Help with Java servlet : getServletContext().

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Vidya - 29 Apr 2005 15:37 GMT

I am newbie to Java, am trying to get a program working, and I have
imported the java packages below along with many other imports :
import javax.servlet.GenericServlet;
....
xsltFile = new File(getServletContext().getRealPath("xslt/" +
template));
if(!xsltFile.canRead()) {
System.out.println("Error reading XSLT template file '"
+ xsltFile + "'.");
return 0;
}

I get the following error, can anyone tell me what the problem is?

com\netod\util\MyClass.java:243: cannot resolve symbol
symbol : method getServletContext ()
location: class com.netod.util.MyClass
xsltFile = new File(getServletContext().getRealPath("xslt/"
+ template));

thanks for any help

Reply to this Message

kaeli - 29 Apr 2005 15:59 GMT

> I am newbie to Java, am trying to get a program working, and I have
> imported the java packages below along with many other imports :
> import javax.servlet.GenericServlet;
> ....
> xsltFile = new File(getServletContext().

What are you getting the servletContext FROM? ;)

someServlet.getServletContext()

Probably, depending on where this statement is running from, you want
this.getServletContext()

You can call a method on nothing.

HTH

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~kaeli~
Practice safe eating - always use condiments.
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Juha Laiho - 30 Apr 2005 19:03 GMT

kaeli <tiny_one@NOSPAM.comcast.net> said:

>> I am newbie to Java, am trying to get a program working, and I have
>> imported the java packages below along with many other imports :
[quoted text clipped - 10 lines]
>
>You can call a method on nothing.

What?

'this.foo()' is equivalent to 'foo()' - at least in all cases I can imagine
(and please educate me if there are cases where this isn't so!). It will
always call method 'foo()' either on the current class, or on the closest
superclass implementing the method.

There are cases where you might need an explicit 'this.' for referencing
instance variables (where you have a local variable of the same name,
shadowing the instance variable), but for method calls, 'this.' is always
superfluous.

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kaeli - 02 May 2005 13:47 GMT

> What?
>
> 'this.foo()' is equivalent to 'foo()' -

Yeah, I realized after I posted that how stoopid that was.
I didn't have time to come correct myself.

Thanks. *embarrassed grin*

Signature

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~kaeli~
Dijon vu - the same mustard as before.
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Ross Bamford - 29 Apr 2005 18:17 GMT

> I am newbie to Java, am trying to get a program working, and I have
> imported the java packages below along with many other imports :
[quoted text clipped - 17 lines]
>
> thanks for any help

Without seeing more of your code, but as a "newbie to Java" I think it's
a fair guess you're after writing a Web servlet, rather than creating a
whole new type of servlet (such as FTP)?

If this is the case, instead of GenericServlet you should extend
javax.servlet.http.HttpServlet.

I'm not sure where the not found is coming from - perhaps you're
implementing straight Servlet (which doesn't have it) ? If changing to
HTTPServlet doesn't help, post more of your code.

Ross

Signature

[Ross A. Bamford] [ross AT the.website.domain]
Roscopeco Open Tech ++ Open Source + Java + Apache + CMF
http://www.roscopec0.f9.co.uk/ + info@the.website.domain

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Vidya - 29 Apr 2005 18:56 GMT

Hi Ross,
I did include the javax.servlet.http.HttpServlet.
Here is more code...if it helps.

import java.io.*;
import java.io.FileOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.*;
import java.util.Hashtable;
import java.util.EventObject;
import java.net.*;
import java.lang.String;
import java.io.StringWriter;
import java.lang.Integer;
import java.applet.*;
import javax.activation.DataHandler;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.http.HttpServlet;
import javax.servlet.GenericServlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
//import javax.servlet.ServletContext; 'this is a redundant class if
serverlet.* has already been imported.
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerConfigurationException;
import org.apache.xml.utils.SAXSourceLocator;
import org.apache.xml.utils.WrappedRuntimeException;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import javax.xml.parsers.* ;
import javax.xml.parsers.DocumentBuilder;
..........
.....
public int ProcessParams() {
transaction = "locmap";
template = "map.xsl";
url = GetParameter("url", "");

if(url == null || url.equals("")) {

Enumeration paramNames = req.getParameterNames();
int numParams = EnumSize(paramNames);

String trans = GetParameter("transaction",
"");

String city = GetParameter("city", "");
String stateProvince =
GetParameter("stateprovince", "");
String postalCode = GetParameter("postalcode",
"");
String recordId = GetParameter("recordid",
"");
String latitude = GetParameter("latitude",
"");
String longitude = GetParameter("longitude",
"");

String origcity = GetParameter("origcity",
"");
String origstateProvince =
GetParameter("origstateprovince", "");
String origpostalCode =
GetParameter("origpostalcode", "");
String origrecordId = GetParameter("origrecordid",
"");
String origlatitude = GetParameter("origlatitude",
"");
String origlongitude =
GetParameter("origlongitude", "");

String destcity = GetParameter("destcity",
"");
String deststateProvince =
GetParameter("deststateprovince", "");
String destpostalCode =
GetParameter("destpostalcode", "");
String destrecordId = GetParameter("destrecordid",
"");
String destlatitude = GetParameter("destlatitude",
"");
String destlongitude =
GetParameter("destlongitude", "");

if (trans != null &&
!trans.equals("") &&
!trans.equals("poimap") &&
nc_input.get("identifyicon") == null) {
if (trans.equals("route")) {

// route trans

// origin
if ((origcity == null ||
origcity.equals("") ||
origstateProvince == null ||
origstateProvince.equals("")) &&
(origpostalCode == null ||
origpostalCode.equals("")) &&
(origrecordId == null ||
origrecordId.equals("")) &&
(origlatitude == null ||
origlatitude.equals("")) &&
(origlongitude == null ||
origlongitude.equals(""))) {
error = 9000; // not enough info for the
origin

// destination
} else if ((destcity == null ||
destcity.equals("") ||
deststateProvince == null ||
deststateProvince.equals("")) &&
(destpostalCode == null ||
destpostalCode.equals("")) &&
(destrecordId == null ||
destrecordId.equals("")) &&
(destlatitude == null ||
destlatitude.equals("")) &&
(destlongitude == null ||
destlongitude.equals(""))) {
error = 9000; // not enough info for the
destination
}

} else {

// other type of trans
if ((city == null || city.equals("")

stateProvince == null ||
stateProvince.equals("")) &&
(postalCode == null ||
postalCode.equals("")) &&
(recordId == null ||
recordId.equals("")) &&
(latitude == null ||
latitude.equals("")) &&
(longitude == null ||
longitude.equals(""))) {
error = 9000; // not enough info for the
center
}

} // if (trans.equals("route"))
} // if (trans != null && (!(trans.equals(""))))

// EnumSize moved the pointer to the end of
paramNames.. reset
paramNames = req.getParameterNames();

while(paramNames.hasMoreElements()) {
String elem = (String)paramNames.nextElement();
String val = req.getParameter(elem);

if (elem.equals("template") &&
!(val == null || val.equals(""))) {
template = val + ".xsl";

} else if (elem.equals("transaction") &&
!(val == null || val.equals(""))) {
transaction = URLEncoder.encode(val);

} else {
if(! val.equals("")) {
// add to hashtable
passed.put(elem, val);

elem = URLEncoder.encode(elem);
val = URLEncoder.encode(val);

if(params.equals("")) {
params = "/?" + elem + "=" + val;
} else {
params += "&" + elem + "=" + val;
}
}
}
}

if (!(params == null || params.equals(""))) {
params += "&clientid=" + clientId;
passed.put("clientid", clientId);

params += "&passwd=" + passwd;
passed.put("passwd", passwd);

params += "&transaction=" + transaction;
passed.put("transaction", transaction);

url = "http://" + server + params;
}

} else {

// Prepend the protocol and server to the returned url
url = "http://" + server + "/?clientId=" + clientId +
"&" + url;

String tmpTemplate = GetParameter("template", "");
if (!(tmpTemplate == null || tmpTemplate.equals(""))) {
template = tmpTemplate + ".xsl";
}
}

xsltFile = new File(getServletContext().getRealPath("xslt/"
+ template));
if(!xsltFile.canRead()) {
System.out.println("Error reading XSLT template file '"
+ xsltFile + "'.");
return 0;
}

return 1;
} // ProcessParams

Thanks
Vidya

> > I am newbie to Java, am trying to get a program working, and I have
> > imported the java packages below along with many other imports :
[quoted text clipped - 35 lines]
> Roscopeco Open Tech ++ Open Source + Java + Apache + CMF
> http://www.roscopec0.f9.co.uk/ + info@the.website.domain

Reply to this Message

Ross Bamford - 29 Apr 2005 19:30 GMT

> Hi Ross,
> I did include the javax.servlet.http.HttpServlet.
> Here is more code...if it helps.

Firstly those imports - You don't need to specifically name the classes
if you're using the javax.something.* syntax - that automatically
imports all public classes in the package. So for this app, all the
javax.servlet.whatever entries could removed, to leave only:

javax.servlet.*;
javax.servlet.http.*;

Most apps can get by with only javax.servlet.ServletContext, and the
servlet.http.* classes. Once your program is up and running, it's a good
idea to remove wildcard definitions but for now, it will make management
easier :)

Okay, so, importing it is part one of the process. The method you sent
looks like it's part of the servlet? Now. I bet your class definition
says:

[public] class YourClass implements Servlet

or maybe 'extends GenericServlet' in place of 'implements Servlet'.
Instead, it should be:

[public] class YourClass extends HttpServlet

You will then be able to override one/both of doGet(HttpServletRequest,
HttpServletResponse) and doPost(HttpServletRequest, HttpServletResponse)
to process get/post requests. Notice these both pass in a ready-to-use
request, with the parameters and what-not, and a response ready for you
to output to.

These methods then do whatever processing they need to, and use the
methods in [Http]ServletResponse to communicate with the client.

Hope this is helpful :)

Ross

Signature

[Ross A. Bamford] [ross AT the.website.domain]
Roscopeco Open Tech ++ Open Source + Java + Apache + CMF
http://www.roscopec0.f9.co.uk/ + info@the.website.domain

Reply to this Message

Vidya - 29 Apr 2005 21:05 GMT

Thank you very very much Ross. The class was not suffixed with the
"extends HttpServlet ". I could compile the class sucessfully after
making this change.
Best Regards,
Vidya.

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Vidya - 26 May 2005 19:58 GMT

Hi,
Although I could compile the class successfully,when I load the jsp
page on my web browser, I get the following error in the weblogic
server logs:

322952,name=myApp,context-path=/myApp)] Servlet failed with Exception
java.lang.NullPointerException.
Could there be any reason why I get NullPointerExeption when I use the
following line in my code?
xsltFile = new
File(getServletConfig().getServletContext().getRealPath("xslt/" +
template));

Any advice/help will greatly be apreciated.
Vidya.

> Thank you very very much Ross. The class was not suffixed with the
> "extends HttpServlet ". I could compile the class sucessfully after
> making this change.
> Best Regards,
> Vidya.

Reply to this Message

Andrew Thompson - 26 May 2005 20:17 GMT

> File(getServletConfig().getServletContext().getRealPath("xslt/" +
> template));
>
> Any advice/help will greatly be apreciated.

The advice I can give you is that when debugging an NPE caused by a
statement such as that, break it down to find out *what* is null!

E.G.

System.out.println( template );
ServletConfig scg = getServletConfig();
System.out.println( scg );
ServletContext sct = scg.getServletContext();
System.out.println( sct );
String s = sct.getRealPath( "xslt/" + template );
System.out.println( s );
File f = new File(s);
System.out.println( f );
...

As an aside, you should not specify the file separator as
you have above, it is better to do it like this..

String s = "xslt" + File.separator + template;

..to ensure your application runs correctly on any platform
on which it runs. Also, if directory 'xslt' is at the top
level of the site, it might be better to specify that.

String s = File.separator + "xslt" + File.separator + template;

HTH

Signature

Andrew Thompson
http://www.PhySci.org/codes/ Web & IT Help
http://www.PhySci.org/ Open-source software suite
http://www.1point1C.org/ Science & Technology
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Vidya - 26 May 2005 21:37 GMT

Hi Thompson,

I used the code below:
System.out.println( template );
ServletConfig scg = getServletConfig();
System.out.println( "scg="+scg );
ServletContext sct = scg.getServletContext();
System.out.println( "sct="+sct );
String s = sct.getRealPath( "xslt/" + template );
System.out.println( "path="+s );
File f = new File(s);
System.out.println( f );

and I get the error below:

scg=null

Why is the scg null here? Where am I going wrong?
Thanks,
Vidya.

> > File(getServletConfig().getServletContext().getRealPath("xslt/" +
> > template));
[quoted text clipped - 36 lines]
> http://www.1point1C.org/ Science & Technology
> http://www.LensEscapes.com/ Images that escape the mundane

Reply to this Message

William Brogden - 29 May 2005 18:16 GMT

> Hi Thompson,
>
[quoted text clipped - 16 lines]
> Thanks,
> Vidya.

Probably because you didn't use the right form of
the init method. If you use
public void init(ServletConfig config) throws ServletException {

You MUST include the line:
super.init(config);

otherwise the ServletConfig keeps the null value it was initialzed with.
Bill

Reply to this Message

Vidya - 31 May 2005 17:04 GMT

Hi Bill,

As you can see in my prevous postings above, I don't have any "init
method" in my code. Since I do not have init method defined anywhere,
am I having this problem?
Can someone post a working version of sample that uses the
getServletContext().getRealPath?

Thanks,

Vidya.

> > Hi Thompson,
> >
[quoted text clipped - 26 lines]
> otherwise the ServletConfig keeps the null value it was initialzed with.
> Bill

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Help with Java servlet : getServletContext().

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