Understanding Java Class Accessibility

I don't understand what makes a Java library class accessible by a Java applet. If an applet has an import statement that imports, say, java.util.TreeMap, then when a web browser accesses a web page containing that applet, does it download the Java code for the TreeMap class at that time, and if so, does that mean that you have to package the TreeMap class as part of your applet class code somehow? Or, must the TreeMap class be installed as part of the Java virtual machine on the computer that is running the browser? If the latter, what determines whether or not the typical computer will have the TreeMap class available? Is the TreeMap class available on a PC running Windows XP, using the Java virtual machine that Microsoft supplies? Where can I read about this sort of thing? How can I determine what classes I can safely use if I want my applet to run on both Windows and Macs?

"I don't understand what makes a Java library class accessible by a Java applet. If an applet has an import statement that imports, say, java.util.TreeMap, then when a web browser accesses a web page containing that applet, does it download the Java code for the TreeMap class at that time, and if so, does that mean that you have to package the TreeMap class as part of your applet class code somehow? "
No.
"Or, must the TreeMap class be installed as part of the Java virtual machine on the computer that is running the browser?"
Yes
"If the latter, what determines whether or not the typical computer will have the TreeMap class available?"
The version of the Java Runtime environment/Plug-in installled on the PC
"Is the TreeMap class available on a PC running Windows XP, using the Java virtual machine that Microsoft supplies?"
No which why some people don't use the newer Java classes or Swing when they write applets.
"Where can I read about this sort of thing? How can I determine what classes I can safely use if I want my applet to run on both Windows and Macs?"
http://java.sun.com/j2se/1.4.1/docs/guide/plugin/developer_guide/using_tags.html

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[http://www.javalobby.org/java/forums/t18345.html]
[http://java.sun.com/developer/onlineTraining/Security/Fundamentals/magercises/ClassLoader/help.html]
[http://publib.boulder.ibm.com/infocenter/javasdk/v1r4m2/index.jsp?topic=/com.ibm.java.doc.diagnostics.142/html/id1100.html]
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[http://www.informit.com/articles/article.aspx?p=1187967]
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does anybody has experience in solving thus question,Please reply ,Thank you for your help.
%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page import = "java.sql.*" %>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
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<style>

</style>
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<body>
<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" width="100%" id="AutoNumber1">
<tr>
<td width="100%">
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<tr>
<td width="100%">@</td>
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<tr>
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<td width="87%">
<img border="0" src="images/mid-rdxw2.gif" width="101" height="18"><p>
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%>
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<%
%>
<p>
<img border="0" src="images/mid-hyxw2.gif" width="94" height="19"></p>
<%
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%>
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<%
%>
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type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: Exception in JSP: /newsMain.jsp:47
44: strSql = "select * from news where TYPE=1";
45:           rs = conn.executeQuery(strSql);
46:
47:           while (rs.next()){
48:
49: %>
50:
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     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
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nogoodatcoding wrote:
Tolls wrote:
Is that Jasper Exception telling us where the problem is in the jsp, though?
If it is, then "rs" is null in the call rs.next()...which means conn.executeQuery() is returning null. Which means that whatever class conn is (news.conn?) has a problem maybe?That's possible. Though, it may just be the case that the 'conn' object itself is null! That line is the first place where it's being used and there are no checks that I can see...we'll have to wait for the OP to investigate and reply I guess.That's what I originally thought, then I noticed it was saying line 47, which is the rs.next() line. Assuming Jasper is correct in its choice of line, then it's the rs that's null. Which means the conn is doing strange things.
Edit: Now that I think about it, going by the previous thread the OP posted, I'm wondering whether news.conn class is their attempt to move the JDBC stuff out of the JSP page, and it's grabbing the "real" connection (java.sql.Connection) and getting the result set and returning it...or getting something wrong and returning null.
Edited by: Tolls on 11-Jun-2009 12:24

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here is the code
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* Created on October 31, 2006, 12:14 PM
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http://search400.techtarget.com/tip/1,289483,sid3_gci1065992,00.html
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http://search400.techtarget.com/tip/1,289483,sid3_gci1065992,00.html
iSeries 400 Tips:
TIPS & NEWSLETTERS TOPICS SUBMIT A TIP HALL OF FAME
Search for: in All Tips All search400 Full TargetSearch with Google
PROGRAMMER
Sample code: Accessing MS SQL Server database from the iSeries
Eitan Rosenberg
09 Mar 2005
Rating: --- (out of 5)
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http://www.microsoft.com/downloads/details.aspx?familyid=07287b11-0502-461a-b138-2aa54bfdc03a&displaylang=en
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msbase.jar
mssqlserver.jar
msutil.jar
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My guess is that the server's host name isn't right. It necessarily (or even usually) the "windows name" of the computer. Try with the numeric IP address instead (type "ipconfig" to see it).
First aid check list for "connection refused":
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Suraj,
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LINK:http://help.sap.com/saphelp_nwpi71/helpdata/EN/e2/e13fcd80fe47768df001a558ed10b6/frameset.htm
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I created a.properties file and loaded it using loadjava.
Next I wrote a class in which I try to load the resource:
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import java.util.*;
public class C {
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java.lang.NullPointerException
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Never mind. I resolved this using a ResourceBundle, thanks to another posting on this forum. I must say, the oracle documentation for this feature is scant and erroneous.
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Jdeveloper Version 11.1.5
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Hi,
I am trying to implement the custom java class for mediator fault handling. However when this class is invoked its not able to access the "oracle.tip.mediator.common.error.recovery.MediatorRecoveryContext" class during run time (which exists in mediator.jar). However its able to access all the other imported class files which exists in other library files.
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Ramesh

Hi Ramesh,
Try out the following
1) Copy mediator.jar from SOA_HOME>/soa/modules/oracle.soa.mediator_11.1.1 to <MW_HOME>//soa/modules/oracle.soa.ext_11.1.1/classes
2) Goto <MW_HOME>//soa/modules/oracle.soa.ext_11.1.1/classes and run the following command:
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3) Now remove the jar file, i.e., mediator.jar from classes folder.
4) Restart the server.
Regards,
Srijith

Accessing java class in JSP on Tomcat 5.5 server

Just i want to use a java class in JSP.
Explanation in following steps :
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b. My Java file - test.java
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Now Brief explanation.
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<%@ page contentType="text/html; charset=iso-8859-1" language="java" import="java.sql.*,test" errorPage="" %>
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<%= obj.getAge(); %>
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package test;
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jre : C:\Program Files\Java\jre1.5.0\bin;
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PATH :
C:\Program Files\Java\jdk1.5.0\bin; C:\Program Files\Java\jre1.5.0\bin;
CLASSPATH :
.;C:\Program Files\Java\jre1.5.0\bin;
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HTTP Status 500 -
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: Unable to compile class for JSP
Generated servlet error:
The import test cannot be resolved
An error occurred at line: 26 in the jsp file: /NRMS/test/SimpleBean.jsp
Generated servlet error:
test cannot be resolved (or is not a valid type) for the field SimpleBean_jsp.obj
An error occurred at line: 26 in the jsp file: /NRMS/test/SimpleBean.jsp
Generated servlet error:
test cannot be resolved or is not a type
An error occurred at line: 26 in the jsp file: /NRMS/test/SimpleBean.jsp
Generated servlet error:
Syntax error on token(s), misplaced construct(s)
An error occurred at line: 26 in the jsp file: /NRMS/test/SimpleBean.jsp
Generated servlet error:
Syntax error on token "32", delete this token
An error occurred at line: 28 in the jsp file: /NRMS/test/SimpleBean.jsp
Generated servlet error:
Syntax error on token ";", delete this token
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     org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:328)
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     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:296)
     org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
     org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.4 logs.
Apache Tomcat/5.5.4
Please explain where i am doing the mistake.
Thanks in advance.
Regards,
Lax.

>
<%@ page contentType="text/html; charset=iso-8859-1"
language="java" import="java.sql.*,test" errorPage=""
%>Your class is test.test.The compiler wouldnt know what test is from your import.
Change import as
java.sql.*,test.test
<%! test obj = new test();
obj.setAge(32); %>The symbol '!' ?

Accessing a java class method from the jsp page.

Hi im a beginner with jsp and im trying to find a way to access a method of my java class file in jsp page. After searching through the forums i tried to use the usebean tag. Im using apache to host the jsp file.Below is an excerpt of my code and the error message i got. What am i doing wrong? anyone know?
<%@ page language="java" %>
<jsp:useBean id="movies" class="movie.Movie" />
<jsp:setProperty name="movies" property="*"/>
<%
movies.getStart("file:///C:/Video/Applications2/sun.mpg");
response.setContentType("text/xml");
%>
exception
org.apache.jasper.JasperException: Exception in JSP: /View.jsp:7
4: <jsp:setProperty name="movies" property="*"/>
5: <%
6:
7: movies.getStart("file:///C:/Video/Applications2/sun.mpg");
8: response.setContentType("text/xml");
9: %>
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     org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:375)
     org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
     org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
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root cause
javax.servlet.ServletException: javax/media/ControllerListener

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import java.io.*;
import java.awt.*;
import javax.media.*;
import javax.media.control.*;
import javax.media.format.*;
import javax.media.protocol.*;
import java.awt.image.*;
import javax.imageio.*;
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     boolean stateOK = true;
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int imgWidth;int imgHeight;
     Image outputImage;
     String sep = System.getProperty("file.separator");
     int[] outvid;
     int startFr = 1;int endFr = 1000;int countFr = 0;
     boolean sunjava=true;
     * Static main method
     public static void main(String[] args)
          if(args.length == 0)
               System.out.println("No media address.");
               new vid2jpg("file:///C:/Video/applications2/sun.mpg");     // or alternative "vfw://0" if webcam
          else
               String path = args[0].trim();
               System.out.println(path);
               new vid2jpg(path);
     * Constructor
     public vid2jpg(String path)
          MediaLocator ml;String args = path;
          if((ml = new MediaLocator(args)) == null)
               System.out.println("Cannot build media locator from: " + args);
          if(!open(ml))
               System.out.println("Failed to open media source");
     * Given a MediaLocator, create a processor and start
     private boolean open(MediaLocator ml)
          System.out.println("Create processor for: " + ml);
          try
               p = Manager.createProcessor(ml);
          catch (Exception e)
               System.out.println("Failed to create a processor from the given media source: " + e);
               return false;
          p.addControllerListener(this);
          // Put the Processor into configured state.
          p.configure();
          if(!waitForState(p.Configured))
               System.out.println("Failed to configure the processor.");
               return false;
          // Get the raw output from the Processor.
          p.setContentDescriptor(new ContentDescriptor(ContentDescriptor.RAW));
          TrackControl tc[] = p.getTrackControls();
          if(tc == null)
               System.out.println("Failed to obtain track controls from the processor.");
               return false;
          TrackControl videoTrack = null;
          for(int i = 0; i < tc.length; i++)
               if(tc.getFormat() instanceof VideoFormat)
                    tc[i].setFormat(new RGBFormat(null, -1, Format.byteArray, -1.0F, 24, 3, 2, 1));
                    videoTrack = tc[i];
               else
               tc[i].setEnabled(false);
          if(videoTrack == null)
               System.out.println("The input media does not contain a video track.");
               return false;
          System.out.println("Video format: " + videoTrack.getFormat());
          p.realize();
          if(!waitForState(p.Realized))
               System.out.println("Failed to realize the processor.");
               return false;
          // Get the output DataSource from the processor and set it to the DataSourceHandler.
          DataSource ods = p.getDataOutput();
          handler = new DataSourceHandler();
          try
               handler.setSource(ods);     // also determines image size
          catch(IncompatibleSourceException e)
               System.out.println("Cannot handle the output DataSource from the processor: " + ods);
               return false;
     //     setLayout(new FlowLayout(FlowLayout.LEFT));
//          currPanel = new imgPanel(new Dimension(imgWidth,imgHeight));
     //     add(currPanel);
     //     pack();
          //setLocation(100,100);
     //     setVisible(true);
          handler.start();
          // Prefetch the processor.
          p.prefetch();
          if(!waitForState(p.Prefetched))
               System.out.println("Failed to prefetch the processor.");
               return false;
          // Start the processor
          //p.setStopTime(new Time(20.00));
          p.start();
          return true;
     * Sets image size
     private void imageProfile(VideoFormat vidFormat)
          System.out.println("Push Format "+vidFormat);
          Dimension d = (vidFormat).getSize();
          System.out.println("Video frame size: "+ d.width+"x"+d.height);
          imgWidth=d.width;
          imgHeight=d.height;
     * Called on each new frame buffer
     int nextframetime = 0;
private void useFrameData(Buffer inBuffer)
try
if(inBuffer.getData()!=null) // vfw://0 can deliver nulls
if(sunjava) // and with import javax.imageio.*;
int frametimesecs = (int)(inBuffer.getTimeStamp()/1000000000);
if(frametimesecs%10 == 0 && frametimesecs==nextframetime)
nextframetime+=10;
BufferedImage bi = new BufferedImage(outputImage.getWidth(null), outputImage.getHeight(null), BufferedImage.TYPE_INT_RGB);
Graphics g = bi.getGraphics();
ImageIO.write(bi, "png", new File("images"+sep+"image_"+(inBuffer.getTimeStamp()/1000000000)+".png"));
catch(Exception e){}
     * Tidy on finish
     public void tidyClose()
          handler.close();
          p.close();
     * Block until the processor has transitioned to the given state
     private boolean waitForState(int state)
          synchronized(waitObj)
               try
                    while(p.getState() < state && stateOK)
                    waitObj.wait();
               catch (Exception e)
          return stateOK;
     * Controller Listener.
     public void controllerUpdate(ControllerEvent evt)
          if(evt instanceof ConfigureCompleteEvent ||     evt instanceof RealizeCompleteEvent || evt instanceof PrefetchCompleteEvent)
               synchronized(waitObj)
                    stateOK = true;
                    waitObj.notifyAll();
          else
          if(evt instanceof ResourceUnavailableEvent)
               synchronized(waitObj)
                    stateOK = false;
                    waitObj.notifyAll();
          else
          if(evt instanceof EndOfMediaEvent || evt instanceof StopAtTimeEvent)
               tidyClose();
     * Inner classes
     * A DataSourceHandler class to read from a DataSource and displays
     * information of each frame of data received.
     class DataSourceHandler implements BufferTransferHandler
          DataSource source;
          PullBufferStream pullStrms[] = null;
          PushBufferStream pushStrms[] = null;
          Buffer readBuffer;
          * Sets the media source this MediaHandler should use to obtain content.
          private void setSource(DataSource source) throws IncompatibleSourceException
               // Different types of DataSources need to handled differently.
               if(source instanceof PushBufferDataSource)
                    pushStrms = ((PushBufferDataSource) source).getStreams();
                    // Set the transfer handler to receive pushed data from the push DataSource.
                    pushStrms[0].setTransferHandler(this);
                    // Set image size
                    imageProfile((VideoFormat)pushStrms[0].getFormat());
               else
               if(source instanceof PullBufferDataSource)
                    System.out.println("PullBufferDataSource!");
                    // This handler only handles push buffer datasource.
                    throw new IncompatibleSourceException();
               this.source = source;
               readBuffer = new Buffer();
          * This will get called when there's data pushed from the PushBufferDataSource.
          public void transferData(PushBufferStream stream)
               try
                    stream.read(readBuffer);
               catch(Exception e)
                    System.out.println(e);
                    return;
               // Just in case contents of data object changed by some other thread
               Buffer inBuffer = (Buffer)(readBuffer.clone());
               // Check for end of stream
               if(readBuffer.isEOM())
                    System.out.println("End of stream");
                    return;
               // Do useful stuff or wait
               useFrameData(inBuffer);
          public void start()
               try{source.start();}catch(Exception e){System.out.println(e);}
          public void stop()
               try{source.stop();}catch(Exception e){System.out.println(e);}
          public void close(){stop();}
          public Object[] getControls()
               return new Object[0];
          public Object getControl(String name)
               return null;
below is the servlet code.
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class ShowMovie extends HttpServlet {
String rootURL="http://127.0.0.1:8080/Video/";
public void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
     //String movie=request.getParameter("movie");
     String movie ="son";
     getStart(movie);
          response.sendRedirect(rootURL+"View.jsp");
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
     public void getStart(String url){
          new vid2jpg(url);
this is the error from the server. Im using tomkat 5
exception
javax.servlet.ServletException: Servlet execution threw an exception
root cause
java.lang.NoClassDefFoundError: javax/media/ControllerListener
     java.lang.ClassLoader.defineClass1(Native Method)
     java.lang.ClassLoader.defineClass(Unknown Source)
     java.security.SecureClassLoader.defineClass(Unknown Source)
     org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1812)
     org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:866)
     org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1319)
     org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1198)
     java.lang.ClassLoader.loadClassInternal(Unknown Source)
     ShowMovie.getStart(ShowMovie.java:31)
     ShowMovie.processRequest(ShowMovie.java:14)
     ShowMovie.doGet(ShowMovie.java:22)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.17 logs.

Accessing java classes from javascript

Hi,
I have the following javascript function
function testjava {
    var myString = new java.lang.String("Hello world"); // line 1
    alert("len:"+myString.length()); // line 2
}It gives me a error at line 1 saying "'java' is undefined" in IE browser 5.5 sp2. But, both the lines execute correctly in netscape 6.
Can someone please help..
Thanks,
Vijay.

It seems that IE 5.5 doesn't support accessing java classes in JavaScript, so try to install IE 6 to see if it works or maybe, you doesn't have installed propertly support for JVM in IE.

Understanding Java Class Accessibility

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