as a 501(c)(3) organization in the United States) to support a number of open source software projects. The ASF was formed from a group of developers of the ...
, released under the
Apache License 2.0 license.
Components
Tomcat 4.x was released with Catalina (a servlet container), Coyote (an HTTP connector) and Jasper (a
JSP engine).
Catalina
Catalina is Tomcat's
servlet container
A web container (also known as a servlet container;
and compare "webcontainer"
) is the component of a web server that interacts with Jakarta Servlets. A web container is responsible for managing the lifecycle of servlets, mapping a URL to a par ...
. Catalina implements
Sun Microsystems
Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...
' specifications for
servlet and JavaServer Pages (JSP). In Tomcat, a Realm element represents a "database" of usernames, passwords, and roles (similar to
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, ...
groups) assigned to those users. Different implementations of Realm allow Catalina to be integrated into environments where such authentication information is already being created and maintained, and then use that information to implement Container Managed Security as described in the Servlet Specification.
Coyote
Coyote is a Connector component for Tomcat that supports the HTTP 1.1 and 2 protocol as a web server. This allows Catalina, nominally a Java Servlet or JSP container, to also act as a plain web server that serves local files as HTTP documents. Coyote listens for incoming connections to the server on a specific
TCP port and forwards the request to the Tomcat Engine to process the request and send back a response to the requesting client. Another Coyote Connector, Coyote JK, listens similarly but instead forwards its requests to another web server, such as Apache, using the
JK Protocol. This usually offers better performance.
Jasper
Jasper is Tomcat's JSP Engine. Jasper
parses JSP files to compile them into Java code as servlets (that can be handled by Catalina). At runtime, Jasper detects changes to JSP files and recompiles them.
As of version 5, Tomcat uses Jasper 2, which is an implementation of the Sun Microsystems' JSP 2.0 specification. From Jasper to Jasper 2, important features were added:
* JSP Tag library pooling – Each tag markup in JSP file is handled by a tag handler class. Tag handler class objects can be pooled and reused in the whole JSP servlet.
* Background JSP compilation – While recompiling modified JSP Java code, the older version is still available for server requests. The older JSP servlet is deleted once the new JSP servlet has finished being recompiled.
* Recompile JSP when included page changes – pages can be inserted and included into a JSP at runtime. The JSP will not only be recompiled with JSP file changes but also with included page changes.
* JDT Java compiler – Jasper 2 can use the Eclipse JDT (Java Development Tools) Java compiler instead of
Ant and
javac
javac (pronounced "java-see") is the primary Java compiler included in the Java Development Kit (JDK) from Oracle Corporation. Martin Odersky implemented the GJ compiler, and his implementation became the basis for javac.
The compiler accept ...
.
Three new components were added with the release of Tomcat 7:
Cluster
This component has been added to manage large applications. It is used for
load balancing that can be achieved through many techniques. Clustering support currently requires the JDK version 1.5 or higher.
High availability
A high-availability feature has been added to facilitate the scheduling of system upgrades (e.g. new releases, change requests) without affecting the live environment. This is done by dispatching live traffic requests to a temporary server on a different port while the main server is upgraded on the main port. It is very useful in handling user requests on high-traffic web applications.
Features
Tomcat 8.x implements the Servlet 3.1 and JSP 2.3 Specifications. Apache Tomcat 8.5.x is intended to replace 8.0.x and includes new features pulled forward from Tomcat 9.0.x. The minimum Java version and implemented specification versions remain unchanged.
Tomcat 9.x implements the Servlet 4.0 and JSP 2.3 Specifications.
Tomcat 10.0.x implements the Servlet 5.0 and JSP 3.0 Specifications.
Tomcat 10.1.x implements the Servlet 6.0 and JSP 3.1 Specifications.
History
Tomcat started off as a servlet
reference implementation by
James Duncan Davidson
James Duncan Davidson is an American software developer and photographer. He's currently the Technology Advisor to Tobias Lütke, CEO of Shopify.
While a software engineer at Sun Microsystems (1997–2001), Davidson created Tomcat, a Java-bas ...
, a software architect at Sun Microsystems. He later helped make the project
open-source
Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized so ...
and played a key role in its donation by Sun Microsystems to the Apache Software Foundation. The
Apache Ant software build automation tool was developed as a side-effect of the creation of Tomcat as an open source project.
Davidson had initially hoped that the project would become open-sourced and, since many open-source projects had
O'Reilly books associated with them featuring an animal on the cover, he wanted to name the project after an animal. He came up with ''Tom
cat'' since he reasoned the animal represented something that could fend for itself. Although the tomcat was already in use for another O'Reilly title, his wish to see an animal cover eventually came true when O'Reilly published their Tomcat book with a
snow leopard on the cover in 2003.
Releases
Apache TomEE
Apache TomEE (pronounced "Tommy") is the
Java Enterprise Edition of Apache Tomcat (Tomcat + Java EE = TomEE) that combines several Java enterprise projects including
Apache OpenEJB, Apache OpenWebBeans,
Apache OpenJPA
OpenJPA is an open source implementation of the Java Persistence API specification. It is an object-relational mapping (ORM) solution for the Java language, which simplifies storing objects in databases. It is open-source software distributed und ...
,
Apache MyFaces
Apache MyFaces is an Apache Software Foundation project that creates and maintains an open-source JavaServer Faces implementation, along with several libraries of JSF components that can be deployed on the core implementation. The project is divi ...
and others. In October 2011, the project obtained certification by
Oracle Corporation
Oracle Corporation is an American multinational computer technology corporation headquartered in Austin, Texas. In 2020, Oracle was the third-largest software company in the world by revenue and market capitalization. The company sells da ...
as a compatible implementation of the Java EE 6 Web Profile.
See also
*
WildFly
WildFly, formerly known as JBoss AS, or simply JBoss, is an application server written by JBoss, now developed by Red Hat. WildFly is written in Java and implements the Java Platform, Enterprise Edition (Java EE) specification. It runs on mu ...
, formerly known as JBoss Application Server
*
Jetty (web server)
*
GlassFish, the
reference implementation of Jakarta EE (and Java EE before that), supporting
EJB
Jakarta Enterprise Beans (EJB; formerly Enterprise JavaBeans) is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component that encapsulates business logic of an application. An EJB web co ...
,
JPA,
JSF,
JMS,
Java RMI
In computing, the Java Remote Method Invocation (Java RMI) is a Java API that performs remote method invocation, the object-oriented equivalent of remote procedure calls (RPC), with support for direct transfer of serialized Java classes and ...
, JSP, servlets etc.
*
Comparison of web server software
Related software that is now obsolete or defunct:
*
MuleSoft, producer of Tcat, an enterprise Tomcat server
*
Apache Geronimo, an application server that can use Tomcat as its web container
*
Resin (software), an application server from
Caucho Technology
Caucho Technology is based in San Diego, CA. It is an information technology company that produces web server software and application server software as well as the originators of Quercus and Hessian open source projects.
Caucho Technology was ...
*
JOnAS
Jonas may refer to:
Geography
* Jonas, Netherlands, Netherlands
* Jonas, Pennsylvania, United States
* Jonas Ridge, North Carolina, United States
People with the name
* Jonas (name), people with the given name or surname Jonas
* Jonas, one of ...
, an application server that can use Tomcat as its web container
*
Apache OpenEJB can be added to Tomcat to turn it into a JavaEE server
References
Bibliography
*
*
*
*
External links
*
{{Web server software
Tomcat
Java enterprise platform
Free software programmed in Java (programming language)
Free web server software
Cross-platform free software
Software using the Apache license
Web server software programmed in Java