Weird Bug While Porting Textml Server Code from JSP to ASP.NET

This morning I was porting an old search results page accessing Textml Server from JSP to ASP.NET. One feature implemented there is search within results. We execute this by storing the original query in the session and then, when a user asks to search within results, we pull it out and re-run it so the second query can reference the first.

We have a line like this in the JSP page...

IxiaResultSpace originalResults = 
  search.SearchDocuments((String)session.getAttribute("resultQuery"));

...followed by a few lines later by a line like this...

"<include TYPE=\"ResultSpace\">" + sessionID + "-ALL</include>"

All was well.

The logic of the page overall is more than a bit wonky, but we decided to port first and revise later. When done, I was getting an error that said

"vrn2nc55cxej5knnemwyzvqv-ALL is not a valid ResultSpace include /query/andkey/include at Ixiasoft.TextmlServer.ResultSpace.ExecuteQuery() at Ixiasoft.TextmlServer.ResultSpace.get_Count() at searchresults.RunSearch() in c:\Greenwood Web Sites\devsite\searchresults.aspx.cs:line 357."

What's that now?

After some trips through the debugger, poking around the documentation and some googling (no one blogs on this thing) I went back to the old method of just writing out strings to the page. Nothing jumped out as an error and nothing worked.

By sheer chance, I decided to see what the string value of the original query was so I added...

string originalQuery = originalResults.TextmlQuery;

...to the page with the intent of displaying it somewhere for review and suddenly the error stopped being thrown and the code functioned as expected. After making sure I made no other changes I tested it again. I commented out that line and the error was thrown. I put the line back in and the page ran fine. A co-worker asked if the Count property forced it work as well and it does.

I can't explain this one.

Apache Xalan from the Command Line

Check your Xalan environment:

C:\>java org.apache.xalan.xslt.EnvironmentCheck

Set your environment for the proper JARs (check the Apache site for updates):

C:\>set classpath=.;C:\jdk1.2.2\jre\lib\ext\xalan.jar;
C:\jdk1.2.2\jre\lib\ext\xercesImpl.jar;
C:\jdk1.2.2\jre\lib\ext\xml-apis.jar

Run a basic XSL transformation:

C:\>java org.apache.xalan.xslt.Process -IN c:\tmp\intput.xml -XSL c:\tmp\transform.xsl -OUT c:\tmp\output.xml

Additional command line options:

Common Options

-XSLTC (use XSLTC for transformation)
-IN inputXMLURL
-XSL XSLTransformationURL
-OUT outputFileName
-V (Version info)
-EDUMP [optional filename] (Do stackdump on error.)
-XML (Use XML formatter and add XML header.)
-TEXT (Use simple Text formatter.)
-HTML (Use HTML formatter.)
-PARAM name expression (Set a stylesheet parameter)
-MEDIA mediaType (use media attribute to find stylesheet associated with a document)
-FLAVOR flavorName (Explicitly use s2s=SAX or d2d=DOM to do transform)
-DIAG (Print overall milliseconds transform took)
-URIRESOLVER full class name (URIResolver to be used to resolve URIs)
-ENTITYRESOLVER full class name (EntityResolver to be used to resolve entities)
-CONTENTHANDLER full class name (ContentHandler to be used to serialize output)

Options for Xalan-Java Interpretive

-QC (Quiet Pattern Conflicts Warnings)
-TT (Trace the templates as they are being called)
-TG (Trace each generation event)
-TS (Trace each selection event)
-TTC (Trace the template children as they are being processed)
-TCLASS (TraceListener class for trace extensions)
-L (use line numbers for source document)
-INCREMENTAL (request incremental DTM construction by setting
http://xml.apache.org/xalan/features/incremental to true)
-NOOPTIMIMIZE (request no stylesheet optimization proccessing by setting
http://xml.apache.org/xalan/features/optimize to false)
-RL recursionlimit (assert numeric limit on stylesheet recursion depth)

For more information see http://xml.apache.org/xalan-j/commandline.html.

Basic Java Questions and Answers

This is a great list of Java Q & A from a JDJ article. I'm repeating it here because I can never find anything on their site after a month or so.

Q1. How could Java classes direct program messages to the system console, but error messages, say to a file?

A. The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output could be re-directed:

Stream st = new Stream(new FileOutputStream("output.txt")); System.setErr(st); System.setOut(st);

Q2. What's the difference between an interface and an abstract class?

A. An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.

Q3. Why would you use a synchronized block vs. synchronized method?

A. Synchronized blocks place locks for shorter periods than synchronized methods.

Q4. Explain the usage of the keyword transient?

A. This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).

Q5. How can you force garbage collection?

A. You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.

Q6. How do you know if an explicit object casting is needed?

A. If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:

Object a; Customer b; b = (Customer) a;

When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.

Q7. What's the difference between the methods sleep() and wait()

A. The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.

Q8. Can you write a Java class that could be used both as an applet as well as an application?

A. Yes. Add a main() method to the applet.

Q9. What's the difference between constructors and other methods?

A. Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.

Q10. Can you call one constructor from another if a class has multiple constructors

A. Yes. Use this() syntax.

Q11. Explain the usage of Java packages.

A. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.

Q12. If a class is located in a package, what do you need to change in the OS environment to be able to use it?

A. You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:

c:\>java com.xyz.hr.Employee

Q13. What's the difference between J2SDK 1.5 and J2SDK 5.0?

A.There's no difference, Sun Microsystems just re-branded this version.

Q14. What would you use to compare two String variables - the operator == or the method equals()?

A. I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.

Q15. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?

A. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses have to be caught first.

Q16. Can an inner class declared inside of a method access local variables of this method?

A. It's possible if these variables are final.

Q17. What can go wrong if you replace && with & in the following code:

String a=null; if (a!=null && a.length()>10) {...}

A. A single ampersand here would lead to a NullPointerException.

Q18. What's the main difference between a Vector and an ArrayList

A. Java Vector class is internally synchronized and ArrayList is not.

Q19. When should the method invokeLater()be used?

A. This method is used to ensure that Swing components are updated through the event-dispatching thread.

Q20. How can a subclass call a method or a constructor defined in a superclass?

A. Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass's constructor.

Q21. What's the difference between a queue and a stack?

A. Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO rule

Q22. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?

A. Sometimes. But your class may be a descendent of another class and in this case the interface is your only option.

Q23. What comes to mind when you hear about a young generation in Java?

A. Garbage collection.

Q24. What comes to mind when someone mentions a shallow copy in Java?

A. Object cloning.

Q25. If you're overriding the method equals() of an object, which other method you might also consider?

A. hashCode()

Q26. You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use: ArrayList or LinkedList?

A. ArrayList

Q27. How would you make a copy of an entire Java object with its state?

A. Have this class implement Cloneable interface and call its method clone().

Q28. How can you minimize the need of garbage collection and make the memory use more effective?

A. Use object pooling and weak object references.

Q29. There are two classes: A and B. The class B need to inform a class A when some important event has happened. What Java technique would you use to implement it?

A. If these classes are threads I'd consider notify() or notifyAll(). For regular classes you can use the Observer interface.

Q30. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it?

A. You do not need to specify any access level, and Java will use a default package access level.

Accessing an IxiaDocument Object from Textml in JSP

This is actually split across an application listener object and a JSP view page after a search result item is clicked on, which is why you'll see an Object being pulled from the session. You'll also see a reference to SearchUtilities, a search helper object.

String textmlRmiUrl = "rmi://servername:1099";
String textmlDomain = "DOMAIN";
String textmlUser = "username";
String textmlPassword = "password"; 
String textmlServer = "servername";
String textmlDocbase = "docbasename";

HashMap parms = new HashMap(1);
parms.put("ServerURL", textmlRmiUrl);

ClientServices cs = com.ixia.textmlserver.ClientServicesFactory.getInstance("RMI", parms); 
cs.Login(textmlDomain, textmlUser, textmlPassword);
// Note that there can be only one login per application

ByteArrayInputStream inputStream = null;

Object sessionResults = session.getAttribute( SearchUtilities.translateTab(tab));
IxiaServerServices ss = cs.ConnectServer(textmlServer); // Get the server Services
IxiaDocBaseServices docbase = ss.ConnectDocBase(textmlDocbase); // then, the DocbaseServices
IxiaSearchServices search = docbase.SearchServices(); // then, the SearchServices
IxiaResultSpace result = null; // then initialize the results space

result = (IxiaResultSpace)sessionResults;

IxiaDocument.Content ixiacontent = result.Item(searchDocId,"highlight").GetContent(); 
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
ixiacontent.SaveTo(outputStream);
inputStream = new ByteArrayInputStream(outputStream.toByteArray());

File xslreader = new File(xslpath);
TransformerFactory tFactory = TransformerFactory.newInstance();
Transformer transformer = tFactory.newTransformer(new StreamSource(xslreader));
transformer.setParameter("book",x); // XSL parameter
transformer.transform(new StreamSource(inputStream), new StreamResult(out));

Building and Iterating Over a LinkedHashMap in Java

Building a Java LinkedHashMap and iterating over it always comes in handy. In a class you can have something like:

private Map myLinks = new LinkedHashMap();
public Map getLinks() { 
  return myLinks; 
}
public void setMyLinks(String key, String value) { 
  this.myLinks.put(key, value); 
}
...
for(int j=0; j<links.getLength(); j++)
{
  setMyLinks( ((Element)links.item(j)).getAttribute("url"), 
              getText(links.item(j)) );
}

Then in a JSP you can do something like:

Map thisMyLinks = ThisState.getMyLinks();
for (Iterator it=thisStateLinks.keySet().iterator(); it.hasNext(); ) 
{
  Object key = it.next();
  Object value = thisStateLinks.get(key);
  out.println("<li><a href=\"" + key.toString() + "\">" + 
               value.toString() + "</a></li>");
}