Dynamic ClassLoader - feasability question

Problem: need to be able to 'hot-replace' a class definition at runtime
Particulars:
A method of this class popuplates a hash map with 'key-<anon.class>' pairs, ie:
public void initTransformerMap() {
   xMap.put("Color", new Transformer() {
       public Object transform(Object in) {
           return ((Car)in).getColor();
   xMap.put("Engine Capacity", new Transformer() {
       public Object transform(Object in) {
           return ((Car)in).getEngine().getCapacity().toString() + " cc";
}I need to be able to define new map entries and change existing ones (including the definition of the anon. classes) and load the class in.
Any sensible suggestions are welcome

You can run the java compiler from your program to compile .java files to class files and then load and use the new classes.
You can't replace a class definition once it is loaded. But if you can load different classes with the same name with different classloaders. Which might look like replacing one class with the other.
search the forum/web and you'll find plenty of examples
regards
Spieler

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Dynamic Classloading

Hello all,
Could someone tell me a practical way to setup dynamic classloading in an EJB app? I'd like to set it up such that all of the shared codebase is deployed within the same ear with the EJB application. Is this practical or does dynamic classloading require the use of an external web-server? Right now I am trying to use the rmi.server.codebase system property via the %JAVA_OPTS% env. variable on appserver start-up to point to a servlet deployed in a .war my .ear. What is the practical approach? Thanks in advance.
Cliff

Thank you crackers,
You've cleared alot for me. So if I follow what you're saying then my problem boils down to how my client talks to the server. And the principles of EJB state that the communication details are left to the vendor. All I have to do then is get my home interface via JNDI. This assumes of course that the stubs are available on the client.
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Dynamic ClassLoader

Hi there,
i am trying to program a dynamic classloader in Abap. by now i came this far:
DATA classname TYPE string VALUE 'ZCL_TEST'.
DATA dref TYPE REF TO data.
DATA type_descr TYPE REF TO cl_abap_typedescr.
FIELD-SYMBOLS <ref> TYPE ANY.
type_descr = cl_abap_typedescr=>describe_by_name( p_name = classname ).
classname = type_descr->absolute_name.
CREATE DATA dref TYPE REF TO (classname).
ASSIGN dref->* TO <ref>.
CREATE OBJECT <ref> TYPE (classname).
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I don't know what would be the use of creating the object with REF TO DATA and than assign it back to the variable REF TO OBJECT to be able to access the data.
CREATE DATA dref TYPE REF TO
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Here you are creating the TYPE at runtime which is type referent to the Interface. You get the object reference to the Field-Symbol. But Since field-symbol is not allowing to access the attributes, we need to cast that into the variable TYPE REF TO OBJECT.
Check this code:
REPORT ztest_np_1.
INTERFACE i1.
DATA: w_num TYPE i.
ENDINTERFACE.                    "i1
CLASS c1 DEFINITION.
PUBLIC SECTION.
    INTERFACES i1.
ENDCLASS.                    "c1 DEFINITION
DATA dref TYPE REF TO data.
FIELD-SYMBOLS <ref> TYPE any.
CREATE DATA dref TYPE REF TO
           ('\program=ZTEST_NP_1\interface=i1').
ASSIGN dref->* TO <ref>.
CREATE OBJECT <ref> TYPE c1.
FIELD-SYMBOLS <attr> TYPE ANY.
DATA: lo_obj TYPE REF TO object.
lo_obj ?= <ref>.
ASSIGN lo_obj->('I1~W_NUM') TO <attr>.
<attr> = 10.
WRITE: 'Test'.
Regards,
Naimesh Patel

Dynamic classloading without default constructor

Just wondering if anyone has done dynamic classloading using a constructor other than the default. I know that newInstance() calls the default constructor. But how would you do it without that? Thanks for the help.

If you know that there is a constructor that takes,
for example, a single String argument you can use
something like this:
Class clazz = ...; // class to instantiate
String stringArg = ...; // argument to pass to constructor
Constructor c = clazz.getConstructor( new Class[] { String.class } );
Object value = c.newInstance( new Object[] { stringArg > } );
And even better, when JDK 1.5 is released, you'll be able to write:
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    String stringArg = ...;
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I didn't read all your note carefully.
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Hi
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Hi:
Here is part of my code in short:
public class TextInputWithAutoComplete extends TextInput
private function addComp():void{
list = new List();
list.id = "autoCompleteList";
list.x = 0;
list.y = 20;
list.addEventListener(MouseEvent.MOUSE_UP, handleMouseDown);
parentDocument.addChild(autoCompleteList); OR addChild(autoCompleteList); //my question is here
private function handleMouseDown():void{
//TODO
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From my experience, it's still able to, but which doesn't make sense to me.
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In Flex there is a lifecycle that represents the contract between the component and its parent. See the chapters on creating custom components and the lifecycle methods createChildren, commitProperties, measure and updateDisplayList.
Some components size to content like Containers. When you add a child to a container it will measure the child and make room for it or add scrollbars if there isn't enough room.
If you add a child to TextInput, it doesn't expect additional children so it will not make room for it. You can subclass and override its measure and updateDisplayList methods to make room for an additional child.
I would not recommend adding another interactive control to an interactive control since that will make managing focus and accessibility much harder. It is better to group these in a container in most cases.
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Alex Harui
Flex SDK Developer
Adobe Systems Inc.
Blog: http://blogs.adobe.com/aharui

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In exercising the MapViewer tool with thematics map I had a view questions on the capabilities of the component:
1. Is there a way in the map _request element reference a dynamically defined expression (column)
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select geom, state , state || '-' || state_abrv concat_state_name from states
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a style rule can only reference columns that exist in the base table either of the base map/theme or in the query .
I cannot seem to use a specification of "concat_state_name"
in the "label_column" attribute ... throws ClassCastException. Should this be possible ?
If not would the workaround would appear to use a view that is dynamically defined and insert a new map based on the view ?
2. In my inline view example, I found in the "<jdbc_query>" element that when I specifed a "render_style" that
was an advanced style with buckets it automatically selected my count expression and rendered the map correctly, which
is great, but it might be a good idea to make it explicit if 1. could be handled (or can).
3. For thematic maps it would be nice to dynamically define the buckets (<AdvancedStyle>)
within the map request as the potient for permutations of numeric ranges in any application could vary.
It looks like <styling_rules> might be able to handle this if you can use the BETWEEN operator or something
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in the map_request ? I did not see them nested anywhere in the DTD yet the Example 2-1 in the documentation would
imply they can be specified in the map request and the tool map definition tool does not seem to support the concept of a
variable in the base table. The workaround would appear to be to dynamically add the theme using an insert.

In exercising the MapViewer tool with thematics map I had a view questions on the capabilities of the component:
1. Is there a way in the map _request element reference a dynamically defined expression (column)
that is returned from the query defined in the value of the "<jdbc_query>" element. I want to show counts from an inline view,
but for brevity consider the the SQL
select geom, state , state || '-' || state_abrv concat_state_name from states
It seems that both the "label_column" attribute of the "<jdbc_query>" element and the "column" attribute of a "<rule>" element in
a style rule can only reference columns that exist in the base table either of the base map/theme or in the query .
I cannot seem to use a specification of "concat_state_name"
in the "label_column" attribute ... throws ClassCastException. Should this be possible ?
If not would the workaround would appear to use a view that is dynamically defined and insert a new map based on the view ? MapViewer does allow dynamic expressions in <jdbc_query>. Can you test the following simple request:
<?xml version="1.0" standalone="yes"?>
<map_request datasource = "mvdemo">
<themes>
<theme name="theme1" min_scale="5.0E7" max_scale="0.0">
<jdbc_query
datasource="mvdemo"
jdbc_srid="0"
spatial_column="geom"
render_style="C.RED"
label_style="T.STREET NAME"
label_column="concat_state_name"
>select geom, state , state || '-' || state_abrv concat_state_name from states where state_abrv='MA' </jdbc_query>
</theme>
</themes>
</map_request>
As long as the name specified in lable_column matches the alias you give in the select list it should work.
If not then maybe you need to use the view-based approach. It will definately work in the up-coming 9.0.4 version.
2. In my inline view example, I found in the "<jdbc_query>" element that when I specifed a "render_style" that
was an advanced style with buckets it automatically selected my count expression and rendered the map correctly, which
is great, but it might be a good idea to make it explicit if 1. could be handled (or can).
3. For thematic maps it would be nice to dynamically define the buckets (<AdvancedStyle>)
within the map request as the potient for permutations of numeric ranges in any application could vary.
It looks like <styling_rules> might be able to handle this if you can use the BETWEEN operator or something
like runway_number >= 10 and runway_number < 20 as expressions. Are these valid and if so where are they specified
in the map_request ? Yes that may indeed be a good thing to have in a future version of mapviewer. In the mean time yes you can always use such expressions as you provided in the styling_rules (which is only for predefined themes) or in a <jdbc_theme>.
I did not see them nested anywhere in the DTD yet the Example 2-1 in the documentation would
imply they can be specified in the map request and the tool map definition tool does not seem to support the concept of a
variable in the base table. The workaround would appear to be to dynamically add the theme using an insert. The map definition tool is lagging behind in terms of supporting all the functions actually available in MapViewer server.
Thanks,
LJ

RMI dynamic classloading problems

I wanted to know if you could help me answer this particular case,
which i still haven't been able to solve in days:
1>RMI Client and Server are on different hosts.
2>the Client makes a RMI method call to a Server who has to execute
dynamically a particular classfile specified by the client itself and
return the result to the client
PROBLEM IS:
at the beginning only the client has the classfile to be executed by
server and needs to transfer him the information in order to have its
RMI method executed,and no ohter protocols except for RMI are
allowed.
QUESTION IS:
how could i solve this case with the use of codebases and
URLClassLoader Objects?
hoping i've clearly made the point,thanXalot
nicholas

The client can set its own codebase. The client class that the server will call needs to implement an interface the server knows. Then the client will pass this object to the server, and the server will make its call on that object. Since this object is not exported it will be serialized to the server, and the call will run on the server.
Quite insecure. But it should work just that simply I do believe.
You do know how to use codebase?

Dynamic classloading and incompatibleclasschangeerror

I have different versions of my applications like v1 v2 v3 and my current version is v4.
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v4 contacts v3, v2, v1 through RMI.
Now the problem is when v4 is calling a remote method of v3 I am getting IncompatibleClassChangeError
I tried to recompile all the required classes in v3 and created a new v3.jar and I have loaded the same dynamically in v4. I also recompiled all the classes of v4, but still the result is same.
Both v3 classes and v4 classes are compiled using the same JRE version.
Can somebody help me to figure out what could be the issue.
Thanks

If you know that there is a constructor that takes,
for example, a single String argument you can use
something like this:
Class clazz = ...; // class to instantiate
String stringArg = ...; // argument to pass to constructor
Constructor c = clazz.getConstructor( new Class[] { String.class } );
Object value = c.newInstance( new Object[] { stringArg > } );
And even better, when JDK 1.5 is released, you'll be able to write:
    Class clazz = ...;
    String stringArg = ...;
    Constructor c = clazz.getConstructor(String.class);
    Object value = c.newInstance(stringArg);Geoff

Dynamic stub downloading question.

It turned out that I've been killing time over and over again when setting up dynamic stubs downloading for RMI implementations.
Wouldn't be it simple if RMI isolates developer from all those steps by
a) creating stubs on the fly when the remote object gets bound and
b) upload them to the client as a part of Naming.lookup() call?
No need to rmic, http-/ftp-/file--server, additional security, etc. Can somebody explain me this or I am missing something here??
Thanks.

It turned out that I've been killing time No, you havent been killing time.
over and
over again when setting up dynamic stubs downloading
for RMI implementations.
Wouldn't be it simple if RMI isolates developer from
all those steps by
a) creating stubs on the fly when the remote object
gets boundDo you know what this will ultimately mean? It means that some PROCESS, either the registry or something else, will NEED TO LOOK AT THE OBJECT THAT IT HAS ACCEPTED TO BE BOUND, OR IS JUST ABOUT TO ACCEPT TO BE BOUND and then check to see if it REALLY does extend the proper superclasses (UnicastRemoteObject for plain RMI, or PortableRemoteObject for all those RMI-IIOP lovers out there), THEN check if the service object REALLY DOES implement the remote interface TO THE LETTER, ........THEN check to see if the proper exceptions are going to be thrown if something goes wrong!!
(i'm panting right now.....)
That's simply madness. Do you have any idea how often an object can be:
1: Bound to the registry
2. REBOUND under a different name
3. Removed and later REBOUND
?????? Its sick. The JVM/registry overhead will hit the roof!!!
ok, lets go on....
and
b) upload them to the client as a part of
Naming.lookup() call?What?? IS IT FOR THE CLIENT TO TRY AND CONNECT TO THE SERVER USING STUBS IT ALREADY HAS .......or is it for the server to somehow keep TABS on its client and SEND the stubs to it, just so it can talk to the server???????
Doesnt make sense at all.
>
No need to rmic, http-/ftp-/file--server, additional
security, etc. Can somebody explain me this or I am
missing something here?Oh, buddy: you ARE missing something.

Dynamic Parameter List questions: Length and Custom Values

I've got a Crystal Report that I want to use Dynamic Values for.
Right now... this report is simply a "SELECT stuff FROM table" SQL query... with a parameter that the report uses to filter.
I use a "Select DISTINCT value from table" to generate a list of values. I put those values into a txt. I then import the text into a static list. This creates a parameter list that is 11 "pages" long on the parameter screen. I also have "custom" values allowed. This is to allow for "new" values and also allow not needing to browse 11 pages for one or two known values.
If I turn the parameter into a Dynamic List based on the same Select statement it stops at 5 pages, obviously cutting off half of the possible values.
Dynamic List also removes the ability to do Custom Values. The filter option wouldn't be a bad alternative BUT it don't work for pages 6+ that aren't there.
How can I remove the 5 page limit (or whatever it is) for Dynamic values?
Thanks
Chris
Edited by: WernerCD on Aug 4, 2010 4:14 PM

There is a limit of 1000 records in dynamic parameters. You can change this by adding a registry value:
registry key : HKEY_CURRENT_USER\SOFTWARE\Business Objects\Suite 11.0\Crystal Reports\DatabaseOptions\LOV
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if you have Crystal 2008 then the above registry folder will say Suite 12.0.

Dynamic ClassLoader - feasability question

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