Raible Designs

Running Spring MVC Web Applications in OSGi

For the past couple of weeks, I've been developing a web application that deploys into an OSGi container (Equinox) and uses Spring DM's Spring MVC support. The first thing I discovered was that Spring MVC's annotations weren't supported in the M1 release. This was apparently caused by a bug in Spring 2.5.3 and not Spring DM. Since Spring DM 1.1.0 M2 was released with Spring 2.5.4 today, I believe this is fixed now.

The story below is about my experience getting a Spring MVC application up and running in Equinox 3.2.2, Jetty 6.1.9 and Spring DM 1.1.0 M2 SNAPSHOT (from last week). If you want to read more about why Spring MVC + OSGi is cool, see Costin Leau's Web Applications and OSGi article.

To get a simple "Hello World" Spring MVC application working in OSGi is pretty easy. The hard part is setting up a container with all the Spring and Jetty bundles installed and started. I imagine SSAP might solve this. Luckily for me, this was done by another member of my team.

After you've done this, it's simply a matter of creating a MANIFEST.MF for your WAR that contains the proper information for OSGi to recognize. Below is the one that I used when I first tried to get my application working.

Manifest-Version: 1
Bundle-ManifestVersion: 2
Spring-DM-Version: 1.1.0-m2-SNAPSHOT
Spring-Version: 2.5.2
Bundle-Name: Simple OSGi War
Bundle-SymbolicName: myapp
Bundle-Classpath: .,WEB-INF/classes,WEB-INF/lib/freemarker-2.3.12.jar,
 WEB-INF/lib/sitemesh-2.3.jar,WEB-INF/lib/urlrewritefilter-3.0.4.jar,
 WEB-INF/lib/spring-beans-2.5.2.jar,WEB-INF/lib/spring-context-2.5.2.jar,
 WEB-INF/lib/spring-context-support-2.5.2.jar,WEB-INF/lib/spring-core-2.5.2.jar,
 WEB-INF/lib/spring-web-2.5.2.jar,WEB-INF/lib/spring-webmvc-2.5.2.jar 
Import-Package: javax.servlet,javax.servlet.http,javax.servlet.resources,javax.swing.tree,
 javax.naming,org.w3c.dom,org.apache.commons.logging,javax.xml.parsers;resolution:=optional,
 org.xml.sax;resolution:=optional,org.xml.sax.helpers;resolution:=optional

Ideally, you could generate this MANIFEST.MF using the maven-bundle-plugin. However, it doesn't support WARs in its 1.4.0 release.

You can see this is an application that uses Spring MVC, FreeMarker, SiteMesh and the URLRewriteFilter. You should be able to download it, unzip it, run "mvn package" and install it into Equinox using "install file://<path to war>".

That's all fine and dandy, but doesn't give you any benefits of OSGi. This setup works great until you try to import OSGi services using a context file with an <osgi:reference> element. After adding such a reference, it's likely you'll get the following error:

SEVERE: Context initialization failed
org.springframework.beans.factory.parsing.BeanDefinitionParsingException:
Configuration problem: Unable to locate Spring NamespaceHandler for
XML schema namespace [http://www.springframework.org/schema/osgi]

To fix this, add the following to your web.xml (if you're using ContextLoaderListener, as an <init-parameter> on DispatcherServlet if you're not):

  <context-param>
    <param-name>contextClass</param-name>
    <param-value>org.springframework.osgi.web.context.support.OsgiBundleXmlWebApplicationContext</param-value>
  </context-param>

After doing this, you might get the following error on startup:

SEVERE: Context initialization failed
org.springframework.context.ApplicationContextException: Custom
context class [org.springframework.osgi.web.context.support.OsgiBundleXmlWebApplicationContext]
is not of type [org.springframework.web.context.ConfigurableWebApplicationContext] 

To fix this, I change from referencing the Spring JARs in WEB-INF/lib to importing the packages for Spring (which were already installed in my Equinox container).

Bundle-Classpath: .,WEB-INF/classes,WEB-INF/lib/freemarker-2.3.12.jar,
 WEB-INF/lib/sitemesh-2.3.jar,WEB-INF/lib/urlrewritefilter-3.0.4.jar
Import-Package:
javax.servlet,javax.servlet.http,javax.servlet.resources,javax.swing.tree,
 javax.naming,org.w3c.dom,org.apache.commons.logging,javax.xml.parsers;resolution:=optional,
 org.xml.sax;resolution:=optional,org.xml.sax.helpers;resolution:=optional,
 org.springframework.osgi.web.context.support,
 org.springframework.context.support,
 org.springframework.web.context,
 org.springframework.web.context.support,
 org.springframework.web.servlet,
 org.springframework.web.servlet.mvc,
 org.springframework.web.servlet.mvc.support,
 org.springframework.web.servlet.view,
 org.springframework.ui,
 org.springframework.web.servlet.view.freemarker 

After rebuilding my WAR and reloading the bundle in Equinox, I was confronted with the following error message:

SEVERE: Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'freemarkerConfig' defined in ServletContext
resource [/WEB-INF/myapp-servlet.xml]: Instantiation of bean failed;
nested exception is java.lang.NoClassDefFoundError:
freemarker/cache/TemplateLoader
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:851) 

As far as I can tell, this is because the version of Spring MVC installed in Equinox cannot resolve the FreeMarker JAR in my WEB-INF/lib directory.

To prove I wasn't going insane, I commented out my "freemarkerConfig" and "viewResolver" beans in myapp-servlet.xml and changed to a regular ol' InternalResourceViewResolver:

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/"/>
    <property name="suffix" value=".jsp"/>
</bean>

This worked and I was able to successfully see "Hello World" from a JSP in my browser. FreeMarker/SiteMesh worked too, but FreeMarker didn't work as a View for Spring MVC.

To attempt to solve this, I create a bundle for FreeMarker using "java -jar bnd-0.0.249.jar wrap freemarker-2.3.12.jar" and installed it in Equinox. I then change my MANIFEST.MF to use FreeMarker imports instead of referencing the JAR in WEB-INF/lib.

Bundle-Classpath:
.,WEB-INF/classes,WEB-INF/lib/sitemesh-2.3.jar,WEB-INF/lib/urlrewritefilter-3.0.4.jar
Import-Package:
javax.servlet,javax.servlet.http,javax.servlet.resources,javax.swing.tree,
 javax.naming,org.w3c.dom,org.apache.commons.logging,javax.xml.parsers;resolution:=optional,
 org.xml.sax;resolution:=optional,org.xml.sax.helpers;resolution:=optional,
 org.springframework.osgi.web.context.support,
 org.springframework.context.support,
 org.springframework.web.context,
 org.springframework.web.context.support,
 org.springframework.web.servlet,
 org.springframework.web.servlet.mvc,
 org.springframework.web.servlet.mvc.support,
 org.springframework.web.servlet.view,
 org.springframework.ui,
 org.springframework.web.servlet.view.freemarker,
 freemarker.cache,freemarker.core,freemarker.template,freemarker.ext.servlet 

Unfortunately, this still doesn't work and I still haven't been able to get FreeMarker to work with Spring MVC in OSGi. The crazy thing is I actually solved this at one point a week ago. Shortly after, I rebuilt Equinox from scratch and I'm been banging my head against the wall over this issue ever since. Last week, I entered an issue in Spring's JIRA, but thought I'd fixed it a few hours later.

I've uploaded the final project that's not working to the following URL:

http://static.raibledesigns.com/downloads/myapp-osgi.zip

If you'd like to see this project work with Spring MVC + JSP, simply modify myapp-servlet.xml to remove the FreeMarker references and use the InternalResourceViewResolver instead.

I hope Spring DM + Spring MVC supports more than just JSP as a view technology. I hope I can't get FreeMarker working because of some oversight on my part. If you have a Spring DM + Spring MVC application working with Velocity or FreeMarker, I'd love to hear about it.

Apache 2 on OS X: Configuring mod_proxy and SSL

I recently had to setup Apache as a front-end web server for multiple backend servlet containers. The backend containers serve up different web applications, and the Apache front-end unites them from a hostname and port standpoint. The following instructions describe how to configure Apache 2 on Mac OS X to proxy requests to Tomcat or Jetty running on localhost:8080. It also shows how to enable SSL on Apache and force it for certain URLs in your Java web application.

Apache comes pre-installed on OS X, so you should be able to start it by enabling "Web Sharing" in System Preferences > Sharing.

$APACHE_HOME on Leopard is /etc/apache2. On Tiger, it's /etc/httpd. If you've upgraded Tiger to Leopard, it's likely you'll have both directories so make sure you're modifying the right one. I lost a few hours figuring this out, so hopefully this knowledge will appease some googler in the future.

Configuring mod_proxy

1. Open $APACHE_HOME/httpd.conf and add the following on line 480 - at the very bottom, just before "Include /private/etc/apache2/other/*.conf".

   #
   # Proxy Server directives. 
   #
   <IfModule mod_proxy.c>
       ProxyRequests On
       ProxyPreserveHost On
   
       ProxyStatus On
       <Location /status>
           SetHandler server-status
   
           Order Deny,Allow
           Deny from all
           Allow from 127.0.0.1
       </Location>
   
       ProxyPass    /myapp    http://localhost:8080/myapp
   </IfModule>

   ProxyPreserveHost allows request.getServerName() and request.getServerPort() to work as if there is no proxy server in place. In other words, even though Tomcat is running on 8080, request.getServerPort() will return 80.

2. The most important line is the last one as this is the dictates the location of your applications. Add more lines as you need to add more applications.
3. If everything is configured correctly, you should be able to run sudo apachectl restart and navigate to http://localhost/status. If you receive a "forbidden" error, make sure your /etc/hosts has an entry mapping 127.0.0.1 to localhost (as one of the last entries), or change "Allow from 127.0.0.1" to "Allow from localhost". If you get a "Server not found" error, you can tail the error log at "/var/log/apache2/error_log".

One issue I've seen with mod_proxy is when a request comes in and the backend server is down. When this happens, Apache returns a 503 Service Temporarily Unavailable and it doesn't seem to go away after the backend server is restarted. It does resume proxying after a while, but I haven't determined what causes the proxy to come back to life. If you know a setting that forces mod_proxy to check for the backend server on every request, please let me know.

Configuring SSL

1. Open $APACHE_HOME/httpd.conf and uncomment the following on line 470:

   Include /private/etc/apache2/extra/httpd-ssl.conf

2. Open $APACHE_HOME/extra/httpd-ssl.conf and change line 78 to:

   ServerName localhost:443

3. In httpd-ssl.conf, change line 99 to:

   SSLCertificateFile "/private/etc/apache2/ssl.key/server.crt"

4. In httpd-ssl.conf, change line 107 to:

   SSLCertificateKeyFile "/private/etc/apache2/ssl.key/server.key"

5. In httpd-ssl.conf, add the following after SSLEngine on to allow proxying via HTTPS:

   SSLProxyEngine on

6. Follow the Using mod_ssl on Mac OS X tutorial. For "Common Name/Server Name", use "localhost". You can download the source for mod_ssl (which you need at one point during the tutorial) at http://www.modssl.org/source/.
7. Run sudo apachectl restart and go to https://localhost. If you get a "Server not found" error, run sudo apachectl -t to verify the syntax of your config files or tail -f /var/log/apache2/error_log to verify there are no errors in the log files.

Forcing HTTPS for certain URLs
If you proxy requests from /myapp -> http://localhost:8080/myapp, request.isSecure() will return false. If you change it to /myapp -> https://localhost:8443/myapp, request.isSecure() will return true. I needed to figure out a way to have http://localhost/myapp go to http://localhost:8080/myapp and https://localhost/myapp to go http://localhost:8443/myapp. Even better, I wanted to configure things in a way so request.isSecure() returned the value based on the originally requested URL, not on the proxied URL. Configuration like the following would be ideal:

ProxyPass    http://*/myapp    http://*:8080/myapp
ProxyPass    https://*/myapp   https://*:8443/myapp

The solution I came up with is to standardize on secure URLs in my application. That is, use /secure/* as a prefix for all URLs that should be accessed via SSL. To follow this convention and force it, I added the following in my application's web.xml file:

<security-constraint>
  <web-resource-collection>
    <web-resource-name>Secure Area</web-resource-name>
    <url-pattern>/secure/*</url-pattern>
  </web-resource-collection>
  <user-data-constraint>
    <transport-guarantee>CONFIDENTIAL</transport-guarantee>
  </user-data-constraint>
</security-constraint>

Once this is in place, accessing http://localhost/myapp/secure/index.html will result in an error. Accessing it using https will succeed. Following this, you can change your ProxyPass rules to the following and all requests to /secure/* will be https; other requests will be sent to http. The order of the rules below is important.

ProxyPass    /myapp/secure   https://localhost:8443/myapp/secure
ProxyPass    /myapp          http://localhost:8080/myapp

If this isn't a good strategy for you, Tomcat has the ability to use a redirectPort (in server.xml) that auto-redirects from http to https when CONFIDENTIAL is used in web.xml. I'm not sure if this redirect will carry through values from a form post.

Upgrading to Spring Security 2.0

This evening I spent a few hours and upgraded AppFuse to use Acegi Spring Security 2.0. The upgrade was fairly straightforward:

• %s/org.acegisecurity/org.springframework.security/g
• Upgraded dependencies (exclusions are necessary if you're using Spring 2.5.x and don't want 2.0.x dependencies pulled in):

  <dependency>
      <groupId>org.springframework.security</groupId>
      <artifactId>spring-security-core-tiger</artifactId>
      <version>${spring.security.version}</version>
      <exclusions>
          <exclusion>
              <groupId>org.springframework</groupId>
              <artifactId>spring-core</artifactId>
          </exclusion>
          <exclusion>
              <groupId>org.springframework</groupId>
              <artifactId>spring-support</artifactId>
          </exclusion>
      </exclusions>
  </dependency>
  ...
  <dependency>
      <groupId>org.springframework.security</groupId>
      <artifactId>spring-security-taglibs</artifactId>
      <version>${spring.security.version}</version>
      <exclusions>
          <exclusion>
              <groupId>org.springframework</groupId>
              <artifactId>spring-web</artifactId>
          </exclusion>
      </exclusions>
  </dependency>
  

• Changed taglib prefix from "authz" to "security" and change the associated taglib declaration to:

  <%@ taglib uri="http://www.springframework.org/security/tags" 
      prefix="security" %>
  

• In web.xml, I changed <filter-class> to org.springframework.web.filter.DelegatingFilterProxy. Since I didn't name my filter springSecurityFilterChain, I also had to add the following <init-param>:

      <init-param>
          <param-name>targetBeanName</param-name>
          <param-value>springSecurityFilterChain</param-value>
      </init-param>
  

• Lastly, I modified security.xml to use the new syntax. AppFuse's security.xml went from 175 lines to 33 with the new security namespace configuration!

It's hard to believe I first looked at Acegi almost 4 years ago. At that time, I said it contained too much XML for my needs. Ben's reaction:

Seriously, the "whole lotta XML" gives you exponentially more power and flexibility than a method such as this could ever hope to provide you.

It's nice to see that Spring Security 2.0 gives you exponentially more power and flexibility without all the XML. Thanks guys!

P.S. You can also view the full changelog for this upgrade.

Update: If you're using <authz:authentication property="fullName"/> in your JSPs, you'll need to change it to <security:authentication property="principal.fullName"/>.

Jetty and Resin closing in on Tomcat's popularity

From Greg Wilkin's Jetty Improves in Netcraft survey (again):

As with most open source projects, it's very hard to get a measure of who/how/where/why Jetty is being used a deployed. Downloads long ago became meaningless with the advent of many available bundling and distribution channels. The Netcraft Web Survey is one good measure, as it scans the internet and identifies which server sites run. In the results released April 2008, Jetty is identified for 278,501 public server, which is 80% of the market share of our closest "competitor" tomcat (identified as coyote in the survey). Jetty is currently 12th in the league table of identified servers of all types and will be top 10 in 6 months if the current trajectory continues.

If you look at the Netcraft numbers, you might also notice that Resin isn't far behind Jetty. If you look at the Indeed Job Trends graphs for the three, there seems to be some interesting information there too. The first graph is absolute and the second is relative.

tomcat, resin, jetty Job Trends

tomcat jobs - resin jobs - jetty jobs

tomcat, resin, jetty Job Trends

tomcat jobs - resin jobs - jetty jobs

If you're using Spring Dynamic Modules to deploy a web application, which server do you think is better? Both Tomcat 6 and Jetty 6 seem to work just fine in Equinox.

Spring MVC's Conventions get even better

Spring 2.5.3 was released this morning and contains a new feature I really like. When I first started working with Spring MVC's annotations (way back in November of last year), I found it awkward that I had to hard-code the URLs for my controllers into @RequestMappings on methods. Previous to annotations, I was using Spring's ControllerClassNameHandlerMapping which allows for more conventions-based URL-mappings.

With 2.5.3, @Controller and ControllerClassNameHandlerMapping have been synced up so you don't have to specify URLs in your annotations anymore. Thanks guys!

The Web Framework Smackdown Questions

I'm doing my Web Frameworks Smackdown this morning at TheServerSide Conference. A few weeks ago, I asked What Would You Ask the Web Framework Experts? on Javalobby and LinkedIn. Here's a summary of those questions:

• What is the overall performance of your framework as it compares to others?
• How does your web framework position themselves in relation to Web Beans?
• How easy is it to create a re-useable component in your framework? Is it as easy as sub-classing an existing component?
• What is the key differentiating characteristic of your framework that makes it better than the rest?
• What do you think about the various scopes introduced by Seam, e.g. conversation vs request or session? If you support these additional scopes, do you also provide some sort of concurrency control?
• Why can't we, the Java Community, come together and adopt the best application framework and settle the web development subject?
• What are you doing to help with developer productivity?
• 2008 is a huge year for the mobile web. How do you help developers build great mobile web applications?
• If you couldn't use your framework, what would you use and why?
• How do you enable rich Ajax applications?
• Can a developer make a change to source, and hit RELOAD in the browser to see the change? If not, why not?
• What do you think about the whole Flex revolution, and do you think you are competitors to this technology?
• How easy is it to create a module and plug it into a bigger application, complete with configuration, code, and view?

Of course, there's many more questions on the aforementioned pages, these are just some that I hope to ask during the panel. Sitting on the panel: Don Brown (Struts 2), Keith Donald (Spring MVC), Ed Burns (JSF), David Geary (GWT), Geert Bevin (RIFE/OpenLaszlo) and Justin Gehtland (Rails). I tried to get Flex and Grails folks, but they'd either left the conference already or are speaking at the same time.

Update: InfoWorld has some modest coverage of this event in Web frameworks debated at TheServerSide Java Symposium.

TSSJS Vegas Begins

This morning, I woke up early and headed down to the opening ceremonies for TheServerSide Java Symposium in Vegas. Joseph Ottinger and Eugene Ciurana kicked off the show and welcomed the seemingly large audience of Java Developers. After the introduction, Neal Ford delivered a keynote titled Language-Oriented Programming: Shifting Paradigms. You can download Neal's presentation from the TSSJS Wiki (requires creating an account).

I started live-blogging Neal's keynote, but quickly gave up when I realized it was going to be a very good talk and I'd miss the essence of it if I tried to write it down. So I closed my laptop, sat back and enjoyed. Neal is an excellent speaker and did a great job of telling a story of the next evolution in Java Development. First off, he talked about artwork, the Renaissance and the Age of Enlightenment.

The plethora of Frameworks today is similar to the Renaissance (where everyone painted Madonna and Child) in that they're all very similar, and most of them are configured with XML. XML is the external DSL that configures the framework and its needed to allow late-binding and flexibility. The reason folks use XML is because of Java's limitations as a language. There are better mechanisms (languages) to construct this DSL. He gave examples using Ruby and Groovy. Furthering the notion of DSLs are Language Workbenches that allow programmers to write DSLs that are IDE-aware, so tools like IntelliJ IDE can offer code completion and such. If DSLs are the next evolution of programming, then tools like IntelliJ's MPS (to be open sourced before year end) are going to become very important.

I think one of the most important things I took away was that the building blocks for the next generation of development is already there. Neal referenced Ola Bini and his idea of the Polygot Language Platform. He showed the following image of what the Polygot Platform might look like, where the Stable Layer is written in Java, it has a low-ceremony/dynamic language on top of it, and then a DSL that pertains to the particular application. If we start developing using this type of platform, we'll quickly move into our own Age of Enlightenment - where we're still using all the frameworks, we're just putting a prettier face (DSL) on them.

This was a very good talk that I enjoyed immensely. I'm glad I sat back and listened instead of typing like mad.

After Neal's Keynote, I went to Brian Goetz's talk on Java Performance Myths. In this session, Brian talked about how object allocation is no longer slow, benchmark frameworks are often flawed, (uncontended) synchronization is not slow and a couple other things. The room was packed and 10-20 people ended up standing up in the back. I didn't learn anything revolutionary as this talk seemed to be written a couple of years ago.

Following Java Performance Myths, I headed to my room to get some work done. On the way, I discovered the "gas is out" at the Venetian and it's recommended folks go across the street to eat lunch and such. I'm about to head back to the conference to grab some grub - it'll be interesting to see if this situation has caused any lunch chaos.

The Thin Server Architecture Working Group

From The Wisdom of Ganesh:

Peter Svensson has set up a website where like-minded people can discuss the brave new world of applications whose common characteristic is that no aspect of presentation logic resides on the server side. I admit that's an overly broad-brush generalisation, and it will be necessary to read what the various authors of this camp have to say.

I thought about doing something similar when I first read about SOFEA. I'm glad to see that someone has taken on this challenge. However, doesn't it seem ironic that this site doesn't use SOFEA/SOUI for its own architecture?

IMO, if this site isn't written with some sort of SOFEA-based framework like it advocates, it's pretty much worthless.

Proposal accepted for OSCON 2008

From an e-mail I received earlier this afternoon:

We are pleased to accept the following proposal for OSCON 2008.

* Web Frameworks of the Future: Flex, GWT, Grails and Rails

It has been scheduled for 16:30 on 23 Jul 2008.

My Abstract:

What if the choices in web framework was reduced to 4? If RIA are the way of the future, it's possible that these 4 frameworks are the best choices for this development paradigm. This session will explore these frameworks, as well as entertain many other's opinions on the future of web development.

RESTful backends are easy to create with both Rails and Grails. Ajax frontends are simple to create and maintain with GWT. Flex gives you flash and a pretty UI. If you're an HTML developer, Rails allows you to quickly develop MVC applications. If you're a Java Developer, GWT + Grails might be a match made in heaven. This session is designed to help you learn more about each framework and decide which combination is best for your project.

I'm really looking forward to learning about GWT and Flex in the coming months. If you have any experience (or opinions) about the abstract above, I'd love to hear it. The louder the better.

For those who haven't been, OSCON is one of those truly special conferences. Possible reasons:

• It's only an hour from my parent's house
• It's a beautiful time of year in Portland
• It's always the same weekend as the Oregon Brewers Festival
• It's a kickass conference with the greatest diversity of Open Source Committers

I'm going for all 4 reasons and even made a reservation to stay at The Kennedy School. Should be a fun show.

Grails vs. Rails - My Thoughts

In a comment, Jared Peterson asked:

I'm curious if you have any thoughts on folks that might be trying to make a decision between Rails and Grails. I like the concept of "Allow Both", but what if you "have neither"?

If you were starting a new project, could choose either one, needed to interact with a lot of existing Java code (JRuby on Rails I guess), what would you pick?

A friend recently asked me "Can I solicit your honest, unadulterated opinion on Grails?" I think the e-mail I sent him may help Jared's question.

I think it's awesome. IMO, it's the same thing as AppFuse, but it has a DSL that's much simpler to learn and remember. Less code -> faster productivity. There does seem to be some maturity issues, but I think it'll get there. The question is - how fast can Groovy become. It's similar to Rails and Ruby in that you start using Grails and you think "This Groovy thing is kinda cool, I'd like to learn more." One of the reasons I really like it is the learning curve for experienced open source Java Developers is virtually flat. You can learn enough to be productive in a single day.

That being said, I think there's also a lot of cool stuff going on with RIA. IMO, Flex or GWT + Grails would be a really fun set of tools to develop with. Here's a excerpt from a write-up I recently did when analyzing Rails and Grails at LinkedIn (in January):

--------
Comparing Rails and Grails
They're both excellent frameworks. Rails is definitely more mature, but the environment is a pain to setup (esp. on Windows). Grails is very easy to setup for Java Developers. Grails needs a lot of improvement as far as hot deploy and stack traces. It's probably Groovy's fault, but its stack traces are hideous - rarely pointing to the class and line number in the first few lines.

As for hot deploy, it doesn't work nearly as well as it does with Rails. Rails' "script/server" starts WEBrick in a few seconds, while "grails run-app" can take up to 10 seconds (even on a brand new application). Even with its warts, Grails is simply awesome. I really, really enjoy writing Groovy code in IDEA and seeing immediate changes. I don't like "test-app" as much as I like Rails' "test:units" (or even better, "test:uncommitted"). It seems to be widely realized that Rails has a better testing story.

Rails is immediate, Grails is immediate 70% of the time.

Groovy is extremely easy to learn for Java Developers. Ruby is easy too learn, and possibly too powerful for OO rookies. Both are fun to program in and very capable of allowing greater developer productivity. If you know Hibernate, Spring, SiteMesh and JSP, you owe it to yourself to look at Grails. If you know these technologies well, you can learn Grails in less than an hour. You can be productive in the next hour and have an application running by the end of the day. That's not to take anything away from Ruby. I believe that Rails is an excellent platform as well. It's pretty cool that profiling and benchmarking are built into the framework and you can easily judge how many servers you'll need to scale.

I used IDEA while developing with both frameworks. IDEA has Rails and Groovy support available via plugins and they both worked quite well. The support for Grails was much better than Rails. Grails offers code completion, Ctrl+click on classes/methods, debugging and starting/ stopping the webapp from your IDE. Rails doesn't offer much in the way of Ctrl+clicking on class names/methods or debugging.
--------

Is there anything that Rails can do that Grails can't? Not as far as I can tell. I think it really comes down to developer passion and team preference. If you have experienced Java Developers that like the ecosystem and its tools, Grails makes a lot of sense. If you have experienced PHP developers or frustrated J2EE developers, they might enjoy Rails more. One thing that's very cool about both frameworks - learning one actually teaches you things about the other. They're so similar in many respects that knowledge is transferable between the two.

Of course, this is all just my opinion after working with both frameworks for a few weeks. For anyone who has tried both, what do you think?

In closing, here's an excerpt from a recent comment I left on Javalobby:

Of course, the hard part now is deciding between Django, Rails, Grails and GWT for your web framework. Then again, that's like having to choose between a Ferrari, Porsche, Lamborghini and a Maserati. No matter which one you choose, it's unlikely you'll be disappointed.