Oop2008 RESTful services with GWT and Apache CXF


Published on

A paper I presented at OOP 2008 in Munich.

Published in: Technology
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Oop2008 RESTful services with GWT and Apache CXF

  1. 1. Building and consuming RESTful JSON services with Apache CXF and Google Web Toolkit Adrian Trenaman, Distinguished Consultant, IONA Technologies services@iona.com 1
  2. 2. Introduction Google Web Toolkit provides an excellent toolkit for RESTful AJAX clients. … but doesn’t provide a compelling solution for the server side. Apache CXF provides a framework for building RESTful servers. GWT and CXF together offer a compelling solution. Agenda: GWT overview A RESTful “Hello, World” (in time honoured tradition) A document-oriented RESTful service This is a technical session; This is a technical session; Convention-based services expect to learn enough about expect to learn enough about Using JSON payload GWT and CXF to go out and GWT and CXF to go out and build your own solutions. build your own solutions. GWT client techniques © 2008 IONA Technologies 2
  3. 3. Google Web Toolkit (GWT) – a brief overview © 2008 IONA Technologies 3
  4. 4. GWT – overview GWT allows you to build dynamic web applications in Java… • Your Java is compiled into cross-browser Javascript. Key components: JRE emulation library, web UI library, java-to-js compiler, and a hosted web browser for debugging. © 2008 IONA Technologies 4
  5. 5. GWT – overview (cont’) GWT is available as open-source under Apache Public License (APL) 2.0. • Website: http://code.google.com/webtoolkit Benefits of GWT: • Small application footprint (~100Kb) • Excellent GUI performance • Faster time-to-development: design, develop, debug, refactor in Java using your favourite IDE, then deploy as JS. © 2008 IONA Technologies 5
  6. 6. GWT and RPC GWT provides an RPC approach based on serialized Java over HTTP. Host a GWT service in a servlet engine – the GWT servlet will handle serialization of parameters, return values and exceptions. Easy to use, but limits the reusability of services. <<browser>> <<servlet-engine>> : :Tomcat <<gwt servlet>> <<gwt servlet>> <<gwt>> <<gwt>> :ServiceImpl :ServiceImpl :Client :Client Serialised Java Objects over HTTP © 2008 IONA Technologies 6
  7. 7. GWT and AJAX GWT supports AJAX-style services • Use asynchronous HTTP requests to transmit text-based payload such as XML or JSON. • Apache CXF (Fuse) can provide the server-side solution. Rapidly produce JSON and XML services for GWT clients. <<browser>> <<servlet-engine>> : :Tomcat <<cxf servant>> <<cxf servant>> <<gwt>> <<gwt>> :ServiceImpl :ServiceImpl :Client :Client CXF JSON or XML over HTTP © 2008 IONA Technologies 7
  8. 8. RESTful JSON Services with Fuse Service Framework / Apache CXF © 2008 IONA Technologies 8
  9. 9. RESTful services with FUSE ContactsService.java ContactsService.java Approach: @WebService @WebService Annotate your Java service. interface ContactsService { interface ContactsService { Deploy - in Spring Framework, @Get @Get Tomcat, J2EE, or standalone. @HttpResource(location=“/contacts/id={id}”) @HttpResource(location=“/contacts/id={id}”) Consume – most likely from public Contact getContact(int id); public Contact getContact(int id); AJAX clients. } } http://frodo:9000/contacts/id=123 Go > <ns4:Contact> <<server>> frodo: <firstName>Ade</firstName> <lastName>Trenaman</lastName> <<fuse-service>> <<fuse-service>> <company>IONA Technologies</company> :ContactsService :ContactsService <title>Principal Consultant</title> GET 9000 HTTP <email>adrian.trenaman@iona.com</email> <mobile>+353-86-6051026</mobile> © 2008 IONA Technologies 9
  10. 10. RESTful services with FUSE (cont’) No formal interface definition language (WSDL, IDL) is used. However, XSD is often used for data definition. A service’s “parameters” are passed via payload and URL, e.g.: http://localhost:9000/contacts/id=007 FUSE supports XML and JSON payloads Services make use of a natural mapping from HTTP verbs to CRUD operations. POST: Create a new item of data on the service. GET: Retrieve data from the service. PUT: Update data on the service. DELETE: Delete data from services. © 2008 IONA Technologies 10
  11. 11. A RESTful “Hello, World” © 2008 IONA Technologies 11
  12. 12. Hello World A simple “Hello, World” application: A client performs a HTTP GET using a URL like: http://localhost:9000/hw/sayHello/user=ade&msg=hello The server receives the parameters and returns a string value. Steps: Write a simple Java bean to match the URI template: in this case, to hold the user and msg parameters. Write your business logic in Java Use a browser, or tools such as curl or wget, to perform a HTTP GET. © 2008 IONA Technologies 12
  13. 13. Parameters bean… Input parameters for the sayHello operation can be modelled easily as a Java bean. Parameters map to bean fields with appropriate getters and setters. URI: http://localhost:9000/hw/sayHello/user=ade&msg=hello Java bean: public class SayHello { private String user; private String msg; public String getMsg() { … } public void setMsg(String message) {…} public String getUser() {…} public void setUser(String user) {…} } © 2008 IONA Technologies 13
  14. 14. Business Logic Annotate the class Annotate the class as aaweb service. as web service. @WebService This method will This method will public class HelloWorld { respond to aaHTTP respond to HTTP GET… GET… … at this … at this @Get location! location! @HttpResource( location="/sayHello/user={user}&msg={msg}“ ) public String sayHello(SayHello params) { System.out.println(params.getUser() + " said '" + params.getMsg() + "'"); return "Thanks for your message!"; } Everything Everything else is just else is just } plain old Java. plain old Java. © 2008 IONA Technologies 14
  15. 15. Deploying your service You can deploy your service into a Spring container, Tomcat, a J2EE application server, or run as a Java mainline. Boiler plate code: String URL = "http://localhost:9000/hw/"; JaxWsServerFactoryBean svc = new JaxWsServerFactoryBean(); svc.setBindingId(HttpBindingFactory.HTTP_BINDING_ID); svc.setAddress(URL); svc.setServiceBean(new HelloWorld()); svc.getServiceFactory().setWrapped(false); svc.create(); System.out.println(“Listening on " + URL); © 2008 IONA Technologies 15
  16. 16. Testing your service You can test your REST services by simply pointing a browser at the URL. This will implicitly perform a GET on your service. Alternatively, you can use command-line tools like wget or curl curl –X GET “http://localhost:9000/hw/sayHello/user=ade&msg=hello” The output should be: <ns2:sayHelloResponse xmlns:ns2="http://wrapped.helloworld/"> Thanks for your message! </ns2:sayHelloResponse> Namespace derived Namespace derived from Java package. from Java package. © 2008 IONA Technologies 16
  17. 17. “Hello, world”: lessons learnt The “Hello, World” example shows how expose a Java method as a RESTful service … with the use of just a few annotations. By default the response payload is returned as XML; later we’ll see how to easily change this to JSON. This approach works well for algorithmic services. Like “calculate my tax”. The next section focuses on more resource-based service. Like “retrieve customer details for customer 007654321”, or “create new customer”. © 2008 IONA Technologies 17
  18. 18. A RESTful resource-based service. © 2008 IONA Technologies 18
  19. 19. Resource-based service Consider a resource such as “Customer contact details”. Perhaps you have this modelled as a Java class. Alternatively, you might have this modelled as an XML Schema. If so, then you can easily generate an equivalent Java class using the JAX-B support provided by FUSE. You want a RESTful service providing CRUD operations for your document: Create, retrieve, update, delete customer contacts. FUSE supports this via the use of URI templates (as before), along with @Post, @Get, @Post, @Delete annotations. FUSE will marshal the payload (if any) into your parameters. © 2008 IONA Technologies 19
  20. 20. RESTful HTTP verbs You can use the full palette of HTTP verbs: Retrieve Create POST http://.../contacts/id=123 GET http://.../contacts Delete GET http://.../contacts/id=123 DELETE http://.../contacts/id=123 GET http://.../contacts/name=ade Update PUT http://.../contacts/id=123 © 2008 IONA Technologies 20
  21. 21. RESTful HTTP verbs However: client technologies may only support GET and POST. Tip: design your service for the lowest common denominator. Retrieve Create POST GET http://.../contacts/create GET http://.../contacts Delete GET http://.../contacts/id=123 DELETE GET http://.../contacts/del/id=123 Update GET http://.../contacts/name=ade PUT POST http://.../contacts/id=123 © 2008 IONA Technologies 21
  22. 22. Contact service: interface Defining an interface for the ContactService: @WebService public interface ContactService { @Get @HttpResource(location="/contacts/create") public Contact createContact() throws CannotCreate; @Get @HttpResource(location="/contacts/delete/id={id}") public void removeContact(RemoveContact params); © 2008 IONA Technologies 22
  23. 23. Contacts service: interface (cont’) @Get @HttpResource(location="/contacts") public Contacts getContacts(); @Get @HttpResource(location="/contacts/id={id}") public Contact getContact(GetContact gc) throws NotFound; @Get @HttpResource( location= "/contacts/firstName={firstName}&lastName={lastName}“ ) public Contacts findContacts(FindContactsByName params); © 2008 IONA Technologies 23
  24. 24. Contacts service: interface (cont’) @Post @HttpResource(location="/contacts/{id}") public void updateContact(Contact params); © 2008 IONA Technologies 24
  25. 25. Convention-based RESTful-services © 2008 IONA Technologies 25
  26. 26. RESTful services by convention FUSE can introspect a Java class and deploy as a RESTful service. You don’t have to provide annotations. FUSE adopts a number of conventions to give an intuitive deployment. The introspection process must determine: What HTTP verb to use – POST, PUT, GET or DELETE? What URL context should the method relate to? Examples: removePerson(long id) DELETE /people/{id} updatePerson(long id) PUT /people/{id} © 2008 IONA Technologies 26
  27. 27. Conventions Conventions are intuitive; best learnt by example. Method: Collection<Contact> getContacts() Maps to: GET /contacts. Method: Contact getContact(long id) Maps to: GET /contacts/{id}. Note the use of a pluralizer in constructing the URI template. Method: void updateContact(long id, Contact c) Maps to: PUT /contacts/{id}. The contact information is transferred as XML payload. © 2008 IONA Technologies 27
  28. 28. Conventions (cont’) Method: void removeContact(long id) Maps to: DELETE /contacts/{id} Methods that begin with remove or delete are mapped to HTTP DELETE. Method: void createContact(Contact c) Maps to: POST /contacts Methods that begin with create or add are mapped to HTTP POST. The contact information is transferred as XML payload. © 2008 IONA Technologies 28
  29. 29. Support for JSON © 2008 IONA Technologies 29
  30. 30. JSON - JavaScript Object Notation The RESTful services shown previously return data formatted as XML. FUSE can generate XML from JAX-B annotated classes, and classes without annotations (applying suitable conventions). Alternative payload formats, such as JSON, may be preferred for RESTful services. JSON (JavaScript Object Notation) is a simple name-value format that facilitates rapid marshalling and unmarshalling: See http://www.json.org. May be preferred by web developers writing Javascript clients. FUSE supports JSON by replacing the XML marshaller with a JSON marshaller. © 2008 IONA Technologies 30
  31. 31. Badgerfish vs. mapped notation Recall: XML elements are typically qualified with their namespace. <getContactResponse xmlns="http://easyrest/"> <ns2:Contact xmlns:ns2="http://www.iona.com/demo/contact" id="123"> <firstName>Joe</firstName> <lastName>Blogs</lastName> <company>IONA Technologies </company> <title>Consultant </title> <email> joe.blogs@iona.com </email> <mobile>+353-1234567</mobile> <phone>+353-1234567</phone> </ns2:Contact> </getContactResponse> © 2008 IONA Technologies 31
  32. 32. Badgerfish vs. mapped notation (cont’) When marshalling as JSON, the XML namespaces can be inserted in a mangled form, using “Badgerfish” notation. {"getContactResponse":{ "@xmlns":{"$":"http://easyrest/"}, "ns2:Contact":{ "@xmlns":{"ns2":"http://www.iona.com/demo/contact"}, "@id":"123", "firstName":{"$":"Joe"}, "lastName":{"$":"Blogs"}, "company":{"$":"IONA Technologies"}, "title":{"$":" Consultant"}, "email":{"$":"joe.blogs@iona.com"}, "mobile":{"$":"+353-1234567"}, "phone":{"$":"+353-1234567"} } }} © 2008 IONA Technologies 32
  33. 33. Badgerfish vs. mapped notation (cont’) Some prefer to perform an explicit namespace mapping: {"easyrest.getContactResponse":{ "contact.Contact":{ "@id":"123", "firstName":"Joe", "lastName":"Blogs", "company":"IONA Technologies", "title":"Consultant", "email":"joe.blogs@iona.com", "mobile":"+353-1234567", "phone":"+353-1234567" } }} © 2008 IONA Technologies 33
  34. 34. Configuring an endpoint for JSON FUSE supports both Badgerfish and mapped approaches; to use Badgerfish: Map <String, Object> properties = …; BadgerFishXMLInputFactory xif = new BadgerFishXMLInputFactory(); properties.put(XMLInputFactory.class.getName(), xif); BadgerFishXMLOutputFactory xof = new BadgerFishXMLOutputFactory(); properties.put(XMLOutputFactory.class.getName(), xof); endpoint.setProperties(properties); © 2008 IONA Technologies 34
  35. 35. Configuring an endpoint for JSON (cont’) For mapped JSON: HashMap<String, String> nstojns = …; nstojns.put("http://www.iona.com/demo/contact", "contact"); nstojns.put("http://easyrest/", "easyrest"); MappedXMLInputFactory xif = new MappedXMLInputFactory(nstojns); properties.put(XMLInputFactory.class.getName(), xif); MappedXMLOutputFactory xof = new MappedXMLOutputFactory(nstojns); properties.put(XMLOutputFactory.class.getName(), xof); endpoint.setProperties(properties); © 2008 IONA Technologies 35
  36. 36. Aside: HTTP content-type When returning JSON payload, the HTTP Content-Type header should be set to something other than text/xml After all, the payload isn’t XML, it’s JSON. Use the properties map to set the content-type: properties.put("Content-Type", "text/plain"); Could also set to application/json if preferred. © 2008 IONA Technologies 36
  37. 37. GWT client code © 2008 IONA Technologies 37
  38. 38. GWT and AJAX – boilerplate Java code RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, "http://..."); try { Request req = builder.sendRequest(null, new RequestCallback() { public void onError(Request request, Throwable exception) { } public void onResponseReceived(Request request, Response response) { } }); } catch (RequestException e) { } © 2008 IONA Technologies 38
  39. 39. GWT and AJAX – boilerplate Java code - notes The RequestBuilder approach is favoured. • An alternative approach, using the raw HTTPRequest class, is internally- focussed and may be deprecated. RequestBuilder only supports HTTP GET and POST. •DELETE and PUT and other verbs not supported, due to a bug in Safari implementation of the XMLHTTPRequest. © 2008 IONA Technologies 39
  40. 40. GWT support for JSON GWT provides support for creating and parsing JSON payload. • See classes in package com.google.gwt.json.client. public String toJSON() { JSONObject obj = new JSONObject(); obj.put("firstName", new JSONString(“Ade”)); obj.put("lastName", new JSONString(“Trenaman”)); JSONObject contact = new JSONObject(); contact.put("er.Contact", obj); return contact.toString(); } {"er.Contact":{"firstName":"Ade","lastName":"Trenaman"}} {"er.Contact":{"firstName":"Ade","lastName":"Trenaman"}} © 2008 IONA Technologies 40
  41. 41. GWT support for JSON (cont’) A similar API exists for parsing JSON. JSONValue jsonValue = JSONParser.parse(responseText); JSONObject obj = jsonValue.isObject(); JSONValue contact = obj.get("er.Contact"); JSONValue firstName = contact.isObject().get("firstName"); © 2008 IONA Technologies 41
  42. 42. Summary © 2008 IONA Technologies 42
  43. 43. Summary Use CXF (Fuse) to provide JSON services for AJAX clients. Native support for RESTful JSON and XML payloads using explicit or implied conventions. CXF first implementation of JSR-311 – Java API for RESTful Web Services. Use GWT to build dynamic, flexible browser-based clients. Full API for JSON and AJAX interactions. Drawbacks: GWT’s JSON API makes you do a lot of the hard work for marshalling and unmarshalling. • Perhaps leverage JSNI? © 2008 IONA Technologies 43
  44. 44. Resources Google Web Toolkit: Go to http://code.google.com/webtoolkit CXF, Fuse Service Framework and IONA: Learn more: http://open.iona.com/ Download: http://open.iona.com/downloads/ Browse demos: samples/restful_http_binding samples/restful_dispatch Contribute! Need help? Visit the forums on Apache and open.iona.com. Contact us: training@iona.com © 2008 IONA Technologies 44