Trail: Deployment
Lesson: Java Applets
Section: Doing More With Applets

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~~The Java Tutorials have been written for JDK 8.~~Java教程是为JDK 8编写的。~~Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.~~本页中描述的示例和实践没有利用后续版本中引入的改进，并且可能使用不再可用的技术。
~~See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.~~有关Java SE 9及其后续版本中更新的语言特性的摘要，请参阅Java语言更改。
~~See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.~~有关所有JDK版本的新功能、增强功能以及已删除或不推荐的选项的信息，请参阅JDK发行说明。

Working With a Server-Side Application

Java applets, like other Java programs, can use the API defined in the java.net package to communicate across the network. A Java applet can communicate with server applications that run on the same host as the applet. This communication does not require any special setup on the server.

Note: Depending on the networking environment that an applet is loaded into, and depending on the browser that runs the applet, an applet might be unable to communicate with its originating host. For example, browsers running on hosts inside firewalls often cannot obtain much information about the world outside the firewall. As a result, some browsers might not allow applet communication to hosts outside the firewall.

When the applet is deployed to a web server, use the Applet getCodeBase method and the java.net.URL getHost method to determine which host the applet came from, as follows:

String host = getCodeBase().getHost();

If the applet is deployed locally, the getCodeBase method returns null. Use of a web server is recommended.

After you have the correct host name, you can use all the networking code that is documented in the Custom Networking trail.

Note: Not all browsers support all networking code flawlessly. For example, one widely used browser compatible with Java technology doesn't support posting to a URL.

For an example of implementing an applet that is a network client, see Network Client Applet Example.

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