Software construction IP 4

servlet API’s suitability to it tasks

The above API provides Packages which assist us in coming up with a platform which initiates communication to the java server. (javax.servlet)

The (javax.servlet) design has several a numbers of ( classes and interfaces) that goes in detail and will define the contracts between a servlet class and the run time environment that fives information for an instance of such design class code by adjusting to servlet container. (javax.servlet.annotation)

The javax.servlet.annotation design contains a number of ( annotations) that allow users to use annotations to declare servlets, filters, and listeners and specify the metadata for the declared component. (javax.servlet.descriptor)

Provides programmatic access to a web application's configuration information that was aggregated from the web.xml and web-fragment.xml descriptors. (javax.servlet.http)

The (javax.servlet.htt) package contains a number of classes and interfaces that describe and define the contracts between a servlet class running under the HTTP protocol and the runtime environment provided for an instance of such a class by a conforming servlet container.

Requests and servlets

When (Application Engine) receives a web request for our Conference application, it will give the servlet that corresponds to the URL, as definition of the design in the application's deployment descriptor (the web.xml file in the WEB-INF/ directory). It uses the Java Servlet API to provide the request data to the servlet, and accept the response data.

The (Application Engine) Design uses several web servers to access the application, and increase adjustment of the number of servers it is using to handle performance requests. Some request may be sent to any server, sometime different types of server that handled a previous request from the same user.

By the beginning level, each HTTP web services will processes only one request at a time. If you mark your application as thread-safe, (Application Engine) may give orders to several requests to each web server in parallel. To do so, simply add a <thread safe>true</thread safe> element to appengine-web.xml as described in Using Concurrent Requests.

Conclusion

You can retrieve the ID of the instance handling a request using particular codes.

In the production environment, a logged-in admin can use the ID in a URL .The request will be routed to that specific instance. If the instance cannot handle the request it returns an immediate 503.

At the time of the request, you can save the request ID, which is unique to the request. The request ID can be used later to correlate a request with the logs for that request. Servlet API is very important type of API when developing our Android Conference Application.

4. API Efficiency, Reliability, and Maintainability (Week 3)

JavaMail API is used to exchange mails between applications. This message sending and receiving is done by using various classes available in the API which allows us to create a customized mail application depending on our needs. It helps us in creating personal mail filter, simple mailing lists and mail applications.

“Java Mail API has classes such as Session, Message, Address, Authenticator, Transport, Store and Folder”. All these classes are found in JavaMail API. The API can be sub classed for providing new protocols.

The Session class is an entry level class of Mail API. This acts as a connection factory which defines a basic session through which everything works. It can be used to get basic information like user name, password and other information that can be shared throughout the lifecycle of the application. The Session class cannot be sub-classed.

Message class is an abstract class and it is used to create a message that can be sent. It includes all the details of an email message like the subject line, recipient email address, sent date etc. To create a message we need to pass the Session object to the MimeMessage class constructor.

Address class is an abstract class which gives us the functionality to address the message. All we need to do here is pass the email address to the Address constructor. After that is done, we connect it to our message by using the setFrom() and setReplyTo() method. We can also add people in CC, BCC by using the Message.RecipientType.CC, Message.RecipientType.BCC.

Authenticator provides authentication in the network connection so that we can access protected resources which is the mail server in this case via a username and password. We need to create an instance of Authenticator and register it with the session in order to do so.

Transport is the mechanism by which a mail sent by a sender is moved towards recipient. The class uses protocol specific language for sending the message. First a connection is established and then the message is sent to the recipients.

Store class is used for storing and retrieving messages. The message stores require the user to authenticate before allowing them access. The Folder class represents the folder for emails. It can have a folder and its sub folders. First we need to connect to the store, then to our folders in order to read messages from it.

One key advantage of JavaMail API is that it is tied to “Java Activation Framework” which is intended to unite many data formats that are available like text, audio, image, video etc. It is reusable. The MailAPI provides protocol like IMAP, POP3 etc. which we can use now and it also gives an option of making a customized mail client depending on our needs and have scope so that the future demands and enhancements can be taken care of. So we see that the API’s used are maintainable and can be easily improved in future.

JavaMail API doesn’t have any support for sending and receiving secure mails though it provides the architecture in such a way that this feature can be added later. JavaMail also doesn’t have a feature of providing facility of maintaining an address book. Every mail server does it differently so to put this in JavaAPI we need to figure out how it is handled by server.

Java Servlet API is a set of classes which includes various interface between a web client and a web servlet. Clients make a request to the Web Server, which in turn invokes the servlet which can be used to service the request through the interfaces provided.

Servlets are protocol and platform independent server side components that provide a general framework for services built on request-response paradigm. They provide customized multiuser experience to the consumer base of an organization in addition to static web page.

We always consider servlet's as an alternative ways to dynamic web technologies. We consider this because of its portability, safety, efficiency etc. Servlet is written in java so it is platform independent. We can make an application in Windows platform and if required we can even use it in Unix using tomcat taking use of the WORA property of Java.

Servlet invocation is also very efficient. One’s it is loaded it stays in memory. It is not necessary to make a process for each request from the client. The load on the server is less as when we are using servlet, a thread is formed which takes less space instead of using a process like in common gateway interface. Servlets also offers other optimizations such as caching previous computations and keeping database connection open.

Servlets are multi-threaded so it can handle multiple requests at a time. So giving response to these multiple requests is faster using servlets as context switching between threads take less time as compared to processes. We can also make our servlets thread safe so they don't undergo any concurrency issues. This can be done by using synchronized keyword or by following a single thread model.

Java’s exception handling makes servlet more reliable to handle any unwanted events and render a page according to it. A server can also use Java Security Manager so that a server can executes it servlet under an agency that enforces a security policy designed to prevent the server from getting damaged because of any poorly written servlet or from some malicious attack. The availability of Permission class allows granting permission to a particular resource. This is done by passing one or more parameter to the Permission class constructor. The first parameter is the target file and the second parameter is the action (read/write etc). We can also provide multiple permissions by using comma separated composite string.

It also provides us with some extra infrastructure for automatically parsing and decoding HTML form, handling cookies and sessions and other utilities like setting and getting HTTP headers.

When it comes to drawbacks or limitation of servlet, the basic one is that it is a mix of java as well as html content. So an application based on servlet becomes complex while doing any enhancement. This is where JSP comes to our rescue.

One also needs Java Runtime Environment to run servlets. In cases where there are no interfaces in java for a particular resource, writing a CGI program is easier than writing a java native method as there are chances that it might not work. It also helps in writing a fully complied code much nearer to the machine on which it is run. Also testing a CGI program is easier as compared to servlets.

5. Configuration and change Management (Week 4)

6. Software Construction Tools and Techniques (Week 5)