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Trail: Deployment
Lesson: Applets
Section: Practical Considerations When Writing Applets
Applets
Getting Started with Applets
Importing Classes and Packages for Applets
Defining an Applet Subclass
The Life Cycle of an Applet
Methods for Milestones
Methods for Drawing and Event Handling
Methods for Adding UI Components
What Applets Can and Can't Do
Taking Advantage of the Applet API
Finding and Loading Data Files
Displaying Short Status Strings
Displaying Documents in the Browser
Sending Messages to Other Applets
Playing Sounds
Defining and Using Applet Parameters
Deciding Which Parameters to Support
Writing the Code to Support Parameters
Giving Information about Parameters
Using the APPLET Tag
Practical Considerations When Writing Applets
Security Restrictions
Creating a User Interface
Creating a GUI
Displaying Diagnostics to the Standard Output and Error Streams
Getting System Properties
Threads in Applets
Threads in Applets: Examples
Working with a Server-Side Application
A Simple Network Client Applet
Using a Server to Work Around Security Restrictions
Finishing an Applet
Before You Ship that Applet
The Perfectly Finished Applet
Deploying Applets
General Deployment Considerations
Using the applet Tag
Using the object Tag
Using the embed Tag
Deploying Applets in a Mixed-Browser Environment
Solving Common Applet Problems
Questions and Exercises
Home Page > Deployment > Applets
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Working with a Server-Side Application

> Applets, like other Java programs, can use the API defined in the `java.net` package to communicate across the network. The only difference is that, for security reasons, the only host an applet can communicate with is the host it was delivered from.

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

> It's easy to find out which host an applet came from. Just use the `Applet` `getCodeBase` method and the `java.net.URL` `getHost` method, like this:

> >     String host = getCodeBase().getHost();

> Once you have the right 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.

### A Simple Network Client Applet

> Here's an example of implementing an applet that's a network client.

### Using a Server to Work Around Security Restrictions

> Here's an example of implementing a server to get around applet security restrictions.

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