Features Of Servlet2.5

Changes introduced in Servlet 2.5:

• A new dependency on J2SE 5.0
• Support for annotations
• Several web.xml conveniences
• A handful of removed restrictions
• Some edge case clarifications

Dependency on J2SE 5.0

Servlet 2.5 specification now lists J2SE 5.0 (JDK 1.5) as its minimum platform requirement. While this limits Servlet 2.5 to those platforms with J2SE 5.0 implementations, this change means that all the new language features from J2SE 5.0 (generics, autoboxing, an improved for loop, a new enum type, static importing, varargs, and metadata annotations) are guaranteed available to Servlet 2.5 programmers.

Annotations

Annotations provide a mechanism for decorating Java code constructs (classes, methods, fields, etc.) with metadata information. Annotations aren't executed like code, but, rather, mark code in such a way that code processors may alter their behavior based on the metadata information.

Several web.xml conveniences -

Multiple patterns in mappings

when writing a <servlet-mapping> or <filter-mapping>, you can now provide multiple match criteria in the same entry. A <servlet-mapping> previously supported just one <url-pattern> element. Now it supports more than one. For example:

<servlet-mapping>

<servlet-name>color</servlet-name>

<url-pattern>/color/*</url-pattern>

<url-pattern>/colour/*</url-pattern>

</servlet-mapping>

Likewise, a <filter-mapping> previously allowed just one <url-pattern> or one <servlet-name>. Now it supports any number of each:

<filter-mapping>

<filter-name>Multipe Mappings Filter</filter-name>

<url-pattern>/foo/*</url-pattern>

<servlet-name>Servlet1</servlet-name>

<servlet-name>Servlet2</servlet-name>

<url-pattern>/bar/*</url-pattern>

</filter-mapping>

Restriction removal

Servlet 2.5 eased a few restrictions around error handling and session tracking. With error handling, Servlet 2.5 removed a rule dictating that error-handling pages configured with <error-page> could not call setStatus() to alter the error code that triggered them. The rule followed the argument that the job of an error page is to report each error but not alter it.

clarifications -

Cross-context sessions

Servlet 2.5 now specifies that resources within a context see the session for that context, regardless of where the request may have started. This means the portlets can track their own state separate from the main page state, and this rule will apply across servlet containers.

Response closure

response.setHeader("Host", "localhost"); response.setHeader("Pragma", "no-cache"); response.setHeader("Content-Length", "0"); response.setHeader("Location", "http://www.sycorax.co.in");

The servlet technically must ignore the Location header because the response must be committed immediately as the zero byte content length is satisfied. The response is over before it began! Servlet containers often refuse to implement this behavior, and the Servlet 2.5 release adds "has been greater than zero" to the rule.

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