JAX-RS 2.0: RESTful Web Services

JAX-RS 2.0: RESTful Java on Steroids
Arun Gupta, Java EE & GlassFish Guy
http://blogs.oracle.com/arungupta, @arungupta
1 Copyright © 2012, Oracle and/or its affiliates. All rights reserved.

The following is intended to outline our general product direction. It is
intended for information purposes only, and may not be incorporated into
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functionality, and should not be relied upon in making purchasing
decisions. The development, release, and timing of any features or
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of Oracle.

2011,

Part I: How we got here ?


How We Got Here?

•  Shortest intro to JAX-RS 1.0
•  Requested features for JAX-RS 2.0
•  JSR 339: JAX-RS 2.0


JAX-RS Origins

•  JAX-RS 1.0 is Java API for RESTful WS
•  RESTFul Principles:
–  Assign everything an ID
–  Link things together
–  Use common set of methods
–  Allow multiple representations
–  Stateless communications


JAX-RS 1.0 Goals

•  POJO-Based API
•  HTTP Centric
•  Format Independence
•  Container Independence
•  Inclusion in Java EE


Example: JAX-RS API
Resources

@Path("/atm/{cardId}") URI Parameter
public class AtmService { Injection

@GET @Path("/balance")
@Produces("text/plain")
public String balance(@PathParam("cardId") String card,
@QueryParam("pin") String pin) {
return Double.toString(getBalance(card, pin));
}

…

HTTP Method Built-in
Binding Serialization


Example: JAX-RS API (contd.)
… Custom Serialization

@POST @Path("/withdrawal")
@Consumes("text/plain")
@Produces("application/json")
public Money withdraw(@PathParam("card") String card,
@QueryParam("pin") String pin,
String amount){
return getMoney(card, pin, amount);
}
}


Requested Features

•  Client API
•  Client-side and Server-side Asynchronous
•  Filters and Interceptors
•  Improved Connection Negotiation
•  Validation
•  Hypermedia
•  Alignment with JSR 330
•  Model-View-Controller

JSR 339 Expert Group

•  EG Formed in March 2011
•  Oracle Leads: Marek Potociar / Santiago Pericas-G.
•  Expert Group:
–  Jan Algermissen, Florent Benoit, Sergey Beryozkin (Talend),
Adam Bien, Bill Burke (RedHat), Clinton Combs, Bill De Hora,
Markus Karg, Sastry Malladi (Ebay), Julian Reschke, Guilherme
Silveira, Dionysios Synodinos
•  Early Draft 3 published on Jun 7, 2012!


Part II: Where We Are Going


In-Scope Features

•  Client API
•  Validation
•  Hypermedia
•  Model-View-Controller

New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Client API - Motivation

•  HTTP client libraries too low level
•  Sharing features with JAX-RS server API
•  E.g., MBRs and MBWs

•  Supported by some JAX-RS 1.0 implementations
•  Need for a standard


Client API – Old and New

•  Client-side API
URL url = new URL("http://.../atm/balance"); 
HttpURLConnection conn = (HttpURLConnection) url.openConnection();  Old
conn.setRequestMethod("GET"); 
conn.setDoInput(true); 
conn.setDoOutput(false); 
 
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream())); 
String line; 
while ((line = br.readLine()) != null) { 
out.println(line); 
}#

Client client = ClientFactory.newClient();#
String balance = client.target("http://.../atm/balance")#
.request()#
.get(String.class);# New

Example: Client API

// Get instance of Client
Client client = ClientFactory.newClient();

Can also inject @URI for the target ß

// Get account balance
String bal = client.target("http://.../atm/balance")
.pathParam("card", "111122223333")
.queryParam("pin", "9876")
.request().get(String.class);


Example: Client API (contd.)

// Withdraw some money
Money mon = client.target("http://.../atm/withdraw")
.pathParam("card", "111122223333")
.queryParam("pin", "9876")
.request("application/json")
.post(text("50.0"), Money.class);


Example: Generic Interface (Command pattern,
Batch processing)
Invocation inv1 =
client.target("http://.../atm/balance")…
.request().buildGet();

Invocation inv2 =
client.target("http://.../atm/withdraw")…
.request()
.buildPost(text("50.0"));


Example: Generic Interface (contd.)

Collection<Invocation> invs =
Arrays.asList(inv1, inv2);

Collection<Response> ress =
Collections.transform(invs,
new F<Invocation, Response>() {
public Response apply(Invocation inv) {
return inv.invoke();
}
});


New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Filters & Interceptors – Motivation

•  Customize JAX-RS implementations via well-defined
extension points
•  Use Cases: Logging, Compression, Security, Etc.
•  Shared by client and server APIs
•  Supported by most JAX-RS 1.0 implementations
•  All using slightly different types or semantics


Filters

•  Non-wrapping extension points
•  Pre: Interface RequestFilter
•  Post: Interface ResponseFilter

•  Part of a filter chain
•  Do not call the next filter directly
•  Each filter decides to proceed or break chain
•  By returning FilterAction.NEXT or FilterAction.STOP


Filter Example: LoggingFilter
@Provider
class LoggingFilter
implements RequestFilter, ResponseFilter {

@Override
public FilterAction preFilter(FilterContext ctx)
throws IOException {
logRequest(ctx.getRequest());
return FilterAction.NEXT;
}

…


Filter Example: LoggingFilter (contd.)

@Override
public FilterAction postFilter(FilterContext ctx)
logResponse(ctx.getResponse());
return FilterAction.NEXT;
}

}


Interceptors

•  Wrapping extension points
•  ReadFrom: Interface ReaderInterceptor
•  WriteTo: Interface WriterInterceptor

•  Part of an interceptor chain
•  Call the next handler directly
•  Each handler decides to proceed or break chain
•  By calling ctx.proceed()


Handler Example: GzipInterceptor!
@Provider
class GzipInterceptor implements ReaderInterceptor,
WriterInterceptor {

@Override
public Object aroundReadFrom(ReadInterceptorContext ctx)
if (gzipEncoded(ctx)) {
InputStream old = ctx.getInputStream();
ctx.setInputStream(new GZIPInputStream(old));
}
return ctx.proceed();
}
… }

Order of Execution

Request WriteTo Request ReadFrom
Filter Handler Filter Handler

ReadFrom Response WriteTo Response
Handler Filter Handler Filter

Client Server


Binding Example: LoggingFilter!
@NameBinding // or @Qualifier ?
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(value = RetentionPolicy.RUNTIME)
public @interface Logged {
}

@Provider
@Logged
public class LoggingFilter implements RequestFilter,
ResponseFilter
{ … }


Binding Example: LoggingFilter!
@Path("/")
public class MyResourceClass {

@Logged
@GET
@Produces("text/plain")
@Path("{name}")
public String hello(@PathParam("name") String name) {
return "Hello " + name;
}
}


New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Asynchronous – Motivation

•  Let “borrowed” threads run free!
•  Container environment

•  Suspend and resume connections
•  Suspend while waiting for an event
•  Resume when event arrives

•  Leverage Servlet 3.X async support (if available)
•  Client API support
•  Future<RESPONSE>, InvocationCallback<RESPONSE>


Example: Suspend and Resume
@Path("/async/longRunning")
public class MyResource {
@Context private ExecutionContext ctx;

@GET @Produces("text/plain")
public void longRunningOp() {
Executors.newSingleThreadExecutor().submit(
new Runnable() {
public void run() {
Thread.sleep(10000); // Sleep 10 secs
ctx.resume("Hello async world!");
} });
ctx.suspend(); // Suspend connection and return
} … }

Example: @Suspend Annotation
@Path("/async/longRunning")
public class MyResource {
@Context private ExecutionContext ctx;

@GET @Produces("text/plain") @Suspend
public void longRunning() {
Executors.newSingleThreadExecutor().submit(
new Runnable() {
public void run() {
Thread.sleep(10000); // Sleep 10 secs
ctx.resume("Hello async world!");
} });
// ctx.suspend(); Suspend connection and return
} … }

Example: Client API Async Support
// Build target URI
Target target = client.target("http://.../atm/balance")…

// Start async call and register callback
Future<?> handle = target.request().async().get(
new InvocationCallback<String>() {
public void complete(String balance) { … }
public void failed(InvocationException e) { … }
});

// After waiting for a while …
If (!handle.isDone()) handle.cancel(true);


New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Improved Connection Negotiation

GET http://.../widgets2
Accept: text/*; q=1
…

Path("widgets2")
public class WidgetsResource2 {
@GET
@Produces("text/plain",
"text/html")
public Widgets getWidget() {...}
}


Improved Conneg (contd.)

GET http://.../widgets2
Accept: text/*; q=1
…

Path("widgets2")
public class WidgetsResource2 {
@GET
@Produces("text/plain;qs=0.5",
"text/html;qs=0.75")
public Widgets getWidget() {...}
}


New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Validation – Motivation

•  Services must validate data
•  Bean Validation already provides the mechanism
•  Integration into JAX-RS

•  Support for constraint annotations in:
•  Fields and properties
•  Parameters (including request entity)
•  Methods (response entities)
•  Resource classes


Example: Constraint Annotations
@Path("/")
class MyResourceClass {

@POST
@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
Built-in public void registerUser(
@NotNull @FormParam("firstName") String fn,
Custom
@NotNull @FormParam("lastName") String ln,
@Email @FormParam("email") String em) {
... }
}


Example: User defined Constraints
@Target({ METHOD, FIELD, PARAMETER })
@Retention(RUNTIME)
@Constraint(validatedBy = EmailValidator.class)
public @interface Email { ... }

class EmailValidator
implements ConstraintValidator<Email, String> {
public void initialize(Email email) {
… }
public boolean isValid(String value,
ConstraintValidatorContext context) {
// Check 'value' is e-mail address
… } }


Example: Request Entity Validation
@CheckUser1
class User { ... }

@Path("/")
class MyResourceClass {
@POST
@Consumes("application/xml")
public void registerUser1(@Valid User u) { … }

@POST
@Consumes("application/json")
public void registerUser12(@CheckUser2 @Valid User u)
{ … }
}

New in JAX-RS 2.0

•  Client API
•  Validation
•  Hypermedia


Motivation

•  REST principles
•  Identifiers and Links
•  HATEOAS (Hypermedia As The Engine Of App State)

•  Link types:
•  Structural Links
•  Transitional Links


Example: Structural vs. Transitional Links
Link: <http://.../orders/1/ship>; rel=ship,
<http://.../orders/1/cancel>; rel=cancel Transitional
...
<order id="1">
<customer>http://.../customers/11</customer>
<address>http://.../customers/11/address/1</customer>
<items>
<item> Structural

<product>http://.../products/111</products>
<quantity>2</quantity>
</item>
... </order>


Example: Using Transitional Links
// Server API
Response res = Response.ok(order)
.link("http://.../orders/1/ship", "ship")
.build();

// Client API
Response order = client.target(…)
.request("application/xml").get();

if (order.getLink(“ship”) != null) {
Response shippedOrder = client
.target(order.getLink("ship"))
.request("application/xml").post(null);
… }


Other Topics Under Consideration

•  Better integration with JSR 330
•  Support @Inject and qualifiers

•  High-level client API?


More Information

•  JSR: http://jcp.org/en/jsr/detail?id=339
•  Java.net: http://jax-rs-spec.java.net
•  User Alias: users@jax-rs-spec.java.net
•  All EG discussions forwarded to this list


Q&A


JAX-RS 2.0: RESTful Web Services

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