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class not found exception in applet servlet communication

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posted 12 years ago

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Hi Guys,

I am trying to create applet servlet communication program. I have created an applet which has the connetion to the servlet(through getConnection() method).And i have sendObject and receive Objects methods in it. I have created an servlet with doPost method in which i write my business logic.i created a html in which i gave my applet classname in codebase attribute. I am trying to run this program in the browser. It shows applet failed and when i open the browser console it shows class not found exception(applet class).

Can any one help me in this issues.

Thanks,
Nanditha.

Ulf Dittmer

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posted 12 years ago

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Welcome to JavaRanch.

What does your applet tag look like? Also post the full error message. Are all required classes in the same directory as the HTML page?

Nanditha Parripati

Greenhorn

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posted 12 years ago

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/*This is my applet program */
import java.applet.* ;
import java.awt.* ;
import java.awt.event.* ;
import java.io.* ;
import java.net.* ;
public class PipelineApplet extends Applet implements ActionListener
{
	
	private static final String servlet = "http://localhost:8080/appletservlet/PipelineServlet";
	private Label text ; // shows my results
	private URLConnection getConnection() throws IOException
	{
		URL u = new URL( servlet );
		URLConnection con = u.openConnection();
		con.setDoInput( true );
		con.setDoOutput( true );
		con.setUseCaches( false );
		con.setRequestProperty("Content-Type","application/x-java-serialized-object");
		con.setAllowUserInteraction( false );
		return con ;
	}
	private void sendObject( URLConnection con , Object obj ) throws
	IOException
	{
		ObjectOutputStream out = new ObjectOutputStream(
				con.getOutputStream() );
		if ( obj != null )
		{
			out.writeObject( obj );
		}
		out.close();
	}
	private Object receiveObject( URLConnection con ) throws Exception
	{
		ObjectInputStream in = new ObjectInputStream( con.getInputStream() );
		Object obj = in.readObject();
		in.close();
		return obj ;
	}
	public void actionPerformed( ActionEvent e )
	{
		try
		{
			URLConnection con = getConnection();
			sendObject( con , text.getText() );
			String s = (String)receiveObject( con );
			text.setText( s );
		}catch( Exception ex ) {
			System.out.println( "Curses! Foiled again: " + ex );
		}
	}
	public void init()
	{
		Button b = new Button("reverse!");
		b.addActionListener( this );
		add( b );
		text = new Label("The Tick sez Spoooooon!");
		add( text );
	}
}

/*This is my servlet program*/

import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class PipelineServlet extends HttpServlet {
	private Object receiveObject( HttpServletRequest req ) throws Exception
	{
		ObjectInputStream in = new ObjectInputStream( req.getInputStream() );
		Object obj = in.readObject();
		in.close();
		return obj ;
	}
	private void sendObject( HttpServletResponse resp , Object obj )
	throws Exception
	{
		ObjectOutputStream out = new ObjectOutputStream( resp.getOutputStream() );
		out.writeObject( obj );
		out.close();
	}
	public void doGet(HttpServletRequest req , HttpServletResponse
			resp){
		doPost(req,resp);
	}
	public void doPost( HttpServletRequest req , HttpServletResponse
			resp )
	{
		
		try {
			System.out.println("inside servlet");
			Object obj = receiveObject( req ) ;
//			reverse the String.
			String old = (String)obj ;
			String s = "";
			for( int i = old.length() - 1 ; i >= 0 ; i-- )
			{
				s += old.charAt( i );
			}
			System.out.println("s--->"+s);
			sendObject( resp , s );
		} catch ( Exception e ){
			System.out.println( "Clang! Thunk: " + e );
		}
	}
}

/*This is my html code where i am calling my applet*/

This is my code where i am trying to execute from the browser.

in the browser i have given as http://localhost:8080/appletservlet/pipeline.html

in this url appletservlet is my project name.

Ulf Dittmer

Rancher

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posted 12 years ago

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Is the file PipelineApplet.class in the "appletservlet" directory?

Nanditha Parripati

Greenhorn

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posted 12 years ago

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yes pipelineApplet.class is in appletservlet directory.

Ulf Dittmer

Rancher

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posted 12 years ago

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Can you download the class file manually by typing http://localhost:8080/appletservlet/PipelineApplet.class in the browser?

Can you see the class file being accessed in the server log files? If so, does it result in a 200 or 404 response code?

Maki Jav

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posted 12 years ago

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Hi,

I compiled everything and run it in Tomcat , I got this in the java console:

Curses! Foiled again: java.io.FileNotFoundException: http://localhost:8080/appletservlet/PipelineServlet

Applet is loading perfectly, but the URL is not being found...

In older Tomcat, your applet could access the Servlet like this:

http://localhost:8080/appletservlet/servlet/PipelineServlet

but now make web.xml file placed in WEB-INF folder like:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>

<servlet>
<servlet-name>PipelineServlet</servlet-name>
<servlet-class>PipelineServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>PipelineServlet</servlet-name>
<url-pattern>/PipelineServlet</url-pattern>
</servlet-mapping>

</web-app>

And your applet is now accessing the servlet.

the output on Applet and tomcat comand prompt, once you press button is:

s--->!noooooopS zes kciT ehT

pressing again gives:

s--->The Tick sez Spoooooon!

...and you can continue as long as you want.

Morale of the story:

>>>Set your paths, fellas!

Thanks,

Maki Jav

Help gets you when you need it!

Ulf Dittmer

Rancher

Posts: 43027

posted 12 years ago

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Instead of hard-coding the servlet URL in the applet code I'd make that a param tag inside of the applet tag (see http://java.sun.com/docs/books/tutorial/deployment/applet/html.html for details). That way you don't need to change any code in case the URL changes; just the HTML file.

Maki Jav

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posted 12 years ago

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Agreed Ulf

Maki Jav

Help gets you when you need it!

Nanditha Parripati

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posted 12 years ago

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hi,

i had given the path in web.xml as how you had given then too i am facing the same problem class not found exception. and i am running this project using eclipse ide

still not solved.

Maki Jav

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posted 12 years ago

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When using Eclipse IDE, you use it's built-in servlet class generator. go to NEW--> other --> type servlet and choose...

If you have had simply made this web application with your "own hands", it would have been much easier for you.

I wrote it all using notepad

I am attaching all the source and compiled classes in a zip file.

Place them in tomcat webapps folder and run tomcat manually.

If don't know how? Tell me where you jdk is installed.
I will send you batch file for starting tomcat. Or if you are using linux, tell me that too.

Your code is running perfectly.

Mak Jav

Help gets you when you need it!

Nanditha Parripati

Greenhorn

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posted 12 years ago

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Hi,

Tanks a lot for helping me. I am not using linux. jdk is installed in c drive program files. i know how to start the tomcat. as you said in the previous discussion you had attached all the files in zip folder but i didn't see any attached files. please send me those and do me a favor.

Thanks,
Nanditha.

Maki Jav

Ranch Hand

Posts: 473

posted 12 years ago