Interstage Studio J Business Kit User's Guide

2.3.15 JavaScript Communication

This section describes the JavaScript communication of JBK Plugin.

JBK Plugin supports the JavaScript communication with Internet Explorer.

This section describes the following items:

• 2.3.15.1 Calling JavaScript from an applet

• 2.3.15.2 Calling a method of an applet from JavaScript

• 2.3.15.3 Accessing cookie information

2.3.15.1 Calling JavaScript from an applet

To call JavaScript from Java applet, it is necessary that Java communicates with JavaScript. JBK Plugin enables Java to communication with JavaScript using netscape.javascript.JSObject object, which is instance of Java wrapper class, in Internet Explorer.

• Class:

  • netscape.javascript.JSObject
    (extends java.lang.Object)

• Methods:

  • getWindow

    Gets the JSObject of the window (Window object of JavaScript) containing the given applet. This method takes only java.applet.Applet object as the parameter.

    public static JSObject getWindow(java.applet.Applet a)

  • call

    Calls the JavaScript method. Equivalent to "this.methodName(args[0], args[1], ...)" in JavaScript.

    public Object call(String methodName, Object args[])

  • eval

    Evaluates the JavaScript expression.

    public Object eval(String s)

  • getMember

    Retrieves the named member of the JavaScript object.

    public Object getMember(String name)

  • getSlot

    Retrieves the indexed member of the JavaScript object.

    public Object getSlot(int index)

  • setMember

    Sets the named member of a JavaScript object.

    public void setMember(String name, Object value)

  • setSlot

    Sets the indexed member of the JavaScript object.

    public void setSlot(int index, Object value)

  • toString

    Converts the JSObject to a String.

    public String toString()

  • removeMember

    Not supported.

    public void removeMember(String name)

    In the specification of Java packages for LiveConnect, removeMember method exists, but is not supported in Internet Explorer.

• Supported objects by JSObject

  The following JavaScript objects can be accessed with JBK Plugin via JSObject.

  JBK Plugin can access the following JavaScript objects via JSObject:

  Anchor/Applet/Array/Boolean/Button/Checkbox/Date/document/Element/Fileupload/Form/
  Frame/Function/Hidden/History/Image/Link/Location/Math/navigator/Number/Object/
  Option/Password/Radio/RegExp/Reset/screen/Select/String/Submit/Text/TextArea/Window

  • arguments.length, arguments[], and caller properties of a Function object cannot be used.

  • If the applet calls a JavaScript method whose parameters are instance of JavaScript object, e.g. concat() method of an Array object, use eval() method of JSObject to process exactly.

• How to use JSObject

  The following is the example to call JavaScript from the applet using JSObject:

  import netscape.javascript.*;
  import java.applet.*;
  
  public class Applet1 extends Applet {
       public void init() {
  
              JSObject win = JSObject.getWindow(this);
  
              try{
                   // call alert method of JavaScript Window object
                   win.call("alert", new Object[]{"Test"});
  
                   // set the status property of JavaScript Window object
                   win.eval("this.status=\"Hello World\"");
  
                   /* document.forms[0].elements[0] is <INPUT TYPE=button>. */
  
                   // refer the button, and set the value property to "Button".
                   JSObject doc = (JSObject) win.getMember("document");
                   JSObject forms = (JSObject) doc.getMember("forms");
                   JSObject aform = (JSObject) forms.getMember("0");
                   JSObject elements = (JSObject) aform.getMember("elements");
                   JSObject script_button = (JSObject) elements.getMember("0");
                   script_button.setMember("value", "Button");
  
              // exception handling for JSObject
              }catch(JSException e){
                   e.printStackTrace();
              }
       }
  }

  The following shows an example of HTML in which a form is called by the above applet.

  [HTML description]

  <HTML>
  <HEAD>
  <SCRIPT src="JBKTag.js" type="text/javascript" language="JavaScript">
  </SCRIPT>
  </HEAD>
  <BODY>
  
  <FORM>
    <INPUT TYPE=button value="button">
  </FORM>
  
  <SCRIPT type="text/javascript" language="JavaScript">
  <!--
      //Use JavaScript and write tags to display applet.
      showapplet();
  //-->
  </SCRIPT>
  </BODY>
  </HTML>

  [JavaScript code(JBKTag.js)]

  function showapplet() {
  
      document.writeln('<OBJECT CLASSID="CLSID:BEA62964-C40B-11D1-AACA-00A0C9216A67" WIDTH=100 HEIGHT=100>');
      document.writeln('<PARAM NAME="TYPE" VALUE="application/x-JBK-Plugin">');
      document.writeln('<PARAM NAME="NAME" VALUE="sample">');
      document.writeln('<PARAM NAME="CODE" VALUE="Applet1.class">');
      document.writeln('<PARAM NAME="color" VALUE="blue">');
      document.writeln('<PARAM NAME="useDefault" VALUE="true">');
  
      document.writeln('</OBJECT>');
  }

The class file for the JSObject class and JSException class is stored in the jar file for the development of the JBK plugin ("classes\jbkstd.jar" in the JBK installation folder). When compiling the class of an applet that uses the PluginAppletContext interface, check whether the jar file for the development of the JBK plugin is included in the classpath.

Note

Observe the following notes derived from Internet Explorer limitations when using JavaScript Communication in Internet Explorer:

• The user cannot use setMember method to set the properties of objects excluding window and document objects.

• The user cannot use eval emthod excluding window objects.

• Because of the security restrictions of Windows XP Service Pack 2, you must use absolute path instead of relative path to designate local files under the following conditions.

  • When opening a local file by using open method of the window object.

  • When setting a local file by using location property of the window object.

• You cannot use getMember method to get the properties of some objects.

• The type of the return value of the following methods of the Date object is Double in Internet Explorer in Netscape though it is Integer.

  • getYear

  • getMonth

  • getDate

  • getHours

  • getMinutes

  • getSeconds

  • getDay

  • getTimezoneOffset

Information

JSObject also supports the array of JavaScript. To get an array from applet using JavaScript, please refer to the following code.

import netscape.javascript.*;
import java.applet.*;

public class Applet1 extends Applet {

     public void init() {
            JSObject win = JSObject.getWindow(this);

            /* Array is set as 'arrayname = new Array("0", "1", "2", ...)' */

            // get JavaScript Array object
            JSObject array = (JSObject)win.getMember("arrayname");
            // get a number of index
            (Integer)array.getMember("length");
            // get the first member of the array
            (String)array.getMember("0");
     }
}

2.3.15.2 Calling a method of an applet from JavaScript

JBK Plugin allows calling a public method of an applet from JavaScript.

If the calling public method is overloaded, it cannot be guaranteed which of the methods is called.

• Setting for Calling Method

  To call a method of the applet from JavaScript, put the following line in the jbkplugin.properties file:

  jbk.plugin.sw.script.enable =<method calling-used-or-not>

  Specify true or false to <method calling-used-or-not>.

  true

  Calling applet method is enabled.

  false

  Calling applet method is disabled.

  By default, the value of this property is set to false.

• How to call a method

  To call a method of an applet from JavaScript, Please refer the following code.

  Example: Calling Hello() method of the applet when the button1 is pushed.

  [HTML description]

  <OBJECT classid="CLSID:BEA62964-C40B-11D1-AACA-00A0C9216A67" width="160" height="120">
              <PARAM NAME="CODE" VALUE="Applet1.class">
              <PARAM NAME="TYPE" VALUE="application/x-JBK-Plugin">
              <PARAM NAME="ARCHIVE" VALUE="TestApplet.jar">
              <PARAM NAME="useDefault" VALUE="true">
      </OBJECT>
  
      <INPUT TYPE="button" NAME="button1" VALUE="Button" onClick="sample()">
  
      <Script language="JavaScript" FOR="window">
      <!---
          function sample() { alert(document.applets[0].Hello("XXXX")); }
      //---->
      </Script>

  [Applet code]

     import java.applet.*;
  
      public class Applet1 extends Applet{
             public void init() { }
  
             // return the formatted String
             public String Hello(String name){
                    String retVal = new String("Hello ");
                    retVal += name ;retVal += "!!" ;return (retVal);
             }
      }

• Type conversion from JavaScript to applet

  When JavaScript calls a method of an applet, JavaScript sends the argument to the applet. JavaScript value is converted to Java value. The conversion specifications are as follows:

  Table 2.3 JavaScript to Java applet type conversion

  argument of applet's method	Type of the value sent from JavaScript
  	Type of JavaScript	Results
  Byte/byte	String values	From "-128" to "127": convert to byte value from -128 to 127 Out of the range or invalid numerical strings: convert to 0 Positive floating decimal string: round up to the integer value Negative floating decimal string: round up to the integer value
  	Number values	From -128 to 127": convert to byte value from -128 to 127 Out of the range: convert to 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Boolean values	true: converted to -1 false: 0
  	null value	converted to 0
  	Object	converted to 0
  Character/char	String values	From "0" to "65535": convert to char value from 0 to 65535 Out of the range or invalid numerical strings: convert to char value 0 Positive floating decimal string: round up to the integer value
  	Number values	From 0 to 65535: convert to char value from 0 to 65535 Out of the range: convert to char value 0 Positive floating decimal: round up to the integer value
  	Boolean values	true: converted to char value 65535 false: converted to char value 0
  	null value	converted to 0
  	Object	converted to 0
  Short/short	String values	From "-32768" to "32767": convert to short value from -32768 to 32767 Out of the range or invalid numerical strings: convert to short value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Number values	From -32768 to 32767: convert to short value from -32768 to 32767 Out of the range: convert to short value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Boolean values	true: converted to short value -1 false: converted to short value 0
  	null value	converted to 0
  	Object	converted to 0
  Integer/int	String values	From "-2147483648" to "2147483647": convert to int value from -2147483648 to 2147483647 Out of the range or invalid numerical strings: convert to int value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Number values	From -2147483648 to 2147483647: convert to int value from -2147483648 to 2147483647 Out of the range: convert to int value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Boolean values	true: converted to int value -1 false: converted to int value 0
  	null value	converted to 0
  	Object	converted to 0
  Long/long	String values	From "-2147483648" to "2147483647": convert to long value from -2147483648 to 2147483647 Out of the range or invalid numerical strings: convert to long value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value
  	Number values	From -2147483648 to 2147483647: convert to long value from -2147483648 to 2147483647 Out of the range: convert to long value 0 Positive floating decimal: round up to the integer value Negative floating decimal: round up to the integer value *If long value is beyond the limits of int value, the result of conversion becomes 0.
  	Boolean values	true: converted to long value -1 false: converted to long value 0
  	null value	converted to 0
  	Object	converted to 0
  Boolean/boolean	String values	"0": converted to boolean value false Digit string except "0": converted to boolean value true Other string: converted to boolean value false
  	Number values	0: converted to boolean value false except 0: converted to boolean value true
  	Boolean values	true: boolean value true false: boolean value false
  	null value	converted to boolean value false
  	Object	converted to boolean value false
  Float/float	String values	From "±1.4e-45" to "±3.4028235e+38": converted to float value from ±1.4e-45 to ±3.4028235e+38 Out of the range or invalid numerical strings: converted to float value 0.0
  	Number values	From ±1.4e-45 to ±3.4028235e+38: converted to float value from ±1.4e-45 to ±3.4028235e+38 Out of the range: converted to float value 0.0
  	Boolean values	true: converted to float value -1.0 false: converted to float value 0.0
  	null value	converted to 0.0
  	Object	converted to 0.0
  Double/double	String values	From "±4.9e-324" to "±1.7976931348623157e+308": converted to double value from ±4.9e-324 to ±1.7976931348623157e+308 Out of the range or invalid numerical strings: converted to double value 0.0
  	Number values	From ±4.9e-324 to ±1.7976931348623157e+308: converted to double value from ±4.9e-324 to ±1.7976931348623157e+308 Out of the range: converted to double value 0.0
  	Boolean values	true: converted to double value -1.0 false: converted to double value 0.0
  	null value	converted to 0.0
  	Object	converted to 0.0
  String	String values	Any string: converted to Java String
  	Number values	Any number: converted to Java String
  	Boolean values	true: converted to String "-1" false: converted to String "0"
  	null value	converted to null Object
  	Object	converted to Java String
  JSObject	String values	Any string: converted to JSObject null
  	Number values	Any digit string: converted to JSObject null
  	Boolean values	converted to JSObject null
  	null value	converted to JSObject null
  	Object	converted to JSObject *Any method of JSObject class cannot be used.

• Type conversion from the return value of applet method to JavaScript

  When an applet returns the result of calling method to JavaScript, the return value is converted to JavaScript value. These conversion specifications are as follows:

  Table 2.4 [Java applet to JavaScript type conversion]

  Return value type of applet method	JavaScript value
  Void	null value
  Byte/byte	Number value
  Character/char	Number value
  Short/short	Number value
  Integer/int	Number value
  Long/long	Number value, the range is from -2147483648 to 2147483647
  Boolean/boolean	Boolean value true is true, false is false.
  Float/float	Number value
  Double/double	Number value
  String	String value
  JSObject	Object value

2.3.15.3 Accessing cookie information

This section describes how to access cookie information.

An applet can access cookie by using cookie property of JavaScript document object which is referred via JSObject.

Example

Gets the cookie information from the browser, and sends it to the server.

import java.applet.*;
import java.net.*;
import netscape.javascript.*;

public class Applet1 extends Applet {
    public void init(){
        JSObject win = JSObject.getWindow(this);

        // refer the cookie property of JavaScript document object
        JSObject doc = (JSObject)win.getMember("document");
        String cookie = (String)doc.getMember("cookie");

        try{
            /* set the URL to send the cookie */
            // get codebase of the applet
            URL url = getCodeBase();
            String strurl = url.toString();

            // set URL
            /* in this case, "/servlet/cookie" */
            strurl = strurl + "/servlet/cookie";
            url = new URL(strurl);

             // set the HTTP request property
             HttpURLConnection urlCon = (HttpURLConnection)url.openConnection();
             urlCon.setRequestProperty("cookie", cookie);

             urlCon.disconnect();

             /* Describe the procedure using HttpURLConnection */

        }catch(Exception e){
             e.printStackTrace();
        }
    }
}