Friday, August 27, 2010

Groovy: Superset of Java

Groovy is a bit like scripting version of Java. Groovy is a superset of Java. It is no way means to replace java, Long time Java
programmers feel at home when building agile applications backed by big architectures. One nice thing about Groovy is that it
reduces the amount of code needed to do common tasks such as parsing XML files and accessing databases. Groovy on Grails is
as the name suggests similar to the Rails framework. For people who don't want to bother with Java's verbosity all the time.

The big advantage is speed, brevity and readability. For instance here is some java code which implements a bag:

public class Bag {

private Map counter = new HashMap();
public void add(Object obj) {
add(obj, 1);


public void add(Object obj, Integer count) {
Integer value = counter.get(obj);
if (value == null)
counter.put(obj, count);
counter.put(obj, value+count);

public Integer getCount(Object obj) {
return counter.containsKey(obj) ? counter.get(obj) : 0;


And here is the same implementation in Groovy:

class Bag {
def counter = [:]
def add(term, count=1) {
if (counter[term] == null)
counter[term] = count

def getCount(term) {
return counter[term] != null ? counter[term] : 0;


So you can see how intuitive the Groovy code is, you don't need to define anything regarding types or default parameter values.

That said, Groovy is essentially Java, just wrapped around a different compiler, class loader and with many added methods and
members. For that reason it is unlikely that it will ever replace Java, not only that but because it IS Java it is bound by the same
limitations and rules and doesn't provide any functionality which is really unique.

Semicolons are optional. Use them if you like (though you must use them to put several statements on one line).
The return keyword is optional.
You can use the this keyword inside static methods (which refers to this class).
Methods and classes are public by default.
Protected in Groovy has the same meaning as protected in Java, i.e. you can have friends in the same package and derived classes can also see protected members.
Inner classes are not supported at the moment. In most cases you can use closures instead.
The throws clause in a method signature is not checked by the Groovy compiler, because there is no difference between checked and unchecked exceptions.
You will not get compile errors like you would in Java for using undefined members or passing arguments of the
wrong type. See Runtime vs Compile time, Static vs Dynamic.
Java can always be made faster, more memory efficient and more robust than Groovy if you are willing to put in the time and

So where would you use Groovy?

I think typically in places where readability, flexibility and speed of development is more important than performance,
extensibility and a large user base. For instance in deployment you can use the Groovy equivalent of Ant called Gant which
allows better flexibility and better readability. Other places might be in a web application framework such as Grails.

You can use Groovy all the time for utilities, both on the command line and on the web. Often, the utilities use jars/class files
from my project, since it is all on the JVM.

For web utils, take a look at Groovlets. You can come up to speed with Groovlets in a couple of hours. A groovlet is simply a
servlet distilled down to its essence.

Also, it does have integration for other open source framework like Spring framework. Groovy is great for writing unit tests for existing Java code and could save lots of development time...

I hope this brief introduction will help in understanding as what's groovy and how it can help in your project.

Friday, August 20, 2010

Scala Vs Java

Form last few days i'm trying to look in to some other dynamic language and trying to compare against java, Scala seems to be the better choice in compare to ruby and others...lets talk about Scala in this post and a small code comparison between Scala and java .. to start with, Scala is a modern multi-paradigm programming language designed to express common programming patterns in a concise, elegant, and type-safe way. It smoothly integrates features of object-oriented and functional languages.

Scala is object-oriented: Scala is a pure object-oriented language in the sense that every value is an object. Types and behavior of objects are described by classes and traits. Class abstractions are extended by subclassing and a flexible mixin-based composition mechanism as a clean replacement for multiple inheritance.

Scala is functional: Scala is also a functional language in the sense that every function is a value. Scala provides a lightweight syntax for defining anonymous functions, it supports higher-order functions, it allows functions to be nested, and supports currying. Scala's case classes and its built-in support for pattern matching model algebraic types used in many functional programming languages.

Scala is statically typed: Scala is equipped with an expressive type system that enforces statically that abstractions are used in a safe and coherent manner.

Scala is extensible: The design of Scala acknowledges the fact that in practice, the development of domain-specific applications often requires domain-specific language extensions. Scala provides a unique combination of language mechanisms that make it easy to smoothly add new language constructs in form of libraries:

any method may be used as an infix or postfix operator, and closures are constructed automatically depending on the expected type (target typing).

A joint use of both features facilitates the definition of new statements without extending the syntax and without using macro-like meta-programming facilities.

Scala interoperates with Java and .NET: Scala is designed to interoperate well with popular programming environments like the Java 2 Runtime Environment (JRE) and the .NET Framework (CLR). In particular, the interaction with mainstream object-oriented languages like Java and C# is as smooth as possible. Scala has the same compilation model (separate compilation, dynamic class loading) like Java and C# and allows access to thousands of high-quality libraries.

Advantages of Scala:

Scala language has been designed to be scalable. It scales according to user needs. The object oriented concepts allows this language to be used for larger and more complex projects while the functional constructs allows programmer to develop short and concise code.

Portability: Scala runs on Java Virtual machine (JVM) this ensures the portability to all the underlying platforms. Also there is an initiative for building Scala on top of .NET Common language Runtime (CLR).

Performance: Scala generate more efficient java code which leads to better runtime performance.

Every value in Scala is an object and every operation is a method call. It is closer to object oriented programming than functional programming and therefore does not support concepts like static fields and methods. Scala allows you to define own objects and constructs which makes it possible to scale up according to user needs.

Scala uses strict typing. But it also allows most of the typing unspecified. When information is unspecified compiler will do smart type interface to infer information from code.

It incorporates ideas from many languages such as Mixins (a way to address multiple inheritances in LISP) and actors (used message passing communication architecture).

Java echo system is available for Scala.
Scala can be embedded into XML since its syntax is somewhat similar to that of XML
New design paradigms become available (working with closures, traits).
Learning speed for Scala is faster than that of C++ or Java for same task.
IDEA (IntelliJ), NetBeans and Eclipse all has good support for Scala.

Disadvantages of Scala:

Inferior quality of the documentation
Native libraries (Scala uses Java or .Net libraries as base for their own)
IDE and debugging support is not as good as Java.
Non-existing localization of documentation
It requires larger syntax to learn.
It consistently breaks backwards compatibility.

Skilled programmers are required to use the features of the language.

It is still in early adopter phase.
Lack of extensive tutorials

Now lets talk about small code and see, how they differ from each other..

A Better OOP Language

Scala works seamlessly with Java. You can invoke Java APIs, extend Java classes and implement Java interfaces. You can even invoke Scala code from Java, once you understand how certain “Scala-isms” are translated to Java constructs (javap is your friend). Scala syntax is more succinct and removes a lot of tedious boilerplate from Java code.

For example, the following Person class in Java:

class Person {

private String firstName;

private String lastName;

private int age;

public Person(String firstName, String lastName, int age) {

this.firstName = firstName;

this.lastName = lastName;

this.age = age;


public void setFirstName(String firstName) { this.firstName = firstName; }

public void String getFirstName() { return this.firstName; }

public void setLastName(String lastName) { this.lastName = lastName; }

public void String getLastName() { return this.lastName; }

public void setAge(int age) { this.age = age; }

public void int getAge() { return this.age; }


can be written in Scala thusly:

class Person(var firstName: String, var lastName: String, var age: Int)

Yes, that’s it. The constructor is the argument list to the class, where each parameter is declared as a variable (var keyword). It automatically generates the equivalent of getter and setter methods, meaning they look like Ruby-style attribute accessors; the getter is foo instead of getFoo and the setter is foo = instead of setFoo. Actually, the setter function is really foo_=, but Scala lets you use the foo = sugar.

Lots of other well designed conventions allow the language to define almost everything as a method, yet support forms of syntactic sugar like the illusion of operator overloading, Ruby-like DSL’s, etc.

You also get fewer semicolons, no requirements tying package and class definitions to the file system structure, type inference, multi-valued returns (tuples), and a better type and generics model.

One of the biggest deficiencies of Java is the lack of a complete mixin model. Mixins are small, focused (think Single Responsibility Principle ...) bits of state and behavior that can be added to classes (or objects) to extend them as needed. In a language like C++, you can use multiple inheritance for mixins. Because Java only supports single inheritance and interfaces, which can’t have any state and behavior, implementing a mixin-based design has always required various hacks. Aspect-Oriented Programming is also one partial solution to this problem.

The most exciting OOP enhancement Scala brings is its support for Traits, a concept first described here and more recently discussed here. Traits support Mixins (and other design techniques) through composition rather than inheritance. You could think of traits as interfaces with implementations. They work a lot like Ruby modules.

Now look at one design patter example and comparing these two language.

Here is an example of the Observer Pattern written as traits, where they are used to monitor changes to a bank account balance. First, here are reusable Subject and Observer traits.

This trait looks exactly like a Java interface. In fact, that’s how traits are represented in Java byte code. If the trait has state and behavior, like Subject, the byte code representation involves additional elements.

trait Observer[S] {

def receiveUpdate(subject: S);


trait Subject[S] {

this: S =>

private var observers: List[Observer[S]] = Nil

def addObserver(observer: Observer[S]) = observers = observer :: observers

def notifyObservers() = observers.foreach(_.receiveUpdate(this))


In Scala, generics are declared with square brackets, [...], rather than angled brackets, <...>. Method definitions begin with the def keyword. The Observer trait defines one abstract method, which is called by the Subject to notify the observer of changes. The Subject is passed to the Observer.

There are lots of other differences between these languages, and I hope with small post will help others. who are trying to evaluate some other language, or trying to see whats out there....

Thursday, August 12, 2010

Spring RestTemplate

Its hard to say anything about spring without seeming biased in favor. Spring's RestTemplate is as solid as can be expected. Their standard call back based approach for safe release of resources works well even for the REST template. If one is using Spring-mvc and their REST support, very few reasons would drive me to consider an alternative framework for the client. One among them is definitely finer grained control, another is Http Client 4.X support. Documentation is sparse on RestTemplate as well. But one has a community to back up on. There might a bit of up front customizations, standard call back etc that an adopter might create but once done I feel that it would be a easy to work with the RestTemplate.
Clearly one has many choices in selecting a client side framework for RESTful HTTP. In most cases it probably makes sense to use the same framework for the service and client end. Then again, if you are only a consumer of a service you have multiple choices among those shown above as well as the option of using Apache HTTP Client or Components directly and bypassing the higher level frameworks. For some, integrating with the spring framework is important and all the above frameworks have means of integration points, both on the service and client sides. Support for Client Proxies is something one might want to consider as they tend to simplify the programming model. Further if Resource definitions can be shared among client server, that can be quite useful in being DRY (Don't repeat yourself) and provide means for contract definition. For those interested in performance and tuning of the HTTP Connections, using a framework that allows you to manage connection pooling and other parameters is definitely the way to go.

For more information on Spring RestTemplate, visit Spring blog

Spring RestTemplate Example: