Apache Overview HOWTO
Daniel Lopez Ridruejo, ridruejo@apache.org
v0.9, 2002-10-10
This document gives you an overview of the different Apache projects,
such as the Apache HTTP server and the Tomcat Servlet and JSP engine.
It provides pointers for further information and implementation
details.
______________________________________________________________________
Table of Contents
1. Introduction
1.1 Apache Software Foundation
1.2 Structure of this document
2. Apache
2.1 Architecture
2.1.1 2.1.1 Apache 1.3
2.1.1.1 Process-based Web server
2.1.1.2 Windows support
2.1.1.3 Modular
2.1.2 2.1.2 Apache 2.0
2.1.2.1 Multi Processing Modules
2.1.2.2 Protocol Modules
2.1.2.3 Module and filter architecture.
2.1.2.4 Compatibility issues
2.1.2.5 Portable
2.2 Security
2.2.1 Authentication
2.2.2 Access Control
2.2.3 SSL/TLS
2.3 Proxy
2.4 Performance and scalability
2.4.1 Load Balancing
2.4.2 Compression
2.5 CGI scripts
2.6 Development Platform Integration
2.6.1 Perl
2.6.2 PHP
2.6.3 Python
2.6.4 Tcl
2.6.5 Microsoft technologies
2.6.5.1 .Net
2.6.5.2 ASP
2.6.5.3 ISAPI
2.6.6 Java
2.6.7 Modules for other languages
2.7 Management
2.7.1 Build tools
2.7.2 User Interfaces for Apache
2.7.3 SNMP
2.8 Publishing
2.9 Protocol modules
2.10 Virtual Hosting
2.11 Commercial support
3. ASF Projects
3.1 Applications and Frameworks
3.1.1 3.1.1 Servers
3.1.1.1 Tomcat
3.1.1.2 JAMES (Java Apache Mail Enterprise Server)
3.1.1.3 Lucene
3.1.1.4 Jetspeed
3.1.2 3.1.2 Content management
3.1.2.1 Slide
3.1.2.2 Alexandria
3.1.3 3.1.3 Frameworks
3.1.3.1 Turbine
3.1.3.2 Avalon
3.2 Presentation
3.2.1 Cocoon
3.2.2 Velocity
3.2.3 AxKit
3.2.4 Xalan
3.2.5 FOP
3.3 Parsers and Document Access libraries
3.3.1 Xerces
3.3.2 Batik
3.3.3 POI
3.4 Interoperability
3.4.1 SOAP
3.4.2 XML-RPC
3.4.3 XML security
3.5 Development
3.5.1 Apache Portable Runtime
3.5.2 Ant
3.5.3 Byte Code Library
3.5.4 Log4j
3.5.5 ORO and Regexp
3.5.6 Struts
3.5.7 Taglibs
3.5.8 Database
3.5.9 Commons
3.6 Testing
3.6.1 httpd-test
3.6.2 Cactus
3.6.3 JMeter
3.6.4 Lakta
3.6.5 Watchdog
4. Where to find more information
4.1 Websites
4.2 Books
4.3 Support forums
5. Contacting the Author
5.1 Translations
6. Open Content Open Publication License
6.1 REQUIREMENTS ON BOTH UNMODIFIED AND MODIFIED VERSIONS
6.2 COPYRIGHT
6.3 SCOPE OF LICENSE
6.4 REQUIREMENTS ON MODIFIED WORKS
6.5 GOOD-PRACTICE RECOMMENDATIONS
6.6 LICENSE OPTIONS
______________________________________________________________________
1. Introduction
This document gives you an overview of the Apache world, including
Apache Software Foundation projects such as the Apache web server and
commercial and open source third party software. Apache is the most
popular server on the Internet <http://www.netcraft.com/survey/>. New
Apache users, especially those coming from a Windows background, are
often unaware of the possibilities of Apache, its useful addons and,
more in general, how everything works together. This document aims to
show a general picture of such possibilities with a brief description
of each one and pointers for further information. The information has
been gathered from many sources, including projects' web pages,
conference talks, mailing lists, Apache websites and my own hands-on
experience. Full credit is given to these authors. Without them and
their work, this document would not have been possible or necessary.
Copyright 2002 Daniel Lopez Ridruejo
Permission is granted to copy, distribute and/or modify this document
under the terms of the Open Content Open Publication License, Version
1.1. A copy of the license is included in the appendix entitled "Open
Content Open Publication License", or at www.opencontent.org/openpub/.
1.1. Apache Software Foundation
The Apache Software Foundation provides support for the Apache
community of open-source software projects. The Apache projects are
characterized by a collaborative, consensus based development process,
an open and pragmatic software license, and a desire to create high
quality software that leads the way in its field. We consider
ourselves not simply a group of projects sharing a server, but rather
a community of developers and users.
The ASF is home to many successful Open Source projects, such as the
Tomcat Servlet/JSP engine and the ANT build tool.
You can learn more about the foundation here
<http://www.apache.org/foundation/>.
1.2. Structure of this document
The first part of this document deals with the Apache Web Server and
related modules. It covers the history, architecture and capabilities
of the server and describes ways in which you can extend and customize
it.
The second part of this document covers projects of the Apache
Software Foundation, such as those form the Jakarta and Java XML
communities. Rather than organizing the projects around a certain
programming language or technology, they are organized based on
functionality provided.
2. Apache
Apache is the leading internet web server, with over 60% market share,
according to the Netcraft survey <http://www.netcraft.com/survey>.
Several key factors have contributed to Apache's success:
· The Apache license <http://www.apache.org/LICENSE.txt>. It is an
open source, BSD-like license that allows for both commercial and
non-commercial uses of Apache.
· Talented community of developers
<http://www.apache.org/foundation/members.html> with a variety of
backgrounds and an open development process based on technical
merits.
· Modular architecture. Apache users can easily add functionality or
tailor Apache to their specific enviroment.
· Portable: Apache runs on nearly all flavors of Unix (and Linux),
Windows, BeOs, mainframes...
· Robustness and security.
Many commercial vendors have adopted Apache-based solutions for
their products, including Oracle <http://www.oracle.com>, Red Hat
<http://www.redhat.com> and IBM <http://www.ibm.com>. In addition,
Covalent <http://www.covalent.net> provides add-on modules and 24x7
support for Apache.
The following websites use Apache or derivatives. Chances are that if
Apache is good enough for them, it is also good enough for you :)
· Amazon.com <http://www.amazon.com>
· Yahoo! <http://www.yahoo.com>
· W3 Consortium <http://www.w3c.org>
· Financial Times <http://www.ft.com>
· Apple <http://www.apple.com>
· MP3.com <http://www.mp3.com>
· Stanford <http://www.stanford.edu>
>From the Apache website <http://httpd.apache.org>:
The Apache HTTP Server Project is an effort to develop and maintain an
open-source HTTP server for modern operating systems including UNIX
and Windows NT. The goal of this project is to provide a secure,
efficient and extensible server that provides HTTP services in sync
with the current HTTP standards.
Apache started its life as modifications to the NCSA Web server, one
of the first HTTP servers. You can learn more about Apache's history
here <http://httpd.apache.org/ABOUT_APACHE.html>:
The Apache project has grown beyond building just a web server into
developing other critical server side technologies. The Apache
Software Foundation, described in a later section, serves as an
umbrella for these projects.
2.1. Architecture
There are two main versions of Apache, the 1.3 series and the 2.0
series. Although both versions are considered production quality, they
differ in architecture and capabilities.
2.1.1. 2.1.1 Apache 1.3
Apache 1.3 has been ported to a great variety of Unix platforms and is
the most widely deployed Web server on the Internet.
2.1.1.1. Process-based Web server
Apache 1.3 on Unix is a process-based Web server. The Apache program
forks several children at startup. Forking means that a parent process
makes identical copies of itself, called children. Each one of the
children can serve a request independent of the others. This approach
has the advantage of improved stability: If one of the children
misbehaves (runs out of control or has memory leaks) it can be
terminated without affecting the others. The stability comes with a
performance penalty. In most Unix operating systems, creating
processes and context switching (assigning processor time to each
process) are expensive operations. Since processes are isolated from
each other, they cannot easily share code and data, consuming system
resources.
2.1.1.2. Windows support
Apache 1.3 is the first version of Apache to support Windows, although
the port is not considered to be as stable as its Unix counterparts.
This is due to the fact that the server had been designed with Unix in
mind and the Windows port was a later addition that did not integrate
very well.
2.1.1.3. Modular
Apache 1.3 has a modular architecture. You can enable or disable
modules to add and remove Web server functionality. You can customize
Apache to improve performance and security. In addition to modules
bundled with the server, there is a great number of third party
modules, providing extended functionality.
2.1.2. 2.1.2 Apache 2.0
Apache 2.0 is the latest and greatest version of the Apache server.
The architecture contains significant improvements over the 1.3
series. The following are some of them.
2.1.2.1. Multi Processing Modules
Apache 2.0 abstracts the request processing architecture in special
server modules, called Multi Processing modules (MPMs). This means
that Apache can be configured to be a pure process-based server, a
purely threaded server or a mixture of those models. Threads are
contained inside processes and run simultaneously. Unlike processes,
threads can share data and code. Threads are thus more "lighweight"
than processes, and in most cases threaded servers scale better than
process based servers. The disadvantage is that the server is less
reliable, since if a thread misbehaves it can corrupt data or code
belonging to other threads.
2.1.2.2. Protocol Modules
The protocol handling has been encapsulated in its own layer in Apache
2.0. That means it is possible to write modules to serve protocols
other than HTTP, such as POP3 for mail or FTP for file transfer. These
protocol modules can take advantage of a solid server framework and
module functionality, such as authentication and dynamic content
generation. This means that, for example, you can authenticate your
POP3 users against the same user database Apache uses for web requests
and that FTP content can be generated dynamically using PHP, CGI or
any other technologies explained later in this document.
2.1.2.3. Module and filter architecture.
Apache 2.0 maintains the 1.3 modular architecture and adds an
additional extension mechanism: filters. Filters allow modules to
modify the content generated by other modules. They can encrypt, scan
for viruses or compress not only static files but dynamically
generated content.
2.1.2.4. Compatibility issues
Unfortunately, though the module API is similar between versions, they
are not identical and Apache 1.3 modules need to be ported to the new
architecture. Most mainstream modules such as PHP and mod_perl already
have Apache 2.0 versions and others, such as mod_dav and mod_ssl, are
now part of the server distribution. Running modules on a threaded
architecture requires specific changes to modules. Modules distributed
with Apache have undergone those changes and are considered `thread-
safe', but third-party modules or libraries may not. If you need one
of those, you will be limited to running Apache as a pure process-
based server.
2.1.2.5. Portable
Apache runs equally well now on Windows and Unix platforms thanks to
the Apache Portable Runtime (APR) library. It abstracts the
differences among operating systems, such as file or network access
APIs. Porting Apache to a new platform is often as simple as porting
the Apache Portable Runtime. This abstraction layer also provides for
platform-specific tuning and optimization.
2.2. Security
Apache provides several security-related modules for securing and
restricting access to the server.
2.2.1. Authentication
Authentication modules allow you to determine the identity of a
client, usually by verifying an username and password against a
backend database. Apache includes modules to authenticate against
plain text and database files. Additional authentication modules
exist that connect Apache to existing security frameworks or
databases, including: NT Domain controller, Oracle, mySQL, PostgresSQL
and so on.
The LDAP modules are specially interesting, as they allow integration
with company and enterprise wide existing directory services. You can
find these modules at . An Apache 2.0 LDAP module can be found at the
Apache website
<http://httpd.apache.org/docs-2.0/mod/mod_auth_ldap.html>.
2.2.2. Access Control
Apache provides the mod_access module that can restrict access to
resources based on parameters of the client request, such as the
presence of a specific header or the IP address or hostname of the
client. Third party modules allow you to restrict access to clients
that misbehave, as explained in later sections on performance and
bandwidth control.
2.2.3. SSL/TLS
The Secure Sockets Layer/Transport Layer Security protocols allow data
between the Web server and client to be encrypted. In Apache 1.3, the
protocols are implemented by mod_ssl, which is distributed separately
from the mod_ssl website <http://www.modssl.org> and requires applying
patches to the server. This was necessary because of export
regulations on encryption. Most of those restrictions have since then
being lifted and starting with Apache 2.0, mod_ssl is now included as
a base module with Apache.
2.3. Proxy
A proxy is a program that performs requests on behalf of another.
There are different kind of Web proxies. A traditional HTTP proxy,
also called a forward proxy, accepts requests from clients (usually
Web browsers), contacts the remote server, and returns the responses.
A reverse proxy is a Web server that is placed in front of other
servers, providing a unified front end and offloading certain tasks,
such as SSL processing, from the backend Web servers.
Apache supports both types of proxy, caching of proxied content and
differente proxy backends such as FTP.
2.4. Performance and scalability
Raw performance is only one of the factors to consider in a web server
(flexibility and stability come usually first).
Having said that, there are solutions to improve performance on heavy
loaded webservers serving static content. If you are in the hosting
business Apache also provides ways in which you can measure and
control bandwidth usage. Throttling in this context usually means
slowing down the delivery of content based on the file requested, a
specific client IP address and so on. This is done to prevent abuse.
· mod_mmap: Included in current Apache 1.3 releases, it maps to
memory a statically configured list of files that are frequently
requested but infrequently changed. This functionality is included
in mod_file_cache in Apache 2.
· Mod_bandwidth <http://www.cohprog.com/mod_bandwidth.html>: This
Apache 1.3 module enables the setting of server-wide or per
connection bandwidth limits, based on the specific directory, size
of files and remote IP/domain.
· Bandwidth share module
<http://www.topology.org/src/bwshare/README.html>: provides
bandwidth throttling and balancing by client IP address. It
supports Apache 1.3 and earlier versions of Apache 2.
· Mod_throttle
<http://www.snert.com/Software/Throttle/index.shtml>:Throttle
bandwidth per virtual host or user. For Apache 1.3
2.4.1. Load Balancing
Using the Apache reverse proxy and mod_rewrite you can have an Apache
process distributing requests among a variety of backend web servers.
You can find more information at
Additionally, mod_backhand is an Apache 1.3 module that allows
seamless redirection of HTTP requests from one web server to another.
This redirection can be used to target machines with under-utilized
resources, thus providing fine-grained, per-request load balancing of
web requests. You can find more information at .
2.4.2. Compression
Apache 2.0 includes mod_deflate, a filtering module that compresses
content before delivering it to clients. This saves bandwidth but can
have a performance impact. The mod_gzip module
<http://www.remotecommunications.com/apache/mod_gzip/> provides this
functionality for Apache 1.3
2.5. CGI scripts
CGI stands for Common Gateway Interface. CGI programs are external
programs that are called when a user requests a certain page. The CGI
program receives information from the web server (form variable
values, type of browser, IP address of the client and so on) and uses
that information to output a web page to the client.
Apache has support for CGIs and there is a third-party Apache 1.3
module that provides support for the FastCGI protocol. It avoids the
performance penalties associated with starting and stopping a CGI
program with every request. You can find it at
2.6. Development Platform Integration
Web applications are written in high-level languages such as Java,
Perl, C# and so on and Apache has several modules that integrate them
with the server. In many cases the modules expose the Apache API so
entire Apache modules can be written in those languages.
2.6.1. Perl
mod_perl <http://perl.apache.org/> is one of the most veteran and
successful Apache projects. It embeds a Perl interpreter in Apache and
allows access to the web server internals from Perl. This allows for
entire modules to be written in Perl or a mixture of Perl and C code.
In the 1.3 Apache versions, one interpreter has to be embedded in each
child, since the server is multiprocess based. In heavy traffic
dynamic sites, the increased size could make a difference. In
threaded versions of Apache 2.0 mod_perl allows for sharing of code,
data and session state among interpreters. This results in a faster,
leaner solution.
mod_perl is in itself another platform, with a great variety of
modules available such as Mason <www.masonhq.com> and Embperl
<http://perl.apache.org/embperl/> for embedding Perl in HTML pages and
AxKit <axkit.org> for XML-driven templates.
2.6.2. PHP
From the PHP <http://www.php.net> website: PHP is a server-side,
cross-platform, HTML embedded scripting language. It is the most
popular module for Apache
<http://www.securityspace.com/s_survey/data/man.200209/apachemods.html>
and this is due to a variety of reasons:
· Learning curve is quite low
· Great documentation
· Extensive database support
· Modularity
PHP has a modular design. Among many others, there are modules that
provide support for:
· Database connetivity for popular databases such as Oracle, MS-SQL
server, ODBC interface, MySQL, mSQL, PostgreSQL and so on.
· XML support
· File transfer: FTP
· HTTP
· Directory support: LDAP
· Mail support: IMAP, POP3, NNTP
· PDF document generation
· CORBA
· SNMP
You only need to compile/use the modules you need. PHP can be used
with Apache, as an external CGI or with other webservers. It is
crossplatform and it runs on most flavors of Unix and Windows. If
you come from a Windows background, you probably have used Internet
Information Server with Active Server Pages and MS-SQL Server. A
common replacement in the Unix world for this trio is Apache with
PHP and MySQL. Since PHP works:
· with Apache and with Microsoft IIS
· with MySQL and with MS-SQL server
· on Unix and on Windows
you have a nice, gradual migration path from a Microsoft-centric
solution to Unix based solutions.
2.6.3. Python
Python is a popular object oriented scripting language. Mod_Python
<http://www.modpython.org>, which is now an official Apache project,
allows you to integrate Python with the Apache web server. You can
develop complex web applications or accelerate existing Python CGI
scripts. Recent versions run on Apache 2.0.
2.6.4. Tcl
The Tcl Apache project <http://tcl.apache.org> integrates Tcl with the
Apache webserver. Tcl is a lightweight, extensible scripting language.
You can learn more about Tcl here <http://tcl.activestate.com/>.
There are several modules currently under the Apache Tcl umbrella:
· Both Mod_dtcl <http://tcl.apache.org/mod_dtcl/> and Neowebscript
<http://tcl.apache.org/neowebscript/> allow embedding Tcl on HTML
pages. Rivet <http://tcl.apache.org/rivet/> combines the best of
both modules.
· Mod_tcl <http://tcl.apache.org/mod_tcl/mod_tcl.html> takes an
approach similar to mod_perl, exposing the Apache API.
· WebSH <http://tcl.apache.org/websh/> provides a Tcl Web application
environment
2.6.5. Microsoft technologies
Several modules allow integration with Microsoft languages and
technologies such as the .Net framework or Active Server Pages.
2.6.5.1. .Net
mod_haydn <http://haydn.sourceforge.net/> integrates Mono
<http://www.go-mono.com> with Apache and exposes the Apache API to the
.Net framework, allowing you to write modules in C#, for example.
Covalent <http://www.covalent.net> provides mod_asp.net, an commercial
Windows module that allows Apache to run ASP.Net applications,
allowing you to replace Microsoft IIS.
2.6.5.2. ASP
ASP stands for Active Server Pages and is a Microsoft technology that
allows you to embed code, usually Visual Basic, in HTML pages. Several
companies such as ChilliSoft <http://www.chilisoft.com/> and Stryon
<http://www.stryon.com/> provide products that can run ASP
applications on Unix environments.
2.6.5.3. ISAPI
ISAPI is an API that you can use to extend Microsoft IIS, similarly to
how you would use the Apache API. Apache includes a module mod_isapi
that mirrors this functionality and allows you to run ISAPI modules.
2.6.6. Java
Most applications servers, such as those from Oracle, IBM and BEA
provide modules to integrate with the Apache web server. Additionally,
several modules such as mod_jk and mod_webapp allow you to connect to
Tomcat, a Servlet and JavaServer Pages container that is also part of
the Apache Software Foundation.
2.6.7. Modules for other languages
This document has described modules for popular server side languages
such as Perl, Python and PHP. You can find additional language modules
(JavaScript, Haskell, Ruby and others) at the Apache modules directory
<http://modules.apache.org>.
2.7. Management
An important part of Web server administration includes building,
configuring and monitoring different servers.
2.7.1. Build tools
Apache can be extended and customized in many different ways.
Integration of different modules with the server can sometimes be a
difficult task. Tools such as the Apache Toolbox
<http://www.apachetoolbox.com> can make this task easier, by providing
a menu driven build framework.
2.7.2. User Interfaces for Apache
Apache is configured thru text configuration files, and that sometimes
can be hard, specially for people coming from a Windows background.
There are open source graphical tools that make this task easier:
· Comanche <http://www.comanche.org>, by yours truly, is
crossplatform and runs on Unix/Linux, Windows and Mac.
· Webmin <http://www.webmin.com/webmin/>: A nice web based interface.
· gui.apache.org <http://gui.apache.org>: GUI interfaces for Apache
project. Programs are in various degrees of development.
2.7.3. SNMP
SNMP stands for Simple Network Management Protocol. It allows
monitoring and management of network servers, equipment and so on.
SNMP modules for Apache help manage large deployments of web servers,
measure the quality of service offered and integration of Apache with
existing management frameworks.
· Open source Mod SNMP
<http://www.simpleweb.org/software/packages/mod-snmp/> for Apache
1.3.
· Covalent SNMP <http://www.covalent.net> provides a commercial SNMP
module, support for the latest SNMPv3 standard, integration with
HP-Openview, Tivoli and so on.
2.8. Publishing
Authors of Web content require a means of managing that content and
uploading it to the server. One of the protocols used for this purpose
is DAV (Distributed Authoring and Versioning). DAV is an extension to
the HTTP protocol that enables users and applications to publish and
modify Web content. DAV technology is widely implemented, Microsoft
supports it at the operating system level (WebFolders) and in its
Office suite. Same goes for Apple OS-X and a variety of third party
products from Adobe, Oracle and so on. You can get the mod_dav module
for Apache 1.3 at . In Apache 2.0, mod_dav is included with the base
distribution.
Previous to DAV, Microsoft had its own publishing protocol, integrated
with the Microsoft FrontPage tool. You can add server-side support for
Frontpage using the modules at , though due to the way they integrate
with Apache they are not considered secure.
2.9. Protocol modules
Apache 2.0 introduced the concept of protocol modules. That means that
developers can reuse the Apache server framework to implement new
protocols such as those dealing with mail and file transfer. mod_ftp
is a commercial Apache-based FTP module from Covalent
<http://www.covalent.net>. mod_pop3
<http://cvs.apache.org/viewcvs.cgi/httpd-pop3/> is an open source
module that implements the POP3 protocol, commonly used by mail
readers to retrieve messages from mail servers.
2.10. Virtual Hosting
Apache provides extensive virtual hosting support which means that you
can serve multiple websites from a single server. In Apache 2.0, with
the per-child MPM you can have multiple children, each one serving a
different domain under different Unix user ids. This is very important
for security in shared hosting scenarios, as it allows you to isolate
customers from each other. The following are additional, alternative,
virtual hosting modules.
· mod_dynvhost <http://funkcity.com/0101/>
· mod_pweb <http://www.joytec.de/mod_pweb.html>
· mod_v2h <http://www.fractal.net/mod_v2h.tm>
2.11. Commercial support
Apache is the web server of choice for many commercial entities,
including big enterprises. These companies have certain requirements
when adopting a technology, specially one that is at the core of their
Internet strategy, such as Web servers. Those requirements include
performance, stability, management capabilities, support, professional
services and integration with legacy systems. A number of commercial
companies, such as IBM <http://www.ibm.com>, Red Hat
<http://www.redhat.com> and Covalent <http://www.covalent.net>,
provide the products and services necessary to make Apache meet the
needs of Enterprise customers.
In addition, many other companies and OEMs ship Apache as a bundled
web server with their products.
3. ASF Projects
Although Apache is probably the most popular, the Apache Software
Foundation is home to many other projects. This section provides an
overview of the most relevant ones, organized logically. Most of them
belong either to the Jakarta project and the XML project. The Jakarta
project hosts Java-based projects and the XML project hosts, surprise,
XML-related projects.
3.1. Applications and Frameworks
The following are application and development frameworks that are part
of the ASF.
3.1.1. 3.1.1 Servers
The following are some ASF server projects.
3.1.1.1. Tomcat
Tomcat is the flagship product of the Jakarta project. It is the
official reference implementation for the Java Servlet and JavaServer
Pages technologies.
You can learn more in the Tomcat homepage
<http://jakarta.apache.org/tomcat/>.
3.1.1.2. JAMES (Java Apache Mail Enterprise Server)
Complementary to the other Apache server side technologies, JAMES
provides a 100% pure Java server designed to be a complete and
portable enterprise mail engine solution based on currently available
open protocols (SMTP, POP3, IMAP, HTTP)
More information can be found here <http://jakarta.apache.org/james/>.
3.1.1.3. Lucene
Jakarta Lucene is a high-performance, full-featured text search engine
written in Java and part of the Jakarta project. You can find more
information at
3.1.1.4. Jetspeed
Jetspeed <http://jakarta.apache.org/jetspeed/> is a web based portal
written in Java. It has a modular API that allows aggregation of
different data sources (XML, SMTP, iCalendar)
3.1.2. 3.1.2 Content management
The following are projects related to content management
3.1.2.1. Slide
Slide is a high-level content management framework. Conceptually, it
provides a hierarchical organization of binary content which can be
stored into arbitrary, heterogenous, distributed data stores. In
addition, Slide integrates security, locking and versioning services.
It also provides a WebDAV <http://www.webdav.org> server and client
implementation. You can learn more at the Slide home page
<http://jakarta.apache.org/slide/index.html>.
3.1.2.2. Alexandria
Alexandria is an integrated documentation management system. It brings
together technologies common to many open source projects like CVS and
JavaDoc. The goal is to integrate source code and documentation to
encourage code documentation and sharing. More information at
3.1.3. 3.1.3 Frameworks
The following are application development frameworks.
3.1.3.1. Turbine
Turbine is a servlet based framework that allows experienced Java
developers to quickly build secure web applications. Turbine brings
together a platform for running Java code and reusable components.
Some of its features include: Integration with template systems, MVC
style development, Access Control Lists, localization support and so
on. You can find more information at the Turbine web site
<http://java.apache.org/turbine>.
3.1.3.2. Avalon
If you are familiar with Perl or BSD systems, Avalon is roughly the
equivalent of CPAN <http://www.cpan.org> or the Ports collection for
Java Apache technologies. It does not only provide guidelines for a
common repository of code, it goes one step further: is an effort to
create, design, develop and maintain a common framework for server
applications written using the Java language. It provides the means so
server side Java projects can be easily integrated and build on each
other. You can find more information at the Avalon web site
<http://java.apache.org/avalon/>.
3.2. Presentation
The following template systems, transformation engines and other
presentation related projects.
3.2.1. Cocoon
Cocoon leverages other Apache XML technologies like Xerces, Xalan and
FOP to provide a comprehensive XML publishing framework. The framework
can talk to many different data sources and can transform the content
into several different delivery formats such as PDF, HTML, XML and
RTF. It can run as a servlet or as a command line program. You can
learn more about Cocoon at the project homepage
<http://xml.apache.org/cocoon/>
3.2.2. Velocity
Velocity is a Java based template engine. It can be used as a stand-
alone utility for generating source code, HTML, reports, or it can be
combined with other systems to provide template services. Velocity
has a Model View Controller paradigm that enforces separation of Java
code and the HTML template. You can learn more about Velocity here
<http://jakarta.apache.org/velocity/index.html>.
3.2.3. AxKit
AxKit <http://axkit.org> is a popular XML-based Application Server
for mod_perl and Apache. It allows separation of content and
presentation and provides on-the-fly conversion from XML to any
format.
3.2.4. Xalan
Xalan is an XSLT processor available for Java and C++. XSL is a style
sheet language for XML. The T is for Transformation. XML is good at
storing structured data (information). You sometimes need to display
this data to the user or apply some other transformation. Xalan takes
the original XML document, reads transformation configuration
(stylesheet) and outputs HTML, plain text or another XML document.
You can learn more about Xalan at the Xalan Java
<http://xml.apache.org/xalan-j/index.html> and Xalan C++
<http://xml.apache.org/xalan-c/index.html> project homepages.
3.2.5. FOP
From the website: FOP is a Java application that reads a formatting
object tree and then turns it into a PDF document. So FOP takes an XML
document and outputs PDF, in a similar way that Xalan does with HTML
or text. You can learn more about FOP here
<http://xml.apache.org/fop>.
3.3. Parsers and Document Access libraries
The following are different libraries that can be used to parse and
manipulate a variety of document formats.
3.3.1. Xerces
The Xerces project provides XML parsers for a variety of languages,
including Java, C++ and Perl. The Perl bindings are based on the C++
sources. An XML parser is a tool used for programatic access to XML
documents. This is a description of the standards supported by
Xerces:
· DOM <http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001/level-one-
core.html>: DOM stands for Document Object Model. XML documents are
hierarchical by nature (nested tags). XML documents can be accessed
thru a tree like interface. The process is as follows:
· Parse document
· Build tree
· add/delete/modify nodes
· Serialize tree
· SAX <http://www.saxproject.org>:Simple API for XML. This is a
stream based API. This means that we will receive callbacks as
elements are encountered. These callbacks can be used to construct
a DOM tree for example.
· XML Namespaces <http://www.w3.org/TR/REC-xml-names/>
· XML Schema: The XML standard provides the syntax for writing
documents. XML Schema provides the tools for defining the contents
of the XML document (semantics). It allows to define that a certain
element in the document must be an integer between 10 and 20 or
contain an IP address.
The Xerces XML project initial code base was donated by IBM. You
can find more information in the Xerces Java
<http://xml.apache.org/xerces-j/index.html>, Xerces C++
<http://xml.apache.org/xerces-c/index.html> and Xerces Perl
<http://xml.apache.org/xerces-p/index.html> homepages.
3.3.2. Batik
Batik is a Java based toolkit for applications that want to use images
in the Scalable Vector Graphics (SVG) <http://www.w3.org/TR/SVG/>
format for various purposes, such as viewing, generation or
manipulation.
It is XML centric and compliant with the W3C specification. It is a
bit atypical from other Apache projects, in that it provides a
graphical component. Batik provides hooks to extend the framework thru
custom tags and it allows conversion from SVG to other formats like
JPEG or PNG. You can learn more at the Batik homepage
<http://xml.apache.org/batik/>
3.3.3. POI
The POI project consists of APIs for manipulating various file formats
based upon Microsoft's OLE 2 Compound Document format using pure Java.
This includes Word and Excel documents. You can find more information
at
3.4. Interoperability
The following are libraries for remote communication and
interoperability between servers.
3.4.1. SOAP
Apache SOAP ("Simple Object Access Protocol") and Axis are
implementations of the SOAP protocol <http://www.w3.org/TR/SOAP>
SOAP is a lightweight protocol for exchange of information in a
decentralized, distributed environment. It is an XML based protocol
that consists of three parts:
· An envelope that defines a framework for describing what is in a
message and how to process it,
· a set of encoding rules for expressing instances of application-
defined datatypes, and
· a convention for representing remote procedure calls and responses.
Basically you can think of SOAP as an remote procedure call system,
based on HTTP and XML. On the one hand this means it is verbose and
slow compared to other systems. On the other hand it eases
interoperatibility, debugging and development of clients and
servers for a variety of languages since most modern languages have
HTTP and XML modules. You can learn more at the Apache SOAP
homepage <http://xml.apache.org/soap/>
3.4.2. XML-RPC
The XML-RPC project <http://xml.apache.org/xmlrpc/> is a Java
implementation of the XML-RPC protocol, a light-weight protocol
similar and predecessor to SOAP.
3.4.3. XML security
The XML security project <http://xml.apache.org/security/> provides
XML document signature verification for secure exchange of documents.
3.5. Development
3.5.1. Apache Portable Runtime
The APR <http://apr.apache.org> project provides a portability layer
that abstracts a number of APIs for file manipulation, network access
and so on. It is written in C and works on most Unix flavors, Windows
and a variety of other systems. It is the basis for Apache 2.0
3.5.2. Ant
Ant <http://jakarta.apache.org/ant/> is a Java based build tool. It
has a modular API and can be extended by creating new tasks. It is
driven by XML configuration files.
3.5.3. Byte Code Library
The Byte Code Engineering Library <http://jakarta.apache.org/bcel/>
(BCEL) is a library to analyze, create, and manipulate binary Java
class files.
3.5.4. Log4j
This package provides a logging framework that Java applications can
use. It can be enabled at runtime without modifying the binary and
has been designed with performance in mind. It can be found at
3.5.5. ORO and Regexp
ORO is a complete package that provides regular expression support for
Java. It includes Perl5 regular expression support, glob expressions
and so on. All under the Apache license. You can learn more about
ORO at . There is another ASF lightweight regular expression package,
Regexp <http://jakarta.apache.org/regexp/>.
3.5.6. Struts
Struts is an Apache project that tries to bring the Model-View-
Controller (MVC) design paradigm to web development. It builds on
Servlet <http://java.sun.com/products/servlet> and JavaServer Pages
<http://java.sun.com/products/jsp> technologies. The model part is
made up of Java server objects, which represent the internal state of
the application. The view part is constructed via JavaServer Pages
(JSP), which is a combination of static HTML/XML and Java. JSPs also
allow the developer to define new tags. The controller part consists
of servlets, which take requests (GET/POST) from the client, perform
actions on the model and update the view by providing the appropriate
JSP. You can learn more at the Struts project pages
<http://jakarta.apache.org/struts/index.html>.
3.5.7. Taglibs
The JavaServer pages technology allows developers to provide
functionality by adding custom tags. The Taglibs project intends to be
a common repository for these extensions. It includes tags for common
utilities (i.e. date), SQL database access and so on.
You can learn about TagLibs at . More documentation is included in
the package.
3.5.8. Database
OJB <http://jakarta.apache.org/ojb/> is a database mapping tool that
allows persistance and storage of Java objects in relational
databases. Xindice <http://xml.apache.org/xindice/> is a native XML
database for storing and querying XML documents.
3.5.9. Commons
The Commons project <http://jakarta.apache.org/commons/> provides a
great variety of reusable Java components with minimal dependencies.
3.6. Testing
The following ASF projects cover testing and performance analisys.
3.6.1. httpd-test
The httpd-test project <http://httpd.apache.org/test/> provides a
testing framework for the Apache web server and tools such as flood
<http://httpd.apache.org/test/flood/> for HTTP load testing.
3.6.2. Cactus
Cactus <http://jakarta.apache.org/cactus/> is a testing framework for
testing server side Java code such as Servlets and EJBs.
3.6.3. JMeter
This is a testing tool written in Java with a GUI frontend. It can be
obtained at .
3.6.4. Lakta
Lakta <http://jakarta.apache.org/lakta/> is an end-to-end HTTP testing
tool
3.6.5. Watchdog
The Watchdog project <http://jakarta.apache.org/watchdog/> is a suite
of validation sets for the Servlet and JavaServer Pages specification.
4. Where to find more information
Additional Apache related resources
4.1. Websites
The following are some useful websites
· Apache Website <http://www.apache.org>
· Apache Week <http://www.apacheweek.com>
· Apache modules directory <http://modules.apache.org>
· Apache today <http://www.apachetoday.com>
· Apache World <http://www.apacheworld.org>
· Slashdot Apache section
<http://slashdot.org/index.pl?section=apache>
4.2. Books
I maintain a list of books
<http://www.apacheworld.org/apache_overview/books/> related to this
document. It is not a comprehensive list, but rather I include only
those books that I have personally found well-written and useful.
4.3. Support forums
You can find the Apache users mailing list at . Similar lists exist
for the rest of projects mentioned there. Make sure you read the
Frequently Asked Questions document before posting . You can also get
support in the newsgroup comp.infosystems.www.servers.unix at .
If you want commercial support, consider contacting Covalent
<http://www.covalent.net>, which provides expert support for Apache
(at a fee, of course). If you are using Apache on Linux, your Linux
vendor may have support plans that include Apache.
5. Contacting the Author
You can contact me at daniel @ rawbyte.com . I welcome suggestions and
corrections, but please, please, do not send me messages asking me to
troubleshoot your Apache installation. I just do not have the time to
answer people individually. If you need support, please refer to the
resources mentioned above.
5.1. Translations
If you want to contribute a translation of this document you should
use the SGML source. Check for info. Please drop me a note so I can
make sure you get the most recent version.
6. Open Content Open Publication License
Open Publication License Draft v1.0, 8 June 1999 (text version)
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The Open Publication works may be reproduced and distributed in whole
or in part, in any medium physical or electronic, provided that the
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incorporation of it by reference (with any options elected by the
author(s) and/or publisher) is displayed in the reproduction.
Proper form for an incorporation by reference is as follows:
Copyright (c) <year> by <author's name or designee>. This material may
be distributed only subject to the terms and conditions set forth in
the Open Publication License, vX.Y or later (the latest version is
presently available at http://www.opencontent.org/openpub/). The
reference must be immediately followed with any options elected by the
author(s) and/or publisher of the document (see section VI).
Commercial redistribution of Open Publication-licensed material is
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Any publication in standard (paper) book form shall require the
citation of the original publisher and author. The publisher and
author's names shall appear on all outer surfaces of the book. On all
outer surfaces of the book the original publisher's name shall be as
large as the title of the work and cited as possessive with respect to
the title.
6.2. COPYRIGHT
The copyright to each Open Publication is owned by its author(s) or
designee.
6.3. SCOPE OF LICENSE
The following license terms apply to all Open Publication works,
unless otherwise explicitly stated in the document.
Mere aggregation of Open Publication works or a portion of an Open
Publication work with other works or programs on the same media shall
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work shall contain a notice specifying the inclusion of the Open
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NO WARRANTY. Open Publication works are licensed and provided "as is"
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6.4. REQUIREMENTS ON MODIFIED WORKS
All modified versions of documents covered by this license, including
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· 1. The modified version must be labeled as such.
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6.5. GOOD-PRACTICE RECOMMENDATIONS
In addition to the requirements of this license, it is requested from
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· 1. If you are distributing Open Publication works on hardcopy or
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· 2. All substantive modifications (including deletions) be either
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· 3. Finally, while it is not mandatory under this license, it is
considered good form to offer a free copy of any hardcopy and CD-
ROM expression of an Open Publication-licensed work to its
author(s).
6.6. LICENSE OPTIONS
The author(s) and/or publisher of an Open Publication-licensed
document may elect certain options by appending language to the
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of the license instance and must be included with the license (or its
incorporation by reference) in derived works.
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To accomplish this, add the phrase `Distribution of substantively
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To accomplish this, add the phrase 'Distribution of the work or
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