Servlet instance variables
This might be a dumb question, but I'll ask it anyway...
I have methods in my servlet to handle registration, specifically creating address, customer and order objects.
All the information needed for creating my objects is coming from the registration form.
Right now if I were to call the createAddress() method, I have to pass the request object.... createAddress(request);
Would it be "thread safe" to make an instance variable of the request and refer to it using getters/setters? Or would it be wiser (and best practice) to make instance variables for the request attributes (like firstName, lastName, etc.)? Or am I way off and shouldn't be doing any of the above?
Thanks for the help.
GB_java_guy wrote:
To answer you question, I think it's different, from what I've read, because request attributes are supposed to be thread safe and I'd be using the request attributes instead of the request object.You said something about "making instance variables for the request attributes." I don't know what you mean by that, but if it's instance variable in the servlet class, don't do it.
I have no clue what you mean by "request attirbutes intead of request object."
So are you saying I should just use the request object and pass that to my methods instead? In general, yes. In some cases you may want to pass individual pieces of it--e.g. if there's a method that doesn't need to know or care about the fact that you're operating in a servlet context, and just needs a couple values to do its job.
Similar Messages
-
Servlet Instance Variable scope
Just want to clarify my understanding of instance variables in regards to Servlets.
public class TestServlet extends HttpServlet
public String instVariable = "";
public void processRequest(HttpServletRequest request, HttpServletResponse response)
instVariable = request.getParameter("param");
response.sendRedirect( instVariable ) ;
}If two users both enter the processRequest logic at the same time, is it possible that they will both get the same
result? My understanding of this was that if they each execute the first line, then each execute the second
line, each user would be redirected to the same instVariable that was set by the second request.
What would be the easiest way to stop this from happening? syncronized? ThreadSafe?
I just want a simple clarification.
Thanks for the insight.If two users both enter the processRequest logic at
the same time, is it possible that they will both get
the same
result? My understanding of this was that if they
each execute the first line, then each execute the
second
line, each user would be redirected to the same
instVariable that was set by the second request. Yes, it is possible, since there is only one instVariable.
What would be the easiest way to stop this from
happening? syncronized? ThreadSafe? The easiest way to avoid that is to simply not use an instance variable. Use a local variable, declared within your processRequest method. Each thread (i.e. each user of the servlet) has its own set of local variables. -
Instance variables in Servlets.
Hi
Is it a good practice to use instance variable in servlet.
Please refer code snippet below.
public class ExcelAction extends HttpServlet {
private int var1 =0;
doGet () {
var1++;
fun1();
fun1 (){
var1++;
}Like in above code I have used an instance variable var1 because I wish the same to be accessible in all servlet functions.
I guess it is not a good practice, as different requests to this servlet at same time will result in multiple threads of this servlet. Which will make the state of var1 unsafe.
If this is correct then what are the alternates if I wish to share variables between functions in a servlet.
Thanksmoney321 wrote:
Because in beginning I was not sure that Servlets instances are also actually threads.They are not not threads. Each call to doGet(), doPost() etc is called in a Thread and since there can be many simultaneous calls each having it's own thread a Servlet has to be thread safe.
My other question was specific to threads as I was trying to implement threads.Why?
>
But in this one I rather used servlets.
But apologies, as instance of servlet are also threads.As I said, they are not threads.
>
But still one last doubt.
Sabre if you could please clarify the same as well :How about you do some reading [http://java.sun.com/developer/onlineTraining/Servlets/Fundamentals/|http://java.sun.com/developer/onlineTraining/Servlets/Fundamentals/] and use Google.
>
in your option 2 and three I will have to pass request object to function fun().No. You will need access to the request object for 2 and the servlet context for 3. You need to pass something
If i am correct on this then is this too a better approach ?My preferred approach is 1 since it makes much of your code testable outside of a Servlet. -
Servlets and their instance variables
I understand that for every request to a servlet, a new thread handles those requests. So it's one request, one thread. But how about instance variables of a servlet class? Are they also one instance variable per thread/request or just like the servlet, one instance?
hi, its exactly as you expect - one instance at all. all threads are working with one intance. you can indeed finetune the number of instances of a servlet using the
<load-on-startup/>tag in the web.xml file, but its up to container if multiple thread will be using many instances.
you can also implement the (deprecated) SingleThreadedModel interface which flags the container not to share that servlet instance to other threads. But this shall not be used in productive environments.
so its always a good idea to put your business impleementation to another class and only use the servlets to connect your business implementation to http like
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException{
new MyBusinessLogic().perform(request.getInputStream(), response.getOutputStream());
} -
Scope of instance variables in servlets..
Hi all,
Sorry for asking a dumb question..
What is the scope of instance variables in a servlet? Is the scope is
limited to thread?
In other words, in the following example, i am setting "testStr", in one
request and when i tried to access the same instance variable from another
request, i am getting it as null. Does it mean instance variable is limited
to that particular thread/request?
thanks in advance..
-ramu
Oops ... I had misunderstood and had the problem backwards ;-)
> Is it known behavior? With registered servlet its working fine (a
> instance variable is shared by all requests)
I believe so; I typically deploy in a WAR so have not seen the problem that
you describe. Servlets can be reloaded, so what you saw could have been
caused bye a date/time mismatch between the .class file and the server's
current time. On the other hand, that could be how WebLogic works.
Peace,
Cameron Purdy
Tangosol, Inc.
http://www.tangosol.com
+1.617.623.5782
WebLogic Consulting Available
"Ramu" <[email protected]> wrote in message
news:[email protected]...
> Hi Purdy,
>
> I got it. I am testing the servlet as a unregistered servlet, which is
> creating instance for every new request!!!, which created this whole
> confusion. Is it known behavior? With registered servlet its working fine
(a
> instance variable is shared by all requests)
>
> > What theory? ;-) Instance variables are on the object, and the object
can
> > be used by multiple threads, thus allowing multiple threads to access
the
> > same instance variables.
> what i mean by theory here is, all instance variables in servlet should
be
> shared by all requests. Now i got it sir.
>
> Thank you..
> -ramu
>
>
> >
> > Peace,
> >
> > --
> > Cameron Purdy
> > Tangosol, Inc.
> > http://www.tangosol.com
> > +1.617.623.5782
> > WebLogic Consulting Available
> >
> >
> > "Ramu" <[email protected]> wrote in message
> > news:[email protected]...
> > > Hi,
> > >
> > > > No, an instance variable in a servlet class is not limited to a
> thread.
> > > There
> > > > is exactly one copy of the servlet created in memory and all
requests
> > pass
> > > > through the same instance, thus sharing any instance variables. A
> > couple
> > > of
> > > > things to remember:
> > > I totally agree with you, But i am wondering why my sample servlet(i
am
> > > attaching the file) is not sharing the instance variables across
> > > threads/reqs. (in 1st request set some string to "testStr" instance
> > > variable, in next request if you read the same instance variable, you
> will
> > > get null!!)
> > > Our current code is having instance variables. But right now we are
not
> > > getting any problems. But as per theory, instance variables should be
> > shared
> > > across threads/requests..
> > >
> > > Any how we are changing our code to remove all instance variables.
> > >
> > > thanks,
> > > -ramu
> > >
> > > >
> > > > 1.) Using instance or class variables in servlets that are not
> read-only
> > > is not
> > > > a good thing to do. This makes the servlet not thread-safe. To
> > maintain
> > > > variables across requests, sessions, etc., use the servlet-defined
> > objects
> > > to
> > > > store the state (e.g., request, session, etc.).
> > > >
> > > > 2.) If you modify the servlet class on disk, WebLogic will reload
the
> > > servlet
> > > > class thus discarding the old instance and creating a new one (of
> > course,
> > > this
> > > > depends on some configuration parameters for servlet reloading).
> > > >
> > > > Hope this helps,
> > > > Robert
> > > >
> > > > Ramu wrote:
> > > >
> > > > > Hi,
> > > > > thanks for quick reply.
> > > > > I am not at all using SingleThreadModel. See the following code.
> > > > > In first request i am passing "abc" value to testStr. But in
second
> > > request,
> > > > > I am getting null for testStr in second request. It looks like
(for
> > me)
> > > for
> > > > > non single threaded model also, scope of instance variables is
> > limited
> > > to
> > > > > Thread/Request.. But as per theory, because its not single
threaded
> > > model,
> > > > > only one instance should be there AND testStr(instace variables)
> > should
> > > be
> > > > > shared across the all threads. But i am not able see that
behaviour
> > > here.
> > > > > But if declare instance variable as static, o am able to share
it
> > > across
> > > > > all threads/requests.
> > > > >
> > > > > note:
> > > > > From browser i am setting testStr to "abc" with URL like
> > > > > "localhost/test1?testStr=abc"
> > > > > And 2nd req from browser is like "localhost/test1" (on server
> output
> > i
> > > am
> > > > > getting null for testStr)
> > > > >
> > > > > Any ideas?
> > > > >
> > > > > thanks,
> > > > > -ravi
> > > > >
> > > > > import java.io.*;
> > > > > import javax.servlet.*;
> > > > > import javax.servlet.http.*;
> > > > >
> > > > > public class test1 extends HttpServlet
> > > > > {
> > > > > public String testStr;
> > > > >
> > > > > public void doGet (HttpServletRequest req, HttpServletResponse
res)
> > > > > throws ServletException, IOException
> > > > > {
> > > > > doPost(req, res);
> > > > > }
> > > > >
> > > > > public void doPost (HttpServletRequest req,
HttpServletResponse
> > res)
> > > > > throws ServletException, IOException
> > > > > {
> > > > > try {
> > > > > res.setContentType("text/html");
> > > > > PrintWriter out = res.getWriter();
> > > > > if(req.getParameter("testStr") != null)
> > > > > {
> > > > > testStr = req.getParameter("testStr");
> > > > > System.out.println("set testStr = " + testStr);
> > > > > }
> > > > > else{
> > > > > System.out.println("get testStr = " + testStr);
> > > > > }
> > > > >
> > > > > }
> > > > > catch(Exception e){
> > > > > e.printStackTrace();
> > > > > }
> > > > >
> > > > > }
> > > > > }
> > > > >
> > > > > "Cameron Purdy" <[email protected]> wrote in message
> > > > > news:[email protected]...
> > > > > > Yes or no, depending on if your servlet implements
> > SingleThreadModel.
> > > > > >
> > > > > > See the servlet 2.2 spec for documentation on how many instances
> of
> > a
> > > > > > servlet will be created. See the doc for the SingleThreadModel
> > > interface.
> > > > > >
> > > > > > Peace,
> > > > > >
> > > > > > --
> > > > > > Cameron Purdy
> > > > > > Tangosol, Inc.
> > > > > > http://www.tangosol.com
> > > > > > +1.617.623.5782
> > > > > > WebLogic Consulting Available
> > > > > >
> > > > > >
> > > > > > "Ramu" <[email protected]> wrote in message
> > > > > > news:[email protected]...
> > > > > > > Hi all,
> > > > > > >
> > > > > > > Sorry for asking a dumb question..
> > > > > > >
> > > > > > > What is the scope of instance variables in a servlet? Is the
> scope
> > > is
> > > > > > > limited to thread?
> > > > > > >
> > > > > > > In other words, in the following example, i am setting
> "testStr",
> > in
> > > one
> > > > > > > request and when i tried to access the same instance variable
> from
> > > > > another
> > > > > > > request, i am getting it as null. Does it mean instance
variable
> > is
> > > > > > limited
> > > > > > > to that particular thread/request?
> > > > > > >
> > > > > > > thanks in advance..
> > > > > > >
> > > > > > > -ramu
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > >
> > >
> > >
> > >
> >
> >
>
>
-
Access of Instance variable in servlet
hi,
If i declare a instance variable in servlet , can i access that variable throughout my application??.
please let me know.
thanks in advance.Servlets are Java classes. They follow all the rules of Java.
-
Problem in recognising instance variables declared in the class
Hi all,
I am trying to deploy an Servlet desiged in WebObjects5.1 application server on application on Iplanet Application server 6.5
Back ground: All of you might be aware that WebObjects5.1 is an J2ee compliant application server. When an application is designed in WebObjects, it creates a WAR file which can be deployed on any J2ee complaint application server.
I tried to create such application in WebObjects and tried to deploy on IplanetApplication server6.5(running on Windows using IIS web server).
I am able to successfully deploy the application. But inorder to do this i had to manually add ias-Web.xml file to the war file generated( gave some arbitrary global id). The aplication just consists some string displaying hello world.
Now when i try to deploy an application which has some instance variables, the instance variables are not getting recognised. This application works fine on WebObjects5.1. But variables are not getting recognised when deployed iplanet application server
Has any one faced such kind of problem earlier? If yes please help me out
Thanks
VenkateshHi,
Please send me your servlet code and war file.
Thanks -
Doubt about scope of instance variable
Hi All,
i have a doubt about scope of instance variable.
if i declare a instance variable in servlet , i want to know whether it can be shared(means everywhere ) or not.
thanks in advance
GopalThe servlet container will create one servlet object, and run multiple threads through its service() / doGet() / doPost() methods.
That means that any instance variables of the servlet are shared between multiple requests, and can cause problems with threads accessing the same variable..
To make your servlets thread-safe
1 - have no instance variables - only use local variables in the doGet/doPost method.
2 - use the session scope for storing variables you need over multiple calls.
Cheers,
evnafets -
How can we differentiate between Servlet instances and threads.
Actuaaly i want to know how a servlet handles multiple client requests at the same time.
what i know is like:::
a client sends a request to the server.
A new thread is generated which will call the instance of the serlvlet on the server for processing..
Is this flow is correct???
am bit confused between threads and instances.
Please help!!!!If you make that your servlets implement the
SingleThreadModel interface (definition below), then
you can configure Tomcat with the size of the pool. I
think that even you can have only one instance, but
this is not very advisable, unless you want your users
to wait...Thnx for reply, Do you know how I can tell Tomcat to start multiple instances or alway stick with single instance. I cannot find this.
"public interface SingleThreadModel
Ensures that servlets handle only one request at a
time. This interface has no methods. Yes I am aware of this.
If a servlet implements this interface, you are
guaranteed that no two threads will execute
concurrently in the servlet's service method. The
servlet container can make this guarantee by
synchronizing access to a single instance of the
servlet, or by maintaining a pool of servlet instances
and dispatching each new request to a free servlet.
This interface does not prevent synchronization
problems that result from servlets accessing shared
resources such as static class variables or classes
outside the scope of the servlet."If only one user can access the servlet using this interface then why would you want syncrhonization??? There shouldn't be synchornization issues with a servlet that implements SingleThreadModel right?? -
Parsing XML and Storing values in instance variable
hi,
i'm new to XML.
here i'm trying to parse an XML and store their element data to the instance variable.
in my main method i'm tried to print the instance variable. but it shows "" (ie it print nothing ).
i know the reason, its becas of the the endElement() event generated and it invokes the characters() and assigns "" to the instance variable.
my main perspective is to store the element data in instance variable.
thanks in advance.
praks
import java.io.*;
import java.net.*;
import java.util.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;
public class mysax extends DefaultHandler
String ctelement;
CharArrayWriter contents;
String vname1,vrcbreg1,vaddress1,vcountry1,vtelephone1,vfax1;
String vname,vrcbreg,vaddress,vcountry,vtelephone,vfax;
public mysax()
vname1 = null;
vrcbreg1 = null;
vaddress1 = null;
vcountry1 = null;
vtelephone1 = null;
vfax1 = null;
contents= new CharArrayWriter();
public void doparse(String url) throws Exception
SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser sp = spf.newSAXParser();
ParserAdapter pa = new ParserAdapter(sp.getParser());
pa.setContentHandler(this);
pa.parse(url);
public void startElement(String namespace,String localName,String qName,Attributes atts)
ctelement = localName;
public void endElement(String uri,String localName,String qName) throws SAXException
public void characters(char[] ch,int start, int length) throws SAXException
try
if(ctelement.equals("name"))
vname = new String (ch,start,length);
System.out.println("The method "+vname1);
}catch (Exception e)
System.out.println("The exception "+e);
public static void main(String args[])
try
mysax ms = new mysax();
ms.doparse(args[0]);
System.out.println("the contents name "+ms.vname1);
catch(Exception e)
System.out.println("this is exception at main" +e);
my XML looks like
<coyprofile_result>
<company>
<name>abcTech</name>
<rcbreg>123456789</rcbreg>
<address>Singapore</address>
<country>sg</country>
<telephone>123456</telephone>
<fax>123155</fax>
</company>
</coyprofile_result>I believe that the problem has to do with the value you assign to ctelement. You are assigning the value of localName to ctElement, however for the element: <name>...</name> the localname is empty string i.e. "", but qName equals "name". Because you are assigning empty string to ctElement, when you do the comparison in characters of ctElement to "name" it will always be false. So in startElement change it to ctElement = qName; Try it and see if it works. I have produced similar programs and it works for me.
Hope this helps. -
How to use an BPM Instance Variable in JSP page
Hi All,
I am using the JSP Presentation, but i don't know how to use an Instance variable in JSP page, that instance already declared in the process. And Can u explain the syntax that to include the JS file into jsp page
Regards
Vasu.
Edited by bpmvasu at 04/03/2007 10:43 PMHi Mariano,
I'm using JSP presentation too. In "Interactive Component Call" active i'm using "Use JSP presentation", but i only can define one instance variable, i need to add more instance variables. In "Advanced" option of this task, i have the argument mapping .. but i don't understand how to use it.
I have a instance variable called "genders" of the type String[Int] (Associative Array) and i'm mapping this instance variable in "Arguments Show In" option of the advanced option of JSP presentation. In JSP presentation i have the code:
<select <f:fieldName att="person.gender"/>>
<c:forEach var="gender" begin="0" items="${genders}" varStatus="status">
<c:choose>
<c:when test="${person.gender == gender}">
<option value="<c:out value="${gender}"/>" selected="true"><c:out value="${gender}"/></option>
</c:when>
<c:otherwise>
<option value="<c:out value="${gender}"/>"><c:out value="${gender}"/></option>
</c:otherwise>
</c:choose>
</c:forEach>
</select>And in my screenflow i have the code:
genders[0] = "Male"
genders[1] = "Female"But when i run my application, i have the error: "The task could not be successfully executed. Reason: 'java.lang.ClassCastException: java.lang.Integer'."
What's the problem? -
How to change value of instance variable and local variable at run time?
As we can change value at run time using debug mode of Eclipse. I want to do this by using a standalone prgram from where I can change the value of a variable at runtime.
Suppose I have a class, say employee like -
class employee {
public String name;
employee(String name){
this.name = name;
public int showSalary(){
int salary = 10000;
return salary;
public String showName()
return name;
i want to change the value of instance variable "name" and local variable "salary" from a stand alone program?
My standalone program will not use employee class; i mean not creating any instance or extending it. This is being used by any other calss in project.
Can someone tell me how to change these value?
Please help
Regards,
Sujeet SharmaThis is the tutorial You should interest in. According to 'name' field of the class, it's value can be change with reflection. I'm not sure if local variable ('salary') can be changed - rather not.
-
Instance variable to hold the element of a tag in the xml file
Hi I have an xml file that is handled using this parser
<attr id="MY_NAME" >
this parser hanled the above tag but now I want to have it handle
<attr id="MY_NAME" desc="GOOD">
but I need to create an instance variable to handle the desc element in the attr tag .
Can some one help me out as this is not my file and I am having trouble to do please......
import java.util.*;
import java.io.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;
The SupportMatrix class provides static variables and methods to simplify
the determination of whether or not a given attribute is supported for a
certain object type (queue manager, channel, etc.), depending on the version
and platform of the queue manager to which it belongs.
The SupportMatrix class may not be instantiated. Its constructor is private.
An instance of the class is created internally in the static initializer so
that the XML parsing methods are available.
A corresponding XML document, SupportMatrix.xml, is parsed to create the various
HashMaps which contain the version/platform dependency information. A number of
inner classes are used to represent the various elements of the XML matrix
definition.
Here's a sample document:
<!-- The supportmatrix tag opens the document -->
<supportmatrix>
<!-- Objects are keyed by classid. "1" is the classid of a queue manager object. -->
<object classid="1">
<!-- Versions group attributes according to the queue manager version where they
were introduced. The "base" cmdlevel encompasses all versions up to 5.1. -->
<version cmdlevel="base">
<!-- Attributes are defined by the attr tag. -->
<attr id="MQCA_Q_MGR_NAME">
<!-- Support elements define the platform-specific requirements for an attribute. -->
<support platforms="UNIX,WINDOWS,OS400,VMS,NSK" maxlen="48" type="MQCFST"/>
<support platforms="MVS" maxlen="4" type="MQCFST"/>
</attr>
<attr id="MQCA_Q_MGR_DESC">
<!-- Specific attribute characteristics, most notably maximum len for string parms,
are defined in the support element. As shown in the following example, it may
apply to all platforms. -->
<support platforms="all" maxlen="64" type="MQCFST"/>
</attr>
<!-- Support elements are optional. -->
<attr id="MQIA_PLATFORM"/>
<attr id="MQIA_COMMAND_LEVEL"/>
</version>
<!-- The version element may 'include' other versions. Note that object elements
may also refer to other objects via the 'include' parm of the object tag.
This is to allow common attributes (especially for queues and channels) to
be shared by multiple definitions in order to reduce some of the
redundancy. -->
<version cmdlevel="520" include="base">
</version>
</object>
</supportmatrix>
The inner classes, and their hierarchical relationships are as follows:
SupportObject - corresponds to the <object> element. Stored in a static HashMap, and
keyed by classid.
VersionObject - corresponds to the <version> element. Stored in a HashMap instance
variable of the SupportObject class, keyed by cmdlevel.
AttributeObject - corresponds to the <attr> element. Stored in a HashMap instance
variable of the VersionObject class, keyed by attribute name.
PlatformObject - corresponds to the <support> element. Stored in HashMaps belonging
to the AttributeObjects, keyed by platform. A single PlatformObject
instance is created when the support tag is encountered. The
"platforms" attribute of the support element is then processed. For
each platform in the comma-delimited list, an entry is added to the
collection of PlatformObjects. This is to greatly simplify later
lookups.
In order to support the 'include' feature of object and version elements, certain
functions are recursive. If the attribute to be validated is not found for the passed
cmdlevel, the 'parent' VersionObject is consulted by means of the 'include' value. If
the chain of VersionObjects has been exhausted and the attribute in question has still not
been located, the next SupportObject in the chain is consulted in a similar fashion.
public class SupportMatrix extends DefaultHandler {
/** The objects collection holds all the SupportObjects, keyed by classid. */
private static HashMap objects;
/** xmlFile will name the xml document to be parsed. Note that using the
default class loader expects the string to be the path to the file. It must
NOT begin with the '/' character. */
private static String xmlFile =
ResourceManager.getApplicationProperties().getProperty("SupportMatrixFile");
private Stack stack;
/** This static initializer allocates the static objects collection, creates an
instance of the SupportMatrix class for xml parsing purposes, and initiates
the parse operation to populate the collection. */
static {
objects = new HashMap();
// Create a parser and process the xml doc
SupportMatrix handler = new SupportMatrix();
InputSource is = null;
try {
is = new InputSource(ClassLoader.getSystemClassLoader().getResourceAsStream(xmlFile));
XMLReader xmlReader =
SAXParserFactory.newInstance().newSAXParser().getXMLReader();
xmlReader.setFeature("http://xml.org/sax/features/namespaces", true);
xmlReader.setContentHandler(handler);
if (is == null) {
System.err.println("No input stream, dammit");
xmlReader.parse(is);
} catch(Exception e) {
e.printStackTrace();
/** Private constuctor, used only for XML parsing. */
private SupportMatrix() {
stack = new Stack();
/** Add a SupportObject instance to the objects collection. */
private void addObject(SupportObject obj) {
String key = obj.getClassId();
objects.put(key, obj);
/* DefaultHandler methods */
/** Not used. */
public void characters(char[] ch, int start, int length) {}
/** Not used. */
public void endDocument() {}
/** For the version, object, and attr elements, pop the top element of the stack. */
public void endElement(String uri, String localName, String qName) {
if (localName.equals("version") || localName.equals("object") || localName.equals("attr")) {
stack.pop();
/** Not used. */
public void setDocumentLocator(Locator locator) {}
/** Not used. */
public void startDocument() {}
/** Most of the work is done here. Create the appropriate inner class instance for
element; for object, version, and attr, push the element onto the stack so that
child elements may be added to their collections as needed. */
public void startElement(String uri, String localName, String qName,
Attributes attributes) {
String include = attributes.getValue("include");
if (localName.equals("object")) {
SupportObject obj = new SupportObject(attributes.getValue("classid"), include);
addObject(obj);
stack.push(obj);
} else if ( localName.equals("version")) {
VersionObject ver = new VersionObject(attributes.getValue("cmdlevel"), include);
((SupportObject)stack.peek()).addVersion(ver);
stack.push(ver);
} else if ( localName.equals("attr")) {
AttributeObject a = new AttributeObject(attributes.getValue("id"));
//String desc = StringFactory.getString(attributes.getValue("desc"));
//if(desc != null)
// a.setAttribute();
String readonly = attributes.getValue("readonly");
String exclude = attributes.getValue("exclude");
if (include != null && exclude != null) {
Log.log(Log.ERROR, this, "include and exclude are mutually exclusive, exclude value ignored");
exclude = null;
if (include != null) {
a.setCondition(include, true);
if (exclude != null) {
a.setCondition(exclude, false);
if (readonly != null)
a.setReadonly(readonly.equals("y"));
((VersionObject)stack.peek()).addAttr(a);
stack.push(a);
} else if (localName.equals("support")) {
String platforms = attributes.getValue("platforms");
String readonly = attributes.getValue("readonly");
String maxlen = attributes.getValue("maxlen");
String type = attributes.getValue("type");
int attrType = 0;
if (type != null) {
if (type.equals("MQCFIN")) {
attrType = CMQCFC.MQCFT_INTEGER;
} else if (type.equals("MQCFIL")) {
attrType = CMQCFC.MQCFT_INTEGER_LIST;
} else if (type.equals("MQCFST")) {
attrType = CMQCFC.MQCFT_STRING;
} else if (type.equals("MQCFSL")) {
attrType = CMQCFC.MQCFT_STRING_LIST;
} else if (type.equals("EXBIN")) {
attrType = MqcConstants.EXCFT_BINARY;
} else if (type.equals("EXPCF")) {
attrType = MqcConstants.EXCFT_PCF;
PlatformObject p = null;
if (readonly == null) {
p = new PlatformObject(platforms);
} else {
p = new PlatformObject(platforms, readonly.equals("y"));
String exclude = attributes.getValue("exclude");
if (include != null && exclude != null) {
Log.log(Log.ERROR, this, "include and exclude are mutually exclusive, exclude value ignored");
exclude = null;
if (include != null)
p.setCondition(include, true);
if (exclude != null)
p.setCondition(exclude, false);
if (attrType != 0)
p.setType(attrType);
if (maxlen != null)
p.setLen(Integer.parseInt(maxlen));
((AttributeObject)stack.peek()).addPlatform(p);
public static boolean isExported(int attribute, TopologyModelNode node) {
String name = ResourceManager.getAttributeName(attribute);
return isExported(name, node);
public static boolean isExported(String attribute, TopologyModelNode node) {
// Find the qmgr node to fetch platform and cmdlevel
TopologyModelNode qmgr = node.getModel().getQMgrNode(node.getAddress());
// If there's no qmgr for this node, it must be one of 'ours'.
if (qmgr == null)
return false; // None of 'our' objects can be exported to MQSC.
String classId = node.getClassId();
String cmdLevel = qmgr.getAttributeValue("MQIA_COMMAND_LEVEL");
String platform = qmgr.getAttributeValue("MQIA_PLATFORM");
return isExported(attribute, classId, cmdLevel, platform, node);
public static boolean isExported(int attribute, String classId, String cmdLevel, String platform,
TopologyModelNode node) {
String name = ResourceManager.getAttributeName(attribute);
return isExported(name, classId, cmdLevel, platform, node);
/** Determine if an attribute is exportable. The attribute name, the classid of the object to
which it belongs, plus the command level and platform of the queue manager are all needed
to make this determination.
Start by finding the AttributeObject for the combination of attribute, classid, and
command level. If we can't find the AttributeObject, we assume that the attribute
is not exported. Otherwise, find out if it is exportable for the selected platform.
public static boolean isExported(String attribute, String classId, String cmdLevel, String platform,
TopologyModelNode node) {
AttributeObject attr = getAttributeObject(attribute, classId, cmdLevel);
if (attr == null) {
return false;
} else {
return attr.isExported(platform, node);
public static boolean isSupported(int attribute, TopologyModelNode node) {
String name = ResourceManager.getAttributeName(attribute);
return isSupported(name, node);
public static boolean isSupported(String attribute, TopologyModelNode node) {
// Find the qmgr node to fetch platform and cmdlevel
TopologyModelNode qmgr = node.getModel().getQMgrNode(node.getAddress());
// If there's no qmgr for this node, it must be one of 'ours'.
if (qmgr == null)
return true;
String classId = node.getClassId();
String cmdLevel = qmgr.getAttributeValue("MQIA_COMMAND_LEVEL");
String platform = qmgr.getAttributeValue("MQIA_PLATFORM");
return isSupported(attribute, classId, cmdLevel, platform);
public static boolean isSupported(int attribute, String classId, String cmdLevel, String platform) {
String name = ResourceManager.getAttributeName(attribute);
return isSupported(name, classId, cmdLevel, platform);
/** Determine if an attribute is supported. The attribute name, the classid of the object to
which it belongs, plus the command level and platform of the queue manager are all needed
to make this determination.
Start by finding the SupportObject for the classid. If it isn't there, we make the assumption
(for now) that the attribute is supported. The only classids for which this can occur are
broker, agent, and the various container objects.
Propagate the isSupported request to the chain of SupportObjects (based on 'include' values)
until we get a 'true' result or we run out of SupportObjects. */
public static boolean isSupported(String attribute, String classId, String cmdLevel, String platform) {
if (attribute == null)
return false;
SupportObject obj = (SupportObject)objects.get(classId);
// If the object type isn't even in the support matrix, we interpret that to
// mean that it's a Broker or Agent, in which case all attributes are supported
// at present.
if (obj == null)
return true;
boolean result = false;
while (result == false && obj != null) {
result = obj.isSupported(attribute, cmdLevel, platform);
if (result == false && obj.getInclude() != null) {
obj = (SupportObject)objects.get(obj.getInclude());
} else
obj = null;
return result;
/** Locate an AttributeObject for a given attribute name, object type, and command level.
This is a helper function for the getMaxLen and getType methods. */
private static AttributeObject getAttributeObject(String attr, String classID, String cmdLevel) {
AttributeObject result = null;
SupportObject obj = (SupportObject)objects.get(classID);
while (result == null && obj != null) {
result = obj.getAttr(attr, cmdLevel);
if (result == null && obj.getInclude() != null) {
obj = (SupportObject)objects.get(obj.getInclude());
} else
obj = null;
return result;
/** Determine the maximum length for a given combintation of attribute name, object type,
command level, and platform. If the AttributeObject can't be found, or if the length
hasn't been set, return -1. */
public static int getMaxLen(String attr, String classId, String cmdLevel, String platform) {
AttributeObject a = getAttributeObject(attr, classId, cmdLevel);
if (a == null)
return -1;
return a.getMaxLen(platform);
/** Determine the PCF parm type for a given combintation of attribute name, object type,
command level, and platform. If the AttributeObject can't be found, or if the length
hasn't been set, return -1. */
public static int getType(String attr, String classId, String cmdLevel, String platform) {
AttributeObject a = getAttributeObject(attr, classId, cmdLevel);
if (a == null)
return -1;
return a.getType(platform);
/** Inner class to contain platform-specific info for an attribute. */
class PlatformObject {
/** This instance variable will contain the comma-delimited string of all
platforms to which this object applies. */
private String platform;
private int maxlen;
private String condition = null;
private boolean include;
private boolean readonly;
private boolean lenSet;
private int attrType;
private boolean typeSet;
public PlatformObject(String p, boolean readonly) {
platform = p;
this.readonly = readonly;
lenSet = false;
typeSet = false;
public PlatformObject(String p) {
this(p, false);
public void setCondition(String condition, boolean include) {
this.condition = condition;
this.include = include;
public boolean isReadonly() {
return readonly;
public boolean isExported(TopologyModelNode node) {
if (condition != null) {
boolean test = false;
try {
test = Utilities.evaluateCondition(node, condition);
} catch (Exception e) {}
if (include ^ test)
return false;
return !readonly;
public void setLen(int len) {
maxlen = len;
lenSet = true;
public void setType(int type) {
attrType = type;
typeSet = true;
public String getPlatform() {
return platform;
public int getMaxLen() {
if (!lenSet)
return -1;
return maxlen;
public int getType() {
if (!typeSet)
return -1;
return attrType;
/** This class represents a specific MQSeries attribute. It can optionally contain
instances of the PlatformObject class as needed. When the 'platforms' collection
is empty, the attribute is supported on all platforms. It is also possible to
include a PlatformObject for the 'all' platform, if specific attribute characteristics
need representation. When the 'platforms' collection is non-empty, it will include one
entry for each platform where the attribute is supported. */
class AttributeObject {
private String attribute;
private String attrValue;
private HashMap platforms;
private String condition = null;
private boolean include;
private boolean readonly = false;
public AttributeObject(String a) {
this(a, false);
public AttributeObject(String a, boolean readonly) {
attribute = a;
platforms = new HashMap();
this.readonly = readonly;
public void setCondition(String condition, boolean include) {
this.condition = condition;
this.include = include;
public void setReadonly(boolean readonly) {
this.readonly = readonly;
public boolean isReadonly() {
return readonly;
public void addPlatform(PlatformObject p) {
for (StringTokenizer st = new StringTokenizer(p.getPlatform(), ","); st.hasMoreTokens() ;) {
platforms.put(st.nextToken(), p);
public PlatformObject getPlatform(String platform) {
PlatformObject p = (PlatformObject)platforms.get(platform);
if (p == null)
p = (PlatformObject)platforms.get("all");
return p;
public String getAttribute() {
return attribute;
public int getMaxLen(String platform) {
PlatformObject p = getPlatform(platform);
if (p == null)
return -1;
return p.getMaxLen();
public int getType(String platform) {
PlatformObject p = getPlatform(platform);
if (p == null)
return -1;
return p.getType();
public boolean isSupported(String platform) {
if (platforms.isEmpty()) {
return true;
if (platforms.containsKey(platform)) {
return true;
if (platforms.containsKey("all")) {
return true;
return false;
public boolean isExported(String platform, TopologyModelNode node) {
if (readonly) {
Log.log(Log.DEBUG, this, attribute + " is readonly, returning false");
return false;
if (condition != null) {
Log.log(Log.DEBUG, this, "Testing condition = " + condition);
boolean test = false;
try {
test = Utilities.evaluateCondition(node, condition);
Log.log(Log.DEBUG, this, "Condition result is " + test);
} catch (Exception e) {
Log.log(Log.ERROR, this, "Condition through an exception");
if (include ^ test)
return false;
if (platforms.isEmpty()) {
return true;
PlatformObject p = getPlatform(platform);
if (p == null) {
Log.log(Log.DEBUG, this, platform + " not found for " + attribute + ", returning false");
return false;
return p.isExported(node);
/** This class represents a specific value of a queue manager's command level. A
given instance of this class may 'include' a 'parent' instance through its
include instance variable. The traversal of the parent/child hierarchy is
delegated to the SupportObject class, since that is where the collection of
VersionObjects lives. */
class VersionObject {
private String cmdLevel;
private String include;
private HashMap attributes;
public VersionObject(String cmdLevel, String include) {
this.cmdLevel = cmdLevel;
this.include = include;
attributes = new HashMap();
public void addAttr(AttributeObject attr) {
attributes.put(attr.getAttribute(), attr);
public AttributeObject getAttr(String attr) {
return (AttributeObject)attributes.get(attr);
public String getCmdLevel() {
return cmdLevel;
public String getInclude() {
return include;
public boolean isSupported(String attr, String platform) {
AttributeObject obj = (AttributeObject)attributes.get(attr);
if (obj == null) {
return false;
} else
return obj.isSupported(platform);
/** This class represents an MQSeries object type, as identified by its classid, e.g.
queue manager or local queue. This class implements an include facility similar to
that described for the VersionObject. The traversal of that hierarchy is delegated
to the static isSupported method, because the collection of SupportObject instances
is a static variable of the SupportMatrix class. */
class SupportObject {
private String classId;
private String include;
private HashMap versions;
public SupportObject(String classId, String include) {
this.classId = classId;
this.include = include;
versions = new HashMap();
public void addVersion(VersionObject obj) {
String key = obj.getCmdLevel();
versions.put(key, obj);
public String getClassId() {
return classId;
public String getInclude() {
return include;
public boolean isSupported(String attr, String cmdLevel, String platform) {
boolean result = false;
VersionObject obj = (VersionObject)versions.get(cmdLevel);
if (obj == null)
obj = (VersionObject)versions.get("base");
// I don't actually know what it means if obj is null at this point.
// It probably can't happen.
if (obj == null)
return false;
while (result == false && obj != null) {
result = obj.isSupported(attr, platform);
if (result == false && obj.getInclude() != null) {
obj = (VersionObject)versions.get(obj.getInclude());
} else
obj = null;
return result;
public AttributeObject getAttr(String attr, String cmdLevel) {
AttributeObject result = null;
VersionObject obj = (VersionObject)versions.get(cmdLevel);
if (obj == null)
obj = (VersionObject)versions.get("base");
// I don't actually know what it means if obj is null at this point.
// It probably can't happen.
if (obj == null)
return null;
while (result == null && obj != null) {
result = obj.getAttr(attr);
if (result == null && obj.getInclude() != null)
obj = (VersionObject)versions.get(obj.getInclude());
else
obj = null;
return result;
}Are you the one who commented out the code you're looking for ?//String desc = StringFactory.getString(attributes.getValue("desc"));You just have to modify you AttributeObject class to hold a new field : String description. And then, it's up to you to create a new constructor or a new setter method.
Btw, this is not a Swing related question. -
How can I use evaluate to get the instance variable in customized tag
1.
At first , I create a class called bean,and declared several params in it and do not define any getter function for the param.
class bean{
String param = "test";
SomeClass scObj = new SomeClass();
2.
The second ,I use
request.setAttribute("beanObj",new bean());
3.
And then I wanna use the customized tag to show a text box , then initialize it's value.
<salt:text name="param" value="beanObj.param">
<salt:text name="obj" value="beanObj.scObj.func()">
4.
I tried the evaluator provided by JexlContext ,Struts, JSTL and it seems that if I do not define the getter for the variable ,I can not get the bean's instance variable's value.
Expression e = ExpressionFactory.createExpression( value );
JexlContext jc = JexlHelper.createContext();
jc.getVars().put(strInitBeanName, request.getAttribute("beanObj"));
Object obj = e.evaluate(jc);
the result of the obj is null....
Can anybody recommand some other evaluator can get the value of a instance variable from an object?do you have any other suggestion ? Nops, somebody else may have though. AFAIK, all lookups of the type
beanName.propertyNameuse reflection on the getXXX() methods to access the property.
Having said that, I guess you could write one though in a custom tag, using the same - reflection (you will ahve to rely on the java.lang.reflect.Field class quite heavily) - but that would be reinventing the wheel for most other functionality that you would have to include (like looking up the bean in scope etc)
cheers,
ram. -
Not able to access parent instance variable in outside of methods in child
Hi,
I am not getting why i am not able to access parent class instance variable outside the child class intance methods.
class Parent
int a;
class Child extends Parent
a = 1; // Here i am getting a compilation error that Syntax error on token "a", VariableDeclaratorId expected after this token
void someMethod()
a = 1; // Here i am not getting any compilation error while accessing parent class variable
}Can any one please let me know exact reason for this and what is the error talks about?
Thanks,
Uday
Edited by: Udaya Shankara Gandhi on Jun 13, 2012 3:30 AMYou can only put assignments or expressions inside methods, constructors or class initializors, or when declaring a variable.
It has nothing to the with Child extending Parent.
class Parent {
int a = 1;
{ a = 1; }
public Parent() {
a = 1;
public void method() {
a = 1;
}
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