Servlet - Web Application Directory Structure

Objective:

Construct File and Directory Structure of web application that may contain

• Static Content
• JSP Pages
• Servlet classes
• Deployment Descriptor
• Tag Libraries
• Jar Files
• Java Class Files

advapps2A

OR *.jpg Context Accessable

*.css Resources

Context Root

:::

:::

*.jsp

WEB-INF

web.xml

classes

*.class

lib

*.jar

tags

*.tld

*.tag

Servlet Specification defines a standard structure for web applications so that every web server

can provide support for that structure irrespective of vendor.

Total static information we have to place within the context root directly. All resources present in

context root are publicly accessable resources. ie any person can access these resouces directly by

its name.Hence we cannot place secured resouces within the context root directly.

http://localhost:7777/advapps1C/login.html

For every web application we have to maintain WEB-INF Folder. All the secured resources we have

to place in this folder and these are not publicly accessable resources. If any person trying to

access these resouces directly by its name then we will get 404 status code.

http://localhost:7777/advapps1B/WEB-INF/web.xml → 404

For every web application, we have to maintain one special xml file named with web.xml. It is also

known as Deployment Descriptor. Web container will use this web.xml to get our servlets

information.Hence this web.xml acts as GUIDE to web container.

We have to place this web.xml in WEB-INF folder directly.

Within the WEB-INF, we have to create classes folder to place all .class files.(Both Servlet classes

and normal java classes)

Within the WEB-INF, we have to maintain lib folder to place all required .jar files(like

ojdbc6.jar,log4j.jar etc)

Note:

if we place our class files in classes folder and lib folder, we are not required to set classpath

explicitly, because web container always searches in these locations by default.

Note:

For the required .class file web container will search first in classes folder and if it is not available

then only it will search in lib folder.i.e classes present in classes folder will get more priority than

classes present in lib folder.

All Tag libraries we have to place inside WEB-INF either directly or indirectly.

secured then we have to place inside WEB-INF

Q. In how many places we can place our servlet in web application?

There are 3 places

Deployment Descriptor: (web.xml)

Objective:

Describe the purpose and syntax of the following deployment descriptor elements?

1.<error-page>

2.<init-param>

3.<mime-mapping>

4.<servlet>

5.<servlet-mapping>

6.<servlet-class>

7.<servlet-name>

8.<welcome-file>

Deployment Descriptor(DD) is an XML File named with web.xml,should be placed in WEB-INF

directly.

Web container uses this web.xml to get web application deployment information. i.e web.xml acts

as GUIDE to web container.

web.xml provides declarative mechanism for customizing our web application without touching

the source code(with the help of initialization parameters).

For every web application we have to maintain exactly one web.xml and should be placed in WEB-

INF folder directly.

Anatomy of web.xml:

until servlet 2.3 version,web.xml is validated by using DTDs where order is important.Hence until

Servlet 2.3V the order of these top level tags is important.

But from Servlet 2.4V onwards web.xml is validated by using Schemas where order is not

important.Hence from servlet 2.4 Version onwards we can take these top level tags in any order.

Among these 27 top level tags , no tag is mandatory.Hence the following are valid web.xml files

</web-app>

1.<servlet>:

We can use <servlet> tag to declare servlets in web.xml.

<servlet> tag contains the following 9 child tags...

The order of these 9 tags is important and we should not change.

Among these 9 tags the following 2 tags are mandatory.

<servlet-name>

<servlet-class> or <jsp-file>

<servlet-name>:

According to Servlet specification there are 3 names are possible for every servlet.

• Original Name OR Developer's Name specified by <servlet-class>
• Deployer's Name OR Logical Name specified by <servlet-name> tag
• End User's Name speficied by <url-pattern>

The main advantages of Logical Name are:

• We can achieve security because we are not highlighting our internal naming conventions to the

end user.

2.Without effecting end user we can change our internal naming conventions.

3.We can map same servlet with different url-patterns

Note:

Within web.xml Logical Name is always unique.

Within the servlet we can get Logical Name by using getServletName() method of ServletConfig

interface.

Note:

All methods of ServletConfig interface are by default available in our servlet.Hence within our

servlet we can call these methods directly.

<servlet-class>:

By using this tag,we can specify the original name of servlet(Developer's name)

Web container will create object for this class only.Hence compulsory it should be concrete class

but not abstract class or interface.

Usually we can place JSPs within the context root directly. In this case end user can access directly

by its name.

But if the JSP is secured then it is not recommended to place in the context root directly. We

have to place such type of jsps inside WEB-INF and we have to provide access through url-pattern.

We can configure JSP by using <jsp-file> tag in web.xml