Thread safety in XMLParserv2 for java

Hello,
I've just posted something about this on the forum, but I have a few more precise questions:
1/ If I instanciate a DOMParser in a singleton class, can I have multiple threads use this single instance to produce XMLDocument objects (e.g. by parsing Strings/Urls, Streams or anything that can be fed in the DOMParser's parse() method).
2/ Once I have a XMLDocument object, can I have multiple threads use it simultaneously? (for read operations, such as getNode(), hasChildNodes() etc...)
3/ Can I have several threads call XMLDocument.getDocumentElement() on the same XMLDocument object or do I have to synchronise the call?
4/ Same for Node.cloneNode(boolean). What if it is called with the boolean parameter set to true (recursive cloning)?
Hope someone can answer these,
Thanks in advance, Rimi
null

Sorry for delay. Basically inside Parser we don't do synchronization, so here is the answers:
1/ No. Currently we dont' support this.
2/ If only read is OK. If Write is involve you have to do the synchronization.
3/ It is read, then it is OK. But if WRITE is doing, No.
4/ You have to lock the Node object, before clone.
Hope this will help.

Similar Messages

What are the thread safety requirements for container implementation?

I rarely see in the TopLink documentation reference to thread safety requirements and it’s not different for container implementation.
The default TopLink implementation for:
- List is Vector
- Set is HashSet
- Collection is Vector
- Map is HashMap
Half of them are thread safe implementations List/Collection and the other half is not thread safe Set/Map.
So if I choose my own implementation do I need a thread safe implementation for?
- List ?
- Set ?
- Collection ?
- Map ?
Our application is always reading and writing via UOW. So if TopLink synchronize update on client session objects we should be safe with not thread safe implementation for any type; does TopLink synchronize update on client session objects?
The only thing we are certain is that it is not thread safe to read client session object or read read-only UOW object if they are ever expired or ever refreshed.
We got stack dump below in an application always reading and writing objects from UOW, so we believe that TopLink doesn’t synchronize correctly when it’s updating the client session objects.
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
at java.util.AbstractList$Itr.next(AbstractList.java:420)
at oracle.toplink.internal.queryframework.InterfaceContainerPolicy.next(InterfaceContainerPolicy.java:149)
at oracle.toplink.internal.queryframework.ContainerPolicy.next(ContainerPolicy.java:460)
at oracle.toplink.internal.helper.WriteLockManager.traverseRelatedLocks(WriteLockManager.java:140)
at oracle.toplink.internal.helper.WriteLockManager.acquireLockAndRelatedLocks(WriteLockManager.java:116)
at oracle.toplink.internal.helper.WriteLockManager.checkAndLockObject(WriteLockManager.java:349)
at oracle.toplink.internal.helper.WriteLockManager.traverseRelatedLocks(WriteLockManager.java:144)
at oracle.toplink.internal.helper.WriteLockManager.acquireLockAndRelatedLocks(WriteLockManager.java:116)
at oracle.toplink.internal.helper.WriteLockManager.checkAndLockObject(WriteLockManager.java:349)
at oracle.toplink.internal.helper.WriteLockManager.traverseRelatedLocks(WriteLockManager.java:144)
at oracle.toplink.internal.helper.WriteLockManager.acquireLockAndRelatedLocks(WriteLockManager.java:116)
at oracle.toplink.internal.helper.WriteLockManager.acquireLocksForClone(WriteLockManager.java:56)
at oracle.toplink.publicinterface.UnitOfWork.cloneAndRegisterObject(UnitOfWork.java:756)
at oracle.toplink.publicinterface.UnitOfWork.cloneAndRegisterObject(UnitOfWork.java:714)
at oracle.toplink.internal.sessions.UnitOfWorkIdentityMapAccessor.getAndCloneCacheKeyFromParent(UnitOfWorkIdentityMapAccessor.java:153)
at oracle.toplink.internal.sessions.UnitOfWorkIdentityMapAccessor.getFromIdentityMap(UnitOfWorkIdentityMapAccessor.java:99)
at oracle.toplink.internal.sessions.IdentityMapAccessor.getFromIdentityMap(IdentityMapAccessor.java:265)
at oracle.toplink.publicinterface.UnitOfWork.registerExistingObject(UnitOfWork.java:3543)
at oracle.toplink.publicinterface.UnitOfWork.registerExistingObject(UnitOfWork.java:3503)
at oracle.toplink.queryframework.ObjectLevelReadQuery.registerIndividualResult(ObjectLevelReadQuery.java:1812)
at oracle.toplink.internal.descriptors.ObjectBuilder.buildWorkingCopyCloneNormally(ObjectBuilder.java:455)
at oracle.toplink.internal.descriptors.ObjectBuilder.buildObjectInUnitOfWork(ObjectBuilder.java:419)
at oracle.toplink.internal.descriptors.ObjectBuilder.buildObject(ObjectBuilder.java:379)
at oracle.toplink.queryframework.ObjectLevelReadQuery.buildObject(ObjectLevelReadQuery.java:455)
at oracle.toplink.queryframework.ObjectLevelReadQuery.conformIndividualResult(ObjectLevelReadQuery.java:622)
at oracle.toplink.queryframework.ReadObjectQuery.conformResult(ReadObjectQuery.java:339)
at oracle.toplink.queryframework.ReadObjectQuery.registerResultInUnitOfWork(ReadObjectQuery.java:604)
at oracle.toplink.queryframework.ReadObjectQuery.executeObjectLevelReadQuery(ReadObjectQuery.java:421)
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at oracle.toplink.queryframework.DatabaseQuery.execute(DatabaseQuery.java:620)
at oracle.toplink.queryframework.ObjectLevelReadQuery.execute(ObjectLevelReadQuery.java:779)
at oracle.toplink.queryframework.ReadObjectQuery.execute(ReadObjectQuery.java:388)
at oracle.toplink.queryframework.ObjectLevelReadQuery.executeInUnitOfWork(ObjectLevelReadQuery.java:836)
at oracle.toplink.publicinterface.UnitOfWork.internalExecuteQuery(UnitOfWork.java:2604)
at oracle.toplink.publicinterface.Session.executeQuery(Session.java:993)
at oracle.toplink.publicinterface.Session.executeQuery(Session.java:950)

Hi Lionel,
As a general rule of thumb, the ATI Rage 128 Pro will not support a 20" LCD. That being said, there are reports of it doing just that (possibly the edition that went into the cube).
I'm not that familiar with the ins and outs of the Cube, so I can't give you authoritative information on it.
A good place to start looking for answers is:
http://cubeowner.com/kbase_2/
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Java Bean Thread Safety

I've been using JavaBeans for years now, and have read at least 30 different texts and online resources about using Java beans in JSPs. But in every single one of them, they are ambiguous and non-committal about how to properly use them to avoid Thread-Safety problems in a multithreaded (web server) environment. Are there any true Java gurus out there who know how to do so in JSPs?
Specifically, when you use the <jsp:useBean> tag, that tag automatically binds an instance of your bean to the PageContext object. Since the PageContext object is shared by many threads, wouldn't this automatically make all of the Java Bean's properties vulnerable for thread problems? Since the pageContext is shared between threads, wouldnt one have to declare every one of the bean's setters and getters as "synchronized", to prevent one thread overwriting another's values?
I ask because in many texts, they make a vague suggestion "be sure to write your beans thread-safe"--but provide no concrete answer as to how (the level at which to declare 'synchronized'). But in all their code examples, I have never once, in all these years, seen the word "synchronized".
How is this possible? Wouldn't the bean, as bound to the thread-shared pageContext object, be completely exposed to thread corruption, with multiple threads simultaneously calling its methods?
Can someone supply some code snippets showing the thread-safe way to use JavaBeans (i.e., where to synchronize)

PageContext is shared by many threads?
Not at one time, I'm pretty certain of that.
From the API: A PageContext instance is obtained by a JSP implementation class by calling the JspFactory.getPageContext() method, and is released by calling JspFactory.releasePageContext().
The to me suggests the contract that a PageContext can only be in use by on one JSP page at a time. As far as I am concerned, pageContext can be treated like a "local variable" to a jsp page.
The contents of the pageContext object are maybe a different story, but we'll get to that.
The things to worry about with thread safety are the same as they are for servlets.
1 - Class attributes are not threadsafe. ie variables declared within <%! %> signs
2 - Session attributes are potentially not threadsafe if the user makes two quick requests in a row (handling two requests for the same session)
3 - Application attributes are never threadsafe as any currently running request can access them. Most Application level attributes I treat as read only (kinda like Singleton access)
I don't see the need to go overboard declaring everything "synchronized". In fact I think it would be hugely detrimental.

Vector Replacement in Java 1.4 - Is Thread Safety Needed In This Scenario?

I have a Java 1.4 application that queries Database # 1, and builds custom strings used to create records that are inserted into Database # 2.
Right now Vectors are used as a container to temporarily hold query output from Database # 1 while building records going into Database # 2, but I want to convert away from this legacy collection type.
This application does this with a single "worker" thread that is started and monitored by the application main thread. If the main thread detects any exceptions, i.e. a network or any database problem, the application main thread will stop the single worker thread and restart a new single worker thread.
There are several instances of this application running simultaneously on the same server but accessing different test databases. When put into the production environment this application will run on a separate server and there will be only 1 instance of the application running.
I have reviewed numerous forums here and Google results and have not found much specific info that would closely apply to my exact design situation. I did not post any code since this is more of a design question than issue with a specific code snippet.
My question is: In the scenario I described, does thread safety need to be a factor in choosing a new collection type (to replace Vectors) and in building code that accesses this new collection type?

The several instances of the application are all independent JVMs and can't interact with each other directly at all. So there's no thread safety issue there and there never was. So what does that leave you? You've got a single worker thread using the Vector? There's no thread safety issue there either. The only time you have to think about thread safety is when two threads are trying to use the same object.

Custom thread pool for Java 8 parallel stream

It seems that it is not possible to specify thread pool for Java 8 parallel stream. If that's so, the whole functionality is useless in most of the situations. The only situation I can safely use it is a small single threaded application written by one person.
In all other cases, if I can not specify the thread pool, I have to share the default pool with other parts of the application. If someone submits a task that takes a lot of time, my tasks will get stuck. Is that correct or am I overlooking something?
Imagine that someone submits slow networking operation to the fork-join pool. It's not a good idea, but it's so tempting that it will be happening. In such case, all CPU intensive tasks executed on parallel streams will wait for the networking task to finish. There is nothing you can do to defend your part of the application against such situations. Is that so?

You are absolutely correct. That isn't the only problem with using the F/J framework as the parallel engine for bulk operations. Have a look http://coopsoft.com/ar/Calamity2Article.html

Urgent question about Thread-safety

Hi all,
the new tiger release provides an "isReachable()" method for the "InetAddress" object.
I've found, this method is not thread-safe (see the source and output below).
It returns true for all threads, when multiple threads using this method with different adresses are running at a time and one of the addresses is reachable. This happens only on WinXp. Running on Linux, the output is like expected.
I've tried to report this as a bug. But the gurus answered, taking care of thread safety would be a "programmers task".
My question is, what can I do, to be thread-safe in my case?
W.U.
import java.util.*;
import java.net.*;
public class IsReachableTest_1 extends Thread{
 static volatile int inst=1;
 static final String NET_ADDR="192.168.111.";
 int instance=inst++;
 public void run(){
 for(int i=19;i<23;i++){
 try{
 long start=System.nanoTime();
 if(InetAddress.getByName(NET_ADDR+i).isReachable(1000))
 System.out.println(""+instance+"--host found at:"+NET_ADDR+i+"--time:"+(System.nanoTime()-start)/1000000);
 else
 System.out.println(""+instance+"--no host at:"+NET_ADDR+i);
 }catch(Exception e){System.out.println(""+instance+"--ERROR "+e.toString());}
 System.out.println(""+instance+"--done.");
 public static void main(String[] args) {
 System.out.println(
 System.getProperty("java.vendor")+" "+
 System.getProperty("java.version")+" running on "+
 System.getProperty("os.name")+" "+
 System.getProperty("os.version"));
 Vector v=new Vector();
 System.out.println("\nTest 1: One after another:");
 for(int i=0;i<10;i++){
 IsReachableTest_1 t;
 t=new IsReachableTest_1();
 t.start();
 try{
 t.join();
 }catch(Exception e){System.out.println("MAIN1: "+e.toString());}
 System.out.println("\nTest 2: All together:");
 inst=1;
 for(int i=0;i<10;i++){
 IsReachableTest_1 t;
 t=new IsReachableTest_1();
 t.start();
 v.addElement(t);
 for(Iterator i=v.iterator();i.hasNext();)
 try{
 ((IsReachableTest_1)i.next()).join();
 }catch(Exception e){System.out.println("MAIN2: "+e.toString());}
 System.out.println("\nALL DONE");
And here is the output, when running on WinXp:
Sun Microsystems Inc. 1.5.0-beta running on Windows XP 5.1
Test 1: One after another:
1--no host at:192.168.111.19
1--no host at:192.168.111.20
1--host found at:192.168.111.21--time:2
1--no host at:192.168.111.22
1--done.
2--no host at:192.168.111.19
2--no host at:192.168.111.20
2--host found at:192.168.111.21--time:4
2--no host at:192.168.111.22
2--done.
3--no host at:192.168.111.19
3--no host at:192.168.111.20
3--host found at:192.168.111.21--time:1
3--no host at:192.168.111.22
3--done.
4--no host at:192.168.111.19
4--no host at:192.168.111.20
4--host found at:192.168.111.21--time:1
4--no host at:192.168.111.22
4--done.
5--no host at:192.168.111.19
5--no host at:192.168.111.20
5--host found at:192.168.111.21--time:3
5--no host at:192.168.111.22
5--done.
6--no host at:192.168.111.19
6--no host at:192.168.111.20
6--host found at:192.168.111.21--time:1
6--no host at:192.168.111.22
6--done.
7--no host at:192.168.111.19
7--no host at:192.168.111.20
7--host found at:192.168.111.21--time:1
7--no host at:192.168.111.22
7--done.
8--no host at:192.168.111.19
8--no host at:192.168.111.20
8--host found at:192.168.111.21--time:1
8--no host at:192.168.111.22
8--done.
9--no host at:192.168.111.19
9--no host at:192.168.111.20
9--host found at:192.168.111.21--time:1
9--no host at:192.168.111.22
9--done.
10--no host at:192.168.111.19
10--no host at:192.168.111.20
10--host found at:192.168.111.21--time:1
10--no host at:192.168.111.22
10--done.
Test 2: All together:
1--no host at:192.168.111.19
2--no host at:192.168.111.19
3--no host at:192.168.111.19
4--no host at:192.168.111.19
5--no host at:192.168.111.19
6--no host at:192.168.111.19
7--no host at:192.168.111.19
8--no host at:192.168.111.19
9--no host at:192.168.111.19
10--no host at:192.168.111.19
2--no host at:192.168.111.20
3--no host at:192.168.111.20
6--host found at:192.168.111.20--time:924 <----- this host does not exist!!
5--host found at:192.168.111.20--time:961 <----- this host does not exist!!
10--host found at:192.168.111.20--time:778 <----- this host does not exist!!
9--host found at:192.168.111.20--time:815 <----- this host does not exist!!
2--host found at:192.168.111.21--time:37
7--host found at:192.168.111.20--time:888 <----- this host does not exist!!
8--host found at:192.168.111.20--time:852 <----- this host does not exist!!
4--host found at:192.168.111.20--time:997 <----- this host does not exist!!
1--host found at:192.168.111.20--time:1107 <----- this host does not exist!!
3--host found at:192.168.111.21--time:38
6--host found at:192.168.111.21--time:1
5--host found at:192.168.111.21--time:1
10--host found at:192.168.111.21--time:2
2--host found at:192.168.111.22--time:3 <----- this host does not exist!!
9--host found at:192.168.111.21--time:2
7--host found at:192.168.111.21--time:1
4--host found at:192.168.111.21--time:3
1--host found at:192.168.111.21--time:39
2--done.
1--host found at:192.168.111.22--time:5 <----- this host does not exist!!
1--done.
10--host found at:192.168.111.22--time:40 <----- this host does not exist!!
3--host found at:192.168.111.22--time:192 <----- this host does not exist!!
6--host found at:192.168.111.22--time:75 <----- this host does not exist!!
8--host found at:192.168.111.21--time:230
5--host found at:192.168.111.22--time:155 <----- this host does not exist!!
4--host found at:192.168.111.22--time:78 <----- this host does not exist!!
9--host found at:192.168.111.22--time:77 <----- this host does not exist!!
7--host found at:192.168.111.22--time:76 <----- this host does not exist!!
10--done.
6--done.
4--done.
5--done.
3--done.
7--done.
9--done.
8--no host at:192.168.111.22
8--done.
ALL DONE

I created this test (it's basically the same as your class):
import java.util.*;
import java.net.*;
public class IsReachableTest_2 implements Runnable {
 private final String[] addresses = new String[] {
 "www.sun.com",
 "129.42.16.99" // www.ibm.com which is not reachable
 public void run(){
 try {
 for (int i = 0; i < addresses.length; i++) {
 final long start = System.nanoTime();
 final String address = addresses;
 if (InetAddress.getByName(address).isReachable(5000)) {
 System.out.println(Thread.currentThread().getName() + ": Host found at: " + address +
 " --time: " + (System.nanoTime() - start) / 1000);
 } else System.out.println("no host at: " + address);
} catch(Exception e){
e.printStackTrace();
System.out.println("Thread " + Thread.currentThread().getName() + " DONE");
public static void main(String[] args) {
System.out.println(
 System.getProperty("java.vendor") +
 " " +
 System.getProperty("java.version") +
 " running on " +
 System.getProperty("os.name") +
 " " +
 System.getProperty("os.version")
for (int i = 0; i < 10; i++) {
 final Thread t = new Thread(new IsReachableTest_2(), "THREAD " + (i+1));
 t.start();
And I get:
Sun Microsystems Inc. 1.5.0-beta running on Windows 2000 5.0
THREAD 1: Host found at: www.sun.com --time: 217653
THREAD 3: Host found at: www.sun.com --time: 214404
THREAD 6: Host found at: www.sun.com --time: 214900
THREAD 4: Host found at: www.sun.com --time: 215901
THREAD 5: Host found at: www.sun.com --time: 216666
THREAD 10: Host found at: www.sun.com --time: 216620
THREAD 9: Host found at: www.sun.com --time: 217405
THREAD 2: Host found at: www.sun.com --time: 220705
THREAD 7: Host found at: www.sun.com --time: 220845
THREAD 8: Host found at: www.sun.com --time: 221384
no host at: 129.42.16.99
Thread THREAD 4 DONE
no host at: 129.42.16.99
Thread THREAD 6 DONE
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
no host at: 129.42.16.99
Thread THREAD 5 DONE
Thread THREAD 10 DONE
Thread THREAD 9 DONE
Thread THREAD 7 DONE
Thread THREAD 3 DONE
Thread THREAD 1 DONE
Thread THREAD 2 DONE
Thread THREAD 8 DONE
HOWEVER: I was getting some strange results every so often. Results like:
Sun Microsystems Inc. 1.5.0-beta running on Windows 2000 5.0
THREAD 3: Host found at: www.sun.com --time: 261132
THREAD 9: Host found at: www.sun.com --time: 264183
THREAD 2: Host found at: www.sun.com --time: 266447
THREAD 6: Host found at: www.sun.com --time: 266596
THREAD 8: Host found at: www.sun.com --time: 267192
THREAD 5: Host found at: www.sun.com --time: 268610
THREAD 4: Host found at: www.sun.com --time: 269849
THREAD 1: Host found at: www.sun.com --time: 280978
THREAD 7: Host found at: www.sun.com --time: 272589
THREAD 10: Host found at: www.sun.com --time: 273162
THREAD 3: Host found at: 129.42.16.99 --time: 13657
Thread THREAD 3 DONE
THREAD 4: Host found at: 129.42.16.99 --time: 4123
THREAD 2: Host found at: 129.42.16.99 --time: 9439
THREAD 5: Host found at: 129.42.16.99 --time: 6681
THREAD 8: Host found at: 129.42.16.99 --time: 7655
THREAD 6: Host found at: 129.42.16.99 --time: 8627
THREAD 9: Host found at: 129.42.16.99 --time: 10586
Thread THREAD 4 DONE
Thread THREAD 2 DONE
Thread THREAD 5 DONE
Thread THREAD 8 DONE
Thread THREAD 6 DONE
Thread THREAD 9 DONE
no host at: 129.42.16.99
Thread THREAD 7 DONE
no host at: 129.42.16.99
no host at: 129.42.16.99
Thread THREAD 10 DONE
Thread THREAD 1 DONE
Usually the first run after I had compiled the class (!?) This isn't a thread safety problem.

Reflection objects and thread safety

Hi,
I believe that I saw that Field and Method objects are thread-safe (i.e., can safely have methods called against a single object instance concurrently from multiple threads), but am having trouble finding such a description in the JDK javadocs static that fact.
I'm assuming that all thread-specific 'state' would be managed by the Object target passed to methods like invoke()/get()/set() and not on the actual Field and Method objects themselves. Ideally, i'd like to only have to look up fields and methods only once reflectively, and thereafter just use the same reflection object instances to access their target objects at runtime as a performance optimizations - possibly in different threads and at the same time - without having to pay the cost of looking it up again. I should be able to do that providing Method.invoke() is thread safe. Otherwise, i'd probably be forced to call Class.getMethod() to get a new Method object to use against each object instance, which would be more costly both from a memory standpoint (more Method objects) and a lookup-cost perspective.
Given that lots of existing performance-critical enterprise infrastructure code, such as OR database APIs, IoC frameworks and J2EE containers use reflection to decouple the generic code from any app specific code (from a compile time perspective) as an alternative to code generation, it's surprising that there's no obvious statement about thread safety in these classes. If I look at the source code for Method, it appears to be thread safe, but I can only get so far with this analysis, as the critical code in Method appears to be implemented using a class named 'sun.reflect.MethodAccessor', whose source I don't have access to.
I know it's possible to invoke a method against multiple objects by calling Method.invoke() against each of the target objects in question. However, there's no mention as to whether it's safe to use a single Method object instance to invoke a method against multiple target object instances at the same time (i.e., from different threads running in parallel). This would fail, for instance, if the Method object had data members that were used to communicate information between internal calls without any synchronization, as the values might be used by one thread while another was changing them.
Just to clarify (as i've seen some confusion in other forum discussions on this topic):
I completely understand that the thread safety of a target object's method (read, small 'm') is entirely dependent upon it's implementation and not the mechanism by which it's invoked - i.e., whether a method is invoked by an explicit compiled-in call against an instance of the target object in some Java source file, or indirectly via Method object-based reflection, is immaterial the the method's thread safety.
What i'm asking about is the thread safety of the Method.invoke() call itself (read, big 'M'). Same question wrt Field.get()/.set() as well. These calls should be thread-safe if they're stateless wrt the Method and Field object instances that they are invoked against.

In general, if a Java API is silent about multi-threading, it is intended to be thread-safe. See the javadoc for HashMap for an example of an explicit warning.
It is true that Java code can have bugs that show up only on unusual implementations of the Java memory model, such as relaxed memory model machines. Most (if not all) implementations of the JDK have been deployed principally on platforms with strong memory models. (Perhaps not coincidentally, those are also the machines that have market share.) There are even bugs found occasionally in the JDK core, so draw your own conclusions about the bug-tail of our software stack on systems with relaxed memory models!
One of the more likely bugs to run into on highly optimized systems is failure of timely initialization of non-final fields in objects which are shared in an unsynchronized manner. See http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#finalRight and related pages. JDK core programmers (at Sun, to my personal knowledge) take care not to write code with such bugs, but application programmers might.
And, yes, caching your own Method objects is a good idea, if only because their lookup is generally cumbersome and slow. If you are very performance sensitive, you'll end up generating bytecode "shim" between your callers and the desired target methods. I expect that the http://openjdk.java.net/projects/mlvm/ (an openjdk project we are just starting) will provide some relief for this; stay tuned.
Finally, since Method objects have no state to speak of (except their "accessible" bit, which is an ahead-of-time configuration), it would be really, really surprising if they could create a race condition of some sort. If you expect race conditions in formally stateless data structures, you are certifiably paranoid. (A normal state on some platforms, hopefully not on Java.)
For more information about method calls, including reflective methods, see my blog post: http://blogs.sun.com/jrose/entry/anatomy_of_a_call_site
Best wishes...

Dumb question about Thread Safety in Servlets

Hi all
I wrote this Client API for sending requests and receiving responses to / from a multivalue database. The API is called by my Servlet. Now it seems my API is not thread safe because when several people open up the servlet at the same time, the API gets totally confused. When the API calls are inside a synchronized(){} it works just fine, but obviously at a big performance hit. Is that the wrong way of doing it??
However when I was doing the ACID test locally on my machine, by opening two command prompts and excuting the same java program (with the same code in it as the servlet, but standalone) my API worked just fine. How come?
Any insights appreciated as I am just learning about thread safety now (the hard way :-( )
cheers
Dejan

Does this help
Are you using one connection to the database shared by all instances
of your servlet
And is this connection create in the init method of the servlet and stored
in the servlet context.
Problem 4 people try and use your servlet at the same time, each servlet trys to
create a connection to the database and then store it in the servlet context and
this causes a problem.
Solution create a listener to create the connection and store it in the servlet context
when the servlet is created.
If this is your problem it is not advisable to use only one connection to the db
try using db pooling

Thread safety! Is this the right way?

Hello,
Lately I'm reading lot about thread-safety in Swing...
so just wondering that is this the right way to code ...
For ex following code executes(which makes DB connection and load some list) when user press the "connect (JButton)" ....
private void prepareAndShowConnBox()
        //System.out.println("prep - EDT: " + javax.swing.SwingUtilities.isEventDispatchThread());
        pwd.setEchoChar('*');
        javax.swing.Box box1 = new javax.swing.Box(javax.swing.BoxLayout.Y_AXIS);
        javax.swing.Box box2 = new javax.swing.Box(javax.swing.BoxLayout.Y_AXIS);
        box1.add(new javax.swing.JLabel("DB URL :     "));
        box2.add(db_url);
        box1.add(new javax.swing.JLabel("User Name : "));
        box2.add(uid);
        box1.add(new javax.swing.JLabel("Password :   "));
        box2.add(pwd);
        final javax.swing.Box box = new javax.swing.Box(javax.swing.BoxLayout.X_AXIS);
        box.add(box1);
        box.add(box2);
        int retval = javax.swing.JOptionPane.showOptionDialog(me, box,
                "Database Connection:",
                javax.swing.JOptionPane.OK_CANCEL_OPTION,
                javax.swing.JOptionPane.QUESTION_MESSAGE,
                null, null, null);
        if(retval == javax.swing.JOptionPane.OK_OPTION)
            status.setText("Connecting...");
            Thread t = new Thread(makeConn, "Conn Thread");
            t.setPriority(Thread.NORM_PRIORITY);
            t.start();
    }And the makeConn is....
private Runnable makeConn = new Runnable()
        boolean success;
        Exception x;
        public void run()
            //System.out.println("Con - EDT: " + javax.swing.SwingUtilities.isEventDispatchThread());
            success = true;
            x = null;
            try
                //load sun JDBC-ODBC bridgr driver...
                Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
                //make connection to DB...
                con = java.sql.DriverManager.getConnection("jdbc:odbc:" + db_url.getText(),
                        uid.getText(), new String(pwd.getPassword()));
            catch(Exception e)
                success = false;
                x = e;
                System.err.println(x);
            java.awt.EventQueue.invokeLater(GUItask);
        Runnable GUItask = new Runnable()
            public void run()
                //System.out.println("Con gui - EDT: " + javax.swing.SwingUtilities.isEventDispatchThread());
                if(success)
                    bConn.setText("Disconnect");
                    status.setText("");
                    status.setIcon(imgLink);
                    imgLink.setImageObserver(status);
                    //load the pic list...
                    Thread t = new Thread(execQuery, "List1 Thread");
                    t.setPriority(Thread.NORM_PRIORITY);
                    t.start();
                else
                    status.setText("Connection Failed.");
                    showErr(x.toString());
    };Here uid,db_url (JTextField) , pwd (JPasswordField) , status (JLabel) are class fields.
Thanks for any comments... :)

Threading looks fine too me... the connection is created on a background thread, but (critically) all GUI updates are performed on the EDT, even if there's an exception. Well done.
My only comment is... why is your GUI creating a database connection at all? Ideally the controler would get the DAO (which would connect itself) and inject it (the connected DAO) into the view... but I'm a server-side boy, so feel free to ignore me.
Cheers. Keith.

XModem via TCP for Java

I am sure that many of you experienced developers have read requests in the past concerning implmentation of Ward Christenen's XModem protocol over a TCP socket. If not, well... you are about to...
This is a major hack... but it is starting to come together... thanks to Fred Potter for his source code to start this project...
Objective:
Basically, I want to create a console application which accepts an incoming connection and starts the receive mode for a XModem file transfer. I am using CGTerm (for Commodore retrocomputing) but can test with HyperTerminal as well...
The user who connects to the server selects SEND and the FILE to send for a XModem file transfer... and the transfer begins...
The incoming blocks of 128 bytes are written to a file
After the transfer is over the server disconnects the client terminal.
Here is what I have so far:
import java.net.*;
import java.lang.*;
import java.io.*;
// X-Modem Server implementation via TCP/IP socket
public class XServer {
public static FileWriter fw;
public static void main(String[] args) throws IOException {
// define the file
try {
fw = new FileWriter("filename.txt");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
int port = Integer.parseInt(args[0]);
ServerSocket server = new ServerSocket(port);
System.out.println("X-Server v1.0 - waiting for connection");
Socket client = server.accept();
// Handle a connection and exit.
try {
InputStream inputStream = client.getInputStream();
OutputStream outputStream = client.getOutputStream();
new PrintStream(outputStream).println("Go to send file mode!"); // sent to client
System.out.println("Ready to receive file via X-Modem...");
* BEGIN TRANSFER HERE!
// set the debug flag
XModem.debug = true;
* Here we are instantiating a new InputStream that represents the remote
* file that we are receiving. In this single line we are attempting to
* start the flow.
* Behind The Scenes: We're sending a NAK across the serial line repeatedly
* until we finaly start seeing the data flow. If we don't see the data
* flow, then we throw an exception.
System.out.println("Sending NAK to start receive mode...");
InputStream incomingFile;
try {
incomingFile = new XModemRXStream(inputStream, outputStream);
} catch (IOException e) {
System.out.println("ERROR! Unable to start file transfer!");
e.printStackTrace();
return;
System.out.println("Starting file transfer...");
* Here we are reading from the incoming file, byte by byte, and printing out.
* Behind The Scenes: Internally, the read() method is handling the task of
* asking for the next data block from the remote computer, processing it (i.e.
* parsing, running checksums), and then putting it in an internal buffer. Not
* all calls to read() will request a new data block as each block contains at
* least 128 bytes of data. Sometimes you will only hit the buffer.
try {
for (;;) {
int c = incomingFile.read();
if (c==-1)
break; // End of File
// print character / byte
System.out.print(c+",");
// write to file
try {
//System.out.print(".");
fw.write(c);
} catch (Exception e) {
System.out.println(e);
System.exit(0);
} catch (IOException e) {
System.out.println("error while reading the incoming file.");
e.printStackTrace();
return;
// done
System.out.println("File sent.");
new PrintStream(outputStream).println("");
new PrintStream(outputStream).println("transfer successful!");
} finally {
//client.close();
// save the file
try {
fw.close();
System.out.println("file saved.");
} catch (Exception e) {
System.out.println(e);
System.exit(0);
* XModem keeps track of settings that the Receive and Transmit Stream classes will
* reference.
* Copyright: Copyright (c) 2004
* @author Fred Potter
* @version 0.1
class XModem {
public static boolean debug = false;
* XModemRXStream is an easy to use class for receiving files via the XModem protocol.
* @author Fred Potter
* @version 0.1
class XModemRXStream
extends InputStream {
// CONSTANTS
private static final int SOH = 0x01;
private static final int EOT = 0x04;
private static final int ACK = 0x06;
private static final int NAK = 0x15;
private static final int CAN = 0x18;
private static final int CR = 0x0d;
private static final int LF = 0x0a;
private static final int EOF = 0x1a;
// block size - DON'T CHANGE - I toyed with the idea of adding 1K support but the code is NOT there yet.
private static final int bs = 128;
// PRIVATE STUFF
private int ebn; // expected incoming block #
private byte[] data; // our data buffer
private int dataPos; // our position with the data buffer
private InputStream in;
private OutputStream out;
* Creates a new InputStream allowing you to read the incoming file. All of the XModem
* protocol functions are handled transparently.
* As soon as this class is instantiated, it will attempt to iniatate the transfer
* with the remote computer - if unsuccessful, an IOException will be thrown. If it
* is successful, reading may commense.
* NOTE: It is important not to wait too long in between calls to read() - the remote
* computer will resend a data block if too much time has passed or even just give up
* on the transfer altogether.
* @param in InputStream from Serial Line
* @param out OutputStream from Serial Line
public XModemRXStream(InputStream in, OutputStream out) throws
IOException {
this.in = in;
this.out = out;
// Initiate the receive sequence - basically, we send a NAK until the data
// starts flowing.
init:for (int t = 0; t < 10; t++) {
if (XModem.debug) {
System.out.println("Waiting for response [ try #" + t + " ]");
long mark = System.currentTimeMillis();
out.write(NAK);
// Frequently check to see if the data is flowing, give up after a couple seconds.
for (; ; ) {
if (in.available() > 0) {
break init;
try {
Thread.sleep(10);
catch (Exception e) {}
if (System.currentTimeMillis() - mark > 2000) {
break;
// We have either successfully negotiated the transfer, OR, it was
// a failure and timed out. Check in.available() to see if we have incoming
// bytes and that will be our sign.
if (in.available() == 0) {
throw new IOException();
// Initialize some stuff
ebn = 1; // the first block we see should be #1
data = new byte[bs];
dataPos = bs;
* Reads the next block of data from the remote computer. Most of the real XModem protocol
* is encapsulated within this method.
* @throws IOException
private synchronized void getNextBlock() throws IOException {
if (XModem.debug) {
//System.out.println("Getting block #" + ebn);
// Read block into buffer. There is a 1 sec timeout for each character,
// otherwise we NAK and start over.
byte[] buffer;
recv:for (; ; ) {
buffer = new byte[bs + 4];
for (int t = 0; t < 10; t++) {
System.out.println("\nReceiving block [ #" + ebn + " ]");
// Read in block
buffer = new byte[buffer.length];
for (int i = 0; i < buffer.length; i++) {
int b = readTimed(1);
// if EOT - don't worry about the rest of the block.
if ( (i == 0) && (b == EOT)) {
buffer[0] = (byte) (b & 0xff);
break;
// if CAN - the other side has cancelled the transfer
if (b == CAN) {
throw new IOException("cancelled");
if (b < 0) {
if (XModem.debug) {
System.out.println("Time out... NAK'ing");
out.write(NAK);
continue recv;
else {
buffer[i] = (byte) (b & 0xFF);
break;
int type = buffer[0] & 0xff; // either SOH or EOT
if (type == EOT) {
if (XModem.debug) {
System.out.println("EOT!");
out.write(ACK);
break;
int bn = buffer[1] & 0xff; // block number
int bnc = buffer[2] & 0xff; // one's complement to block #
if (
(bn != ebn) && (bn != (ebn - 1)) ||
(bn + bnc != 255)) {
if (XModem.debug) {
System.out.println("NAK'ing type = " + type + " bn = " + bn +
" ebn = " +
ebn + " bnc = " + bnc);
out.write(NAK);
continue recv;
byte chksum = buffer[ (buffer.length - 1)];
byte echksum = 0;
for (int i = 3; i < (buffer.length - 1); i++) {
echksum = (byte) ( ( (echksum & 0xff) + (buffer[i] & 0xff)) & 0xff);
if (chksum != echksum) {
out.write(NAK);
continue recv;
out.write(ACK);
if (ebn == 255) {
ebn = 0;
else {
ebn++;
break;
// We got our block, now save it in our data buffer.
data = new byte[bs];
for (int i = 3; i < (buffer.length - 1); i++) {
data[(i - 3)] = buffer;
dataPos = 0;
public synchronized int read() throws IOException {
// If at the end of our buffer, refill it.
if (dataPos == bs) {
try {
getNextBlock();
catch (IOException e) {
throw new IOException();
// If we're still at end of buffer, say so.
if ( dataPos == bs) {
return -1;
int d = data[dataPos];
if (d == EOF)
return -1;
dataPos++;
return d;
* A wrapper around the native read() call that provides the ability
* to timeout if no data is available within the specified timeout value.
* @param timeout timeout value in seconds
* @throws IOException
* @return int an integer representing the byte value read.
private int readTimed(int timeout) throws IOException {
long start = System.currentTimeMillis();
for (; ; ) {
if (in.available() > 0) {
return (in.read());
try {
Thread.sleep(10);
catch (InterruptedException ex) {
//if (System.currentTimeMillis() - start > timeout * 1000) {
if (System.currentTimeMillis() - start > timeout * 5000) {
return -1;
Here was the output...
Original file:
(Commodore CBM SEQ file exported to PC using DirMaster)
��
� �
� ��
� ��
� ��
��
� ��
� � ��
��
� � ��OWERED BY �OLOR 64 �� V8
�UNNING �ETWORK64 V1.26A
�
�UPPORTING 38400 �AUD �ATES
��/��/��
�
�ESTING �CHO-�ET V1 BETA
�
�EATURING �ESSAGES, �ILES,
�ET�AIL, AND �NLINE �AMES!
�YS�P: � � � � � � � � �
�
�RESS ANY KEY TO LOGIN\C�
The result when the file was uploaded and received by my XServer:
? ? ??OWERED BY ?OLOR 64 ??? V8
?UNNING ?ETWORK64 V1.26A
?UPPORTING 38400 ?AUD ?ATES
?ESTING ?CHO-?ET V1 BETA
?EATURING ?ESSAGES, ?ILES,
?ET?AIL, AND ?NLINE ?AMES!
?YS?P: ? ? ? ? ? ? ? ? ?
?RESS ANY KEY TO LOGIN\C?
The result is different!
Can someone help me along here... I have been trying to figure out how to do this for approx. a year or so... it has been a very slow process.
I could use a guru to help me out so I can write the upload and download routines for my Commodore BBS PETSCII Emulation Server.
Visit http://www.retrogradebbs.com for details.
Thanks.
Please help out a dedicated developer who is in over his head...
-Dave

Ok. Fair enough. What about general information about Xmodem. This is a hard project because of how obscure the legacy technology is that I am having to implement using Java and MySQL.
I have two major issues which I have to figure out how to troubleshoot and debug, if possible.
1. The 23+ blocks exception when a file is being received
2. The exception which is thrown immediately if I try to receive a binary file instead of an ASCII file.
I read that telnet is a 7-bit technology and that is why Xmodem, which is an 8-bit technology is not that popular as a viable protocol via telnet, whereas Kermit is, since it was developed for 7-bit systems, i.e. mainframes and minicomputers.
Is this correct?
If that is the case, why does www.serio.com have a viable X-Y-ZModem library available (for several hundred $$$ of course) which can be used with both RS-232 serial ports and TCP socket ports? Obviously, it can be done. They are the ONLY company with this library for sale for Java to do this. I cannot justify that $$$ amount for a mere hobby (writing the BBS emulation server for supporting Commodore PETSCII (CG) callers via CGTerm or a native C-64 terminal program using Jim Brain's TCPSER middleware, which emulates a Hayes modem via telnet for telBBSing/retrocomputing.
I really want to learn how to implement a file transfer protocol, since back in the 80s, I used Xmodem, Punter, Y/Z Modem, etc., a lot to upload and download files via modem at baud rates of 2400, 14.4, 19.2, and 38.4, respectively.
It's fun to learn how the old skool gurus of telecommunications technology did it. It is one thing to run a BBS which supports these technologies and features, and it is an entirely other thing to learn how to design and develop them yourself for implementation into a project such as I taken on.
It CAN be done. It WILL be done. However, I have just started my exhaustive research on how it needs to be done. I have read up as much as I could on XModem by Ward C., the father of the protocol.
But, I have no information to help me figure out why the communications are acting as they do so far.
Can someone please download the xserver.zip file on my website at:
www.retrogradebbs.com/projects/xserver.zip
Compile it. Run it. Connect using HyperTerminal, Netrunner, or another telnet terminal emulation program which supports Xmodem file transfers using WinSock.
See what happens. With finals due in the next two days, this project will have to be put on hold until after I submit my two final projects.
If anyone knows what needs to be done to support both ASCII and BINARY file transfers via Xmodem via a socket instead of a modem with RTS/CTS hardware flow control, please respond.
I know for a fact that this can be done.
- Dave

ANN: XML Class Generator for Java Available

The Oracle XMCL Class Generator for Java is now available as an
initial beta release on the Oracle Technology Network at
http://technet.oracle.com. Select 'xml' from the Technology menu.
The XML Class Generator will generate a set of Java source files
based on an input DTD. The generated Java source files can then
be used to construct, optionally validate, and print a XML
document that is compliant to the DTD specified. This is an early
beta release and has the following features:
* Creates Java Classes from DTDs to enable the programmatic
construction of XML documents.
* Supports validation mode to assist debugging.
* Works with the Oracle XML Parser in Java.
* Creates documents conforming to the W3C XML 1.0
Recommendation.
* Supports creating documents in the following encodings:
UTF-8
UTF-16
ISO-10646-UCS-2
ISO-10646-UCS-4
US-ASCII
EBCDIC-CP-US
ISO-8859-1
Shift_SJIS
Oracle XML Team
http://technet.oracle.com
Oracle Technology Network
null

Thanks,
Rob
Oracle XML Team wrote:
: First, the link has been fixed. As to your access exception,
we
: have traced it to a difference between JDK 1.1.x and JDK 1.2.
: You can solve it by using a 1.1.x version of the JDK or wait
till
: our production version of our XML Parser becomes available
within
: a week which will work with 1.2.
: Oracle XML Team
: http://technet.oracle.com
: Rob Edagr (guest) wrote:
: : 1) The HREF on the download page for the NT version points
to
: : the version 102 parser not the classgen.
: : 2) After downloading and installing the classgen (by
guessing
: : what the url was) I ran it and get the following
: : C:\jdk1.2\xml\ora\classgen\sample>java SampleMain -root
: : wddxPacket wddx_0090.dtd
: : Exception in thread "main" java.lang.IllegalAccessError: try
to
: : access class oracle/xml/parser/XMLNode from class
: : oracle/xml/classgen/ClassGenerator
: : at oracle.xml.classgen.ClassGenerator.generate
(Compiled
: : Code)
: : at SampleMain.main(SampleMain.java:65)
: : Any idea on what the problem is (same error with sample dtd)
: : Rob
: : Oracle XML Team wrote:
: : : The Oracle XMCL Class Generator for Java is now available
as
: : an
: : : initial beta release on the Oracle Technology Network at
: : : http://technet.oracle.com. Select 'xml' from the
Technology
: : menu.
: : : The XML Class Generator will generate a set of Java source
: : files
: : : based on an input DTD. The generated Java source files can
: : then
: : : be used to construct, optionally validate, and print a XML
: : : document that is compliant to the DTD specified. This is
an
: : early
: : : beta release and has the following features:
: : : * Creates Java Classes from DTDs to enable the
programmatic
: : : construction of XML documents.
: : : * Supports validation mode to assist debugging.
: : : * Works with the Oracle XML Parser in Java.
: : : * Creates documents conforming to the W3C XML 1.0
: : : Recommendation.
: : : * Supports creating documents in the following
encodings:
: : : UTF-8
: : : UTF-16
: : : ISO-10646-UCS-2
: : : ISO-10646-UCS-4
: : : US-ASCII
: : : EBCDIC-CP-US
: : : ISO-8859-1
: : : Shift_SJIS
: : : Oracle XML Team
: : : http://technet.oracle.com
: : : Oracle Technology Network
: Oracle Technology Network
null

Ebusiness Suite SDK for Java session management

Hi, I am trying to try sample java application mentioned in Oracle® E-Business Suite Software Development Kit for Java Release 11i and 12 Part No. E28169-02
Current version i am trying is Jdeveloper 11.1.1.4.0 and Ebiz suite 12.1.3
able to create Apps Data source with out any issue.
when Home.jsp is accessed through application menu, user name and all session related information is showing as NULL.
how to resolve this issue.

Hi Shay,
I gone through the webinar.
Here is more explanation of my issue.
I created Apps Data source earlier. That time i registered external node in ebusiness suite with node_name as ip_address of weblogic server.
But that time session details came as Null on sample Java application.
Then i realized that may be the issue and corrected registration of external node and corrected ebiz profile options accordingly.
When i tried to create Apps data source with fresh dbc file, i got into invalid username/pwd issue.
As per following forum discussion topic, hyphen and dots in host name will cause issue with Apps data source creation, which is confirmed by couple of discussion participants and Juan also.
https://kr.forums.oracle.com/forums/thread.jspa?threadID=2489849&start=30&tstart=0
My weblogic host name is like WL-SOADEV-01.domainname.com
what should be my further actions to resolve this issue.
Thanks
Maheedhar.J

Hi i wrote a java program for scanning a system for java.exe 's

hi ,
i wrote a program which scans the system for java.exe 's and then it captures them in a linked list and then i
iterate through it for "\\Java\\jdk1.5.0_08\\bin\\java.exe and my aim is to return true in case the linked list contains the string "\\Java\\jdk1.5.0_08\\bin\\java.exe" and stop scanning the system.
If the linked list does not contain "Java\\jdk1.5.0_08\\bin\\java.exe" it should return false.
But my problem is the program is continuing to scan the system even if the linked list has "\\Java\\jdk1.5.0_08\\bin\\java.exe"
Any sort of help is appreciated.
The code is as follows:
package com.installanywhere.exper;
import com.zerog.ia.api.pub.CustomCodeRule;
import com.installanywhere.exper.SearchTool;
* @author
public class eFileTool extends CustomCodeRule {
 /* (non-Javadoc)
 * @see com.zerog.ia.api.pub.CustomCodeRule#evaluateRule()
 @Override
 public boolean evaluateRule() {
 // TODO Auto-generated method stub
 SearchTool searchtool=new SearchTool();
 boolean valueTocheckfor=false;
 valueTocheckfor=searchtool.find();
 String someothervalue=Boolean.toString(valueTocheckfor);
 if(someothervalue.equalsIgnoreCase("true")){
 return true;
 //System.exit()
 else if(someothervalue.equalsIgnoreCase("false")){
 try {
 Thread.sleep(5000);
 } catch (InterruptedException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 System.out.println(valueTocheckfor+"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
 return valueTocheckfor;
The code of search tool is
package com.installanywhere.exper;
import java.io.*;
import java.util.*;
public class SearchTool
 * @param args
static boolean valuesToReturn=false;
static boolean anothervalueToRefer=false;
 public static void main(String[] args) {
 // TODO Auto-generated method stub
 SearchTool t = new SearchTool();
 System.out.println("xxxxxxxxxxxxxxxxxxxx");
 boolean someArgument=t.find();
 System.out.println(someArgument+"iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii"+"");
 public boolean find()
 System.out.println("2222222222222222222");
 boolean someThing=searchcomp("java.exe");
 System.out.println(someThing+"inside the othere one");
 return someThing;
 public boolean searchcomp(String file)
 System.out.println("3333333333333333333333");
 File[] drives=File.listRoots();
 boolean valueIdentified=false;
 for (int ctr=0;ctr<(drives.length-1);ctr++)
 valueIdentified=search(drives[ctr],file);
 System.out.println("4444444444444444444");
 System.out.println(valueIdentified+"something i need to accomplish");
 return valueIdentified;
 public boolean search(File dir,String file)
 File[] directories=dir.listFiles();
 System.out.println("55555555555555555555555");
 if (directories == null)
 System.out.println("666666666666666666666666");
 return false;
 for(int ctr=0;ctr<directories.length;ctr++)
 if(directories[ctr].isDirectory())
 System.out.println("77777777777777777777777777");
 valuesToReturn=search(directories[ctr],file);
 System.out.println(valuesToReturn+"india is great");
 else
 if(directories[ctr].getName().equals(file))
 String path = directories[ctr].getAbsolutePath().toString();
 System.out.println(path);
 List someList=new LinkedList();
 anothervalueToRefer=allPaths(path);
 System.out.println(anothervalueToRefer+"god damn it");
 //System.out.println(anothervalueToRefer+"let me seeeeeeeeeeeeeeeeeee");
 return anothervalueToRefer;
 return valuesToReturn;
 public boolean allPaths(String allPath)
 List l=new LinkedList();
 String somepath=allPath;
 l.add(somepath);
 //return l;
/*if(l.contains("C:\\Program Files\\Java\\jdk1.5.0_08\\bin\\java.exe")){
 System.out.println("yepeeeeeeeeeeeeee");
 //System.exit(0);
else{
 System.out.println(" the face");
 ListIterator li = l.listIterator();
 System.out.println("inside the method of all paths");
 if(li.hasNext())
 if(li.next().toString().contains("\\Java\\jdk1.5.0_08\\bin\\java.exe"))
 System.err.println(somepath+"this is the path i wanted to resolve correctly");
 return true;
 else{
 System.out.println("trueeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee");
 return false;
 else {
 return false;
 }

A good place to ask advice about web development is at the MozillaZine "Web Development/Standards Evangelism" forum.
*http://forums.mozillazine.org/viewforum.php?f=25
The helpers at that forum are more knowledgeable about web development issues. 
You need to register at the MozillaZine forum site in order to post at that forum.

Any difference between webdynpro for java and webdynpro for abap ?

Hi all:
   I would like to build one small system in EP.
   I can choose to use webdynpro for java and webdynpro for abap.
   I would like to ask any major difference between webdynpro for abap and webdynpro for java ?
   Is fpm supported in webdynpro for abap ?

Hi,
see this thread,
ABAP Vs JAVA WebDynpro
Regads,
J.Joe

Discussion: Why no centralize development for Java (like the one in ABAP)

I am reading the NetWeaver Development Infrastructure, and noticed that due to the distributed development nature of Java, SAP recommend The Four-System Landscape for the development lifecycle.
Each developers has their own local development environment, that's why it is necessary to 'reconcile' the environment using one more layer of system. Although they checked out the particular Development Object, the necessary library from the central is being copied by DTR to the local environment. However, there are still possibilities that someone changes the library, or other classes that being refered. And we are not talking only about the business logic, but other object in the persistance level too. Let's say your program refered to a certain field in a certain table, but someone else had changed the field name. Or even worse, you want to get the setting value from a certain setting table, but someone else had deleted the value of that record (for whatever reason).
In short, I believe there are many 'reconcilliation' process that need to be done when the development environment is not centralized. These problems won't happen in the ABAP world, because you will notice the problem straight away when you activate your component, or test run it. In distributed environment, you will only notice it when you check-in your development object back, but it might be after some time lags, and you might not remember which part need to be taken care of.
Not only this, the setting of 'correct' IDE environment in each local PC must be done properly. Again, in ABAP you just need to install SAP GUI and it will be your development environment.
So, I had discussion with a friend of mine, and he asked, why there is no central development environment, like the one in ABAP? Hmm, to be frank, I also don't know. Performance problem? I notice that most IDE in the market based on the assumption that development will be done locally. Or is it for the convenient purpose, so that people can keep the development eventhough there is no connection to central server? But what is the cost for this convenient?
What other people think?
rgs,
Hiroshi
ps: As you might notice, this thread is not marked as question. I am just curious of what other people think about this issue. There will be no points rewarded for the replies.

Hello Satya,
So if it's a 'mere' technical limitation, then there should be a way to create centralized development for Java
It might be an old mainframe environment, but from the development process point of view, centralized environment offers benefit where lots of versioning problem (library or data dictionary) can be solved.
I used to work in a distributed development environment to create a web based FI/SD/MM related application. We have tons of classic problem of 'it is working in my environment, but not in yours' type of thing. With centralized (read: ABAP), version integrity problem can be reduced to minimum.
For the NWDI itself, I think SAP now moves toward embracing the open source platform to support the development environment. From what I've understood, Ant, for example will be used as the build tool. My personal opinion is, better if SAP creates it's 'proprietary' environment to centralized the java development process. Then it will save lot's of hidden cost during the implementation of new application/enhancement/maintenance in the whole supply chain.
rgs,
hiroshi

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