2 Developing Java-based Applets for MapleNet

In this Chapter

• Writing Java-based Applets
• Compiling Java Code
• Creating a JAR File
• Creating an HTML Page
• Publishing Applets to the MapleNet Server

Important Note to Previous MapleNet Users: prior to MapleNet, Release 2.0, your applets used the Java package com.maplesoft.client.*, for example, class com.maplesoft.client.MapleStatement. Due to the repackaging of Java classes within all Maplesoft products, the classes in com.maplesoft.client.* are now found in the package com.maplesoft.maplenet.client.* The imports in your existing applets must be changed and recompiled to work in MapleNet, Release 2.5 and higher.

2.1 Writing Java-based Applets

The following Sample Integration Applet (Figure 1) requires a user to enter a username, password, and expression. By clicking the Calculate button, a request is sent to the MapleNet server to integrate the expression. The result is displayed in the Result textbox. This applet illustrates how requests are passed to the MapleNet server. The input (Enter Expression textbox) and output (Result textbox) are text-based Maple syntax.

Figure 1: Sample Integration Applet

Passing Requests to MapleNet

The Sample Integration Applet Code (Listing 1) provides the section of code that performs the connection with MapleNet. In this example, the computer name is derived from the web page that contains the applet during the initialization phase of the applet, which is stored in the host string variable. The code for this example is in the source file integration.java, which is available in the Publisher/samples folder created during installation.

Listing 1 Sample Integration Applet Code
*	//Routine to take the input expression and //send it to the MapleNet Server //using the MapleStatement class void do_calc (ActionEvent e) {
1	//Erase current answer TF_Result.setText( " ");
2	//Retrieve the expression String expression = TF_Expression.getText();
*	//If there is an expression, process it if ( expression.length () > 0 ) {
3	//Need user and password String user = TF_Username.getText () ; String pswd = TF_Password.getText () ;
4	//Must encapsulate the `execute()` method in a try/catch //block try {
5	//Create the user login object UserInfo userinfo = new UserInfo( user, pswd );
6	//Create the MapleStatement that will connect to the server // - use the Applet (this) to set connection information MapleStatement stmnt = new MapleStatement( this ); stmnt.setUser( userinfo );
7	//Encapsulate the expression into maple integration form String question = "int( "+ expression + ", x)";
8	//Get MapleNet server to process the question String answer = stmnt.execute( question ); //Verify that an answer was retrieved if (answer==null || answer.length() <= 0 ) { //No answer - check the XML returned from the server answer = "Error: " +stmnt.getXMLString(); }
9	//Display the result TF_Result.setText( answer ); } catch (Exception ex ) { //Catch all exceptions here //MapleStatement.execute will throw // MapleStatementException - usually syntax error in question // MapleException - server connection or login errors System.out.println("do_calc exception = " + ex.toString() ); } //Put keyboard focus back to expression box TF_Expression.setSelectionStart (0); TF_Expression.setSelectionEnd( equation.length() ); TF_Expression.requestFocus(); } else { // No expression specified Toolkit.getDefaultToolkit() .beep(); }
	}

Sequence of Events

When the user clicks the Calculate button on the Sample Integration Applet (Figure 1), the do_calc() routine is invoked with the following sequence of events:

1. The Result textbox is set to blank.
2. The expression is extracted from the Enter Expression text box.
3. The username and password are obtained from the appropriate text boxes.
4. A try/catch block is used to catch any exceptions that are raised when communicating with the MapleNet server.
5. The UserInfo object is created.
6. A MapleStatement object is created using the Applet for establishing the host and port. Note that this step creates only the object. The actual connection to the server is not made until the MapleStatement execute method is used. The user information is set in the created stmnt.
7. The actual request for the server is built using the Maple syntax for integration of the expression from event 2.
8. The question is passed to the server using the MapleStatement execute method. The result is stored in the String variable answer. Note that any error from the server is raised as an exception. If an exception occurs, it is handled in the catch() portion of code.
9. The answer is displayed in the Result text box.

Maple Notes

• To pass multiple questions to the server, you can build a string array containing the questions and pass them to the execute method. This method returns a string array of resulting answers corresponding to each question.
• Expression sequences cannot be rendered in MathML. Therefore, the output for any Maple command you are using that returns an expression sequence (for example, solve) must be converted to a list if you want to render it in MathML. If you do not convert it, only the first element of the expression sequence will be displayed.
• As of MapleNet 10.5, the preferred method for creating the MapleStatment is with the MapleStatement( Applet applet ); constructor. With this method, MapleNet can determine the connection information, host, and port from the applet. Now, hostname and port do not have to be hardcoded into the application and are not tied to a particular setup.

2.2 Compiling Java Code

Compiling the applet code with a Java compiler produces an integration.class file. This class file contains the executable code for the applet. To use the executable code, create an HTML page that references the class as an applet.

The mnc-maplenet.jar file must be included in the classpath argument of the compiler. For a complete list of necessary JAR files, see the Appendix. Listing 2 illustrates how to compile a Java class named integration.java.

Listing 2 Compiling integration.java

The following examples would be typed into a DOS or console window.

On Windows:

 javac -classpath \path\to\mnc-maplenet.jar integration.java



 Note: 1) the above command is typed as a single line.

       2) Replace \path\to with the actual path to the file mnc-maplenet.jar

  

On other platforms (Macintosh, Linux, and UNIX):

 

  javac -classpath /path/to/mnc-maplenet.jar integration.java 



 Note: 1) the above command is typed as a single line.

       2) Replace /path/to with the actual path to the file mnc-maplenet.jar

 

Notes:

1. The Java SDK bin directory is required to be included in the PATH environment variable. Otherwise use the complete path to the javac program.

2. Ensure that you use the correct file path specification for the mnc-maplenet.jar file so that the javac program can locate it.

3. The path separator character is a semi-colon (;) in Windows and a colon (:) on other platforms.

Important note to previous MapleNet users: In earlier versions, all MapleNet client code was packaged in a single JAR file (maplenetclient.jar). In MapleNet 10, the code is separated into several JAR files to improve download efficiency. To be compatible with MapleNet 10, your existing code must be recompiled with these new JAR files.

2.3 Creating a JAR File

Use the following command to create a JAR file, for example, myapplet.jar, that contains the required class files. This example assumes the class files are in the current directory.

jar -cf myapplet.jar *.class

where myapplet.jar is the name of the JAR file being created and *Class is used to include all class files in the present directory.

For some classes in the API to be executed (PlotComponent, mathmlEquation and mathmlEditEquation), the application JAR file must be signed for appropriate permissions on the client machine. For complete instructions on how to sign a JAR file, refer to http://download.oracle.com/javase/tutorial/security/toolsign/index.html.

Once this JAR file is created (and signed, if necessary), specify it in the .html file, as shown in the following section.

2.4 Creating an HTML Page

Before you can publish to the MapleNet server, you must create an HTML page that references the compiled Java code (the Class file) as an applet.

The following Integration.html sample code (Listing 3) illustrates how to build a page for Microsoft® Internet Explorer® and Mozilla® browsers.

Note: Java applets that require a Java version greater than 1.1 must use the Java Plugin. Use the <object> tag in Internet Explorer and the <embed> tag in Mozilla browsers (e.g., Firefox®). For a complete discussion of setting up web pages for simultaneous Internet Explorer and Firefox support, refer to http://download.oracle.com/javase/1.5.0/docs/guide/plugin/developer_guide/using_tags.html.

Listing 3 Integration.html

<html>

  <head>

    <title>Integration Example</title>

  </head>



  <body>

    <center>

      <H2>Integration Applet will appear below in a Java-enabled browser</H2>

      <object classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93"

              width="400" height="300"

              align="middle" >

        <param name="type" value="application/x-java-applet;version=1.6" />

        <param name="CODEBASE" value = "./" />

        <param name="CODE" value = "integration.class" />

        <param name="NAME" value = "IntegrationApplet" />

        <param name="ARCHIVE" value = "myapplet.jar,/maplenet/jar/mnc-index.jar" />

        <param name="expression" value="3*x^2 + 2*x +1" />

        <comment>

          <embed type="application/x-java-applet;version=1.6"

                 width="400"

                 height="300"

                 align="middle"

                 code="integration.class"

                 codebase="./"

                 archive= "myapplet.jar,/maplenet/jar/mnc-index.jar"

                 expression="3*x^2 + 2*x +1">

                 <noembed></comment> Error Java 1.6 not supported</noembed>

          </embed>

      </object>

    </center>

  </body>

</html>

Note: the relative path to mnc-index.jar must be specified. Ensure that all mnc-*Jar files listed in the Appendix are in the same directory as mnc-index.jar.

If you choose to use an applet tag in your web site, the parameters must be specified as shown in Listing 4.

Listing 4 Applet Parameter Syntax

<applet width="400" 

        height="300"

        align="middle

        code=" integration.class "

        codebase="./"

        archive=" myapplet.jar, /maplenet/jar/mnc-index.jar" >

  <param name=" expression " value="3*x^2 + 2*x +1"/>

</applet>

Specifying Parameters

In the .html file, specify the parameters listed in Table 1.

Table 1 HTML File Parameters
Parameter	Description
height	Specifies the size of the applet on the web page.
width	Specifies the size of the applet on the web page.
codebase	Specifies the directory from which to load the class file.
code	Specifies the class of the applet. In the example, integration.class is specified.
archive	Specifies mnc-index.jar and additional JAR files that are required, for example, myapplet.jar.

Notes on Host, Port, and Codebase

The host and port can be set via several different mechanisms. You can explicitly set the host and port using the constructor
       MapleStatment( String host, int port, String user, String password )
With this method, if you move the application to another server, your application will be responsible for determining the new host name and/or port number. An alternative is to use the constructor
       MapleStatment( Applet applet )
so that the connection information is determined from the URL of the web page that displays the applet. Therefore, if the web page is moved to another server, the application will automatically use the new server with no changes.
A third alternative is to specify the host but set the port to -1 with the constructor
       MapleStatment( String host, int port, String user, String password )
In this instance, the code will try to load the maplenetConfig.properties file from the classpath. In the case of applets, the classpath is set by the codebase parameter. The installer creates the file
       /maplenet/jar/maplenetConfig.properties
with the required port settings. If you point your codebase to the directory ".", the directory containing your applet and web page, your application will not find the maplenetConfig.properties configuration file. You would need to copy the config file to the directory that corresponds to ".".

For this example, integration.java, you can add optional input parameters in the Java source code, as listed in Table 2.

Table 2 Java Source Code File Parameters
Parameter	Description
host	Specifies the name of the MapleNet server. The default is the name of the server for the web page.
expression	Specifies the initial value for the Enter Expression text box. The applet does not perform the integration until the Calculate button is clicked. If not specified, the field is blank.

Loading the Web Page

When the web page loads, it runs the applet specified by the code parameter. This code accesses the MapleNet server using the classes indexed in the mnc-index.jar file. This file and all other files listed in the Appendix must be accessible to the web browser.

Once the applet is compiled and the web page is created, publish the associated files (.html, .java, and .jar) to the MapleNet server.

2.5 Publishing Applets to the MapleNet Server

Publishing a Java applet to the MapleNet server requires copying the applet JAR file and its associated HTML page to the appropriate directory on the server. The files can be copied to the server using any network file transfer tool, such as FTP, SSH, or WebDAV.

Consult your site administrator for specific details on where your files should be placed and what method should be used to transfer them.

Once the files are copied to the server, your content will be available by accessing the appropriate URL. Using the example developed in Section 2.4 with the files

myapplet.jar

Integration.html

then assuming the MapleNet server is myserver.com, and that your files were transferred to the applets directory of the MapleNet web application, the applet can be accessed by pointing your browser to http://myserver.com/maplenet/applets/Integration.html.

Consult your site administrator for the exact URL to access your content.