Why use helper classes?

I am confused about the purpose of helper classes when using EJB's. Is the idea simply to make the code more maintainable? To separate data access code from the business logic? To aid the reuse of code? Why should I choose to use a helper class rather than creating a new EJB to do the job?
I have been unable to find any comprehensive articles, and am a bit confused!
Thanks in advance.

- split out code into distinct functional models
- split out code that can be reused effectively elsewhere
- wrap objects that need to be passed to other modules as a whole
- performance (EJBs are slow compared to standard beans)
- keep code shorter (per file/method) so it's easier to read and maintain
etc. etc.

Similar Messages

Why use abstract classes?

Why should I use abstract classes instead of a regular class with empty method bodies? Just better design? Is there some logical or performance based reason?

Why should I use abstract classes instead of aregular
class with empty method bodies? Just better design?Is
there some logical or performance based reason?Because it describes what you're doing.
If you define a "regular" class with empty message
bodies, everyone who looks at it will say "WTF is he
trying to do" or, if they're charitable, "Look,
Harvey, someone who's trying to make Java look just
like C++!".
sigh Maybe answers like THIS are why people keep asking the same question.
Here's a couple things an abstract class does that a "regular" class with empty methods bodies doesn't:
1) An abstract class cannot be instantiated.
2) An abstract class forces it's abstract methods to be implemented.
If you were to extend a non-abstract class with empty method bodies, you wouldn't have to override the methods... you could just leave them empty. An abstract class forces it.
There's a lot more reasons... those are a couple obvious ones.

Why use Factory classes

Why do we use Factory classes such BorderFactory, to get an instance of Border class, why cant we directly create an object of such classes like we do with regular concrete classes

Why do we use Factory classes such BorderFactory, to
get an instance of Border class, why cant we directly
create an object of such classes like we do with
regular concrete classesFactory methods (I mean static create methods here) have two advantages.
First, the library designer doesn't have to expose concrete classes to the outside world, just interfaces. This adds flexibility.
Second, the library designer is free to make object creations more flexible. The create method may take parameters that doesn't exactly correspond to a constructor of one specific class.

Why Use Nested Classes

Hi All,
Why do we use Nested Classes ? Explain it with example ....
If we say - It is a way of logically grouping classes that are only used in one place. Then we can say we use it through "Package" so why inner class ??
Thanks in advance ....

A real life example to jschell's explaination may be this.
The pistons in your automobile engine are encapsulated by the engine block -- or the engine block encapsulates the pistons inside. This is the desired effect because as soon as we take the pistons out of the engine block, and put them say, in the backseat of the car instead, they no longer perform the function they were intended. There is another side effect to this analogy. When the pistons are properly installed in the engine block, there is only one movement the pistons can move -- up and down movement, that's it... they cannot rotate, spin, twist around or anything inside the engin block. Furthermore, the up and down movement is the only useful thing a piston can do. As soon as we throw the pistons in the backseat of the car, they can roll around, spin, and generally rotate to any configuration or orientation -- which does not produce any useful power.
Inner classes are generally the same way. So we can see this example with a little code -- which we like.
public class Engine
Piston[] pistons = new Piston[8];
class Piston
// the usual methods here..
}Of course, if your program is extremely sohisticated, this may not be a good solution -- for example, if you are making a catalog of automotive parts, then you would probably want your <tt>Piston</tt> class to be stand-alone.
Edited by: pierrot_2. Also notice that the class <tt>Piston</tt> is not an INNER class of Backseat!

Helper Classes

Hi,
going through the J2EE Tutorial you'll read on page 76 that Helper Classes "... must reside in the EJB JAR file that contains the enterprise bean class".
Now, when deploying the cart example, the BookException class is included in both EJB JAR and Client JAR files.
I would like to understand this construction. Can you help me?
TIA
Ivo

Hi Iwo,
The reason why the BookException is placed both in the EJB Jar and in the Client Jar is that both the server and the client must know the Exception. Basically you can devide your bean into three parts:
Remote interface, which is known both by the client and the server.
Home interface, do.
EJB class, which only the server knows.
When an exception is declared thrown at an interface, then the Exception must be included beside the interface otherwise a ClassNotFoundException will be thrown.
Second, the reason why the helper classes must be included in the EJB jar is that the enterterprise bean is using the classes. If you do not include the Helper classes the bean will not be able to instantiate the Helper classes and it will not work.
Hope this information will be helpful to you.
Regards,
Jess

Help,about why we use inner class?

Hi,
when i read "java Tutorial"
i found there is one chapter about inner class .
i copy it down as follow.
the context is about there is a class Stack, and this class want to implement some function of interface Iterator,but as the book said
we should not let class Stack implement the Iterator directly, we should add a inner class inside the Stack .
i know it's very import ,but i still can not understand the reason why add a inner class here.
hope somebody can explain it a little more for me or give an example.
thank in advance!
Iterator defines the interface for stepping once through the elements within an ordered set in order. You use it like this:
while (hasNext()) {
next();
The Stack class itself should not implement the Iterator interface, because of certain limitations imposed by the API of the Iterator interface: two separate objects could not enumerate the items in the Stack concurrently, because there's no way of knowing who's calling the next method; the enumeration could not be restarted, because the Iterator interface doesn't have methods to support that; and the enumeration could be invoked only once, because the Iterator interface doesn't have methods for going back to the beginning. Instead, a helper class should do the work for Stack.
The helper class must have access to the Stack's elements and also must be able to access them directly because the Stack's public interface supports only LIFO access. This is where inner classes come in.
Here's a Stack implementation that defines a helper class, called StackIterator, for enumerating the stack's elements:
public class Stack {
private Object[] items;
//code for Stack's methods and constructors
not shown
public Iterator iterator() {
return new StackIterator();
class StackIterator implements Iterator {
int currentItem = items.size() - 1;
public boolean hasNext() {
public Object next() {
public void remove() {
or you can visit here
http://java.sun.com/docs/books/tutorial/java/javaOO/innerclasses.html

the context is about there is a class Stack, and this
class want to implement some function of interface
Iterator,but as the book said
we should not let class Stack implement the Iterator
directly, we should add a inner class inside the
Stack .Simply because the implementation of the Iterator is nobody's business. By declaring it to be a private inner clss, nobody will ever know about it and only see the Iterator interface.

Help using scanner class to count chars in file

Hi all, I am learning Java right now and ran into a problem. I need to use the Scanner class to accurately count the number of chars in a file including the line feed chars 10&13.
This what I have and it currently reports a 201 byte file as having 194 chars:
     File file = new File(plainFile);
     Scanner inputFile = new Scanner(file);
     numberOfChars = 0;
     String line;
     //count characters in file
     while (inputFile.hasNextLine())
          line = inputFile.nextLine();
          numberOfChars += line.length();
I know there are other ways using BufferedReader, etc but I have to use Scanner class to do this.
Thanks in advance!

raichle wrote:
Wow guys, thanks for the help! I've got a RTFMWell, what's wrong to have a look at the API docs for the Scanner class?
and directions that go against the specs I said.Is that so strange to suggest a better option? What if I ask a carpenter "how do I build a table with a my stapler?". Should I give the man an attitude if he tells me I'd better use a saw and hammer?
I'm also aware that it "eats" those chars and obviously looking for a way around that.
I've looked through the java docs, but as I said, I'm new to this and they're difficult to understand. The class I am auditing req's that this be done using Scanner, but I don't see why you demand an explanation.
Can anybody give me some constructive help?Get lost?

Needs help.....Please about using different classes

I don't know how to use differenet classes.
Please tell me how to write class to suit Start. This stuff me up. Please .... help me
<<My program>>
//Start
public class Start
{ private Artist[] Artists;
private Record[] records;
private Person[] Manager;
private TextMenu makeMenu = new TextMenu();
public static void main(String[] args)
 Start studio = new Start();
studio.menu();
public Start()
{ //Person.Manager(ManagerName,HouseNumber,StreetNumber,PhoneNumber)
 Manager = new Person[1];
 Manager[0] = new Person("Yangfan",88,"Young ST",11118888);
 //Artist(GroupID,ArtistName,HouseNumber,StreetNumber,PhoneNumber)
 Artists = new Artist[5];
Artists[0] = new Artist(1,"Backstreet Boys",58,"Music ST",99998888);
Artists[1] = new Artist(2,"Santana",68,"Music ST",99998899);
Artists[2] = new Artist(3,"Macy Gray",78,"Music ST",55558888);
Artists[3] = new Artist(4,"Ricky Martin",88,"Music AVE",77778888);
Artists[4] = new Artist(5,"Did Rock",55,"Music Road",66667777);
//Record(RecordingID,RecordName,Artist,StartTime,FinishTime,RecordingDate,GuestArtist1,GuestArtist2)
records = new Record[6];
records[0] = new Record(1,"I want it that way",Artists[0],11,12,"05/08/2001",Artists[1],Artists[3]);
records[1] = new Record(2,"Smooth",Artists[1],11,12,"05/08/2001",Artists[1],"");
records[2] = new Record(3,"Do something",Artists[2],11,"05/08/2001",Artists[3],"");
records[3] = new Record(4,"Livin La Vida Loca",Artists[3],11,12,"05/08/2001",Artists[1],Artists[3]);
records[4] = new Record(5,"Bawitdaba",Artists[4],11,13,"05/08/2001",Artists[1],"");
records[5] = new Record(6,"The one",Artists[0],11,14,"05/08/2001",Artists[1],"");
public void menu()
{ String[] choices = {">>>List Manager Details",">>>List All Artist Names",">>>List An Artist Telephone-Number",">>>Show Details For One Recording",">>>Add A New Recording",">>>List The Recording Costs For All Artists",">>>List Artist's Reocording",">>>Exit Program"};
while (true)
{ switch (makeMenu.getChoice(choices))
{ case 1: showAllArtists();
break;
case 2: showAllRecords();
break;
case 3: System.exit(0);
break;
case 4: System.exit(0);
break;
case 5: System.exit(0);
break;
case 6: System.exit(0);
break;
case 7: System.exit(0);
break;
case 8: System.exit(0);
break;
default:
public void showAllArtists()
{ int numArtists = Artists.length;
for(int i = 0; i < numArtists; i++)
{ Artists[i].displayArtistDetails();
public void showAllRecords()
{ for (int i = 0; i < records.length; i++)
{ System.out.println();
records.printRecordDetails();
<<Assignment>>
Due - midnight, Wednesday August 22nd
This assignment will test your knowledge of Java programming using classes, encapsulation and javadoc.
The base requirements
Write a complete Java class to manage a Digital Recording Studio. The studio wants to keep a list of all Artists that use the studio and also wishes to keep track of all Recordings that have been made. An important function of the program is to calculate the time spent making a recording and charge the Artist for the time used.
You must create at least the following classes, Start, Studio, Person, Artist, Recording, Address. You may create other classes if needed as well
Start will contain main(), create one instance of a Studio and execute a Menu of commands to test your code. Studio should contain a studio name, an array of Artist and an array of Recording plus the studio manager (a Person). Each Artist should contain the name of the group and an Address. Each Person will have a name and a home address. Each recording will have a Title (usually song title), an Artist (only one), and a list of guestArtist (they are Artist�s but will not receive royalties) the number of the CD the recording is stored on (numbers are numerical and recordings are saved on CD-R), plus the recording start and finish times for the recording session (suggest you use Java Date class � refer to the API). An Address will contain, house number (integers only), a street name and a telephone number. There is no need to store city and country.
To enter a set of data for testing your program � main() should call a method in the Start class that will fill in a set of values by creating objects and filling in values by calling methods in each class. This is the ONLY method allowed to be longer than 1 page long � normally we would read the data from a file but there are no O-O principles that can be learnt with simply filling in data values. It is suggested to create say at least 4 Artist�s and 6 Recordings (at least one with 1 guest Artist and one with 2 guestArtist�s)
A menu for testing your program should be provided (it is suggested to put the Menu into a separate class as you need at least 3 menus). While other commands are possible, only the following ones will receive marks.
Menu commands needed are
List the Managers name, address and telephone number
List all Artist Names
List an Artist telephone number (a sub menu showing valid Artist�s is required)
Show all details for one Recording ( sub menu of valid Recordings will be needed and remember there can be more than one guestArtist)
Add a new Recording, user will need to be prompted for all details.
List the recording costs for all Artists � show each Artist on a separate line with their name and total amount, charge for using the studio is $1000 per hour or part thereof, example for a 1 hour and 10 minute recording the Artist will be billed for 2 hours.
List all the Recording�s one Artist has worked on (sub menu of Artists needed), the list should show whether they were the Artist or a guestArtist
Exit program
Use fixed sizes for arrays, suggest 20 is suitable for all arrays. Java can handle dynamic data structures (where the number of elements can grow or shrink), but that is beyond a first assignment.
Do NOT make ANY methods static - this defeats the Object Oriented approach and will result in ZERO marks for the entire assignment.
Data MUST be encapsulated, this means that all the data relating to an object are to be stored INSIDE an object. None of the data detail is to be globally available within your program - hence do not store Artist names in either Studio or Recordings � just store a reference instead. Do NOT create ID numbers for Artists, you should use References instead � for many students this will be the hardest part as you have to use Objects, not program in a C style to solve the problem. Note that if there are any non-private data in classes then zero will given for marks for encapsulation.
Good programming style is expected (see web page or lecture notes). In particular, you must use javadoc to generate a set of html pages for your classes. Make sure you use the special javadoc style comments in your source code. Marks will be granted for both using javadoc and also for including sensible javadoc comments on each class and each public method.
What to Hand In
Read the turnin page, basically the .java files, a readme.txt to tell the marker which file the program starts from plus the javadoc (html) files. Do NOT send .class files (if you do send these we will delete them and recompile your program), do NOT compress with gtar, tar, zip or use any other tool on your files. Turnin automatically compresses all your files into a single archive for us to mark.
The simplest way to turnin all your files is to place all files in one directory then just use the *.* wildcard to turn in all files within that one directory.
You must turnin all files that are not part of Java 1.3. In particular, you are allowed (actually encouraged) to use EasyIn or SavitchIn but should include the one you use in the files you submit. It is STRONGLY suggested that you copy all the files into another directory, test it works there by compiling and executing then turnin files from that directory. A common problem is students adding comments at the last minute then not testing if it still compiles. The assignment will be marked as submitted � no asking later for leniency because you added comments at the last minute and failed to check if it still worked.
If the tutors are unable to compile your submission, they will mark the source code but you will lose all the execution marks. Sorry, but it is your responsibility to test then hand in all files.
Comments
For CS807 students, this program should be fairly easy if it was to be programmed in C (you would use several struct). The real art here is to change over to programming objects. Data is contained in an object and is not global. This idea is essential to using Java effectively and is termed encapsulation. Instead of using function(data), you use objectName.method( ). Effectively you switch the data and functions around, the data has a method (function) attached to it, not the other way around as in C (where you have a function and send data to it).
While there will be some marks for execution, the majority of the marks will be given for how well you write your code (including comments and documentation) and for how well you used O-O principles. Programs written in a C style with most of the code in one class or using static will receive ZERO marks regardless of how well they work.
You are responsible for checking your turnin by reading the messages turnin responds with. Failure to read these messages will not be an acceptable excuse for submitting an incorrect assignment. About 2% of assignments sent to turnin are unreadable (usually empty) and obtain 0.
Late submissions
Late submissions will only be accepted with valid reasons for being late. All requests for assignment extensions must be made via email to the lecturer. Replies for acceptance or refusal will made by email. Instant replies are unrealistic (there is usually a flood of queries into my mail box around assignment due dates) and the best advice is to ask at least 4 days in advance so that you will have a reasonable chance of getting a timely reply and allow yourself enough time to submit something on time if the extension is not granted.
ALL late submissions will be marked LAST and will NOT be sent to tutors for marking until all other assignments have been marked. As an example, if you submit late and your assignment is not yet marked by the time assignment 2 is due then it will be pushed to the end of the marking pile as the assignments that were submitted on time for assignment 2 will take priority.
If you make a second submission after the submission date, only the first submission will be marked. We will not mark assignments twice! You can update your submission BEFORE the submission date if you need to - this will just overwrite the first submission. The latest time for a late submission is 5pm on the Wednesday after the due date. This is because, either a solution will be handed out at that lecture or details of the assignment will be discussed at the lecture. I cannot accept any assignment submissions after that time for any reason at all including medical or other valid reasons. For those who are given permission to be later than the maximum submission time � a different assignment will be handed out. Remember, if you decide to submit late you are VERY UNLIKELY to receive feedback on your assignments during semester.
Assignments will be removed from turnin and archived elsewhere then forwarded to tutors for marking on the morning after the assignment is due. A different tutor will mark each of your assignments � do not expect the tutor you see at the tutorials to be your marker.
Marks will be returned via email to your computer science yallara account � ideally within 2 weeks. I will send marks out when I receive them so do not send email asking where your marks are just because a friend has theirs. If you want your email forwarded to an external account, then place a valid .forward file into your yallara account. The Help Desk on level 10 can assist you in setting this up if you do not know how to do it.

I have seen other people who have blatantly asked for
other people to do their homework for them, but you
are the first person I've seen to actually cut and
paste the entire assignment as it was handed to you.
Amazing.
Well, unlike some of the people you're talking about, it seems like zyangfan did at least take a stab at it himself, and does have a question that is somewhat more sepcific that "please do this homework for me."
Zyangfan,
marendoj is right, though. Posting the entire assignment is kind of tacky. If you want to post some of it to show us what you're trying to do, please trim it down to the essential points. We don't need to see all the instructor's policies and such.
Anyway, let me see if I understand what you're asking. You said that you know how to write the code, but only by putting it all in one class, is that right? What part about using separate classes do you not understand? Do you not know how to make code in one class aware that the other class exists? Do you not know how code in class A can call a method in class B?
Please be a bit more specifice about what you don't understand. And at least try using multiple classes, then when you can't figure out why something doesn't work, explain what you did, and what you think should have happened, and what did happen instead.
To get you started on the basics (and this should have been covered in your course), you write the code for two classes just like for one class. That is, for class A, you create a file A.java and compile it to A.class. For class B, you create a file B.java and compile it to B.class. Given how rudimentary you question is, we'll skip packages for now. Just put all your class files in the same directory, and don't declare packages in the .java files.
To call a method in class B from code that's in class A, you'll need an object of class B. You instantiate a B, and then call its methods.
public class B {
int count;
public B() { // constructor
public void increment() {
 count++;
public class A {
public static void main(String args[]) {
 B b = new B();
 b.increment();
}Is this what you were asking?

I need a clarification : Can I use EJBs instead of helper classes for better performance and less network traffic?

My application was designed based on MVC Architecture. But I made some changes to HMV base on my requirements. Servlet invoke helper classes, helper class uses EJBs to communicate with the database. Jsps also uses EJBs to backtrack the results.
I have two EJBs(Stateless), one Servlet, nearly 70 helperclasses, and nearly 800 jsps. Servlet acts as Controler and all database transactions done through EJBs only. Helper classes are having business logic. Based on the request relevant helper classed is invoked by the Servlet, and all database transactions are done through EJBs. Session scope is 'Page' only.
Now I am planning to use EJBs(for business logic) instead on Helper Classes. But before going to do that I need some clarification regarding Network traffic and for better usage of Container resources.
Please suggest me which method (is Helper classes or Using EJBs) is perferable
1) to get better performance and.
2) for less network traffic
3) for better container resource utilization
I thought if I use EJBs, then the network traffic will increase. Because every time it make a remote call to EJBs.
Please give detailed explanation.
thank you,
sudheer

Please suggest me which method (is Helper classes or Using EJBs) is perferable :
1) to get better performance
EJB's have quite a lot of overhead associated with them to support transactions and remoteability. A non-EJB helper class will almost always outperform an EJB. Often considerably. If you plan on making your 70 helper classes EJB's you should expect to see a dramatic decrease in maximum throughput.
2) for less network traffic
There should be no difference. Both architectures will probably make the exact same JDBC calls from the RDBMS's perspective. And since the EJB's and JSP's are co-located there won't be any other additional overhead there either. (You are co-locating your JSP's and EJB's, aren't you?)
3) for better container resource utilization
Again, the EJB version will consume a lot more container resources.

XSLT Mapping : RFC Lookup using java helper class

Hi All,
I am doing RFC Lookup in xslt mapping using java helper class. I have found blog for the same (http://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/05a3d62e-0a01-0010-14bc-adc8efd4ee14) However this blog is very advanced.
Can anybody help me with step by step approach for the same?
My basic questions are not answered in the blog as:
1) where to add the jar file of the java class used in xslt mapping.
I have added zip file of XSLT mapping in imported archived and using that in mapping.
Thanks in advace.
Regards,
Rohan

Hi,
Can u please have look at this in detail , u can easily point out yourself the problem...
http://help.sap.com/saphelp_nw04/helpdata/en/55/7ef3003fc411d6b1f700508b5d5211/content.htm
Please observe the line,
xmlns:javamap="java:com.company.group.MappingClass
in XSLT mapping..
The packagename of class and class name and XSLT namespace should be matching...
Babu
Edited by: hlbabu123 on Sep 29, 2010 6:04 PM

Code Sample: Easy RFC Lookup From XSLT Mappings Using a Java Helper Class

Hi everyone,
This is just a shameless plug for my article: <a href="https://www.sdn.sap.comhttp://www.sdn.sap.comhttp://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/05a3d62e-0a01-0010-14bc-adc8efd4ee14">Easy RFC Lookup From XSLT Mappings Using a Java Helper Class</a>. I hope you're interested in reading it, and I welcome your comments in this thread.
Kind regards,
Thorsten

Hi Stefan. Thanks for your post. I have already done that. It still does not work. As a base for my java helper class I have usesd Thorstens code.
The problem is quite confusing. I will try to ouline both issues here.
First of all, when try to test from within the Operation Mapping, I always get a java error saying it cannot find the communication channel (it is there and working because I have tested it with the RFCLookup in graphical mapping). I have found a way to work around this, and that is to uncheck the "Use SAP XMLToolkit" checkbox --> switch to test tab, enter my ReceiverService in the parameter tab (header parameter) --> switch back to Definition tab, check the "Use SAP XMLToolkit" checkbox --> switch to Test tab and run the test. Then the XSLT and call to java helper class will work. Of course this is not really something you want to do all the time. Maybe there is a bug.
Secondly, it never works when I try to do it "live". I am using a file adapter to pick up one file, convert it and a file adapter to drop the converted file. I get the following error code in SXMB_MONI.
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>

<SAP:Error xmlns:SAP="http://sap.com/xi/XI/Message/30" xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/" SOAP:mustUnderstand="">
<SAP:Category>Application</SAP:Category>
<SAP:Code area="MAPPING">TRANSFORMER_CONF_EX</SAP:Code>
<SAP:P1>ATJ_Accounting2XML_Accounting.xsl</SAP:P1>
<SAP:P2>http://rd.accounting.logica.com</SAP:P2>
<SAP:P3>fd552c30-bad9-11dd-9761-c21dac1b818c</SAP:P3>
<SAP:P4>-1</SAP:P4>
<SAP:AdditionalText />
<SAP:Stack>TransformerConfigurationException triggered while loading XSLT mapping ATJ_Accounting2XML_Accounting.xsl; http://rd.accounting.logica.comfd552c30-bad9-11dd-9761-c21dac1b818c-1</SAP:Stack>
<SAP:Retry>M</SAP:Retry>
</SAP:Error>
Using an XSLT without a call to a java helper class, works just fine.
I am totally at a loss here. Any more input would be much appreciated.
/Patrik

Add helper class public parts as used DC in EJB DC

Hi Experts,
I have created a JAVA DC project containing the helper classes.
For this helper classes i have created a Jar file.
I have also created two public parts
1) with an option Can be packaged into other build results (e.g. SDAs)
2) with an option Provides an API for developing/compiling other DCs
Now i want to use these public parts in my EJB DC.
I have added the API public part in my EJB DC as build time design time and run time.
Now when i am getting java.lang.NoClassDefFoundError: for the class defined in JAVA DC helper class.
Can you help me in resolving this?
Regards,
Ashish Shah

Hi
I have done following things:
1) I have a java DC containing helper classes and an EJB DC referring to it.
2) Now to access this EJB DC, I have created a java command bean DC.
3) And I am using this command bean Java dc in my WebDynpro application.
4) Now for deploying the helper class, I have created a library project.
5) To this library project I have added the SDA and API public part of helper class as used dc.
6) I have added this java library file as used DC in WebDynpro DC and in EJB DC.
7) I have added the library reference to the WebDynpro DC for J2ee server component library DC As pg.comaptsc~dc_aptjl
8) When i checked in Visual admin i could see the Assembly (SDA) helper class jar file.
In my helper class files, I am getting this warning.
Checking package reservation
Warning: Package pg.com.apt.help.cls is not reserved for DC : apt/sc/dc_apthc.
Now in my webdynpro DC when I refer to the helper class through the EJB, I get this error.
java.lang.NoClassDefFoundError: pg/com/apt/help/cls/TargetMarket at pg.com.atos.WebModuleProject.FetchSDCDataBean.SearchGTINTMDataEJB(FetchSDCDataBean.java:133) at pg.com.atos.WebModuleProject.FetchSDCDataObjectImpl0.SearchGTINTMDataEJB(FetchSDCDataObjectImpl0.java:119) ... 35 more ; nested exception is: java.lang.NoClassDefFoundError: pg/com/apt/help/cls/TargetMarket
Can you please guide on what I am missing.
Thanks in advance.
Regards,
Ashish Shah
Edited by: ashish shah on Dec 18, 2007 3:23 PM

Need help with tomcat 5.5 and using java classes

hey there,
i am trying to set up tomcat 5.5 on my computer at home and have sucessfully done so. i have been trying to use Java classes inside my JSP files however tomcat thows an internal servlet error as follows:
org.apache.jasper.JasperException: Unable to compile class for JSP
An error occurred at line: 144 in the jsp file: /order.jsp
Generated servlet error:
ProductList cannot be resolved to a type
An error occurred at line: 144 in the jsp file: /order.jsp
Generated servlet error:
ProductList cannot be resolved to a type
An error occurred at line: 144 in the jsp file: /order.jsp
Generated servlet error:
Product cannot be resolved to a type
i have the classes located as the setup tutorial recommends (root/WEB-INF/classes/) and still nothing works. i would appreciate any help anyone can give.
thanks,

Which tutorial are you following?
As of java1.4, all classes must be in packages for them to work in Tomcat. This means your beans and servlets too.
Put your beans in a package, and then recompile them, and put them in the right place.
eg
package com.mypackage
public class MyClass ...
once compiled would go into WEB-INF/classes/com/mypackage/MyClass.class
Are you using Product and ProductList classes in scriptlet code?
Have you imported them with a page directive
<%@ page import="com.mypackage.Product, com.mypackage.ProductList" %> ?

Is there any practical reason to use DB helper class?

Is there any practical reason to use database helper class ( e.g. database.bookDB in Duke's bookstore)in servlet design? What if I setup a DB connection for every servlet?

to ken_robinson
I am currently setup DataSurece in servlet init().Usually (I know WebLogic is this way), if you configure the DataSource through the app server's configuration app, it is available to all applications.
The most efficient way to look up the DataSource in a particular app is have a ServletContextListener lookup the DataSource from JNDI and set it in the Context as an Attribute. Each servlet would then, in it's init() method, get the DataSource from the ServletContext (faster than using JNDI for each Servlet. The ServletContextListener requires the container you are running in support the 2.3 spec. If it does not, simply use a startup servlet (servlet that is loaded when the app is loaded) and do the same thing.

Is there any advantage to use database helper class

Is there any advantage to use database helper class ( e.g. database.bookDB in Duke's bookstore)in servlet design? What if I setup a DB connection for every servlet?

If there is not much relation between servlets.For example one servlet working on authentication againist user name/password in database another one work on searching book by keywords?
and if we want to have servlets written by difference programmers?

Why use helper classes?

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