Lab 4
Java-based Backend
Authors:
Sahand Sadjadee
Alexander Kazen
Gustav Bylund
Per Jonsson
Tobias Jansson
Spring 2014
TDDI15 Advanced Programming and Interactivity on the WWW
http://www.ida.liu.se/~TDDD24/
Department of Computer and Information Science (IDA)
Linköping University
Sweden
1. Introduction
In this fourth lab, you will use Java to rewrite the Twidder backend previously developed in lab 2. The new
version of backend shall contain all the functionality previously implemented in lab 2, as well as some new
one.
Once you are finished with this lab, you will present your work to your responsible lab assistant. For
more specific information about the presentation and evaluation process of lab 4, please check section 4:
Presentation and Evaluation. For more general information about the presentation and examination
process, please check the course page.
2. Development tools
Eclipse
We shall use Eclipse in this lab, as Google has provided the Google Plugin for Eclipse which provides the
whole API and tools required for developing web applications which can be uploaded and hosted by
Google App Engine. Eclipse is available as an addable module on IDA Solaris systems. You can add it to
your environment using the following command:
module add prog/eclipse/4.2.1
once done you can run Eclipse by executing the following command:
eclipse&
Google Plugin
In this lab, we will use Google Plugin which integrates Google App Engine SDK and Eclipse and helps us
not directly work with GAE SDK. Google Plugin is pre­installed with Eclipse Juno on IDA computers.
More information on Google Plugin can be found at the following links: Please keep in mind that although
the App Engine has support for Python, we will be using Java in this lab.
Note: As we developed the Twidder front­end directly using HTML/Javascript/CSS, we will not use GWT
which has been designed for front­end development using Java language. We recommend that you have a
look at GWT once you are done with this lab series and explore how it works. Once you intend to
create a new web application project, please remember to unmark Google Web Toolkit and on
IDA Solaris systems change the version of Google App Engine from 1.3.4 to 1.7.4.
Google Plugin for Eclipse
https://developers.google.com/appengine/docs/java/tools/eclipse
A Quick Start
https://developers.google.com/eclipse/
3. Lab instructions
As specified in the following, you at least need to fulfill the requirements for grade 3 to pass this course.
For grade 4 and 5 more functionality is requested which are explained afterwards.
Grade 3,
All the server­functions implemented in lab 2 using Python will be re­implemented using Java Servlets. As
Google App Engine provides only Google Channel API for full­duplex communication, you will use it to
implement the auto refreshing mechanism for the Home tab wall. As Google uses a cloud environment to
store all your application data, You will use the Datastore API, including JDO and JPA libraries, available
as part of Google App Engine to implement the data­handling layer. Once you are done, your application
shall be uploaded on Google App Engine. Please notice that your static files will be assigned arbitrary
URLs which make them accessible from the client­side. the client.html shall be loaded and displayed as
the application is opened by the user.
What is Google App Engine
https://developers.google.com/appengine/docs/whatisgoogleappengine
https://developers.google.com/appengine/training/intro/whatisgae
Google App Engine Introduction
https://developers.google.com/appengine/docs/java/gettingstarted/introduction
Google Channel API for Java
https://developers.google.com/appengine/docs/java/channel/
Google Datastore API
https://developers.google.com/appengine/docs/java/datastore/
Java Servlet Technology
http://docs.oracle.com/javaee/6/tutorial/doc/bnafd.html
Google App Engine API Javadoc
https://developers.google.com/appengine/docs/java/javadoc/
Oracle Servlet API Javadoc
http://docs.oracle.com/cd/E17802_01/products/products/servlet/2.5/docs/servlet­2_5­mr2/
Note: All the implemented server­functions shall be implemented exception free, in a way to be able to
stand any possible input.
Note: Please remember you will use Servlets built­in session handling mechanism.
Grades 4 and 5
For receiving grade 4, you need to implement one of the following two functionalities. For grade 5, you
must implement both functionalities.
Media Handling
As an extra functionality to what you have done for grade 3, you shall add the functionality by which a
user will be able to upload a photo for his/her profile as he/she signs up. The uploaded image for each user
shall be displayed in the following cases:
1. In the home tab along with other personal information as the user signs in.
2. In the browse tab, the image of viewed user shall be displayed along with his/her other
information.
3. For each post, the image of the user posting the message will be displayed along with his/her
name.
The uploaded image shall be stored in the database using Datastore API and will be sent to the client as
needed. In order to stream down the image to the client, you need to create a servlet named (for example)
“/image” which takes a unique id, like the email of the owner of image, and streams the image from the
database to the client. You can also use Base64 binary­text encoding for embedding the image as returned
from the server as a text string and display it using <img> tag.
Note: for creating dynamic images using a Servlet, the Servlet should return the image content read from
the database with an appropriate MIME type.
Base64 binary­text encoding on Wikipedia
http://en.wikipedia.org/wiki/Base64
Java Server Pages
As an extra task, you need to add a new functionality to your application by which the signed­in user can
see all the messages he/she has posted on other users’ walls. For doing that you shall use a Java Server
Page, which is accessible to the signed­in user via an additional link or button located in the home tab. The
specified Java Server Page shall open in a new window displaying the whole history of the posted
messages. Please remember that you will not use JSP built­in session handling mechanism.
Java Server Pages are used for performing server­side rendering against what we have been doing
through the whole lab series. As our Twidder application has been a Single Page Application, we avoided
using cookies as cookies are exchanged among the client and server continuously.
Using Java Server Pages in Google App Engine
https://developers.google.com/appengine/docs/java/gettingstarted/usingjsps
Java Server Pages Syntax Reference
http://www.oracle.com/technetwork/java/syntaxref12­149806.pdf
Note: The sent token to the Java Server Page shall not be displayed in the address bar.
4. Presentation and Evaluation
Once you are finished with lab 4, you will present your work to your responsible lab assistant during a
scheduled lab session. The result of your work is evaluated based on what you have been required to do
and how you have achieved it.