Dropwizard Java REST services

To sum it up; Dropwizard rocks.

I’ve done quite a bit of WS development both the on client side and server side; interacting with both SOAP, REST and variants of XML/JSON RPC hybrid services. For my latest project I need to expose a set of REST services to a myriad of clients: phones, fat JS clients etc. This application also needs to talk to other nodes or “agents” that are also doing work in a distributed cloud environment. The core engine of this application really has no need for a bloated higher level MVC/gui supporting stack and bringing that into this library would just be a pain. I’ve always like the simplicity of being able to skip the whole JEE/Spring/Tomcat based container stack and just do a plain old “java -jar”… run my application…. but the reality of being able to do that has been lacking… until now.

In looking at the available options for picking the framework to use (such as Restlet, Spring-MVC REST, Spring Data REST etc and others), I immediately became discouraged when looking at examples for setting them up; they are full of complexity and lots of configuration and generally require a full application server container to run within, which just adds further complexity to your setup.

Then I stumbled across Dropwizard by the folks at Yammer. I encourage everyone reading this to just try the simple Hello World example they have on their site. If you have any experience in this space and an appreciation and vision for decoupling; you will immediately recognize the beauty of this little framework and the power it can bring to the table from a deployment standpoint. Build your core app engine back-end library as you normally would, toss in Dropwizard, expose some REST services to extend your interfaces to the outside world; throw it up on a server and “java -jar myapp server myconfig.yml” and you are ready to rock. (they make this possible by in-lining Jetty). Create a few little JS/HTML files for a fat JS client, (i’d recommend Angular) and hook into your REST services and you will have an awesome little decoupled application.

Integrating Restlet with Spring

For those of you out there who would like to get Restlet 2.0 (currently the M5) release up integrated with your existing Spring application, hopefully this post will be of some help. I recently had to do this and unfortunately the documentation related to Spring integration on the Restlet site is scattered across various docs and some of it appears out of date. What I am describing below worked with source code straight from the Restlet SVN trunk just before the M5 release so you should be good to go if you use the M5 release (JEE edition)

First off, I am assuming you have an existing web application with a web.xml file and are using Spring. Secondly I am just trying to give you some working web.xml and the corresponding Spring configuration to get up and running. I am not explaining the details of how Restlet works as you can find that on the Restlet site.

First you will want to make sure you have the Restlet JEE 2.0 M5 edition. Make sure you grab the JEE version and not the JSE version as the latter does not include the Spring integration extension. Once downloaded extract the ZIP to a location on your drive. The JEE zip package contains a ton of Restlet Jar files. The three we care about are org.restlet.jar, org.restlet.ext.spring.jar, org.restlet.ext.servlet.jar

If you are using Maven you can add the following repository and dependencies to your POM by using the repository instructions on the Restlet site. NOTE as of today: the Restlet repository currently does NOT have the M5 release up there so you are going to manually have to add the M5 jar to your repository by doing the following for each of the 3 jars.

mvn install:install-file -Dfile=/PATH/TO/RESTLET-m5-ZIP-EXTRACT-DIR/lib/org.restlet.jar -DgroupId=org.restlet -DartifactId=org.restlet -Dversion=2.0-SNAPSHOT-M5 -Dpackaging=jar

mvn install:install-file -Dfile=/PATH/TO/RESTLET-m5-ZIP-EXTRACT-DIR/lib/org.restlet.ext.spring.jar -DgroupId=org.restlet -DartifactId=org.restlet.ext.spring -Dversion=2.0-SNAPSHOT-M5 -Dpackaging=jar

mvn install:install-file -Dfile=/PATH/TO/RESTLET-m5-ZIP-EXTRACT-DIR/lib/org.restlet.ext.servlet.jar -DgroupId=org.restlet -DartifactId=org.restlet.ext.servlet -Dversion=2.0-SNAPSHOT-M5 -Dpackaging=jar

The above 3 commands will manually install the three Jars into your Maven repository. Next you can configure your POM to add the official Maven repository plus the dependencies to the 3 Jars you installed above. Note that the repository entry is sort of meaningless at this point because you manually installed the jars above. It is IMPORTANT that the version elements in your dependencies below MATCH exactly the versions you specified in the commands above!

	<repository>  
    	<id>maven-restlet</id>  
    	<name>Public online Restlet repository</name>  
    	<url>http://maven.restlet.org</url>  
	</repository>

	<dependency>
    	<groupId>org.restlet</groupId>
    	<artifactId>org.restlet</artifactId>
    	<version>2.0-SNAPSHOT-M5</version>
	</dependency>

	<dependency>
    	<groupId>org.restlet</groupId>
    	<artifactId>org.restlet.ext.spring</artifactId>
    	<version>2.0-SNAPSHOT-M5</version>
	</dependency>

	<dependency>
    	<groupId>org.restlet</groupId>
    	<artifactId>org.restlet.ext.servlet</artifactId>
    	<version>2.0-SNAPSHOT-M5</version>
	</dependency>

Ok, great. Next we need to configure your web.xml, open it up and add the following entries in the appropriate spots:

  	<servlet>
      	<servlet-name>myRESTApi</servlet-name>
      	<servlet-class>org.restlet.ext.spring.SpringServerServlet</servlet-class>
      	 <init-param>
                <param-name>org.restlet.component</param-name>
                 <!-- this value must match the bean id of the Restlet component you will configure in Spring (below) -->
                <param-value>restletComponent</param-value>
         </init-param>
  	</servlet>

  	<servlet-mapping>
        <servlet-name>myRESTApi</servlet-name>
        <url-pattern>/my/REST/api/*</url-pattern>
  	</servlet-mapping>

Now your web.xml is configured to take all requests to /my/REST/api/* and send those to a Restlet Component which you will wire up in your Spring configuration. So... bring up your applicationContext.xml or whatever you have it named and add the following entries:

<!-- our SpringComponent which binds us to the Restlet servlet configured above -->
<bean id="restletComponent" class="org.restlet.ext.spring.SpringComponent">
         <!-- the defaultTarget for this component is our Restlet Application -->
	<property name="defaultTarget" ref="myRestletApplication" />
</bean>

<!-- your Restlet application. This class extends "org.restlet.Application" -->
<bean id="myRestletApplication" class="my.restlet.MyRestletApplication">
         <!-- all requests to this Application will be sent to myPath2BeanRouter -->
	<property name="root" ref="myPath2BeanRouter"/>
</bean>

<!-- This router automagically routes requests to beans that extend org.restlet.resource.ServerResource or org.restlet.Restlet who's name starts with a "/" slash which matches the request-->
<bean name="myPath2BeanRouter" class="org.restlet.ext.spring.SpringBeanRouter"/>
 
<!-- This extension of org.restlet.resource.ServerResource bean will handle all requests to made to /my/REST/api/myResource (GET/POST/PUT etc) 
This class extends "org.restlet.Restlet" or "org.restlet.resource.ServerResource" -->
 <bean name="/myResource" autowire="byName" scope="prototype" 
    		class="my.restlet.package.resources.MyResourceBean">
    		
    	<property name="somePropertyOfMine" ref="someOtherSpringBean"/>
 </bean>

Ok, well if you were having trouble trying to get Spring working with Restlet I hope this helped get you rolling. Restlet is a cool project that works great and can get a REST API up and running pretty quickly (granted you are good at crawling through somewhat scattered documentation) Here are a few other links which you may want to reference:

Restlet 2.0 Extensions API
Restlet 2.0 JEE API

Also, I am posting the following error messages that troubled me when trying to get this to work. The configuration I show above was the result of getting beyond the below errors by using the correct fixed releases. To AVOID the errors below, ENSURE you are using Restlet 2.0 M5 or a custom build from the trunk. Prior to 9/25/09 people were getting the errors below.

Message ID
No target class was defined for this finder
Complete Message org.restlet.ext.spring.SpringFinder $$ EnhancerByCGLIB

Review: RESTful Web Services

This is a book review for “RESTful Web Services” by Leonard Richardson and Sam Ruby

If you want to get under the hood and really understand how to properly implement a RESTful web service then this book is for you. The treatment of the topic is excellent. After reading this book, I feel that so many folks out there writing “REST” apis, myself included, have written variants of a REST-RPC hybrid, versus a true REST implementation. REST after all in its true form is really a total change of mindset when it comes to creating a web-service and this book helps you get there. The author does not turn this into a REST vs. SOAP discussion but rather preps the reader quite well by exploring the history of web-services and very clearly explaining the differences between all the different approaches, and positives/negatives of each (RPC, REST-RPC, SOAP, WS-*, etc) Secondly the author give a primer on the basic tools used to implement REST clients in various languages by covering the various popular HTTP client libs out there (cURL, Apache HttpClient, rest-open-uri, libcurl etc). The author also presents a discussion and explanation of “Resource Oriented Architecture” and walks the reader through several example implementations (both Read-only and read-write) as well as the RESTful thought process behind the design. The author gives excellent treatment to the differences between when to use a PUT vs. POST and explains the rules around making that decision, which, can be difficult to understand which to use in the real world. The book also shows various ways of implementing a REST service when some of the HTTP methods simply are not available (primarily PUT/DELETE) due to your HTTP server setup. Lastly the book covers some server-side frameworks that are available and the one I found the most interesting, which I hope to work with soon, is the Java project called Restlet.

Readers will also find the HTTP status code and headers reference very valuable, as for each status code/header, the author gives very clear descriptions of their meaning in a RESTful web-service. Very valuable!

Recommeded? Yes, go get it today.
Skills: Java/Ruby/Python – intermediate to advanced.

Advanced HTTP operations in Flex outside of AIR

I am currently pretty deep into a Flex/AS3 RIA desktop app project whereby I have several advanced needs. Such as to download partial files to the desktop (byte-range requests), execute HEAD requests to get remote file sizes, execute multipart POSTs, talk to some REST apis, and finally be able to read any write HTTP headers….. outside of AIR? Good luck with URLStream, URLRequest, URLRequestMethod and URLRequestHeader

Due to security sandbox restrictions, unless your application is running within Adobe AIR you are restricted to simple GETs and POSTs. You are also NOT allowed to touch the following headers:

Accept-Charset, Accept-Encoding, Accept-Ranges, Age, Allow, Allowed, Authorization, Charge-To, Connect, Connection, Content-Length, Content-Location, Content-Range, Cookie, Date, Delete, ETag, Expect, Get, Head, Host, Keep-Alive, Last-Modified, Location, Max-Forwards, Options, Origin, Post, Proxy-Authenticate, Proxy-Authorization, Proxy-Connection, Public, Put, Range, Referer, Request-Range, Retry-After, Server, TE, Trace, Trailer, Transfer-Encoding, Upgrade, URI, User-Agent, Vary, Via, Warning, WWW-Authenticate, x-flash-version.

That’s basically all of the ones I needed to touch…..so what to do? In my case I was developing some file management functionality that runs in both Adobe AIR as well as MDM Zinc. Amongst other protocols such as FTP, I needed to be able to pull file updates over HTTP as well (+authentication, HEAD checks etc). So I had to create an generic IHttpClient interface abstraction which then allowed me to implement runtime specific clients. So for the AIR side of things I was good to go by using all of Adobe’s URL* classes right out of the box and they work great for the AirHttpClient implementation of my interface. However for my Zinc client I was still stuck, until I ran across a fantastic little HTTP library out there that provides a custom HTTP library built on top of the Flex socket stack.

The AS3 library that ended up being used in my ZincHttpClient was: as3httpclientlib. as3httpclientlib solved all of my problems when running outside of the AIR environment. With as3httpclientlib you can do all of the following and more:

* GET, HEAD, PUT, POST, DELETE
* multipart/form-data (PUT and POST)
* HTTPS support using AS3Crypto TLS
* Post with application/x-www-form-urlencoded
* Reading chunked (Transfer-Encoding)

If you have the need to access a bit more advanced HTTP functionality and need to do it outside of the AIR runtime. I HIGHLY recommend as3httpclientlib. I have put this library through the works doing byte range requests, HEAD requests, header manipulation and downloading and posting all sorts of file sizes, the library works great. My only note is that it is a tad slower than URLStream based HTTP downloads under Adobe AIR, regardless, this little HTTP library is worth it. Kudos to the AS3HttpClientLib team!