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Student side
Student side
Student side
Message receiving route
Learning page
Real-time discussion
Pract icing
Test ing
Rout e of t ransfer
controlled by teacher
Message management
route assemble
Teaching control
Discussion interface
Message receiving route
Student side
ODBC
Database
Figure 1. Overall design of the system.
established. The communication between the two users’
browsers must be transferred by the Java application
program in a Web server. To sum up, in order to achieve
the function of the system, the overall design of the
system is shown in Figure 1.
Instructions:
a) The students and teachers, respectively, establish
communication links with the Java application program
in the Web server by means of client/server. The
connection monitoring route of the server side is
responsible for monitoring the Socket connection
application from the clients. The server side should
establish a message management route for each linked
client, and the message management route is responsible
for receiving messages from the corresponding client, and
analyzing and managing the messages.
b) The students and teachers, respectively have a
message receiving route which is responsible for
receiving message from the serve side. The message
receiving route reflects the requirement of the received
messages on the user interface by calling the method in
the object of the user interface. Therefore, during the
process of designing the message receiving route, it is a
basic method to achieve the exchange visits between the
objects in Java that the objects of the user interface are set
as a parameter passed to the objects in the message
receiving route.
c) The process of accessing the test database is
executed as follows: the students send the corresponding
message to the serve, the serve side accesses ODBCbased
database via the COM component RDO to access,
and feedbacks the accessing results to the students.
III. SEVERAL KEY TECHNOLOGY
A. Database Access
Visual J + + do a special extension for the Java class
database according to the Microsoft operation system,
and the users can access any software supporting COM in
the Java programs. For accessing to the database, two
methods of DAO(Date Access Object) and RDO (Remote
Data Object) are provided in J + +. The software in this
article adopts the RDO objects to realize the data access
to the ODBC data source.
The security of IE should be checked strictly, and Java
classes are divided into credible classes and discredible
class. The discredible class can not use COM services.
All classes not loaded from the classpath are not credible,
the discredible classes includes the classes downloaded
from the internet, unless the classes are packaged in a
CAB file with a digital signature. In order to avoid the
trouble raised by the security and reduce the ODBC
configuration of the client side, the author adopts the
method of visiting the database by the Java application
program of the serve side to access the test database, and
this method has no any security restrictions. The Applet
program of the browser side passes accessw requests and
results by means of communicating with the application
program of the server side.
B. Message Design
The whole system is built based on the messages, the
server side and client side both bear message
management work. For a large number of messages based
on collaborative applications, the serve side is only
responsible for transferring such messages and such
messages are managed by the client side. Each kind of
messages is consisted of the message header and the
content, and the message header is used for the system
discrimination. The whole system mainly comprises six
kinds of messages: chat messages; whiteboard messages;
guide messages; users log in and log off messages;
accessing to the test database messages, and other
messages (such as boarding grade and checking grade).
C. Achieve of URL Guide
Inputting and transferring of URL The teachers click
on "Page guide" button, the system accesses learning
content index and pop up a dialog box so that the teachers
can select the chapters and problems to study. Then the
system sends the corresponding URL address to the
student client side via the Socket path, and a new browser
displaying the page is pop up for the confirmation.
Displaying of URL The steps are as follows:
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