Servlet 3.0

Servlet 3.0

Minh Hoang TO

Portal Team

Servlet 3.0 Specification

- Java Specification Request JSR-315

- Part of Java Enterprise Edition 6

- Compliant servers:

Apache Tomcat 7, JBoss AS 7, Jetty 8, GlassFish 3, ...

www.exoplatform.com - Copyright 2012 eXo Platform 2

Agenda

- Annotations

- Web Fragment

- Dynamic Registration

- Programmatic Login

- Asynchronous Servlet

- File Upload


Annotations

- Use annotations to declare servlet, filter, listener and specify metadata for the
declared component

@WebServlet
@WebFilter
@WebInitParam
@WebListener
@ServletSecurity
@HttpConstraint

- Servlet container detects annotated class and injects metadata into declared
components at deploy time


Annotations

Declare servlet via deployment descriptor:

<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.mto.presentation.HelloServlet</servlet-class>
</servlet>

<servlet-mapping>
<url-pattern>/greeting/*</url-pattern>
</servlet-mapping>

<servlet-mapping>
<url-pattern>/sayhello/*</url-pattern>
</servlet-mapping>


Annotations

Declare servlet via annotated class

@WebServlet
(
name = “hello”,

urlPatterns = {“/greeting/*“, “/sayhello/*“}
)
public class HelloServlet extends HttpServlet {

}


Annotations

Declare filter via deployment descriptor:

<filter>
<filter-name>hello</filter-name>
<filter-class>com.mto.presentation.HelloFilter</filter-class>
</filter>

<filter-mapping>
<url-pattern>/greeting/*</url-pattern>
</filter-mapping>

<filter-mapping>
<url-pattern>/sayhello/*</url-pattern>
</filter-mapping>


Annotations

Declare filter via annotated class

@WebFilter
(
name = “hello”,

urlPatterns = {“/greeting/*“, “/sayhello/*“}
)
public class HelloFilter implements Filter {

}


Annotations

- Type safe and less error-prone

- Facilitate work of developers

- No need to master XSD of deployment descriptor

BUT

- Frequent recompilation is a big obstacle


Web Fragment

- Divide WEB-INF/web.xml into multiples META-INF/web-fragment.xml :

1. Each web-fragment.xml is packed in a .jar artifact under WEB-INF/lib

2. Web application components could be declared in web-fragment.xml

3. Order of fragment processing is manageable


Web Fragment

Filter configuration in a web.xml

<filter><filter-name>filterA</filter-name><filter-class>FilterA</filter-class></filter>
<filter><filter-name>filterB</filter-name><filter-class>FilterB</filter-class></filter>

<filter-mapping>
<filter-name>filterA</filter-name>
<url-pattern>/testWebFragment/*</url-pattern>
</filter-mapping>

<filter-mapping>
<filter-name>filterB</filter-name>
</filter-mapping>


Web Fragment

META-INF/web-fragment.xml under filterA.jar

<web-fragment>
<name>A</name>
<filter><filter-name>filterA</filter-name><filter-class>FilterA</filter-class></filter>

<filter-mapping>
<filter-name>filterA</filter-name>
</filter-mapping>

<ordering>
<before>
<others/>
</before>
</ordering>
</web-fragment>


Web Fragment

META-INF/web-fragment.xml under filterB.jar

<web-fragment>
<name>B</name>
<filter><filter-name>filterB</filter-name><filter-class>FilterB</filter-class></filter>

<filter-mapping>
<filter-name>filterB</filter-name>
</filter-mapping>

<ordering>
<after>
<name>A</name>
</after>
</ordering>
</web-fragment>


Web Fragment

- Base to implement pluggable/extensible configuration

BUT

- Quite limit as relevant .jar artifacts must be under WEB-INF/lib


Dynamic Registration

- Inject dynamically components, callbacks to ServletContext object on starting
the context

Use cases:

1. Inject a PortletProducerServlet servlet to ServletContext object of each web-
application containing WEB-INF/portlet.xml

2. Register callbacks for deploy/undeploy events on web applications containing
gatein-resources.xml

- Prior to Servlet 3.0, dynamic registration has to handler native work to
containers (WCI project)

- Doable in a portable manner with Servlet 3.0



- As container starts, it detects all implementations of ServletContainerInitializer
thanks to java.util.ServiceLoader mechanism, then invokes the method onStartup
on each initializing ServletContext

public interface ServletContainerInitializer
{
public void onStartup(Set<Class<?>> c, ServletContext ctx);
}

- Complex dynamic registration could be plugged to onStartup entry point



- Simple implementation for dynamic registration

public SimpleInitializer implements ServletContainerInitializer{
public void onStartup(Set<Class<?>> c, ServletContext ctx)
{
if(“/sample”.equals(ctx.getContextPath())
{
//Code handling ClassLoader elided from example
Class clazz = ctx.getClassLoader().loadClass(“abc.DynamicServlet”);
ServletRegistration.Dynamic reg = ctx.addServlet(“dynamicServlet”, clazz);
reg.addMapping(“/dynamic/*”);
}
}
}

- Declare fully-qualified name of implementation class in META-
INF/services/javax.servlet.ServletContainerInitializer



- Portable code for dynamic registration

BUT

- Class loading issues must be handled gracefully

- Container detects ServletContainerInitializer via service loader, so the .jar
containing ServletContainerInitializer must be visible to container 's bootstrap
class loader


Programmatic Login

- Prior to Servlet 3.0, any authentication flow must pass through a redirect request
with predefined params

1. j_security_check
2. j_username
3. j_password

Container intercepts that request and delegates to JAAS

- From Servlet 3.0

request.login(“root”, “gtn”);

The whole authentication process could be managed in the scope of a single
request


Asynchronous Servlet

- Use in server-push communication model:

1. Client sends request for real time data such as: livescore, exchange rate
2. Server queues the request as there is no event on real time data
3. As there is update on real time data, server loops through queued request
and respond to client

- Prior to Servlet 3.0, implementation of such communication model (using Servlet
API) is not scalable as request handling thread is not released during request
lifecycle.

- In Servlet 3.0, request handling thread could be released before the end of
request lifecycle


@WebServlet(
name=”livescore”,
asyncSupported=true,
urlPatterns = {“/livescore/*”}
)
public class LivescoreServlet extends HttpServlet
{
//Synchronization code elided from example
public void doGet(HttpServletRequest req, HttpServletResponse res)
{
AsyncContext ctx = req.startAsync(req, res);
//Thread handling request is released here but the res object is still alive
queue.add(ctx);
}

//Typically event from a messaging service
public void onServerEvent(EventObject obj)
{
//Loop over queue and send response to client
}
}


- Scalable threading model

BUT

- Header fields of HTTP protocol results in unnecessary network throughput

- WebSocket – better solution is going to appear in future version of Servlet
Specification


File Upload

@WebServlet(
name = “uploadServlet”, urlPatterns = {“/uploadFile/*”}
)
@MultipartConfig
public class UploadServlet extends HttpServlet
{
public void doPost(HttpServletRequest req, HttpServletResponse res)
{
Collection<Part> parts = req.getParts();
for(Part part : parts)
{
….......
part.write(System.getProperty(“java.io.tmpdir”) + “/” + part.getName());
….......
}
}
}


File Upload

<form action=”/uploadFile/ method=”post”>
<input type=”file” name=”part_name”/>
<input type=”submit” value=”Upload”/>
</form>


File Upload

- Nice API for uploading files

BUT

- Lack of public API to monitor upload progress


Servlet 3.0

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