Research on Flood Control Information System Based on J2ME

In this system, the client and server communicate mainly through the HTTP protocol, and the workflow is as follows:

(1) The user starts the MIDlet on the phone and enters the login interface, where he enters his username and password to log in. The MIDlet uses the open method of the Connector class to establish a connection to the server and casts the connection to an HttpConnection type.

(2) The client uses the openInputStream method and openOutputStream method of the HttpConnection class to return input and output streams and use them to send requests and receive response information.

(3) After receiving the connection request from the client, the server encapsulates it into an HttpServletRequest object, calls the corresponding Servlet, accesses the database through EJB or JavaBean, and returns the processing result to the client's MIDlet.

(4) The client MIDlet uses the input stream to receive the results returned by the server, and presents different interfaces on the screen depending on whether the returned result is "station" (station), "person" (ordinary user) or "none" (no such user).

(5) After successful login, MIDlet re-establishes HttpConnection to perform data update or query operations.

4. Technical Difficulties and Solutions

4.1 Receiving User Customized Information

There are two ways to send user-customized information:

(1) Scheduled delivery: Used to send user-customized daily information to users on a scheduled basis every day.

(2) Emergency sending: When an emergency flood situation occurs, the information will be sent immediately to the relevant responsible persons.

On the client side, the reception of relevant information is achieved through the PUSH registration function of J2ME. Push technology is a mechanism that enables Midlet applications to start running automatically without user operation. In a normal network connection, the client actively connects to the server, and the server accepts the request and returns the processing result to the client. Push technology is different. It does not require the application to obtain data through the network in a "pull" manner. The data required by the client will be actively "pushed" to the client's mobile device. When the mobile device receives the information, the relevant Midlet will be activated and start running to process the sent data.

The server can automatically send data to the client connected to it using Socket, which provides a guarantee for Push technology. The client's MIDlet first registers the service type, address, and port number. When the server detects an emergency or user-customized situation, it will send the corresponding message to the client through Socket, and the client will start the corresponding MIDlet to process the message accordingly.

J2ME platform has added support for Push registration since MIDP2.0. Push mechanism can activate Midlet in the following two ways: one is based on the connected network connection, when the client receives the information pushed from the network, it will automatically start the Midlet to run; the other is based on the timer warning notification. Push registration mechanism can make MIDlet run automatically, and there are two running modes: one is based on timing technology, when a specific time is reached, the program will run; the other is based on the network, when the device receives the information pushed by the network, it can start the program to run. This system adopts the first method to realize the sending of customized information.

To use Push technology on the client side, Push registration must be performed in advance. There are two methods for Push registration: static registration and dynamic registration. Static registration requires adding Push registration information to the JAD file and completing the registration when the Midlet Suite is installed. The disadvantage of static registration is that it must be implemented through the Midlet Suite installation process. Once installed, new registrations cannot be added. At the same time, if you want to cancel Push registration, you must also uninstall the Midlet Suite. Dynamic registration is implemented by MIDlet through the Push Registry interface API. Push registration can be added or canceled while the program is running, which increases flexibility. This article adopts the dynamic registration method.

During dynamic registration, the MIDlet needs to tell the AMS the IP address and port number of the server to which it is connected and the MIDlet class to be started. The implementation code is as follows:

…

String midletClassName = "com.water.PushInfo"; //This is the Midlet that automatically runs and processes data

String ConnectionURL =”socket://:6789”;

String AllowedSender = "*"; //* indicates that it is allowed to receive messages sent from any address

PushRegistry.registerConnection(midletClassName, ConnectionURL, AllowedSender);

…..

In this way, when AMS detects the data sent by the Socket server with port number 6789, it will start PushInfo under the com.water package to process the data.

Unregistering can be done using PushRegistry.unregisterConnection(ConnectionURL). [page]

4.2 Database Connection Pool Technology

This example uses database connection pool technology. Traditional Web applications generally go through three steps when performing database operations: (1) establishing a database connection; (2) performing database addition, deletion, modification, and query operations; and (3) disconnecting the database connection. This method has an important disadvantage: a database connection must be established and managed for each Web request, and these operations consume a lot of time and resources. The basic idea of ​​a database connection pool is to establish some connections in advance and place them in memory objects for future use. When a database connection needs to be established in the program, just take one out of the memory instead of establishing a new connection. Similarly, after use, just put the connection back into the memory, and the establishment and disconnection of the connection are managed by the connection pool itself. WebLogic Server provides a graphical interface for establishing a database connection pool, which is relatively simple to set up. After establishing the database connection pool and data source, you can call it in the Servlet through JavaBean or EJB. The code is as follows:

…

Hashtable ht = new Hashtable();

ht.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");

ht.put(Context.PROVIDER_URL,"t3://localhost:7001");

try

{

Context ctx=new InitialContext(ht);

DataSource ds=(DataSource)ctx.lookup("WaterJNDI");

Connection con=ds.getConnection();

…

}catch(Exception e){

…

}

…

V. Conclusion

This system provides query services for flood control information (including historical and real-time water and rainfall conditions, work conditions, drought conditions, disaster conditions, etc.) for relevant personnel of flood control departments at all levels, and actively notifies relevant responsible persons in case of emergency, so that flood control personnel can obtain the latest flood control information anytime and anywhere, thereby improving the efficiency of flood control work.

With the development of mobile communication technology and the upcoming implementation of 3G technology, wireless networks have a good future, and using small devices such as mobile phones and PADs to communicate with the Internet will surely become one of the future development directions. With the continuous improvement of J2ME technology and the maturity of small device functions, applications supporting mobile commerce and mobile communications will surely be developed faster and more widely used.

6. Innovation

The innovation of this paper is to apply J2ME to flood control projects, and use Push registration in MIDP2.0 to actively send messages to the client. The database connection pool technology is used on the server side to improve the efficiency of accessing the database.

This system can effectively improve the efficiency of flood prevention work, so that emergency situations can be handled in a timely manner, thereby greatly reducing the mistakes in flood prevention work. The estimated economic benefits of this system are 500,000 yuan.

References

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