What are REST clients for Java

Question

With JSR 311 and its implementations, we have a powerful standard for exposing Java objects via Rest. However, on the client side there seems to be something missing that is comparable to Apache Axis for SOAP - something that hides the web service and marshals the data transparently back to Java objects.

How do you create Java RESTful clients? Using HTTPConnection and manual parsing of the result? Or specialized clients for e.g. Jersey or Apache CXR?

Answer 1

These are the few options :

• Apache CXF has three different REST Client options
• Jersey (mentioned above).
• Spring also has its own called RestTemplate
• Commons HTTP Client build your own for older Java projects.

• Apache HTTP Components (4.2) Fluent adapter - Better than old Commons HTTP Client 3 and easier to use for building your own REST client. You'll have to use something like Jackson for JSON parsing support and you can use HTTP components URIBuilder to construct resource URIs similar to Jersey/JAX-RS Rest client. HTTP components also supports NIO but I doubt you will get better performance than BIO given the short request nature of REST.

UPDATE 2016:

• OkHttp - Supports newer HTTP protocols (SPDY and HTTP2). Works on Android. Unfortunately it does not offer a true reactor-loop based async option (see Ning and HTTP components above). However if you use the newer HTTP2 protocol this is less of a problem (assuming connection count is problem).
• Retrofit - Will auto create clients based on interface stubs similar to some Jersey and CXF extensions. Uses OkHttp.
• Apache HttpComponents 5 will supposedly have HTTP2 support

A caveat on picking HTTP/REST clients. Make sure to check what your framework stack is using for an HTTP client, how it does threading, and ideally use the same client if it offers one. That is if your using something like Vert.x or Play you may want to try to use its backing client to participate in whatever bus or reactor loop the framework provides... otherwise be prepared for possibly interesting threading issues.