Howdy folks.
I'm having trouble with my servlet again...please don't laugh at my
attempts! I have placed the jess.Main file into my servlet, and I've been
fiddling with it to try and get it to work. I'm getting the following error,
and I can't work out why. Please note that the code compiles just fine.
Also note, my jess folder is located within the servlet directory (it
wouldn't work for me otherwise):
c:\jdk1.2.2\jsdk2.1\examples\Web-inf\servlets\jess
but the source jess file (proto.clp) would only open when I placed it in the
server root directory:
c:\jdk1.2.2\jsdk2.1
and I moved the scriptlib.clp file there also, otherwise I got "can't open
file error" in the Dos window.
With all that "fixed", I run my servlet Proto.class, from an html page with
this code:
<FORM METHOD=GET ACTION="../servlet/Proto">Enter "start"
<INPUT TYPE=TEXT NAME="name">
<P>
<INPUT TYPE=SUBMIT>
</FORM>
and that submits ok, but then the response I get is:
Error: 500
Internal Servlet Error:
java.lang.NullPointerException
at Proto.doGet(Proto.java:35)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:715)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:840)
at com.sun.web.core.ServletWrapper.handleRequest(ServletWrapper.java:140)
at com.sun.web.core.InvokerServlet.service(InvokerServlet.java:169)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:840)
at com.sun.web.core.ServletWrapper.handleRequest(ServletWrapper.java:140)
at com.sun.web.core.Context.handleRequest(Context.java:375)
at com.sun.web.server.ConnectionHandler.run(ConnectionHandler.java:135)
My source code (adapted jess.Main) is as follows:
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;
import jess.*;
public class Proto extends HttpServlet implements Serializable, JessListener
{
private Rete m_rete;
private Reader m_fis;
private Jesp m_j;
private boolean m_readStdin = true;
// invoked by the browser doing a GET
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
{
res.setContentType("text/html");
PrintWriter out = res.getWriter();
String name = req.getParameter("name");
String s = "proto.clp";
if (name.equals("start"))
{
Proto m = new Proto();
m.initialize(s, new Rete());
m_rete.addOutputRouter("t", res.getWriter()); //send standard output
from JESS to the servlet's output
m.execute(true);
}
}
/** **********************************************************************
* A command-line interface for Jess; also displayed in a window by the
* Console classes.
* <P>
* (C) 1998 E.J. Friedman-Hill and the Sandia Corporation
********************************************************************** */
/**
* Set a Main object up for later execution.
* @param argv Command-line arguments
* @param r An initialized Rete object, with routers set up
*/
public Proto initialize(String proto, Rete r)
{
m_rete = r;
/*
//
**********************************************************************
// Process any command-line switches
int argIdx = 0;
boolean doLogo=false;
if (argv.length > 0)
while(argIdx < argv.length && argv[argIdx].startsWith("-"))
{
if (argv[argIdx].equals("-nologo"))
doLogo = false;
argIdx++;
}
//
**********************************************************************
*/
//
**********************************************************************
// Open a file if requested
m_fis = m_rete.getInputRouter("t");
String name = proto;
try
{
if (name != null)
{
if (m_rete.getApplet() == null)
m_fis = new FileReader(name);
else
{
URL url
= new URL(m_rete.getApplet().getDocumentBase(),
name);
m_fis = new InputStreamReader(url.openStream());
}
m_readStdin = false;
}
}
catch (IOException ioe)
{
m_rete.getErrStream().println("File not found or cannot open file:"
+
ioe.getMessage());
m_rete.getErrStream().flush();
System.exit(0);
}
//
**********************************************************************
// Load in optional packages, but don't fail if any are missing.
String [] packages = { "jess.BagFunctions",
"jess.ViewFunctions" };
for (int i=0; i< packages.length; i++)
{
try
{
m_rete.addUserpackage((Userpackage)
Class.forName(packages[i]).newInstance());
}
catch (Throwable t) { /* Optional package not present, OK */ }
}
//
**********************************************************************
// Arrange for handling of the 'bsave' & 'bload' commands
try
{
DumpFunctions df = new DumpFunctions();
m_rete.addUserpackage(df);
df.addJessListener(this);
//
**********************************************************************
// Read script library file, if one exists; arrange to have it reloaded
on CLEAR
m_rete.executeCommand("(batch scriptlib.clp)");
m_rete.addJessListener(new JessListener() {
public void eventHappened(JessEvent je) {
if (je.getType() == JessEvent.CLEAR)
{
try
{
m_rete.executeCommand("(batch scriptlib.clp)");
}
catch (JessException re) {}
}
}
});
}
catch (JessException re)
{
m_rete.getErrStream().println("Error processing script library
file:");
re.printStackTrace(m_rete.getErrStream());
if (re.getNextException() != null)
{
m_rete.getErrStream().println("Nested exception is:");
re.getNextException().printStackTrace(m_rete.getErrStream());
}
m_rete.getErrStream().flush();
}
return this;
}
/**
* Repeatedly parse and excute commands, from location determined during
initialize().
* @param doPrompt True if a prompt should be printed, false otherwise.
* Prompts will never be printed during a (batch) command.
*/
public void execute(boolean doPrompt)
{
//
**********************************************************************
// Process input from file or keyboard
if (m_fis != null)
{
m_j = new Jesp(m_fis, m_rete);
do
{
try
{
// Argument is 'true' for prompting, false otherwise
m_j.parse(doPrompt && m_readStdin);
}
catch (BloadException re)
{
m_rete.getErrStream().println("(bload) called, engine
restarting...");
}
catch (JessException re)
{
if (re.getNextException() != null)
{
m_rete.getErrStream().write(re.toString());
m_rete.getErrStream().write("\nNested exception is:\n");
re.getNextException().printStackTrace(m_rete.getErrStream());
}
else
re.printStackTrace(m_rete.getErrStream());
}
catch (Exception e)
{
m_rete.getErrStream().println("Unexpected exception:");
e.printStackTrace(m_rete.getErrStream());
}
finally
{
m_rete.getErrStream().flush();
m_rete.getOutStream().flush();
}
}
// Loop if we're using the command line
while (m_readStdin);
}
// If called again, read stdin, not batch file
m_readStdin = true;
m_fis = m_rete.getInputRouter("t");
}
/**
* @param je
* @exception BloadException
*/
public void eventHappened(JessEvent je) throws JessException
{
if (je.getType() == JessEvent.BLOAD)
{
// Restart engine. This won't work right if bload is called from a
// command-line argument file
m_rete = (Rete) je.getObject();
m_j = new Jesp(m_fis, m_rete);
// Reinstall listener
DumpFunctions df = new DumpFunctions();
m_rete.addUserpackage(df);
df.addJessListener(this);
throw new BloadException();
}
}
class BloadException extends JessException
{
BloadException() { super("(bload)", "engine restarting...", ""); }
}
}
Any help greatly appreciated. Debbie Lampon
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