JavaOne India 2011 - Servlets 3.0

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Servlets 3.0
Asynchronous, Extensible, Ease-of-use
Arun Gupta, Java EE & GlassFish Guy
blogs.oracle.com/arungupta, @arungupta

The preceding is intended to outline our general product
direction. It is intended for information purposes only,
and may not be incorporated into any contract. It is
not a commitment to deliver any material, code, or
functionality, and should not be relied upon in making
purchasing decisions.
The development, release, and timing of any features
or functionality described for Oracle’s products remains
at the sole discretion of Oracle.

2

Agenda
• Overview
• Ease of Development
• Dynamic Registration of Servlets etc
• Pluggability
• Asynchronous Support
• Security Enhancements
• Miscellaneous

3

Overview
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Java Servlet 3.0 done as part of JSR 315
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~20 members in the expert group
–Major Java EE vendors, open source web container developers, framework
authors
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Main areas of focus
–Ease of Development
–Pluggability
–Asynchronous support
–Security

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Ease of Development

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Enhanced APIs to use new Java SE language features introduced
since J2SE 5.0
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Generics for type safety in API where possible
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Annotations for declarative style of programming
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Optional web.xml
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Convention over configuration

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Ease of Development
Use of annotations

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Annotations to declare Servlets, Filters, Listeners and servlet
security
–@WebServlet – Define a Servlet
–@WebFilter – Define a Filter
–@WebListener – Define a Listener
–@WebInitParam – Define init param
–@MultipartConfig – Define file upload properties
–@ServletSecurity – Define security constraints
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Can override using “web.xml”

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Servlet 2.5 example
At least 2 files

 /* Code in Java Class */
<web-app>
<servlet> package com.sun;
<servlet-name>MyServlet public class MyServlet extends HttpServlet
</servlet-name> {
<servlet-class> public void
com.sun.MyServlet doGet(HttpServletRequest
</servlet-class> req,HttpServletResponse res)
</servlet> {
<servlet-mapping>
...
<servlet-name>MyServlet
</servlet-name> }
<url-pattern>/myApp/* ...
</url-pattern>
</servlet-mapping> }
...
</web-app>

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@WebServlet – Sample Code
@WebServlet(urlPatterns={“/myApp”})
public class SimpleSample extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res) {

}
}

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@WebServlet Async – Sample Code
@WebServlet(urlPatterns=“/myApp”, name=”MyServlet”, asyncSupported=true)
public class SimpleSample extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res) {

}
}

9

Dynamic Registration
Create and/or register
• ServletContext#add[Servlet | Filter]
• Overloaded versions take [Servlet | Filter] name and
– Fully qualified [Servlet | Filter] class name or
– Class <? extends [Servlet | Filter]> or
– [Servlet | Filter] instance
• User returned Registration handle to configure all aspects of [Servlet |
Filter]
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ServletContext#create[Servlet | Filter]
–Takes Class<? Extends [Servlet | Filter]> argument
–Supports resource injection by container
–Returned [Servlet | Filter] instance may be fully customized before it is registered

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Lookup

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ServletContext#find[Servlet |Filter]Registration
–Takes [Servlet | Filter] name as argument
–Returned Registration handle provides subset of configuration methods
–May only be used to add initialization parameters and mappings
–Conflict returned as java.util.Set

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Register example

ServletRegistration.Dynamic dynamic =
servletContext.addServlet(
"DynamicServlet",
"com.mycom.MyServlet");
dynamic.addMapping("/dynamicServlet");
dynamic.setAsyncSupported(true);

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Lookup example

ServletRegistration declared =
servletContext.getServletRegistration("DeclaredServlet");
declared.addMapping("/declaredServlet");
declared.setInitParameter("param", "value");

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Pluggability
• Plugin libraries using web fragments
– Modular web.xml
– Absolute ordering: <absolute-ordering>
– Relative ordering: <ordering>, <before>, <after>
• Bundled in framework *.jar/META-INF
• Zero-configuration, drag-and-drop for web frameworks
– Servlets, servlet filters, context listeners for a framework get discovered
and registered by the container
• Only JAR files in WEB-INF/lib are used

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Pluggability – Sample Code

<web-fragment>
<filter>
<filter-name>wicket.helloworld</filter-name>
<filter-class>org.apache.wicket.protocol.http.WicketFilter</filter-class>
<init-param>
<param-name>applicationClassName</param-name>
<param-value>...</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>wicket.helloworld</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-fragment>

http://blogs.oracle.com/arungupta/entry/totd_91_applying_java_ee

15

Pluggability – Sample Code

<web-fragment>
<filter>
<filter-name>LiftFilter</filter-name>
<display-name>Lift Filter</display-name>
<description>The Filter that intercepts lift calls</description>
<filter-class>net.liftweb.http.LiftFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>LiftFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-fragment>

http://blogs.oracle.com/arungupta/entry/totd_101_applying_servlet_3

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Extensibility
ServletContainerInitializer

• Shared copies of frameworks
• Container installed JARs
– App or Library
• Discovered using the service provider API
– META-INF/services/javax.servlet.ServletContainerInitializer
• Expresses interest in classes via @HandlesTypes

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Extensibility
ServletContainerInitializer

• Who uses it ?
– Mojarra (JSF2) is bootstrapped into GlassFish
• No “faces-config.xml” or “web.xml”
– Jersey (JAX-RS) registers root Application
• No (or portable) “web.xml”

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Java Server Faces
@SuppressWarnings({"UnusedDeclaration"})
@HandlesTypes({
ManagedBean.class,
FacesComponent.class,
FacesValidator.class,
FacesConverter.class,
FacesBehaviorRenderer.class,
ResourceDependency.class,
ResourceDependencies.class,
ListenerFor.class,
ListenersFor.class,
UIComponent.class,
Validator.class,
Converter.class,
Renderer.class
})
public class FacesInitializer implements ServletContainerInitializer {
// NOTE: Loggins should not be used with this class.
private static final String FACES_SERVLET_CLASS = FacesServlet.class.getName();

19

Java Server Faces

public void onStartup(Set<Class<?>> classes, ServletContext servletContext)
throws ServletException {
if (shouldCheckMappings(classes, servletContext)) {
Map<String,? extends ServletRegistration> existing =
servletContext.getServletRegistrations();
for (ServletRegistration registration : existing.values()) {
if (FACES_SERVLET_CLASS.equals(registration.getClassName())) {
// FacesServlet has already been defined, so we're
// not going to add additional mappings;
return;
}
}
ServletRegistration reg =
servletContext.addServlet("FacesServlet",
"javax.faces.webapp.FacesServlet");
reg.addMapping("/faces/*", "*.jsf", "*.faces");
servletContext.setAttribute(RIConstants.FACES_INITIALIZER_MAPPINGS_ADDED,
Boolean.TRUE);

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Resource Sharing

• Static and JSP not confined to document root of the web
application
• May be placed in WEB-INF/lib/[*.jar]/META-
INF/resources
• Resources in root take precedence over those in bundled JAR
• Container must honor this new location when
– Processing HTTP requests
– Calls to ServletContext#getResource[AsStream]

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Resource Sharing – Sample Code

myapp.war
WEB-INF/lib/catalog.jar
/META-INF/resources/catalog/books.html

http://localhost:8080/myapp/catalog/books.html

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Why Asynchronous Servlets?

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Not for Async IO
–Requests mostly small (single packet)
–Hard to asynchronously produce large responses
–Async IO support waiting for NIO2

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Async Servlets are for:
–Waiting for resources (eg JDBC connection)
–Waiting for events (eg Chat)
–Waiting for responses (eg web services)

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Blocking waiting consumes resources

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Web Application using remote web services
–Handling 1000 requests / sec
–50% requests call remote web service
–500 threads in container thread pool

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If remote web service is slow (1000ms)
–Thread starvation in 1 second!
–50% of requests use all 500 threads

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Asynchronous API
Enable asynchronous support

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Configured in
–web.xml:
<async-supported>true</async-supported>
–With annotation: @WebServlet(asyncSupported=true)
–Programmatic: registration.setAsyncSupported(true)

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Asynchronous Servlets – Sample Code

AsyncContext context = request.startAsync();
context.addListener(new AsyncListener() { … });
context.dispatch(“/request.jsp”);
//context.start(Runnable action);
. . .
context.complete();

http://blogs.oracle.com/arungupta/entry/totd_139_asynchronous_request_processing

26

Security
Annotations to define security constraints

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@ServletSecurity used to define access control constraints
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@HttpConstraint for all HTTP methods
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@HttpMethodConstraint for specific HTTP methods
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More specific wins

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Security – Sample Code

@ServletSecurity(
httpMethodConstraints = {
@HttpMethodConstraint(value = "GET", rolesAllowed = "R1"),
@HttpMethodConstraint(value = "POST", rolesAllowed = "R2")
}
)
public class MyServlet extends HttpServlet {
// Servlet methods
}

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Security
Programmatic container authentication and logout

>HttpServletRequest#login(String username, String
password)
–Replacement for FBL
–Application supervises credential collection
>HttpServletRequest#authenticate(HttpServletRespo
nse)
–Application initiates container mediated authentication from a resource that is
not covered by any authentication constraints
–Application decides when authentication must occur

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Miscellaneous Features
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Session tracking cookie configuration
–Via web.xml
–Programmatic via javax.servlet.SessionCookieConfig
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Support for HttpOnly cookie attribute
–Example:
servletContext.getSessionCookieConfig().setHttpOnly(true)
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Default error page <error-page>
<error-code>...</error-code>
<exception-type>...</exception-type>
<location>/404.html</location>
</error-page>

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Miscellaneous Features / API (contd)

ServletRequest#getServletContext
ServletRequest#getDispatcherType
Servlet[Request|
Response]Wrapper#isWrapperFor
HttpServletResponse#getStatus
HttpServletResponse#getHeader
HttpServletResponse#getHeaders
HttpServletResponse#getHeaderNames

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Miscellaneous Features / API (contd)
File upload

ServletRequest#getParts
ServletRequest#getPart
@MultipartConfig
Changes to web.xml

32

Summary
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Major revision since Servlet 2.5
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Comprehensive set of new features enable modern style of web
applications and greatly increases developer productivity
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Simplifies assembly of large applications from reusable
components

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Servlets 3.1 (JSR 340)
http://jcp.org/en/jsr/detail?id=340
NEW

• Cloud support
• Multi-tenancy
– Security / Session state / Resources isolation
• Asynchronous IO based on NIO2
• Simplified Asynchronous Servlets
• Utilize Java EE concurrency utilities
• Enable support for Web Sockets

34

References

• oracle.com/javaee
• glassfish.org
• oracle.com/goto/glassfish
• blogs.oracle.com/theaquarium
• youtube.com/GlassFishVideos
• Follow @glassfish

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JavaOne India 2011 - Servlets 3.0

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