LruCache in Java

Java collections has LinkedHashMap which is a combination of a HashMap and a linked list which allows for predictable iteration order. There are two options for iteration - Based on insertion order, or based on Access order.

Now to create a Least Recently Used cache, the implementation need to use the access order for iteration and override the hook method removeEldestEntry() which should check the required size of the map to remove entries. I've posted the code in the example below.

Also present in the example is how you should *not* use the map in an multithreaded fashion. The class is not thread-safe and you end up with non deterministic behavior and the size invariant and probably other things go wrong.

Functional Programming Principles in Scala

I just completed the Functional Programming Principles in Scala course at https://www.coursera.org/course/progfun with my solutions at https://github.com/rrevo/progfun . It was a good experience learning both about Functional programming and Scala.

Overall the new features compared to an OO language like Java were-

1. Higher-order functions
2. Case classes and pattern matching
3. Immutable collections
4. Flexible evaluation strategies: strict/lazy/by name

It was refreshing to try and solve problems without mutation. However this also has a higher performance cost. Most of my current work is in Java and so I can translate some of these ideas to my work. Preferring immutability is a good idea for concurrency anyways and this was also brought up by Effective Java and Concurrency in Practice.

Scala as a language was also pretty interesting. Higher-order functions and the other features made code much more succinct than java. I did find myself trying to minify code into a single line at times. But at the same time this density meant that reading code at a later time was definitely much harder. Since types are also inferred, I did end up spending quite a bit of time trying to reason about the types of variables.

Java 8 will have some form of higher-order functions. That should close the gap between the languages slightly. However scala also has many other features and libraries that also have immense value. Choosing between either still depends on many other factors.

Spring vs Guice default scopes

Spring and Guice are popular Inversion Of Control (IoC) frameworks. One of the most important aspects of IoC is how the framework creates new instances for value. This is the Scope. Some of the scopes are-

1. Singleton (Spring default) - A single instance is created by the IoC container for the entire application lifetime.
2. Prototype (Guice default) - A new instance is created whenever a value is needed.

In addition there are other scopes valid in a web context and custom scopes can also be defined. For additional details on scopes see Spring docs.

For stateless objects the programmer can choose either Singleton or Prototype. Guice docs recommend that prototype scope be used for Stateless objects even though only a single instance should suffice really. The rationale is to optimize for speed instead since singleton scopes require synchronization for implementation and today's JVMs are good at garbage collection.

How does JDBC Connection Pooling work?

This post is an excerpt from the jtracer blog.

Overview

The Apache commons DBCP component provides Connection pooling for JDBC connections. In this blog I am going to use JTracer to reveal how DBCP works internally.

JDBC Primer

To connect to a database using JDBC a java.sql.Connection is needed. For creating a Connection, a JDBC driver needs to be loaded. Connection parameters like url and credentials should also be set. Once a Connection is obtained you can create a Statement to execute queries. After the Statement and Connection are used, they should be closed to clean up the resources. The DataSource API as part of the javax.sql package provides an alternate way to create connections.

Creation of Connections is an expensive process. It is better to use a connection pool that will re-use Connections for running queries rather than creating only new Connections. The DBCP project from Apache provides a BasicDataSource which also implements Connection pooling.

Continue

Continue reading at the jtracer blog.

Overview of OSGi

What is OSGi?

OSGi is a module system and service platform for the Java platform.

For the module system, it extends the code level visibility controls that Java provides via the private, protected, public and package-private access. An application is usually packaged as multiple jars in java. Some of these are external libraries. With OSGi it is possible to specify version for a jar and dependency information between jars.

OSGi enables Service Oriented Architecture in a Virtual Machine. It provides APIs for providing a way to register services, discover and bind to them.

Specifications

The OSGi Alliance is an industry backed non-profit organization that manages the OSGi specifications. There are a many implementations like Apache Felix, Eclipse Equinox and Knopflerfish. Building on top of the core OSGi framework are runtimes that provide additional services like Apache Karaf.

Architecture

OSGi Platform

The OSGi platform is composed of the Framework and Standard services. The framework is the runtime that implements and provides OSGi functionality. The standard services define reusable APIs for common tasks.

Core framework

The core framework itself can be broken down into 3 layers - Module, Lifecycle and Service. Each layer is dependent on the layer below. The Module layer has to be used by an application but the Lifecycle and Service layers are optional.

1. Module Layer
In OSGi the unit of modularity is called a Bundle. A Bundle is basically a jar file containing additional metadata in headers with an additional file - META-INF/MANIFEST.MF.

Headers Bundle-SymbolicName and Bundle-Version are used to uniquely identify a Bundle and its version. Using the header Export-Package the Bundle can specify the packages that are visible to other packages. Import-Package and Require-Bundle are used to specify the dependencies of a Bundle.

2. Lifecycle Layer

There are 4 phases of a Bundle lifecycle

1. Installation - The bundle jar has to be installed first from a URL. The framework automatically resolves its dependencies based on the Import-Package and Require-Bundle headers. Resolution happens transitively for all the dependent bundle as well.
2. Execution - When the Bundles classes are first accessed or the bundle is explicitly started, it moves to a starting state
3. Update - Bundles may be updated to a different version using the API
4. Removal - Finally bundles may be uninstalled.

Some of the important APIs that allow this functionality are-
org.osgi.framework.BundleActivator
org.osgi.framework.BundleContext
org.osgi.frameword.Bundle

3. Service Layer

The OSGi framework allows registration of services, discovery and binding to them. Bundles may be installed and uninstalled allowing for dynamic services and possibly multiple implementations.

The org.osgi.framework.BundleContext class provides APIs for this service layer.

Services

An OSGi platform provides core services some of which are-

• Package Admin (org.osgi.service.packageadmin) provides the ability to control and reflect over bundle and package level resolution
• Start Level (org.osgi.service.startlevel) controls the relative order of bundle startup by assigning start levels to bundles
• Service Hooks (org.osgi.framework.hooks.service) allows bundles to monitor and limit service registry events and access

Some of the optional services are-

• Log (org.osgi.service.log) for logging by bundles
• HTTP (org.osgi.service.http) for a HTTP server with Servlet support
• Configuration Admin (org.osgi.service.cm) Manages bundle configuration data storage and injection
• Preferences (org.osgi.service.prefs) for management of Preferences
• Event Admin (org.osgi.service.event) for publish-and-subscribe and topic-based event notification

Summary

OSGi does provides some valuable extensions to the core java language. Just being able to specify packages to external clients allows to design APIs without leaking unnecessary information. Classpath resolution is also well managed.
The service layer further adds to the idea of well defined APIs.

Being based on plain java classes the framework does not feel heavy like EJBs. However figuring out how to use a particular runtime is not an easy task.

Integrating with existing code and converting them to bundles is also non-trivial. If jars are not well designed APIs then there is always a problem that there are some references that will never be cleaned causing a leak. Existing code also needs to be refractored to use the OSGi services of logging and configuration.

In all OSGi has value but there is also a cost to using the framework.

The Concurrency Revolution II

In Dec 2004 Mohnish had posted The Concurrency Revolution based on Herb Sutter's article on the multi-core paradigm shift in processors.

Well, it's time to read the follow up - Welcome to the Jungle .

Ubuntu Tour

I'm running a slightly old version of ubuntu .. trying to hold moving to the new UI. I wanted to have a peek at the current state.

Opened the Ubuntu Tour and expected to see a few screenshots. But ..

The tour is actually a working Ubuntu desktop built as an HTML page! Amazing. The dash works, the start bar works with date, volume etc and other basic controls. Some applications are just images which you can drag around. Thunderbird is more complex with demo emails. Firefox is the best because you can open other webpages.. recursive browsing.

When drafting this blog, noticed that the layout reconfigures when the width of the page changes.

HTML layouts have come a long way.

Know what libraries are used for this?

Simplicity

Simplicity is the ultimate sophistication - Leonardo da Vinci

Rich Hickey presented a fantastic talk, Simple made easy - "Rich Hickey emphasizes simplicity’s virtues over easiness', showing that while many choose easiness they may end up with complexity, and the better way is to choose easiness along the simplicity path."

Anders Hejlsberg mentioned simplexity in an interview a while back as well where he says "Let me first talk a little bit about how I view simplicity in general. No one ever argues that simplicity isn't good, but people define simplicity in a variety of ways. There's one kind of simplicity that I like to call simplexity. When you take something incredibly complex and try to wrap it in something simpler, you often just shroud the complexity. You don't actually design a truly simple system. And in some ways you make it even more complex, because now the user has to understand what was omitted that they might sometimes need. That's simplexity. So to me, simplicity has to be true, in the sense that the further down you go the simpler it gets. It shouldn't get more complicated as you delve down. "


Over time I have seen quite a few systems with too much complexity. And mostly it was not needed. Just a lot of code added without too much thought to design. More thought should be put into design and refractoring and testing.

It is also funny how this parallels to a sense of minimalistic design for design and architecture.

Installing mercurial on CentOS or RHEL 4

For mercurial/hg you need a relatively new version of python installed. Since that is not available as an rpm let's compile the source.

From http://python.org/download/ download a python source version like http://python.org/ftp/python/2.7.2/Python-2.7.2.tgz

From http://mercurial.selenic.com/release/ download a mercurial source drop like http://mercurial.selenic.com/release/mercurial-1.7.5.tar.gz

Run the following commands as root:

#Install some dependencies
yum install zlib-devel.i386 ncurses-devel.i386 openssl-devel.i386 readline-devel.i386 bzip2-devel.i386

#Extract the python code
tar xvzf Python-2.7.2.tgz
cd Python-2.7.2

# Python will be installed in /opt/python27
make clean; ./configure --prefix=/opt/python27; make; make install
cd ..

# Extract the mercurial code
tar xvzf mercurial-1.7.5.tar.gz
cd mercurial-1.7.5

#Python will be installed in /opt/hg17
make install PYTHON=/opt/python27/bin/python PREFIX=/opt/hg17

#Add new python and mercurial to PATH
export PATH=/opt/python27/bin:/opt/hg17/bin:$PATH

Java7 Automatic resource management

ARM:

One of the useful features in Java7 is the Automatic resource management via the try-with-resources statement.

In the olden days thou would (or atleast were supposed to) code like:

void doSomething() throws IOException {
  OutputStream out = null;
  try {
    out = new FileOutputStream("");
    out.write(data);
  } finally {
    if (out != null) {
      out.close();
    }
  }
}

Which is error prone if you do forget to close the resources.

The new way is:

void doSomethingNew() throws IOException {
  try (OutputStream out = new FileOutputStream("")) {
    out.write(data);
  }
}

This is syntactically much more pleasing and does the right thing internally.

Going deep:
The try-with syntax works with any AutoCloseable implementation and you can have multiple resources as well.

The compiler will transform the above code into something like:

void doSomethingNew() throws IOException {
  OutputStream out = null;
  Throwable localThrowable1 = null;
  try {
    out = new FileOutputStream("");
    out.write(blah);
  } catch (Throwable localThrowable2) {
    // We keep a reference to which can add a suppressed exception
    localThrowable1 = localThrowable2;
    throw localThrowable2;
  } finally {
    if (out != null) {
      if (localThrowable1 != null) {
        // Already have an exception thrown
        try {
          out.close();
        } catch (Throwable localThrowable3) {
          // Add the suppressed exception during close
          localThrowable1.addSuppressed(localThrowable3);
        }
      } else {
        // Potentially throw an IOException due to failure when close'ing
        out.close();
      }
    }
  }
}

The pattern is:

• If there are no exception - close() in the finally block OR
• If there are no exception during operation but there is an exception during close() then throw it OR
• If there is an exception thrown then throw it after closing the resource OR
• If there is an exception1 thrown then throw it .. and if there is an exception2 closing the resource.. then exception1.addSuppressed(exception2). This is new in theThrowable class

Sidenote:
There was a huge effort to get closures into Java7 but none of the solutions was light on syntax/complexity. After the backlash over Generics a smaller but better step has been taken.

Sidenote++:
For scala see using. You do not need to wait for language changes to make syntactically pleasing APIs because of curry-ing and other fancy stuff.


More References:
ARM spec
Article on ARM

Beautiful software

<moody>
I feel a deep sense of happiness when I use Google products like gmail and chrome. Every now and then they update the applications and things just work. They make things look so simple but they must be super complex in the back. That's great software.

Great software can only be built by great teams. That means everyone from engineers to managers. Give enough freedom to the team to execute. Treat them like people. Understand software.

No software methodology can save you. Let the team define its processes. Let common sense prevail. And then greatness will follow.
</moody>

Where did the class get loaded from?

As with most enterprise apps gone crazy you have a bunch of duplicate jars or some jars at places you don't even know were in the classpath. And once a while you need to know from which jar a particular class file was loaded. To find this out run java with the -verbose:class flag. For each class loaded, the VM will print out the folder or jar where the class was found.

~ $ java -verbose:class HelloWorld
...
[Loaded HelloWorld from file:/C:/work/cygwin/home/rrevo/]
Hello World
[Loaded java.lang.Shutdown from shared objects file]
[Loaded java.lang.Shutdown$Lock from shared objects file]

Read java options for more info.

PS: It's time to start blogging again.

Linux on the desktop

Recently I performed some upgrades on my laptop and the sound broke once again. Sound has been flaky for a while now and I've had to use windows to use skype. This was a pretty useful tutorial which helped me sort out the issues - http://ubuntuforums.org/showthread.php?t=789578

But it got me thinking more about experience on Linux once again. Applications like OpenOffice, Gimp are inferior in usability to MS Office and Photoshop. Its painful when I need a newer version of software but the distro is older and so only an older version is available in the repo. Maybe its time to move back to Windows...

An Overview of Spring

Spring is a very popular framework in the Java space and quickly becoming an alternative to JEE. Spring started of as an implementation of the ideas in the book "Expert One-on-One J2EE Design and Development" in 2002 by Rob Johnson. Today the project has grown into to a large framework with multiple modules to assist with different areas of serverside programming. Spring provides a lightweight container and uses POJOs. This makes code much simpler to reason about and also test. No starting a mega EJB container anymore with remoting when you don't really need it.

Inversion Of Control (IoC)
At its core, Spring is an IoC container. Generally at some point in code you use 'new' instances. If you are coding against an interface you end up with code like:

class Bar {
 Foo foo;
 void Bar() {
   foo = new FooImpl();
 }
}

Now the class Bar has a dependency on Foo and its implementation FooImpl. Now you could remove this dependency by using the ServiceLocator pattern but then you end up with a dependency to the ServiceLocator class and your code is not that testable anymore.
In Spring you instead inject the actual implementations at runtime and rules about which instances are to be returned are written in an XML configuration file (or via Annotations). So code becomes like:

class Bar {
 Foo foo;
 void Bar(Foo foo) {
   this.foo = foo;
 }
}

with an instance of FooImpl being returned where Foo is expected. Now Bar depends only on the interface Foo but not the implementation of Foo which is simply passed to it. Hence the name Inversion of Control as Bar does not depend on FooImpl but gets it.

More importantly the code can be tested very easily. If I wanted to test the Bar class I can very easily provide a mock implementation of the Foo instance. Writing testable code is difficult and a major part of the problem is breaking dependencies. You should probably never need to new objects again but just get them injected.

In the above example Foo is set in the constructor. This is an example of a Constructor based injection. Another way to inject dependencies is via setter methods. However I prefer Constructor based injection as it allows for final fields which should be the default to help with immutability.

Another important idea is how instances are created. This is known as scopes. By default instances are created only once and that reference will be passed everywhere similar to a Singleton. So one FooImpl instance is created and passed wherever a Foo is needed. A lot of code can be written in a style where there is no local state allowing for Singletons. Again since the Singleton pattern is not explicitly needed, code remains testable. Another scope is prototype in which a new instance of FooImpl will be created whenever a Foo needs to be injected. For web programming other scopes like Request, Session and Application also exist.

The complete lifetime of instances can be managed and there are many other features but thats another post. If you just need an IoC container then there are alternatives like Google Guice.

Aspect Oriented Programming

AOP allows for crosscutting code to be written external to the main business logic. This allows cleaner code in areas like logging. The implementation of AOP in Spring is based on Proxy based interceptors which happen at runtime. AspectJ integration is also provided in some form.
One of the major uses of AOP is defining transactions which will be covered soon.

Data Access and Transaction management

Most serverside code needs to talk to a database. Spring provides neat abstractions over JDBC and other frameworks to simplify code to a great extent.

A DataSource is usually configured and injected.
JDBC code is wrapped with classes like the SimpleJdbcTemplate. Queries become like:

String daString = getSimpleJdbcTemplate().queryForObject(
    "SELECT daString FROM DaStringTable WHERE daStringId = ?",
    String.class, daStringId);

Thats one line of code for what would have been multiple lines of JDBC like getting a connection, then statement, then query and result parsing. And there are no SQLExceptions. All of those are wrapped into a DataAccessException instance which is a RuntimeException. Create a generic handler in your code for exceptions because thats what you'll mostly be interested in. You can easily provide mapper classes to map from db values to object instances for custom types. Also variations exist for returning mutiple rows and other SQL CRUD operations.
And I almost forgot to mention that there are also named parameters for queries.

Using Hibernate is even easier. Use HibernateTemplate instead and get access to a hibernate API. Or JPATemplate if you want to use JPA. All of this code is obviously going to be tucked under a DAO tier!

Transaction management is also dead simple with usage of Java annotations. You declare the Transaction rules for a method invocation like Isolation level (Read uncommitted, Read committed, Repeatable Read, Serializable), Propagation (Required, New), timeout and exceptions for rollback. An AOP proxy is created over the method which enforces the Transaction rules over the underlying datastore.

Web MVC

Built on the core IoC functionality Spring has a Web MVC framework as well. Like Struts it is a request or action based framework. The DispatcherServlet class is a FrontController and acts as the entry point to the MVC framework. Typically request URIs are mapped to Controller classes. Controllers compute the Model and then render a View based on the Model for the request. A general multi tier architecture for applications is another topic.

Even more

There are quite a few other projects under the Spring banner. WebFlow extends Web MVC for richer work flows in webapps. Spring WebServices for WebService (duh). Spring IDE is a bunch of Eclipse plugins to help with Spring development.

Spring Framework 3 is going to be released. It adds better Java 5 support across various APIs. There is also a lot of annotation usage.

The company and future

Spring started off as a simple open source project and has now morphed into a complete stack framework backed by a company.
The core framework helps building applications. Further they added Groovy language and Grails. Mostly spring apps need a web container like Tomcat or Jetty to run. SpringSource also provides a custom Tomcat build known as tcServer with additional capabilities. Another environment is the dmServer which adds OSGi capabilities. For management and diagnostics they have additional tools. All of these play together to provide a really strong stack against the usual JEE standard running in an application container.

VMWare bought SpringSource which means that soon Cloud-deployed apps based on Spring are going to be dead simple to make. This means that VMWare will now compete with the likes of Google App Engine and Microsoft Azure as well by providing virtualized application frameworks.

Links

Spring 3 presentation

Spring Community project

SpringSource

List of countries and timezones

I'm pasting a csv file containing a list of timezone data of some of the cities from timeanddate.com. I was unable to find such a list and eventually had to do a lot of manual work. Do comment if there are any errors.

Afghanistan - Kabul,Asia/Kabul,Afghanistan Time,UTC/GMT +4:30
Algeria - Algiers,Africa/Algiers,Central European Time,UTC/GMT +1:00
Argentina - Buenos Aires,America/Argentina/Buenos_Aires,Argentine Time,UTC/GMT -3:00
Australia - Australian Capital Territory - Canberra,Australia/Canberra,Eastern Standard Time (New South Wales),UTC/GMT +10:00
Australia - New South Wales - Sydney,Australia/Sydney,Eastern Standard Time (New South Wales),UTC/GMT +10:00
Australia - Northern Territory - Darwin,Australia/Darwin,Central Standard Time (Northern Territory),UTC/GMT +9:30
Australia - Queensland - Brisbane,Australia/Brisbane,Eastern Standard Time (Queensland),UTC/GMT +10:00
Australia - South Australia - Adelaide,Australia/Adelaide,Central Standard Time (South Australia),UTC/GMT +9:30
Australia - Victoria - Melbourne,Australia/Melbourne,Eastern Standard Time (Victoria),UTC/GMT +10:00
Australia - Western Australia - Perth,Australia/Perth,Western Standard Time (Australia),UTC/GMT +8:00
Austria - Vienna,Europe/Vienna,Central European Time,UTC/GMT +1:00
Bahamas - Nassau,America/Nassau,Eastern Standard Time,UTC/GMT -5:00
Bangladesh - Dhaka,Asia/Dhaka,Bangladesh Time,UTC/GMT +6:00
Belarus - Minsk,Europe/Minsk,Eastern European Time,UTC/GMT +2:00
Belgium - Brussels,Europe/Brussels,Central European Time,UTC/GMT +1:00
Bolivia - La Paz,America/La_Paz,Bolivia Time,UTC/GMT -4:00
Brazil - São Paulo - Sao Paulo,America/Sao_Paulo,Brasilia Time,UTC/GMT -3:00
Bulgaria - Sofia,Europe/Sofia,Eastern European Time,UTC/GMT +2:00
Canada - Alberta - Edmonton,America/Edmonton,Mountain Standard Time,UTC/GMT -7:00
Canada - British Columbia - Vancouver,America/Vancouver,Pacific Standard Time,UTC/GMT -8:00
Canada - Manitoba - Winnipeg,America/Winnipeg,Central Standard Time,UTC/GMT -6:00
Canada - Newfoundland and Labrador - St. John's,America/St_Johns,Newfoundland Standard Time,UTC/GMT -3:30
Canada - Nova Scotia - Halifax,America/Halifax,Atlantic Standard Time,UTC/GMT -4:00
Canada - Ontario - Toronto,America/Toronto,Eastern Standard Time,UTC/GMT -5:00
Canada - Quebec - Montreal,America/Montreal,Eastern Standard Time,UTC/GMT -5:00
Chile - Santiago,America/Santiago,Chile Time,UTC/GMT -4:00
China - Shanghai,Asia/Shanghai,China Standard Time,UTC/GMT +8:00
Colombia - Bogota,America/Bogota,Colombia Time,UTC/GMT -5:00
Croatia - Zagreb,Europe/Zagreb,Central European Time,UTC/GMT +1:00
Cuba - Havana,America/Havana,Cuba Standard Time,UTC/GMT -5:00
Czech Republic - Prague,Europe/Prague,Central European Time,UTC/GMT +1:00
Denmark - Copenhagen,Europe/Copenhagen,Central European Time,UTC/GMT +1:00
Dominican Republic - Santo Domingo,America/Santo_Domingo,Atlantic Standard Time,UTC/GMT -4:00
Egypt - Cairo,Africa/Cairo,Eastern European Time,UTC/GMT +2:00
El Salvador - San Salvador,America/El_Salvador,Central Standard Time,UTC/GMT -6:00
Estonia - Tallinn,Europe/Tallinn,Eastern European Time,UTC/GMT +2:00
Ethiopia - Addis Ababa,Africa/Addis_Ababa,Eastern African Time,UTC/GMT +3:00
Fiji - Suva,Pacific/Fiji,Fiji Time,UTC/GMT +12:00
Finland - Helsinki,Europe/Helsinki,Eastern European Time,UTC/GMT +2:00
France - Paris,Europe/Paris,Central European Time,UTC/GMT +1:00
Germany - Berlin - Berlin,Europe/Berlin,Central European Time,UTC/GMT +1:00
Greece - Athens,Europe/Athens,Eastern European Time,UTC/GMT +2:00
Guatemala - Guatemala,America/Guatemala,Central Standard Time,UTC/GMT -6:00
Honduras - Tegucigalpa,America/Tegucigalpa,Central Standard Time,UTC/GMT -6:00
Hong Kong - Hong Kong,Asia/Hong_Kong,Hong Kong Time,UTC/GMT +8:00
Hungary - Budapest,Europe/Budapest,Central European Time,UTC/GMT +1:00
Iceland - Reykjavik,Atlantic/Reykjavik,Greenwich Mean Time,UTC/GMT +0:00
India - Delhi - New Delhi,Asia/Kolkata,India Standard Time,UTC/GMT +5:30
India - Maharashtra - Mumbai,Asia/Kolkata,India Standard Time,UTC/GMT +5:30
India - West Bengal - Kolkata,Asia/Kolkata,India Standard Time,UTC/GMT +5:30
Indonesia - Java - Jakarta,Asia/Jakarta,West Indonesia Time,UTC/GMT +7:00
Iran - Tehran,Asia/Tehran,Iran Standard Time,UTC/GMT +3:30
Iraq - Baghdad,Asia/Baghdad,Arabia Standard Time,UTC/GMT +3:00
Ireland - Dublin,Europe/Dublin,Greenwich Mean Time,UTC/GMT +0:00
Israel - Jerusalem,Asia/Jerusalem,Israel Standard Time,UTC/GMT +2:00
Italy - Rome,Europe/Rome,Central European Time,UTC/GMT +1:00
Jamaica - Kingston,America/Jamaica,Eastern Standard Time,UTC/GMT -5:00
Japan - Tokyo,Asia/Tokyo,Japan Standard Time,UTC/GMT +9:00
Jordan - Amman,Asia/Amman,Eastern European Time,UTC/GMT +2:00
Kazakstan - Almaty,Asia/Almaty,Alma-Ata Time,UTC/GMT +6:00
Kenya - Nairobi,Africa/Nairobi,Eastern African Time,UTC/GMT +3:00
Kiribati - Christmas Island - Kiritimati,Pacific/Kiritimati,Line Is. Time,UTC/GMT +14:00
Kuwait - Kuwait City,Asia/Kuwait,Arabia Standard Time,UTC/GMT +3:00
Lebanon - Beirut,Asia/Beirut,Eastern European Time,UTC/GMT +2:00
Madagascar - Antananarivo,Indian/Antananarivo,Eastern African Time,UTC/GMT +3:00
Malaysia - Kuala Lumpur,Asia/Kuala_Lumpur,Malaysia Time,UTC/GMT +8:00
Mexico - Federal District - Mexico City,America/Mexico_City,Central Standard Time,UTC/GMT -6:00
Morocco - Casablanca,Africa/Casablanca,Western European Time,UTC/GMT +0:00
Myanmar - Yangon,Asia/Rangoon,Myanmar Time,UTC/GMT +6:30
Nepal - Kathmandu,Asia/Kathmandu,GMT+05:45,UTC/GMT +5:45
Netherlands - Amsterdam,Europe/Amsterdam,Central European Time,UTC/GMT +1:00
New Zealand - Auckland,Pacific/Auckland,New Zealand Standard Time,UTC/GMT +12:00
New Zealand - Chatham Islands,Pacific/Chatham,Chatham Standard Time,UTC/GMT +12:45
Nicaragua - Managua,America/Managua,Central Standard Time,UTC/GMT -6:00
Nigeria - Lagos,Africa/Lagos,Western African Time,UTC/GMT +1:00
Norway - Oslo,Europe/Oslo,Central European Time,UTC/GMT +1:00
Pakistan - Karachi,Asia/Karachi,Pakistan Time,UTC/GMT +5:00
Paraguay - Asuncion,America/Asuncion,Paraguay Time,UTC/GMT -4:00
Peru - Lima - Lima,America/Lima,Peru Time,UTC/GMT -5:00
Philippines - Manila,Asia/Manila,Philippines Time,UTC/GMT +8:00
Poland - Warsaw,Europe/Warsaw,Central European Time,UTC/GMT +1:00
Portugal - Lisbon,Europe/Lisbon,Western European Time,UTC/GMT +0:00
Puerto Rico - San Juan,America/Argentina/San_Juan,Argentine Time,UTC/GMT -3:00
Romania - Bucharest,Europe/Bucharest,Eastern European Time,UTC/GMT +2:00
Russia - Anadyr,Asia/Anadyr,Anadyr Time,UTC/GMT +12:00
Russia - Kamchatka,Asia/Kamchatka,Petropavlovsk-Kamchatski Time,UTC/GMT +12:00
Russia - Moscow,Europe/Moscow,Moscow Standard Time,UTC/GMT +3:00
Russia - Vladivostok,Asia/Vladivostok,Vladivostok Time,UTC/GMT +10:00
Saudi Arabia - Riyadh,Asia/Riyadh,Arabia Standard Time,UTC/GMT +3:00
Serbia - Belgrade,Europe/Belgrade,Central European Time,UTC/GMT +1:00
Singapore - Singapore,Asia/Singapore,Singapore Time,UTC/GMT +8:00
South Africa - Johannesburg,Africa/Johannesburg,South Africa Standard Time,UTC/GMT +2:00
South Korea - Seoul,Asia/Seoul,Korea Standard Time,UTC/GMT +9:00
Spain - Madrid,Europe/Madrid,Central European Time,UTC/GMT +1:00
Sudan - Khartoum,Africa/Khartoum,Eastern African Time,UTC/GMT +3:00
Sweden - Stockholm,Europe/Stockholm,Central European Time,UTC/GMT +1:00
Switzerland - Zurich,Europe/Zurich,Central European Time,UTC/GMT +1:00
Taiwan - Taipei,Asia/Taipei,China Standard Time,UTC/GMT +8:00
Thailand - Bangkok,Asia/Bangkok,Indochina Time,UTC/GMT +7:00
Turkey - Ankara,Turkey,Eastern European Time,UTC/GMT +2:00
Turkey - Istanbul,Turkey,Eastern European Time,UTC/GMT +2:00
U.K. - England - London,Europe/London,Greenwich Mean Time,UTC/GMT +0:00
United Arab Emirates - Dubai - Dubai,Asia/Dubai,Gulf Standard Time,UTC/GMT +4:00
Uruguay - Montevideo,America/Montevideo,Uruguay Time,UTC/GMT -3:00
U.S.A. - Alaska - Anchorage,America/Anchorage,Alaska Standard Time,UTC/GMT -9:00
U.S.A. - California - Los Angeles,America/Los_Angeles,Pacific Standard Time,UTC/GMT -8:00
U.S.A. - Colorado - Denver,America/Denver,Mountain Standard Time,UTC/GMT -7:00
U.S.A. - Hawaii - Honolulu,Pacific/Honolulu,Hawaii Standard Time,UTC/GMT -10:00
U.S.A. - Illinois - Chicago,America/Chicago,Central Standard Time,UTC/GMT -6:00
U.S.A. - Michigan - Detroit,America/Detroit,Eastern Standard Time,UTC/GMT -5:00
U.S.A. - New York - New York,America/New_York,Eastern Standard Time,UTC/GMT -5:00
Uzbekistan - Tashkent,Asia/Tashkent,Uzbekistan Time,UTC/GMT +5:00
Venezuela - Caracas,America/Caracas,Venezuela Time,UTC/GMT -4:30
Vietnam - Hanoi,Asia/Vientiane,Indochina Time,UTC/GMT +7:00
Yemen - Aden,Asia/Aden,Arabia Standard Time,UTC/GMT +3:00
Zimbabwe - Harare,Africa/Harare,Central African Time,UTC/GMT +2:00

Flex

I had an opportunity to look into Flex a few weeks back. I've been mostly focused on Swing last couple of years and before that was fairly involved with web development (pre-ajax). So it's been a nice exercise to investigate what it offers and compare and contrast.

Flex has a good out of the box widget set, similar to Swing. One of its major strengths is its UI designer - no real surprise there, given it grew out of flash. Actionscript, the ECMAScript compliant language, tries to be dynamic with optional static typing. This can be useful, especially during at development time with code completion. Debugging can be a challenge though, especially the mix between actionscript and mxml. End up falling back on Alerts which isn't the greatest thing (more so given that they don't block and you can end up with a flurry of alert boxes). I also found that there are multiple ways to do the same thing. This can be quite confusing especially when looking at samples on the web. You don't really know which is the best way or why. One other small thing - event names don't follow "on[event_name]" convention... it's very easy to confuse them with attributes in mxml. Overall, there's a big similarity with the html/js/css style of development - mxml/as/css.

Flex demos really well. For creating small simple apps involving fetching data from a remote data source and rendering it, it is probably unrivaled from a productivity perspective. Drag a datagrid onto the canvas, construct an http service and attach a result event handler to bind the result to the datagrid. Simple. Done. I think the 'Bindable' attribute is a big part of why Flex is so successful for these types of apps. It takes care of all that plumbing of syncing model with view. It's interesting to note that JavaFX has introduced the 'bind' keyword in JavaFX Script.

Most of what I've come across - articles/examples deal with small apps. I'm interested in how development in Flex would scale. It can be double edged sword. Given that it is so simple to just drag/drop and attach handlers, I would think it would require more discipline and good coding practices. It would be all too easy to keep doing this all over without really giving much thought to overall design and code hygiene. I don't particularly like the script tag in the MXML file. There should've been strict separation between the .mxml file and the .as file. I understand this was probably done to emulate the html/js model but why not force the separation as with separate .js files.

Running a fairly complicated app - like TourDeFlex which chronicles the wonders of the various flex widgets - sucks up a lot of resources. Usability suffers. The experience feels sluggish. A similarly "heavy" "ajaxy" app doesn't. What's worse is that on more than one occasion, the browser has crashed running that demo. It's no surprise I haven't seen full fledged flex apps out on the 'open web'. Enterprises can, and have, embraced it since they can dictate the environment.

There's a lot of revival in interest in web standards. Just as Adobe has AIR, Microsoft has Silverlight and Sun/Oracle has JavaFX, Google is embracing and evangelizing open web standards - HTML5/CSS/Javascript - as their RIA platform. GWT is the browser independent development platform with generated Javascript as the bytecode. I've started playing around with GWT recently and am quite impressed with its abilities - especially the development environment/cycle. Version 2.0 promises more useful features.

It'll be interesting to see where these platforms end up 3-4 years from now.

TurboStringMap for Gwt

In my previous post I did mention that Gwt has the basic Java collections emulated in Javascript. In the browser such rich interfaces may not be needed. There is a lightweight Map implementation where the keys are constrained to String types only called FastStringMap. It is directly backed by a Js array. Want to go even lighter then here is the derived TurboStringMap which even a thinner API over a Js array to act like a Map.

The rest of the this post is Gwt Java code-

package com.onyem.finance.client;

import com.google.gwt.core.client.JavaScriptObject;

class TurboStringMap {

 /*
 * Accesses need to be prefixed with ':' to prevent conflict with built-in
 * JavaScript properties.
 */
@SuppressWarnings("unused")
private JavaScriptObject map;

public TurboStringMap() {
 init();
}

public void clear() {
 init();
}

private native void init() /*-{
   this.@com.onyem.finance.client.TurboStringMap::map = {};
 }-*/;

// Prepend ':' to avoid conflicts with built-in Object properties.
public native T get(String key) /*-{
   return this.@com.onyem.finance.client.TurboStringMap::map[':' + key];
 }-*/;

// Prepend ':' to avoid conflicts with built-in Object properties.
public native T put(String key, T value) /*-{
   key = ':' + key;
   var map = this.@com.onyem.finance.client.TurboStringMap::map;
   var previous = map[key];
   map[key] = value;
   return previous;
 }-*/;

// Prepend ':' to avoid conflicts with built-in Object properties.
public native T remove(String key) /*-{
   key = ':' + key;
   var map = this.@com.onyem.finance.client.TurboStringMap::map;
   var previous = map[key];
   delete map[key];
   return previous;
 }-*/;

// only count keys with ':' prefix
public native int size() /*-{
   var value = this.@com.onyem.finance.client.TurboStringMap::map;
   var count = 0;
   for(var key in value) {
     if (key.charAt(0) == ':') ++count;
   }
   return count;
 }-*/;

public boolean isEmpty() {
 return size() == 0;
}

public native String[] keys() /*-{
   var value = this.@com.onyem.finance.client.TurboStringMap::map;
   var keys = [];
   for(var key in value) {
     keys.push(key.substring(1));
   }
   return keys;
}-*/;
}

GWT

I've been working with Gwt since a while and in this post will dump some of my learnings

What is Gwt
Gwt is a toolkit primarily to enable writing webapps in Java which will then be cross compiled into plain Javascript and Html. The core is based on this java to javascript compiler. Additionally they have libraries for purposes like web gui creation, dom manipulation, json and xml parsing, RPC calls with java server support and also unit testing. The Gwt guys are seem pretty obsessed with performance so a lot of the design choices are based on this.

To code in Gwt you use your standard Java tools. This is a great advantage as you get great tool/ide support and java's static checking for code. Java generics are also supported. To create UIs a SWT-like library has been created which can be used. The library contains both Widget classes for common controls as well as layout classes for positioning. There are some quirks which you have to be aware of but thats true for almost any new platform. The layout library is one of the first reasons which got me to Gwt as I was (and still am) simply too scared to use CSS for managing a layout. Using the UI libraries for building interfaces is a bit painful in Java just as it is in Swing and Swt. But more importantly it does not translate to the best Html/Css layout code. For example to place child elements horizontally next to each other you can use the HorizontalPanel and add elements to this. Now when this code is cross compiled the HorizontalPanel is converted to a Html table with a single tr and all the child elements will be placed in td elements. Which depending on your style may not look that good. In the next version of Gwt a new UI Binder feature is going to be added. This will allow declaring the UI in an XML format and then writing the actual event handlers in Java. I guess a lot of UI frameworks are moving to this style which really does make sense in this domain. Also the code generated may be closer to the layout code you would have written by hand (if you knew CSS). You can also create your own Widgets and Panels if you want to. I also almost forgot to mention that you have access to a subset of the Java library. The API can be read here. Basic java.lang and other important packages like some collections are supported.

Now that you have written some Java code you compile it by using the GwtCompiler which can be invoked by an ant task. You get a whole bunch of files into your dist folder. Now these are plain html, js and css files. You dont need any Java support in your webserver to run these. Gwt will generate separate optimized files for each browser supported. A client using IE7 will get a file separate from a FF client and each file will manage the quirks of that browser. So a client downloads almost only what is needed. I lied a bit in this process though. When the browser first hits the entry point html file special js code will decide what browser is running the code. After that the client code for that browser is then loaded in another Http request. Search for more on deferred binding to learn more. Importantly most of the code generated can be cached with long expiration headers.

The Gwt compiler essentially compiles Java (source code) to Js. But from where does it get the java.lang and other code of the standard library? The Gwt team has re-written supported Java libraries in a more Js friendly fashion. The String class is based on a normal Js string but the extended Java API for the string class is supported. Similarly the ArrayList class is not something that Bloch wrote but a simpler Js friendly version. Just like the layout code generated some of this is overkill for Js. You dont really need the whole Collections API most of the time. You dont need the whole class hierarchy. Like I just needed a lame Map implementation with put and get and nothing else. And since some part of the Gwt library may use the collections in some way you end up using them anyways. See my bug for an extended rant

Atleast one compiler optimization has to mentioned at this point - dead code elimination. For example if you dont use the substing method in the String class.. that method will not be compiled to Js. Additionally Js code is minified and obfuscated which greatly helps in reduction of download size.

Where should you use GWT

Gwt is great for Ajax apps like Gmail, Google calendar etc. As a Java developer I dont think I could do better/faster had I been coding Js/Html for Onyem. There are deficiencies right now but things are improving and are already optimized enough.

I would not still recommend Gwt in sites that have a lot content like news sites or sites where you just want a small widget in one corner. Use jquery or yui for that.

Also there can be no substitute for knowing CSS and also how to build websites. With a desktop mindset you will end up just bulding really slow apps.

More Features

These may come in some other post-

Hosted mode to OOPHM

Async pattern

Jsni

RPC

Deferred binding

More Compiler optimizations

Open Source is Magic

"Any sufficiently advanced technology is indistinguishable from magic." - Sir Arthur C. Clarke

Anti-social

In relation with normal human behaviour I am "anti-social". Personally I know I am just different-social which is great for me.

I've been emailing a few people of late whom I don't know that well. And shockingly those gmail contacts started popping up in my gtalk list. The reason was gmails default setting of over-friendly behaviour. If you want more privacy then you need to disable the "Auto-add suggested contacts" feature in chat as described in this help page