Apache Tomcat (Tomcat, formerly also Jakarta Tomcat)

8/2/2019 Apache Tomcat (Tomcat, formerly also Jakarta Tomcat)

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Jakarta Tomcat:

A look inside a servlet container


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What well cover:

History of Tomcat

Relationship to J2EE

Tomcat Features

Tomcat Architecture


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In the beginning..

Web servers serving static html

Web servers using cgi for dynamic content

Modules to handle dynamic content

Ex: Apache and Mod-Perl

Then along came servlets


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Web Containers Using Servlets

and JSPs

Java alternative to CGI

Servlets - Java with a bit of HTML thrown in

JSPs (JavaServer Pages) - HTML with a bit ofJava thrown in

JSP converted to a Servlet the first time accessed

Servlets stay in memory - big plus over CGI


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History of Tomcat

Java Web Server First servlet container

Created by Sun to demonstrate Servlet technology

Jserv Integrated with Apaches web server

Created by ASF (Apache Software Foundation)

Tomcat 3.x Merger of Java Web Server & Jserv

Reference implementation of Servlet & JSP specs


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History of Tomcat (cont)

Tomcat 4.0 released in 2001

Major architecture overhaul

Tomcat 5.x the most recent version

Builds on version 4

Updated to implement Suns latest Servlet & JSPspecifications


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How does this fit into J2EE?

What is J2EE? Java 2, Enterprise Edition

For creating distributed applications

Open standard created by Sun

For application servers and apps that connect to them

Components of a J2EE application server:

Deployment tools EJB container - session beans, entity beans

Servlet container - servlets and JSPs

Web server - html pages


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J2EE (cont)

Examples of J2EE application servers

BEA Weblogic

IBM WebsphereJboss

Tomcat & J2EE

Just implements the servlet container and webserver portions of the specification

Not a full-fledged application server


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Tomcat Features

Runs as a service (Windows) or daemon(Unix)

Run stand-alone or on beefier web server

Manager Application provides tools: Deploy, undeploy, list, start and stop applications

Shared hosting - handling multiple sites

Clustering - running multiple instances For scalability and availability


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How Does Tomcat Work?

Nested hierarchy of components:

Top-level components - containers

Nested components - reside in containers anddo not contain other components

Components are all configurable

Not all components are required


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Directory Structure

bin

Start and Stop Server

Scripts + useful Toolscommon

common used classesand libraries (Tomcat

and Applications)conf

Config files of Tomcat


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Directory Structure

logs

Logs all log files of

Tomcat

server

classes and libraries only

for Tomcat + system Web

applications, e.g. the

manager App or the

Admin Tool


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Directory Structure

shared

classes and libraries only forWeb applications

tempthe JVM temporary files putshere

webapps

contains all user-defined Webapplications

work

contains temporary files ofTomcat, e.g. to Servletscompiled JSP files


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Directory Structure


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Simple Servlet Container

Client1

Client2

Client3

Servlet1

Servlet2

Servlet Container


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Tomcat Components

Server

Service

Connectors

Engine

Realm

Valves

Logger

Host

Context


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The Major Components

Service - has one or more connectors

and one or more containersCatalina - the servlet container

Jasper - the JSP engine

Coyote - the web connector


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The Connector

Manages the connection between

applications and clients

Point at which client requests are received

Implements org.apache.catalina.Connector

Example implementations:

Coyote (HTTP) - the default

Apache Jserv Protocol (SSL)


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The Connector (cont)

Waits for incoming HTTP requests

Parses HTTP request headers

Creates request and response objects

Passes these objects to the container

Default port for HTTP apps is 8080 but can

change it to 80 for stand-alone mode


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The Container/Engine

Request processing component

Passes the request and response objects

from connector to the servlet

Implements org.apache.catalina.Container

Catalina is the default implementation


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The Container/Engine (cont)

Passes objects to the Servlet through service()

On first request for a servlet, the container:

loads the servlet classcalls the servlets init() method

calls servlets service() method

On subsequent requests for the servlet the

container only calls service()


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Servlet Lifecycle in Tomcat

Container instantiates the Servlet and callsinit()

Container gets a request and calls service()The Servlet receives HttpServletRequest

and HttpServletResponse objects

Servlet finds HTTP request data in therequest object - ex: form data, cookies,headers


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Servlet Lifecyle (cont)

Servlet processes the data and writes

output to the response object

Container passes the response object backto the connector

Connector sends reply back to client

Container calls destroy() before removing

a servlet instance


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Why Tomcat?

Highly configurable

Modular design

means you cancustomize it by

writing your own

modules

No longer just areference

implementation


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Server Configuration Reference

Configuration directives that can be included ina conf/server.xml file to configure the behaviorof the Tomcat 4 servlet/JSP container

The configuration element descriptions areorganized into the following major categories:

Top Level Elements - is theroot element of the entire configuration

file, while represents a groupof Connectors that is associated with anEngine.

Connectors - Represent the interfacebetween external clients sending requeststo (and receiving responses from) aparticular Service.

Containers - Represent componentswhose function is to process incoming

requests, and create the correspondingresponses. An Engine handles all requestsfor a Service, a Host handles all requestsfor a particular virtual host, and a Contexthandles all requests for a specific webapplication.

Nested Components - Representelements that can be nested inside theelement for a Container. Some elementscan be nested inside any Container, while

others can only be nested inside a Context


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The Server Component

A Server element represents the entire

Catalina servlet container. Therefore, it must

be the single outermost element in theconf/server.xml configuration file. Its

attributes represent the characteristics of the

servlet container as a whole.


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Common Attributes

All implementations ofServer support the

following attributes

Attribute DescriptionclassName Java class name of the implementation to use. This

class must implement the org.apache.catalina.Server

interface. If no class name is specified, the standardimplementation will be used

port The TCP/IP port number on which this server waitsfor a shutdown command. This connection must be

initiated from the same server computer that is

running this instance of Tomcat

shutdown The command string that must be received via aTCP/IP connection to the specified port number, inorder to shut down Tomcat


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Standard Implementation The standard implementation of

Server isorg.apache.catalina.core.StandardServer. It

supports the following additional attributes (in addition to

the common attributes listed above):

Attribute Description

debug The level of debugging detail logged by thisServer to the associated Logger. Higher numbers

generate more detailed output. If not specified, thedefault debugging detail level is zero (0).
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.html


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Nested Components

The following components may be nested

inside a Server element:

Service - One or more service element.GlobalNamingResources - Configure the

JNDI global resources for the server
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/globalresources.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/globalresources.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.html


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The Service Component

A Service element represents the

combination of one or more Connector

components that share a single Enginecomponent for processing incoming

requests. One or more Service elements

may be nested inside a Server element.
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/server.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/server.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.html


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Common Attributes

Attribute DescriptionclassName Java class name of the implementation to use. This class

must implement the org.apache.catalina.Service

interface. If no class name is specified, the standardimplementation will be used

name The display name of this Service, which will be included

in log messages if you utilize standard Catalina

components. The name of each Service that is associated

with a particular Server must be unique

S d d I l i Th d d i l i f
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/server.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/server.html


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Standard ImplementationThe standard implementation of

Service isorg.apache.catalina.core.StandardService. It

supports the following additional attributes (in addition to

the common attributes listed above):


debug The level of debugging detail logged by

this Service to the associated Logger.Higher numbers generate more detailed

output. If not specified, the default

debugging detail level is zero (0).
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.html


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Nested Components

The only components that may be nested

inside a Service element are one or more

Connector elements, followed by exactlyone Engine element
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.html


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The Context Container

The Context element represents a web application, which is run within aparticular virtual host

The web application used to process each HTTP request is selected byCatalina based on matching the Request URI against the context path of eachdefined Context. Once selected, that Context will select an appropriate

servlet to process the incoming request, according to the servlet mappingsdefined in the web application deployment descriptorfile (which MUST belocated at /WEB-INF/web.xml within the web app's directory hierarchy).

You may define as many Context elements as you wish, nested within aHost element in conf/server.xml. Each such Context MUST have a uniquecontext path, which is defined by the path attribute

In addition, you MUST define a Context with a context path equal to a zero-

length string. This Context becomes the defaultweb application for thisvirtual host, and is used to process all requests that do not match any otherContext's context path.

C Att ib t
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.html


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Common Attributes

All implementations of Context support the


Attribute DescriptionclassName Java class name of the implementation to use. This class

must implement the org.apache.catalina.Context

interface. If not specified, the standard value (definedbelow) will be used.

cookies Set to true if you want cookies to be used for session

identifier communication if supported by the client (this

is the default). Set to false if you want to disable the use

of cookies for session identifier communication, and rely

only on URL rewriting by the application

docBase The Document Base (also known as the Context Root)directory for this web application, or the pathname to the

web application archive file (if this web application is

being executed directly from the WAR file).

C Att ib t


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Common Attributes

All implementations of Context support the


Attribute Descriptionpath The context path of this web application, which is

matched against the beginning of each request URI to

select the appropriate web application for processing. Allof the context paths within a particular Host must be

unique. If you specify a context path of an empty string

(""), you are defining the default web application for this

Host, which will process all requests not assigned to

other Contexts
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.html


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The Engine Container

The Engine element represents the entire requestprocessing machinery associated with a particularCatalina Service. It receives and processes all

requests from one or more Connectors, andreturns the completed response to the Connectorfor ultimate transmission back to the client

Exactly one Engine element MUST be nested

inside a Service element, following all of thecorresponding Connector elements associatedwith this Service..

C Att ib t
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/service.html


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Common Attributes

All implementations of Engine support the

following attributes:


defaultHost The default host name, which identifies the Host thatwill process requests directed to host names on this

server, but which are not configured in this configurationfile. This name MUST match the name attributes of one

of the Host elements nested immediately inside

name Logical name of this Engine, used in log and errormessages
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.html


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Nested Components

You can nest one or more Host elements inside this Engine element,each representing a different virtual host associated with this server.At least one Host is required, and one of the nested Hosts MUSThave a name that matches the name specified for the defaultHostattribute, listed above

You can nest at most one instance of the following utilitycomponents by nesting a corresponding element inside your Engineelement Logger - Configure a logger that will receive and process all log

messages for this Engine, plus messages from Connectors associatedwith this Engine in the surrounding Service. In addition, this Logger will

log messages from subordinate Hosts and Contexts, unless overridden bya Logger configuration at a lower level.

Realm - Configure a realm that will allow its database of users, and theirassociated roles, to be shared across all Hosts and Contexts nested insidethis Engine, unless overridden by a Realm configuration at a lower level.
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/host.html


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The Host Container

The Host element represents a virtual host,

which is an association of a network name

for a server (such as"www.mycompany.com" with the

particular server on which Catalina is

running

C A ib


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Common AttributesAll implementations of Host support the following

attributes:


appBase The Application Base directory for this virtual host. Thisis the pathname of a directory that may contain web

applications to be deployed on this virtual host. You mayspecify an absolute pathname for this directory, or a

pathname that is relative to the $CATALINA_HOME

directory.

name Network name of this virtual host. One of the Hostsnested within an Engine MUST have a name that

matches the defaultHost setting for that Engine.
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/engine.html


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Nested Components

You can nest one or more Context elements inside this Hostelement, each representing a different web application associatedwith this virtual host. In addition, you can nest a singleDefaultContext element that defines default values forsubsequently deployed web applications.

You can nest at most one instance of the following utilitycomponents by nesting a corresponding element inside your Hostelement

Logger - Configure a logger that will receive and process alllog messages for this Host, plus messages from Contextsassociated with this Host .

Realm - Configure a realm that will allow its database ofusers, and their associated roles, to be shared across allContexts nested inside this Host
http://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/defaultcontext.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/realm.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/logger.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/defaultcontext.htmlhttp://jakarta.apache.org/tomcat/tomcat-4.1-doc/config/context.html


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References

How Tomcat Works: A Guide to DevelopingYour Own Java Servlet Container

(Kurniawan & Deck)

J2EE 1.4: The Big Picture (Haugland, Cade, & Orapallo)

Java Extreme Programming Cookbook (Burke & Coyner)

The Apache Jakarta Tomcat Website (http://jakarta.apache.org/tomcat/)

Tomcat-Einfuehrung.pdf
http://jakarta.apache.org/tomcat/http://jakarta.apache.org/tomcat/

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Apache Tomcat (Tomcat, formerly also Jakarta Tomcat)

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