StreamCorruptedException

The How to fix... section, looking at common Java bugs and problems, has an additional section on a couple of common causes of StreamCorruptedException. This is a serialisation error that often occurs when the streams reading and writing serialised data get "out of kilter". It's surprisingly common for this to occur accidentally.

If you haven't seen the How to fix... section yet, then it's worth a look, as it deals with a couple of other common headaches such as OutOfMemoryError and StackOverflowError. If you've got another Java bête noir that you'd like to see covered there, please let us know by posting to the Javamex forum.

Using strings in Java

Various questions and problems commonly arise with Java Strings. Especially for C programmers, strings in Java have certain quirks, notably the fact that they're immutable (once you've created a String object, you can't change its contents; if you need a mutable string, then you generally have to use some other CharSequence class such as StringBuilder).

At the aforementioned link, I show code examples of some common string functions in Java. Surely, there'll be things I've missed out/forgotton. So please let me know if there's some thing you find yourself needing to do with strings in Java that I haven't mentioned!

New section: Java cryptography

Several pages of the new section on Java Cryptography are now available for review and general criticism. Topics currently covered include:

• how to encrypt data in Java, looking at encryption with symmetric block ciphers as well as the RSA encryption scheme commonly used for passing session keys;
• different block modes, and how to use block modes in Java (including how to set an initialisation vector necessary in many cases via the IvParameterSpec class);
• how to choose and set the key size to use with encryption, and how to remove the key length restriction which is imposed by current versions of Sun's JDK by default.

Topics not currently covered, but planned for the near future include:

• comparison of block cipher algorithms: performance and security considerations;
• secure hash functions and authentication;
• cryptographic protocols;
• secure random number generation (note that the Java SecureRandom class is currently discussed in the site's section on random numbers in Java);
  
• digital signatures.

As usual, comments about the currently published sections are always welcome, as are suggestions for future additions to the cryptography section or to any other section of the web site. Please leave comments either on this blog or in the Java cryptography section of the Javamex discussion forum.

Update 12/04/09: The section now contains some information on secure hash functions in Java, plus a comparison of encryption algorithms.
19/04/09 As discussed in a separate blog entry, some information on password-based encryption is now included.

Enjoy...!

PIFTS.EXE: Symantec finally own up

So, the world can rest easy in their beds. A message tucked away on Symantec's forums-- the same forums from which all communication about the issue was previously banned-- in which they have finally owned up to what happened:

• they released a patch to do some boring things that any old patch might have done
• but they released the patch unsigned, causing it to hit the firewall when it otherwise wouldn't have done
• because some of the posts on the Symantec forum were judged to be abusive, all posts were pulled down.

Whilst this seems to be an astonishing example of customer relations, and has brought the world's attention to the kind of behaviour that such patches may be conducting on a routine basis, it does at least appear that the Feds are not about to plunder our computers for illicit chocolate chip cookie recipes. We were spared... this time.

(And yes, I did back up my recipe collection... just in case.)

What is the mysterious PIFTS.EXE?

Update 10/03/09 11:50am Luckily, it does appear that PIFTS.EXE is just a storm in a teacup. Symantec still appear to be saying about as much as the Queen did after Diana died.

So after a mysterious PIFTS.EXE program hits the Kaspersky firewall asking to connect out from one of our machines, I hit the Internet to find that nobody knows, but the world is wondering. According to Google Trends, it has been hovering between the 15th and 25th most frequent search for the last couple of hours. Various theories about PIFTS.EXE appear to be emerging: was it some component of Norton Antivirus that went wrong? Is it some mad terrorist plot to wipe the Internet off the face of the earth and thus prevent people from finding out about why Lil' Kim went to jail?

Update 10/03/09 Reading things so far, and just possibly maybe having had a quick look at a disassembly of the exe in IDAPro, the consensus seems to be that the file is essentially harmless, but was an attempt by Symantec to gather some statistics from users' machines about installed antivirus components. A user posting to Reddit also suggests that a code review of PIFTS.EXE does not reveal anything too nafarious, and that automated code analysers such as ThreatExpert don't pull anything up either (then again, a "well written" virus wouldn't do, would it?).

Sometimes in cases like this, it's not so much whether there is anything wrong but whether there appears to be. Pulling down all forum posts about the file when there is clear user anxiety without then making an official statement doesn't making it look as though everything's hunky-dory...

Java Certification Tips

A new page of Java Certification Tips gives a "cribsheet" of some of the "syntactic niggles" and other commonly overlooked features of Java that could trip up an otherwise moderately experienced programmer when taking the Sun Certified Java Programmer (SCJP) exam. Did you know, for example that:

• this is invalid Java syntax?
  float f = 2.5;
• goto is a Java keyword?
• this line does not assign the value 13 to the variable?:
  int i = 013;

See the page of tips for more information on these and other niggles.

Regular expression tutorial: new example

The Java regular expression tutorial section has been updated with a new example of using regular expressions. In this example, we look at how to perform what is sometimes referred to as HTML scraping: pulling out data from an HTML page (or indeed XML document).

The example is located here: HTML scraping with Java regular expressions. As explained in this tutorial, regular expressions are a good candidate for data scraping because they are flexible. Various libraries exist to parse an HTML or XML document and return an object representation of that document. But such libraries are often "too fussy": many if not most web pages actually do not conform strictly to HTML standards. Similarly, many XML parsing libraries are too fussy for real-life RSS feeds, which are often malformed, strictly speaking. Using regular expressions cuts through the fuss.

When should you scrape web pages?

Note that the article focusses on how technically to scrape HTML pages in Java. It doesn't deal with the "political" issue of whether the site in question wants its content scraped in the first place. In general, it is good practice to do the following:

• find out if he web site in question has an API to provide the data in a more convenient format (and in a format that it would prefer to provide it to you in!)
• be open about what you're doing: if the web site administrator things you're trying to "hide" something, they may block your IP address
• respect server resources: if you are retrieving multiple pages, consider putting a thread sleep between fetches