Advanced Java API for RESTful Web Services (JAX-RS) Jakub Podlek - - PowerPoint PPT Presentation

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Advanced Java API for RESTful Web Services (JAX-RS) Jakub Podlek - - PowerPoint PPT Presentation

Oct 03, 2022 473 likes •860 views

Advanced Java API for RESTful Web Services (JAX-RS) Jakub Podlek Jersey Tech Lead, Oracle Agenda The current status of JAX-RS JAX-RS basics in one slide Selected topics The future of JAX-RS Q&A What this Presentation

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SLIDE 1

Advanced Java API for RESTful Web Services (JAX-RS)

Jakub Podlešák

Jersey Tech Lead, Oracle

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SLIDE 2

Agenda

  • The current status of JAX-RS
  • JAX-RS basics in one slide
  • Selected topics
  • The future of JAX-RS
  • Q&A
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SLIDE 3

What this Presentation is Not About

  • The REST style per se
  • The basics of JAX-RS
  • Bootstrap slide for those new to JAX-RS
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SLIDE 4

The Current Status of JAX-RS, The Java API for RESTful Web Services

  • JSR 311: JAX-RS 1.1 released 23rd Nov 2009
  • Part of Java EE 6; Not part of the Web profile!
  • Specifies integration with:
  • CDI 1.0
  • EJB 3.1
  • Servlet 3.0
  • Jersey 1.8 shipped with GlassFish 3.1.1
  • 7 implementations (Apache CXF, Apache Wink, eXo, Jersey,

RESTEasy, Restlet, Triaxrs)

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SLIDE 5

JAX-RS Basics in One Slide

@Path("widgets") @Produces("application/xml, application/json") public class WidgetsResource { @GET public WidgetsRepresentation getWidgetList() { ... } @GET @Path("{id}") public WidgetRespresentation getWidget(PathParam("id") String widgetId) { ... } }

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SLIDE 6

Selected Topics

  • Runtime resource resolution
  • Runtime content negotiation
  • Conditional HTTP requests
  • Dealing with type erasure
  • Pluggable exception handling
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SLIDE 7

Runtime Resource Resolution

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SLIDE 8

Runtime Resource Resolution

  • Root resources can declare sub-resources that will

match the unmatched part of the URI path

  • Root resources implement sub-resource locator

methods

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 9

Runtime Resource Resolution GET http://example.com/foo/bar/baz HTTP/1.1

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 10

Runtime Resource Resolution GET http://example.com/foo/bar/baz HTTP/1.1

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 11

Runtime Resource Resolution GET http://example.com/foo/bar/baz HTTP/1.1

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 12

Runtime Resource Resolution GET http://example.com/foo/bar/baz HTTP/1.1

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 13

Runtime Resource Resolution GET http://example.com/foo/bar/baz HTTP/1.1

@Path("foo") public class Foo { @Path(“bar”) public Bar getBar() { return new Bar(); } } public class Bar { @Path("baz") @GET public String get() { … } }

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SLIDE 14

Runtime Resource Resolution

  • Sub-resource classes are processed at runtime
  • The sub-resource locator method controls life-

cycle of sub-resource

  • Can combine with injection for use with EJBs or

CDI-managed beans

  • Warning: easy to confuse sub-resource methods

with sub-resource locators

@Path("sub") public Object getSubResource() { if ( /bar is preferred/) return new Bar(); else return new Baz(); }

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SLIDE 15

Runtime Content Negotiation

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SLIDE 16

Runtime Content Negotiation

  • Static content/media type negotiation of

representation supported with @Produces

  • Runtime content negotiation of representation

supports 4 dimensions

  • Media type, character set, language, encoding
  • Each representation has a Variant which is a point

in the 4 dimensional space

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SLIDE 17

Runtime Content Negotiation

  • List<Variant> may be pre-calculated
  • Variant or its extensions may be instantiated

directly

List<Variant> vs = Variant. mediaTypes("application/xml", "application/json"). languages("en", "cs").build() assert va.size() == 4; // [["application/xml", "en"] ["application/xml", "cs"] // ["application/json", "en"] ["application/json", "cs"]]

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SLIDE 18

Runtime Content Negotiation

  • Selection will compare the list of variants with the

correspond acceptable values in the client request

  • Accept, Accept-Language, Accept-Encoding, Accept-Charset

@GET public Response get(@Context Request r) { List<Variant> vs = ... Variant v = r.selectVariant(vs); if (v == null) { return Response.notAcceptable(vs).build(); } else { Object rep = selectRepresentation(v); return Response.ok(rep, v); } }

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SLIDE 19

Conditional HTTP Requests

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SLIDE 20

Conditional HTTP Requests

  • Save bandwidth and client processing
  • A GET response can return 304 (Not Modified) if the

representation has not changed since the previous request

  • Avoid lost update problem
  • A PUT response can return 412 (Precondition Failed) if the

resource state has been modified since the previous request

  • A date and/or entity tag can be used
  • Last-modified and Etag headers
  • HTTP dates have a granularity of 1 second; entity tags are

better for use with PUT

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SLIDE 21

Conditional HTTP Request

@GET public Response get(@Context Request r) { EntityTag et = ... Response.ResponseBuilder rb = r.evaluatePreconditions(et); if (rb != null) { // Return 304 (Not Modified) return rb.build(); } String rep = ... return Response.ok(rep).tag(et).build(); }

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SLIDE 22

Dealing with Type Erasure

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SLIDE 23

Dealing with Type Erasure

How many of you think you understand Java Generics?

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SLIDE 24

Dealing with Type Erasure

If you think you understand Java Generics you probably do not understand Java Generics.

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SLIDE 25

Dealing with Type Erasure

Well the JSR-311 expert group thought they did...

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Dealing with Type Erasure

  • Type information is lost when returning Response

@GET public List<Bean> getBeanList() { ...}

  • Resource method can return an entity

@GET public Response getBeanList() { List<Bean> list = … return Response.ok(list).build(); }

  • MessageBodyWriter supporting List<Bean> will

not work when type information is lost

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SLIDE 27

Dealing with Type Erasure

  • Use GenericEntity to preserve type information at

runtime

@GET public Response getBeanList() { List<Bean> list = … GenericEntity<List<Bean>> ge = new GenericEntity<List<Bean>>(list) {}; return Response.ok(ge).build(); }

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SLIDE 28

Pluggable Exception Handling

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Pluggable Exception Handling

  • Propagation of unmapped exceptions to the Web

container

  • A runtime exception thrown by the JAX-RS

implementation or application is propagated as is

  • A checked exception thrown by the application is

propagated as the cause of a ServletException

  • Propagated exceptions can be mapped to error

pages

  • Runtime/checked exceptions can be “caught” and

mapped to a Response using ExceptionMapper

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SLIDE 30

Pluggable Exception Handling class A extends RuntimeException { …} class B extends A { … } class C extends B { … }

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SLIDE 31

Pluggable Exception Handling

@Provider public class AMapper implements ExceptionMapper<A> { public Response toResponse(A a) { ... } } @Provider public class BMapper implements ExceptionMapper<B> { public Response toResponse(B b) { ... } }

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SLIDE 32

Pluggable Exception Handling

// Throwing A maps to Response of AMapper @GET public String a() throws A { … } // Throwing B maps to Response of BMapper @GET public String a() throws B { … } // Throwing C maps to Response of BMapper @GET public String a() throws C { … }

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SLIDE 33

Pluggable Exception Handling

  • ExceptionMapper “closest” to exception class is

selected to map exception

  • Can map Throwable

@Provider public class CatchAll implements ExceptionMapper<Throwable> { public Response toResponse(Throwable t) { // Internal Server Error return Response.status(500).build(); } }

  • Inject Providers to delegate
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SLIDE 34

The Future of JAX-RS

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SLIDE 35

The Future of JAX-RS

  • JSR-339: JAX-RS 2.0
  • Expert group formed in February 2011
  • Early draft published on Oct 21
  • Final release anticipated in Q2 2012
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SLIDE 36

JAX-RS 2.0

  • Client API
  • Asynchronous processing
  • Filters, Handlers
  • Declarative hyperlinking
  • Parameter Validation
  • Improved integration with JSR-330
  • Quality of source
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SLIDE 37

Questions?

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SLIDE 38

References

  • http://jersey.java.net (Jersey project, JAX-RS 1.1 RI)
  • http://jsr311.java.net (JAX-RS API)
  • http://jax-rs-spec.java.net/ (JAX-RS 2.0 API)
  • http://marek.potociar.net (JAX-RS 2.0 spec co-lead blog)
  • See the recent post on Devoxx there
  • http://www.java.net/blogs/spericas
  • (Santiago Pericas-Geertsen, JAX-RS 2.0 spec co-lead)
  • http://blogs.oracle.com/japod (my blog)