Presented at DevNexus 2013

1. Spring MVC to iOS and the REST
Roy Clarkson, Senior Engineer, VMware
Twitter/GitHub: @royclarkson
Josh Long, Spring Developer Advocate
Twitter: @starbuxman GitHub: @joshlong
© 2013 SpringSource, by VMware

2. About Roy Clarkson
• Georgia Tech Alum
• SpringSource Engineer at VMware
• Lead on Spring for Android and Spring Mobile
• Twitter/GitHub: @royclarkson
• rclarkson@vmware.com
• http://www.slideshare.net/royclarkson
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3. About Josh Long (⻰龙之春)
Spring Developer Advocate
twitter: @starbuxman
weibo: @springsource
josh.long@springsource.com
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4. About Josh Long
Spring Developer Advocate
twitter: @starbuxman
josh.long@springsource.com
Contributor To:
•Spring Integration
•Spring Batch
•Spring Hadoop
•Activiti Workflow Engine
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5. Agenda
• REST
• Spring MVC
• iOS
• Demos
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6. The term Representational State Transfer was introduced and
defined in 2000 by Roy Fielding in his doctoral dissertation.
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7. What is REST?
• REpresentational State Transfer
• An architectural style for designing distributed systems
• Not a standard, but rather a set of constraints
– Client/Server, Stateless, Uniform Interface, etc.
• Not tied to HTTP, but associated most commonly with it
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8. The Principles of REST
• Resources
– Expose directory structure-like URIs
– URI’s should be easily understood
• Representations
– Transfer XML, JavaScript Object Notation (JSON), or both
– Use XML or JSON to represent data objects or attributes
• Messages
– Use HTTP methods explicitly (i.e. POST, GET, PUT,
DELETE)
– CRUD operations can be mapped to these existing methods
• Stateless
– State dependencies limit or restrict scalability
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9. What is HATEOAS?
• Hypermedia As The Engine Of Application State
• The client doesn’t have a built in knowledge of how to
navigate and manipulate the model
• Instead server provides that information dynamically to the
user
• Implemented by using media types and link relations
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10. HTTP GET
• Retrieve information
– Must be safe and idempotent
• Can have side effects, but since the user doesn’t expect
them, they shouldn’t be critical to the operation of the
system
• GET can be conditional or partial
– If-Modified-Since
– Range
GET /pizzas/1
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11. HTTP DELETE
• Request that a resource be removed
• The resource doesn’t have to be removed immediately
– Removal may be a long running task
DELETE /pizzas/1
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12. HTTP PUT
• Requests that the entity passed be stored at the URI
• Can be used to create a new entity or modify an existing
one
– Creation of new entities is uncommon as it allows the client
to select the id of the new entity
PUT /toppings/1
{ “name” : “Cheese” }
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13. HTTP POST
• Requests that the resource at a URI do something with the
enclosed entity
• The major difference between POST and PUT are what
resource the request URI identifies
• For example, use PUT to create and POST to modify
POST /toppings/1
{ “name” : “Cheddar Cheese” }
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14. HTTP Status Codes
• Status codes are an indicator the result of the server’s
attempt to satisfy the request
• Broadly divided in categories
– 1XX: Informational
– 2XX: Success
– 3XX: Redirection
– 4XX: Client Error
– 5XX: Server Error
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15. Success Status Codes
• 200 OK
– Everything worked
• 201 Created
– The server has successfully created a new resource
– Newly created resource’s location returned in the Location
header
• 202 Accepted
– The server has accepted the request, but it is not yet
complete
– A location to determine the request’s current status can be
returned in the Location header
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16. Client Error Status Codes
• 400 Bad Request
– Malformed Syntax
– Should not be repeated without modification
• 401 Unauthorized
– Authentication is required
– Includes a WWW-Authenticate header
• 403 Forbidden
– Server has understood, but refuses to honor the request
– Should not be repeated without modification
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17. Client Error Status Codes
• 404 Not Found
– The server cannot find a resource matching a URI
• 406 Not Acceptable
– The server can only return response entities that do not
match the client’s Accept header
• 409 Conflict
– The resource is in a state that is in conflict with the request
– Client should attempt to rectify the conflict and then resubmit
the request
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18. Media Types
• Accept & Content-Type HTTP Headers
• Client or server describes the content
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20. Spring Web MVC DispatcherServlet
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21. Annotations of Spring MVC
• @Controller
• @RequestMapping
• @RequestParam
• @PathVariable
• @ResponseBody
• @RequestBody
• @ResponseStatus
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22. @Controller
@Controller
public class PizzaController {
...
}
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23. @RequestMapping
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// POST /pizzas/bake
@RequestMapping(value = "/bake", method = POST)
public void bake() {
...
}
}
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24. @RequestParam
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// POST /pizzas/bake?temp=400
@RequestMapping(value = "/bake", method = POST)
public void bake(@RequestParam Integer temp) {
...
}
}
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25. @PathVariable
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// POST /pizzas/bake/400
@RequestMapping(value = "/bake/{temp}", method = POST)
public void bake(@PathVariable Integer temp) {
...
}
}
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26. @ResponseBody
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// GET /pizzas
@RequestMapping(
method = GET, produces = "application/json")
public @ResponseBody List<Pizza> list() {
...
}
}
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27. @ResponseBody
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// GET /pizzas
@RequestMapping(method = GET,
produces = MediaType.APPLICATION_JSON_VALUE )
public @ResponseBody List<Pizza> list() {
...
}
}
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28. @RequestBody
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// PUT /pizzas
@RequestMapping(
method = PUT, consumes = "application/json")
public void create(@RequestBody Pizza pizza) {
...
}
}
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29. @ResponseStatus
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
// PUT /pizzas
@ResponseStatus(HttpStatus.CREATED)
@RequestMapping(
method = PUT, consumes = "application/json")
public void create(@RequestBody Pizza pizza) {
...
}
}
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30. Async MVC Processing: Callable
@Controller
@RequestMapping("/pizzas")
public class PizzaController {
@RequestMapping(value = "/orders", method = POST)
@ResponseBody
public Callable<String> upload(MultipartFile file) {
return new Callable<Pizza>() {
public Pizza call() throws Exception
// ...
return pizza;
}
}
}
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31. Async MVC Processing: DeferredResult
@RequestMapping("/quotes")
@ResponseBody
public DeferredResult quotes() {
DeferredResult deferredResult = new DeferredResult();
// Add deferredResult to a Queue or a Map...
return deferredResult;
}
// In some other thread:
// Set the return value on the DeferredResult
deferredResult.set(data);
- thread managed outside of Spring MVC
- JMS or AMQP message listener, another HTTP request, etc.
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32. Async MVC Processing: AsyncTask
@RequestMapping(name =“/upload”,
method=RequestMethod.POST)
public AsyncTask<Foo> processUpload(MultipartFile file) {
TaskExecutor asyncTaskExecutor = new AsyncTaskExecutor(...);
return new AsyncTask<Foo>(
1000L, // timeout
asyncTaskExecutor, // thread pool
new Callable<Foo>(){ ..} // thread
);
}
- same as Callable, with extra features
- override timeout value for async processing
- lets you specify a specific AsyncTaskExecutor
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33. Message Converters
• RSS/ATOM
• java.awt.BufferedImage
• JSON
• JAXB
• Write your own!
– iCal
– GSON
• Third Party:
• https://github.com/joshlong/spring-advanced-marhshallers-and-service-exporters
– supports Google PB, Avro, Thrift, MessagePack, Google Snappy
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34. Spring MVC Demo

35. Testing
• Testing of web APIs isn’t easy
– In container, end-to-end, string comparison, etc.
– Out of container, Java objects, bypassing much of Spring’s
magic
• What we want is out of container, but with as much of
Spring as we can get
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36. Spring MVC Testing
• Available in Spring 3.2
• Bootstraps most of Spring’s MVC infrastructure so that
you unit and integration test your web application end-to-
end
• Provides APIs for testing interesting parts of requests and
responses
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38. REST on iOS
• HTTP Client
– NSURLConnection
• JSON Processor (iOS 5)
– NSJSONSerialization
• Data
– NSData
– NSDictionary
– NSArray
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39. NSURLConnection
• Loading Data Synchronously
+ sendSynchronousRequest:returningResponse:error:
• Loading Data Asynchronously
+ sendAsynchronousRequest:queue:completionHandler:
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40. Basic HTTP Request
NSURL *url = [NSURL URLWithString:@"http://localhost"];
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSData *data = [NSURLConnection sendSynchronousRequest:request
returningResponse:nil
error:nil];
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41. Basic HTTP Request... Improved
NSURL *url = [NSURL URLWithString:@"http://localhost"];
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSURLResponse *response;
NSError *error;
NSData *data = [NSURLConnection sendSynchronousRequest:request
returningResponse:&response
error:&error];
NSInteger status = [(NSHTTPURLResponse *)response statusCode];
if (status == 200 && data.length > 0 && error == nil)
{
// do something with data
}
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42. Asynchronous HTTP Request
NSURL *url = [NSURL URLWithString:@"http://localhost"];
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
[NSURLConnection
sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response,
NSData *data, NSError *error)
{
NSInteger status = [(NSHTTPURLResponse *)response statusCode];
if (status == 200 && data.length > 0 && error == nil)
{
// do something with data
}
}
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43. HTTP Headers
NSURL *url = [NSURL URLWithString:@"http://localhost"];
NSMutableURLRequest *request =
[[NSMutableURLRequest alloc] initWithURL:url];
[request setHTTPMethod:@"PUT"];
[request setValue:@"application/json"
forHTTPHeaderField:@"Accept"];
[request setValue:@"application/json"
forHTTPHeaderField:@"Content-Type"];
[request setValue:contentLength
forHTTPHeaderField:@"Content-Length"];
[request setHTTPBody:postData];
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44. JSON Serialization
// deserialize JSON data
NSError *error;
NSDictionary *d = [NSJSONSerialization JSONObjectWithData:data
options:0
error:&error];
// serialize JSON data
NSError *error;
NSData *data = [NSJSONSerialization dataWithJSONObject:dictionary
options:0
error:&error];
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45. iOS Demo

46. Conclusion
• API Design Matters
– URIs represent resources, not actions
– HTTP verbs are general, but can be used in ways that make
anything possible
• Implementation isn’t rocket science
– Spring MVC
– Spring HATEOAS
• Easy testing
– Out-of-container, but full Spring stack
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47. More Information
• Roy Fielding’s Dissertation
http://www.ics.uci.edu/~fielding/pubs/dissertation/
evaluation.htm#sec_6_1%7C
• Spring MVC Reference
http://static.springsource.org/spring-framework/docs/
current/spring-framework-reference/html/mvc.html
• URL Loading System Programming Guide
http://developer.apple.com/library/ios/#documentation/
Cocoa/Conceptual/URLLoadingSystem/
URLLoadingSystem.html
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48. Related Spring Projects
• REST Shell
https://github.com/SpringSource/rest-shell
• Spring HATEOAS
https://github.com/SpringSource/spring-hateoas
• Spring MVC Test
https://github.com/SpringSource/spring-test-mvc
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49. Questions?
• All Sample Code:
https://github.com/royclarkson/rest-demo
https://github.com/joshlong/the-spring-tutorial
• Presentation:
http://www.slideshare.net/royclarkson
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