How to show Java applet in HTML page

Details: Written by Nam Ha Minh; Last Updated on 09 August 2019 | Print Email

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An applet is a Java program runs inside a web browser. Typically, you write the applet as a normal Java class (extending from JApplet class) and embed it into an HTML page using the <applet> tag so the users can see and interact with your applet. This article describes various examples of how to display a Java applet inside an HTML page:

1. Syntax of <applet> tag

According to Oracle documentation, following is a complete syntax of the <applet> tag:

<APPLET
   CODEBASE = codebaseURL
   ARCHIVE = archiveList
   CODE = appletFile...or... OBJECT = serializedApplet
   ALT = alternateText
   NAME = appletInstanceName
   WIDTH = pixels HEIGHT = pixels
   ALIGN = alignment
   VSPACE = pixels HSPACE = pixels
   >
       <PARAM NAME = appletAttribute1 VALUE = value>
       <PARAM NAME = appletAttribute2 VALUE = value>
       . . .
       alternateHTML
</APPLET>

The elements in bold and red are required. Others are optional. Put the <applet> tag with its attributes inside the <body> element of the HTML page, it can be nested in other container tags like <div> or <table>. All the applet’s files (classes, jars, resources, etc) should be placed in the same folder as the HTML page.

2. The simplest way to show a Java applet

Suppose you write an applet in SimpleApplet.java file and compile it to SimpleApplet.class file, the following code quickly shows off your applet:

<applet code="SimpleApplet.class"></applet>

Or set size for the applet explicitly:

<applet code="SimpleApplet.class" width=”125” height=”125”></applet>

3. Show a Java applet bundled in a jar file

It’s very common that you package the applet and its related classes as a single jar file. In this case, use the following code:

<applet 
	archive="SimpleApplet.jar" 
	code="net.codejava.applet.SimpleApplet.class">
</applet>

That displays the applet bundled in a jar file named SimpleApplet.jar and the applet class file is SimpleApplet resides under the package net.codejava.applet.

4. Show a Java applet with parameters

Sometimes you need to send some parameters from the HTML page to the Java applet. In this case, use following code:

<applet
	archive="SimpleApplet.jar"
	code="net.codejava.applet.SimpleApplet.class">
		<param name="user" value="tom">
		<param name="password" value="secret">
</applet>

That sends two parameters called user and password with corresponding values to the applet. And inside the applet, we can access these parameters as follows:

String user = getParameter("user");
String password = getParameter("password");

5. Show a Java applet having external jar files

In case your applet comes with external library jar files, specify these jar files as follows:

<applet
	archive="SimpleApplet.jar, mail.jar, video.jar"
	code="net.codejava.applet.SimpleApplet.class">
</applet>

In the above code, we specify two additional jar files mail.jar and video.jar which are required by the applet. The jar files are separated by commas. If the jar files in a directory:

<applet
	archive="SimpleApplet.jar, lib/mail.jar, lib/video.jar"
	code="net.codejava.applet.SimpleApplet.class">
</applet>

In the above code, the additional jar files are placed under lib directory.

6. Be prepared if the user cannot run your applet

In practice, the users may have problems of running your applet, such as the JRE/JDK or Java Plug-in have not installed, or their browser’s setting prevents Java applet from running, or even the browser does not understand the <applet> tag. So you need to anticipate such cases, for example:

<applet
	archive="SimpleApplet.jar"
	code="net.codejava.applet.SimpleApplet.class"

	alt="You need to have compatible browser to run this Java applet">
	
	Your browser does not support running applet. <br>
	Please install Java Plug-in from <a href="http://java.com">java.com</a>

</applet>

In the above code, we use the altattribute and alternate HTML text between the opening and closing elements of the <applet> tag to tell the browse should display that information if it cannot run the applet.

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.