Deep Java Virtual Machine (4)--Network mobility

First, several stages of software application development

Software application development has undergone the following stages:

Mainframe systems for multiple end-users
running orphaned software on an isolated PC
client/server mode
Distributed processing Mode
Content Service Model (the embodiment of network mobility)

Distributed processing mode synthesizes the advantages of network and processor development, distributes processes across multiple processors, and allows these processes to share data. Although this model has many advantages unmatched by large computer systems, it has a drawback: it is difficult to manage. Software updates, installation, maintenance is very difficult.

The Content service mode (the embodiment of network mobility) is based on the popular distributed processing mode, and the software can be automatically transferred to each computer through the network. This solves the problem of system management in distributed processing system.

Ii. Java architecture support for network mobility

The Java architecture support for network mobility is reflected in the following areas:

(1) platform Independence and security : The Java architecture is inextricably linked to network mobility support and its support for platform independence and security. Although platform independence and security are not necessary for network mobility, they provide a great help for the implementation of network mobility. Platform agnostic makes it easier to transfer programs on the network without having to prepare different versions for different platforms. Enables users to confidently download class files from a variety of sources.

(2) Dynamic connection : The main problem of network mobility is time. Java is supported for dynamic connections. The Java architecture cuts the traditional single binary executable into a small binary fragment-java class file-to solve the time problem, the class is dynamically connected when the program needs it, and the user does not have to wait until all the class files have been downloaded.

(3) dynamic expansion : In addition to dynamic connections, the Java architecture allows for dynamic scaling. A dynamic extension is another way to load a class file that can be deferred until the Java application runs.

(4) Compact class file : In addition to dynamic connectivity and dynamic expansion, the Java architecture's direct support for network mobility is also reflected in the class file format. To reduce the time it takes to transfer programs over the network, the class is designed to be compact. The Java compiler does not do much local optimizations. Leave the optimization work to the Java virtual machine.

(5)jar file : Allows multiple files to be transferred during one network transfer, reducing the time of network protocol handshake.

(6) do not use on-demand download : Another strategy to reduce the end-user wait time is to not take the practice of downloading class files on demand, there are several different technologies, such as the adoption of subscription mode.

Third, Java Network mobility examples

(1)Java applet (example of Network Mobile code): It shows all the features of the Java Network: platform-Independent, network mobility, security. Java applets can be run on any platform, as long as there is a Java-enabled browser. Java applets also demonstrate the security capabilities of Java because they run in a tightly restricted sandbox. Most importantly, the Java applet shows its network mobility. Java applets can be maintained on a central server and can be routed over a network to many kinds of computers. To upgrade an applet, you only need to upgrade the server. The next time the user uses it, they can get the upgraded version. Therefore, the maintenance is local and the operation is distributed.

(2)Jini service Object (example of a network moving object): In addition to the network mobility of the code, the Java architecture has a promise: The network mobility of the object. Objects travel through the network, carrying their own classes, plus snapshot data that represents the state of the object. The network mobility of objects simplifies the work of software developers in designing and deploying distributed systems. Through object serialization and remote method invocation (RMI), the Java API provides a distributed object model that expands on the local object model, breaking the boundaries between Java virtual machines.

Deep Java Virtual Machine (4)--Network mobility