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Showing posts from October, 2010

Initial thoughts on Fantom

Recently I started playing with Fantom language. So far my reaction is "Wow!". Its a beautiful language with a lot of cool things. I also ran into a few gotchas, but none that falls in the category of "ugly!".


Here are the things I really liked about the language (not necessarily in any order):
Before any technical merits, the first thing I liked is the documentation. Most of the time, when I look for some documentation for a open source project, they notoriously suck. Fantom is the second project whose documentation I really liked and found my way around most of the time. (The first one is SLF4J.) The language is statically typed, with room for dynamically invoking methods on objects using a mechanism called "trap". One central theme I observed in the language is being able to reliably create an immutable objects ("const" classes). This simplifies a lot of analysis when it comes to concurrent programming. Also the language supports creating…

SecretKeyFactory is broken in JDK 1.6 update 22

If you upgrade JDK to 1.6 update 22 (build 04), the SecretKeyFactory is broken. As a result you will not be able to load any PKCS12 key stores. You will get NoSuchAlgorithmException thrown.

I have reported this issue in the bug database. You can view the bug here. I guess it will take upto a day for this bug to be externally visible, if you don't have a SDN account.

Here is the sample program to reproduce the issue:
public static void main(String[] args) { SecretKeyFactory instance = SecretKeyFactory.getInstance("PBEWithMD5AndDES"); System.out.println("Returned instance: " + instance.getAlgorithm()); }
You will get the exception below:
Exception in thread "main" java.security.NoSuchAlgorithmException: PBEWithSHA1AndRC2_40 SecretKeyFactory not available at javax.crypto.SecretKeyFactory.<init>(DashoA13*..) at javax.crypto.SecretKeyFactory.getInstance(DashoA13*..) at main.TestClient.main(TestClient.java:96)
Work around:

Performance of BigInteger.toString(radix)

Problem:
You are given a byte array, that represents a number in big endian format (the most significant byte first). You have to convert the byte array to its equivalent hex string. What is the most efficient way to do it?

Solution:
There are many ways to do it. But let us start with the easiest and correct one and optimize our solution. BigInteger class provides a constructor to convert the byte array to a BigInteger. We can convert that BigInteger to a hex string using the BigInteger.toString(radix) method. The solution is given below:
public static final String toHexStringUsingBigInteger(byte[] input) { BigInteger bi = new BigInteger(input); return bi.toString(16); }
We can also come up with a hand crafted solution that extract nibble by nibble and convert them into their equivalent hex character and finally forming a string. This solution is given below:
public static final String toHexStringUsingCharArray(byte input[]) { int i = 0; if (input == …

Issue of autoboxing and reflection

Problem: Consider that you want to have a method called "Object invokeAndGet(Object targetObject, String methodName, Object... args)". This method should be able to invoke the given method on the target object and return the value returned by the invocation. If the method has overloaded forms, then depending on the argument types, the invokeAndGet method should invoke the correct form.

Solution:
Though this problem looks trivial and seems like it can be solved by using reflections APIs, it gets really tricky when you have to deal with primitive types. This is due to the fact that autoboxing converts the primitives into their corresponding wrapper types. For e.g. an integer value is autoboxed into Integer object, etc.

To begin with let us assume that we have the following implementation of the method:

public static Object invokeAndGet(Object obj, String methodName, Object... args) { try { Class<?>[] argsTypes = new Class[args.length]; …

Creating a HashMap with entries

Problem: Create an instance of HashMap in Java with entries in it. I don't want to create a new HashMap instance and keep adding entries to it. I want to have a concise way of creating a HashMap with entries.

Solution: Guava library comes with factory methods that can create a HashMap without using the verbose form of "Map myMap = new HashMap()". You can simply say "Map myMap = newHashMap()", assuming you have done a static import of the Maps.newHashMap method. But that is not sufficient. It would be better to provide a utility method that looks like this: "Map myMap = newHashMapWithEntries(firstKey, firstValue, secondKey, secondValue)". That way it is easy to create static-final maps instead of writing a separate method to populate them or to populate them from constructor, as given below:
public class MyClass {    private static final Map<String, URL> serviceUrls = createServiceUrlsMap();    private static Map<String, String> createServ…

Bottle - A simple web framework in Python

I recently came across the Bottle. It is a web framework written in Python. Its very simple to learn and use. It is ideal for prototyping kind of work or you want to run a web application in no time.