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JavaScript code on a web page can interact with Java applets embedded on the page. JavaScript code can perform operations such as the following:
TheLiveConnect Specification describes details about how JavaScript code communicates with Java code.
Security warnings are shown when JavaScript code makes calls to a Java applet. To suppress these warnings, add theCaller-Allowable-Codebase attribute to the JAR file manifest. Specify the location of the JavaScript code that is allowed to make calls to the applet. SeeJAR File Manifest Attributes for Security for information about theCaller-Allowable-Codebase attribute.
This topic explores JavaScript code to Java applet communication using the Math applet example. TheMathApplet class and supportingCalculator class provide a set of public methods and variables. The JavaScript code on the web page invokes and evaluates these public members to pass data and retrieve calculated results.
Here is the source code for theMathAppletgetCalculator method returns a reference to theCalculator helper class.
package jstojava;import java.applet.Applet;public class MathApplet extends Applet{ public String userName = null; public String getGreeting() { return "Hello " + userName; } public Calculator getCalculator() { return new Calculator(); } public DateHelper getDateHelper() { return new DateHelper(); } public void printOut(String text) { System.out.println(text); }}The methods in theCalculator
package jstojava;public class Calculator { private int a = 0; private int b = 0; // assume b > a public void setNums(int numA, int numB) { a = numA; b = numB; } public int add() { return a + b; } public int [] getNumInRange() { int x = a; int len = (b - a) + 1; int [] range = new int [len]; for (int i = 0; i < len; i++) { range[i]= x++; System.out.println("i: " + i + " ; range[i]: " + range[i]); } return range; }}ThegetDate method of theDateHelper
package jstojava;import java.util.Date;import java.text.SimpleDateFormat;public class DateHelper { public static String label = null; public String getDate() { return label + " " + new SimpleDateFormat().format(new Date()); }}Deploy the applet in a web page,AppletPage.html
<script src= "https://www.java.com/js/deployJava.js"></script><script> <!-- applet id can be used to get a reference to the applet object --> var attributes = {id:'mathApplet', code:'jstojava.MathApplet', width:1, height:1} ; var parameters = { jnlp_href: 'math_applet.jnlp'} ; deployJava.runApplet(attributes, parameters, '1.6');</script>Next, add some JavaScript code to theAppletPage.htmlCalculator). The JavaScript code is able to handle primitive, array, and object return types.
<script language="javascript"> function enterNums(){ var numA = prompt('Enter number \'a\'?','0'); var numB = prompt( 'Enter number \'b\' (should be greater than number \'a\' ?','1'); // set applet's public variable mathApplet.userName = "John Doe"; // invoke public applet method var greeting = mathApplet.getGreeting(); // get another class referenced by applet and // invoke its methods var calculator = mathApplet.getCalculator(); calculator.setNums(numA, numB); // primitive datatype returned by applet var sum = calculator.add(); // array returned by applet var numRange = calculator.getNumInRange(); // check Java console log for this message mathApplet.printOut("Testing printing to System.out"); // get another class, set static field and invoke its methods var dateHelper = mathApplet.getDateHelper(); dateHelper.label = "Today\'s date is: "; var dateStr = dateHelper.getDate(); <!-- ... --></script>The Math applet displays the following results on the web page when the number a = 0 and b = 5:
Results of JavaScript to Java CommunicationHello John Doea = 0 ; b = 5Sum: 5Numbers in range array: [ 0, 1, 2, 3, 4, 5 ]Today's date is: 5/28/13 4:12 PM //shows current date
OpenAppletPage.html
Checksecurity restrictions placed on applets invoked by JavaScript code.
Download source code for theInvoking Applet Methods From JavaScript Code example to experiment further.
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