Category: java

RESTful error handling with Tomcat and SpringMVC 3.x

Handling errors in a REST way is seemingly simple enough: upon requesting a resource, when an error occurs, a proper status code and a body that contains a parseable message and using the content-type of the request should be returned.
The default error pages in Tomcat are ugly. Not only they expose too much of the server internals, they are only HTML formatted and making them a poor choice if a RESTful web service is deployed in that Tomcat container. Substituting them to simple static pages is still no enough since I want a dynamic response containing error information.

Here’s how to do it in 3 simple steps:

Continue reading “RESTful error handling with Tomcat and SpringMVC 3.x”

Using Spring 3.0 MVC for RESTful web services (rebuttal)

Update Mar.04 Thanks to @ewolff some of the points described below are now official feature requests. One (SPR-6928) is actually scheduled in Spring 3.1 (cool!). I’ve updated the post and added all open tickets. Please vote!

This post is somewhat a response to InfoQ’s Comparison of Spring MVC and JAX-RS.
Recently I have completed a migration from a JAX-RS implementation of a web service to Spring 3.0 MVC annotation-based @Controllers. The aforementioned post on InfoQ was published a few days after my migration so I’m dumping below the list of problems I had, along with solutions.

Full list of issues:


Same relative paths in multiple @Controllers not supported
Consider two Controllers where I use a versioned URL and a web.xml file that uses two URL mappings:

@Controller
public class AdminController {
   @RequestMapping("/v1/{userId}")
   public SomeResponse showUserDetails(String userId) {
      ...
   }
}

@Controller
public class UserController {
   @RequestMapping("/v1/{userId}")
   public SomeOtherResponse showUserStreamtring userId) {
      ...
   }
}
In web.xml:
	<servlet-mapping>
	  <servlet-name>public-api</servlet-name>
	  <url-pattern>/public</url-pattern>
	</servlet-mapping>
	<servlet-mapping>
	  <servlet-name>admin-api</servlet-name>
	  <url-pattern>/admin</url-pattern>
	</servlet-mapping>

Continue reading “Using Spring 3.0 MVC for RESTful web services (rebuttal)”

Unit testing with Commons HttpClient library

I want to write testable code and occasionally I bump into frameworks that make it challenging to unit test. Ideally I want to inject a service stub into my code then control the stub’s behavior based on my testing needs.
Commons Http Client from Jakarta facilitates integration with HTTP services but how to easily unit test code that depends on the HttpClient library? Turns out it’s not that hard.
I’ll cover both 1.3 and the newer 1.4 versions of the library since the older v1.3 is still widely used.
Here’s some typical service (HttpClient v1.3) we want to test. It returns the remote HTML page title:

public class RemoteHttpService {
   private HttpClient client;
   
   public String getPageTitle(String uri)  throws IOException {
     String contentHtml = fetchContent(uri);
     Pattern p = Pattern.compile("<title>(.*)</title>");
     Matcher m = p.matcher(contentHtml);
     if(m.find()) {
        return m.group(1);
     }
     return null;
   }

   private String fetchContent(String uri)  throws IOException {
      HttpMethod method = new GetMethod("http://blog.newsplore.com/" + uri);
      int responseStatus = client.executeMethod(method);
      if(responseStatus != 200) {
        throw new IllegalStateException("Expected HTTP response status 200 " +
"but instead got [" + responseStatus + "]");
      }
      byte[] responseBody = method.getResponseBody();
      return new String(responseBody, "UTF-8");
   }

   public void setHttpClient(HttpClient client) {
      this.client = client;
   }
}

with the HttpClient is injected at runtime (via some IoC container or explicitly).
To be able to unit-test this code we have to come-up with a stubbed version of the HttpClient and emulate the GET method.

Continue reading “Unit testing with Commons HttpClient library”

New Spincloud feature: heat map overlay

heatmap-overlayIt took a while since the previous feature update to Spincloud. I have done a number of upgrades to the underlying tech and some intensive code refactoring but nothing visible. The time has come for another eye candy: heat maps. It is a map overlay that shows a color-translated temperature layer based on interpolated values of the current weather conditions. It gives a quick indication of the average temperature across all land masses where data is available.
Naturally in areas where data is more dense, the visual representation is better. The toughest job was to figure-out the interpolation math. I still have to refine the algorithm currently based on the inverse distance weighting algorithm which interpolates scattered points on a surface. Apparently a better one to use is kriging but I have yet to implement it.
The temperature map is generated from current temperatures and is updated once every hour. You can toggle the overlay by clicking the “Temp” button found on the top of the active map area.

Reviewing Google AppEngine for Java (Part 2)

In the first part I’ve left-off with some good news: successful deployment in the local GAE container. In this second part I’ll talk about the following:


Loading data and browsing
After finishing-off the first successful deployment, next on the agenda was testing out the persistence tier but for this I needed some data to work with in the GAE datastore.
Along with the local container Google makes available a local datastore but so far the only way to populate the datastore is described here and it uses python. Furthermore, currently there is one documented way to browse the local datastore using the local development console but this again requires the python environment. There’s a hint from Google though that there will be a data viewer for the Java SDK. In the mean time I voted up the feature request.

Back to bulk loading, after voting on the feature request to have a bulk uploader, I decided not to use the python solution but to handcraft a loader that will fill-in two tables: COUNTRY and COUNTRY_STATE (for federated countries like US and CAN). Since there’s no way to schedule worker threads (but is on it’s way) the only mechanism to trigger the data loading is via URLs. I’m using Spring 3.0 and so it wasn’t hard to create a new @Controller, some methods to handle data loading then map them to URLs:

@Controller
public class BulkLoadController {
	@RequestMapping("/importCountries")
	public ModelAndView importCountries() {
           ...
        }
	@RequestMapping("/importProvinces")
	public ModelAndView importProvinces() {
           ...
        }
}

Continue reading “Reviewing Google AppEngine for Java (Part 2)”

Upgrading to Spring 3.0.0.M3 and Spring Security 3.0.0.M1

A short two months back I posted an article describing how to upgrade to Spring 3.0 M2. Spring folks are releasing at breakneck speed and so I got busy again upgrading spincloud.com to Spring 3.0 M3 released at the beginning of May. Just yesterday (June 3rd) the team released Spring Security 3.0 M1 and I decided to roll this in Spincloud as well.

Upgrading Spring Security from 2.0.4 to 3.0.0 M1
For Spring Security 3.0.0 M1 I’m doing a “soft” upgrade since I had done my homework when I migrated from Acegi. I won’t use any of the new 3.0 features, just getting ready to use them.

To digress a bit, Spring Security a technology that is harder to swallow due to its breadth. To simplify the picture, Spring Security (former Acegi) provides three major security concerns to enterprise applications:
– Authorization of method execution (either through standard JSR-250 JEE security annotations or via specific annotation-based method security).
– HTTP Request authorization (mapping URLs to accessible roles using Ant style or regexp’ed paths, dubbed channel security).
– Website authentication (integrating Single Sign On (SSO) services by supporting major SSO providers, HTTP BASIC authentication, OpenId authentication and other types).
For Spincloud I’m using OpenId for authentication and Channel Security to secure website pages.
Continue reading “Upgrading to Spring 3.0.0.M3 and Spring Security 3.0.0.M1”

Reviewing Google AppEngine for Java (Part 1)

appengine_lowres

When Google announced that Java is the second language that the Appengine will support I almost didn’t believe it given the surge of the new languages and the perception that Java entered legacy but the JVM is a powerful tried-and-true environment and Google saw the potential of using it for what it is bound to

become: a runtime environment for the new and exciting languages (see JRuby and Grails). The JVM is the new gateway drug in the world of languages.

Note: I’ll break down this review into two posts as it’s too extensive to cover everything at once. This first part is about initial setup, JPA and some local webapp deployment issues. In the second part I’ll describe how to load data into the datastore, data indexing, how I reached some of the limitations of the AppEngine and how to get around some of them.

I managed to snatch an evaluation account and last few days I have been playing with it. (as of today Google opened the registrations to all). My goal was (again) simple: to port Spincloud to the AppEngine. The prize: free hosting which amounts to $20/month in my case (see my post about Java hosting providers), some cool monitoring tools that I can access on the web and of course the transparent super-scalability that Google is touting, in case I get techcrunched, slashdotted or whatever (slim chances but still…).
I am a couple of weeks into the migration effort and I can conclude that the current state of the AppEngine is not quite ready for Spincloud as I’ll detail below but it comes quite close. The glaring omission was scheduling but Google announced today that the AppEngine will support it (awesome!) and I plan to use it from day one.

My stated goal is running Spincloud on AppEngine. Here are the technologies I use in Spincloud:
– Spring 3.0 (details here)
– SpringAOP
– SpringSecurity with OpenId
– Webapp management with JMX (I know, it won’t fly)
– Job scheduling using Spring’s Timer Task abstraction (not optimistic about this one either)
– SiteMesh (upgraded to 2.4.2 as indicated)
– Spatial database support including spatial indexing
– JPA 2.0 (back story here)
– Level 2 JPA cache, query cache.
– Native SQL query support including native SQL spatial queries.
– Image processing (spincloud scraps images and processes pixel-level information to get some weather data)
Continue reading “Reviewing Google AppEngine for Java (Part 1)”

Selecting location data from a spatial database

I have been thinking to write about this subject a while back when project Spincloud was still under development. I was even thinking about making this the first post on my blog.
The idea is simple: you have location-based data (POIs for instance) stored in some database (preferably a spatial DB) and now you want to perform a select statement that will indicate the area that should include the points we want. In case of Spincloud’s weather map, we want the weather reported by the stations located within a given area determined by the Google Map viewport that the user is currently browsing.
In all my examples I’ll use SQL Spatial Extensions support, specifically MSQL spatial extensions.
Here’s a visual representation of the spatial select (the red grid is the area where we want to fetch the data):

select_smpl

This is quite easy to accomplish by issuing a spatial select statement on the database:

select * from POI where Contains(GeomFromText
    ('POLYGON ((-30 32, 30 -8, -89 -8, -89 32, -30 32))', LOCATION))

But what about selecting an area that crosses the 180 degrees longitude? Let’s say we want to select data in an area around New Zealand that starts at 170 degrees latitude and ends at -160 degrees latitude going East. The selected area will look like this:
Continue reading “Selecting location data from a spatial database”

Evaluating EclipseLink 1.1

As I’m using the ubiquitous Hibernate 3.3 as the JPA 1.0 provider for Spincloud, I decided to try out another one. I had tried OpenJPA (spawned from Kodo JDO) when they only supported build-time bytecode enhancement and it was a pain to make it work. It worked all right but boy what a pain. There’s now an agent to provide on-the-fly enhancement but I’ll take transparent enhancement anytime.
I’ve heard about EclipseLink before. The project started when Oracle donated the respectable TopLink project to the Eclipse foundation. If the solid reputation behind TopLink was a good enough argument for me to try it, the announcement that it will be the JPA 2.0 reference implementation convinced me that I should try it out.
My goal is to evaluate if EclipseLink is production-ready. I’m applying a complex set of evaluation criteria (joking): if it can run Spincloud then it is (I was inspired by Seifer’s interview on Infoq about Ruby VMs; when asked what was the criteria for qualifying if a Ruby VM is production ready, he answered: if it runs Rails).

I have the following JPA requirements:
– column mappings, one-to-one, one-to-many
– supports BLOB fields
– supports NamedQueries and NamedNativeQueries
– support for object cache and query cache
– deployment/operational nice to have: ease of maintaining compatibility with both EclipseLink and Hibernate in the source code and runtime. Ideally I should plug-in any JPA provider without changing a single line of code. This was not attainable as I’ll explain below.

I started by downloading the binaries. I’m using Maven to bring the jars so I’ve followed the instructions here. I only changed the version since I wanted to use v1.1.0:

  <dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>eclipselink</artifactId>
    <version>1.1.0</version>
    <scope>provided</scope>
  </dependency>

There’s a single jar file called eclipselink-1.1.0.jar downloaded which is a nice change from the multitude of Hibernate jars I was accustomed with.
Continue reading “Evaluating EclipseLink 1.1”

Choosing a Java hosting provider

TL;DR: Go for a VPS. I now use Digitalocean, they’re awesome.

Selecting a web hosting provider is a tough job for any web developer that wants to put a Java/JEE web application online. The choice is much simpler when it comes to publishing a PHP web site and there are a load of cheap (and sometimes quite reliable) PHP hosting providers to choose from with LAMP being the de facto standard in the web hosting world. But when it comes to Java hosting providers the picture becomes blurrier. The common thing that all these environments need is a Java container. The most popular choice is Tomcat but there are providers that use Resin, Weblogic or Websphere (the latter two are full fledged JEE containers).
With the raise of lightweight J2EE servers started by the Spring folks, a little revolution began in the Java world: running enterprise-grade JEE webapps without the need for an EJB container; a servlet container is enough. Tomcat should fill the bill for just about any Java web application that doesn’t use EJBs. The advantage that comes from running a servlet container is the smaller footprint compared with an EJB container. This is critical when it comes to selecting hosting environments since you’re paying for resources (especially RAM) that have to be sized to accommodate the memory requirements of the web application.

Self hosting: Home-based dedicated server (near $0)
homepcYou can use your home internet connection and a PC where the web container runs and deploys your web application. There is an obvious advantage since the server is physically located close to the development team: complete control and physical access to the machine. The other big plus is the price: you’re already paying for the internet connection and chances are you already have a PC that can be transformed into a server. And chances are that you already have a development environment that can be the basis of the production deployment. Here are the shortcomings:- Bandwidth limitations: the webserver where the webapp lives will upload content to the web browsers that access the application. The upload bandwidth is smaller than the download bandwidth and will result in longer load times for web clients.
– Some internet providers cap the internet traffic so you may run beyond the limit.
– You may violate contractual obligations you agreed with your Internet provider by running your own web server.
– The internet connection is not reliable: provider’s downtime directly translates in downtime for your webapp.
Continue reading “Choosing a Java hosting provider”