Java network function and programming

Java network function and programming

Xu Yingxiao

(Shanghai University Computing Center 25 #)

Summary: Java language is the most popular programming language on the Internet. This article is aimed at Java's network function, which has made a preliminary introduction from the programming method such as image, sound, HTML document and text files from the Internet. The method of resources on the network has been introduced. A large number of concise understandable examples are provided.

Keywords: Java; Internet; network

The Java language is an emerging programming language on the Internet. There are many articles on Java's characteristics and basic programming methods. However, the majority of Java enthusiasts more want to know more about Java more step-by-step programming methods, this article on Java's network function and its programming method

A preliminary introduction.

In order to facilitate the first time to contact Java readers, this article briefly introduces some of Java programming. I. Introduction to Java Programming 1. Programming Environment: For most readers, the following configuration is a more economical option: operating system Win95 compile software JDK1.01 browsing software Netscape 2.0 or more (32-bit) 2. Programming method: first Enter the Java program with the text editor such as Edit, Notepad, etc., with .java as the file name suffix store. Perform the command line: "Javac file name" to compile the Java program. After compiling, generate the character code file that suffix .class. Finally, if it is Java Applitcation, execute the command line: "Java Byte Code File Name" to run the Java program. If it is a java applet, enter the HTML document of the Java Applet with the text editor, with .htm as the file name subsequent replication. Perform the command line: "AppletViewer HTML File Name" to run the Java Applet. Or open the HTML document with Netscape. 3. Description of the procedures in this article In order to make the program to be the most concise programming method, the procedures in this paper generally use the simplest form, omitting the thread and other content. Therefore, the procedure of this article is not a "good" program, but it is easier to understand the beginner. After all the programs in this article, the generated byte code file and the corresponding HTML document are uploaded to http://www.shu.edu.cn/~xyx/test/jvnet, can run correctly. The reader connected to the Internet can open the address with the browser to view the running effect. Readers connecting the Internet can also enter and compile the program in the local hard drive. Open the HTML document with Netscape's File / Open File menu, experience the programming method and view the running effect. If the reader wants to put Java Applet on your host or other FTP server, use the HTTP protocol or FTP protocol in Netscape, which should be modified as follows: If the reader has an account on a WWW host You can do your personal homepage (usually in the user's root directory to create a WWW or public_html directory, HOMEPAGE's address is http: // Hostname / ~ Personal account), you can put the corresponding http://www.shu.edu in this article .cn / ~ xyx / part is modified to reader's own web node address, and then load the generated byte code file and the corresponding HTML document to your own node. If the reader's computer is connected to the Internet, you can also find an FTP node that can be uploaded, such as: ftp: //ftp.shnet.edu.cn/incoming, the corresponding http: //www.shu in this article. The edu.cn/~xyx/ section is changed to the address of the FTP node, and the generated byte code file and the corresponding HTML document are uploaded to the node to view the running effect. If the reader's computer is not connected, it is also possible to run the web service software such as WebStar for Win95 on a single machine to modify the corresponding http: // www. Shu.edu.cn/~xyx/ part of this article to "http: // The local IP address "to simulate network programming.

Second, Java Network Functions and General Steps Java programs for access to networks can obtain resources such as images, sounds, HTML documents, and texts such as network nodes, and can process the obtained resources. For example, a Java program can read the latest data provided by a node every other time, and displayed in the form of a chart. On programming processing, it is generally manually made into a URL type object, and then obtains the resources represented by the object with the corresponding method (Method) in Java. Several examples of Java network functions are described below, and there are several different programming methods. Third, obtain image Java Applet from the network can directly obtain an image directly from the network and display it. In order to understand the programming method and from the local display image, we don't consider the network function first, to see an example of a simple image display: ● Program 1Import java.applet. *;

Import java.awt. *;

Public class imag0 extends applet {

Image image;

Public void init () {

Image = getImage (GetDocumentBase (), "Test.gif");

}

Public void paint (graphics g) {

g.drawImage (image, 0, 0, this);

}

}

This is the simplest acquisition and display image, in this example, first use getImage (getDocumentbase (), image file name to call the image Test.gif from the HTML document, and generate an image Type Object Image, then display the image on the screen with DrawImage (Image, 0, 0, 0, this).

If you want to get images from the other nodes on the network, the key is to create an object corresponding to other nodes on the network. Once the object of the iMage type is obtained, you can make any possible image operations.

Java provides the following ways to create images corresponding to other nodes:

GetImage (New URL)

It can be used in the format:

String URL = "Non-point URL";

Image image;

Try {

Image = GetImage (New URL (URL));

}

Catch (Exception E) {

System.out.println ("Can't Open THE URL");

}

or

URL IMGUR = NULL;

Image image;

Try {

Imgur = New URL ("Nonpare URL");

}

Catch (Malformedurlexcection E) {

System.out.println ("Can't Open THE URL");

}

Image = getImage (IMGUR);

The previous format generates a URL object with "New URL (URL)" and directly as a parameter of GetImage, and the latter format first uses "New URL (URL)" to generate a URL object, and then transmit it to GetImage. The two formats are essentially the same. In both formats, parts of generating URL objects are included

Try {

Get URL objects

}

Catch (Malformedurlexcection E) {

Error prompt

}

in.

For example, to call the image of http://www.shu.edu.cn/~xyx/img/shnet.jpg, the first format is as follows:

● Program 2

Import java.applet. *;

Import java.net. *;

Import java.awt. *;

Public class imag extends applet {image image;

Public void init () {

String Url = "http://www.shu.edu.cn/~xyx/img/shnet.jpg";

Try {

Image = GetImage (New URL (URL));

} catch (exception e) {}

}

Public void paint (graphics g) {

g.drawImage (image, 0, 0, this);

}

}

The second format is complete, as follows:

● Program 3

Import java.applet. *;

Import java.net. *;

Import java.awt. *;

Public class imag2 extends applet {

Image image;

URL IMGUR = NULL;

Public void init () {

Try {

Imgur = New URL ("http://www.shu.edu.cn/~xyx/img/shnet.jpg");

}

Catch (Malformedurlexcection E) {

System.out.println ("Can't Open THE URL");

}

Image = getImage (IMGUR);

}

Public void paint (graphics g) {

g.drawImage (image, 0, 0, this);

}

}

The two programs described above are imag.java and imag2. Java store, execute javac imag.java and javac imagaac2.java, will get the generated image of iMag.class and iMag2.class, and finally create the two Java Applets. HTML documentation, if iMag.class corresponds to the HTML document as follows: