I know there are a lot of answers on this questions , but i am still confused about difference between JAX-RS API(the specification), and Jersey framework( reference implementation).
I read that:
Jersey framework basically uses com.sun.jersey.spi.container.servlet.ServletContainer servlet to intercept all the incoming requests. As we configure in our projects web.xml, that all the incoming rest request should be handled by that servlet. There is an init-param that is configured with the jersey servlet to find your REST service classes. REST service classes are not Servlet and they need NOT to extend the HttpServlet as you did in your code. These REST service classes are simple POJOs annotated to tell the jersey framework about different properties such as path, consumes, produces etc. When you return from your service method, jersey takes care of marshalling those objects in the defined 'PRODUCES' responseType and write it on the client stream
My question is when you say :" jersey takes care of marshalling those objects in the defined 'PRODUCES' responseType and write it on the client stream", what you mean by jersey , what is actual class or library that handles objects .
I am confused when i read that jersey is the engine that handles JAX-RS API specification. Can someone please explain what exactly is behind word jersey in this sentence? What actual class from Jersey do do the job of processing requests and responses in Jersey?
The concept of specification and implementation is really pretty basic software engineering concepts. Your specification is the high level design. To help understand, I just came up with a really simple example.
Say I want to have a parsing library. I know how I want to be able to use it. The only problem is that I am not very good at writing parsing code. So I create a high level specification, and I outsource the implementation. Here are the three classes that are part of the spec. They are all contained in one "API jar", say myparsers-api.jar
public interface Parser {
String[] parse(String s);
}
public interface ParserFactory {
Parser getBySpaceParser();
Parser getByCommaParser();
}
public class ParserDepot {
private static ServiceLoader<ParserFactory> loader
= ServiceLoader.load(ParserFactory.class);
public static ParserFactory getDefaultParserFactory() {
final List<ParserFactory> factories = new ArrayList<>();
loader.forEach(factories::add);
if (factories.isEmpty()) {
throw new IllegalStateException("No ParserFactory found");
}
return factories.get(0);
}
}
So at this point, I can actually code against this jar. If I were to uses it as is right now in another project, the project would compile just fine.
ParserFactory factory = ParserDepot.getDefaultParserFactory();
Parser parser = factory.getBySpaceParser();
String[] tokens = parser.parse("Hello World");
System.out.println(Arrays.toString(tokens));
So even though there is no implementation of this specification, I can still code against it, and compile against it. But when I try to actually run the program, it won't work, as there is no implementation. You can try to run this code, and you will get an IllegalStateException (see the docs for ServiceLoader if you're unfamiliar with this pattern).
So I outsource the implementation to say a company called Stack Overflow. They get my myparsers-api.jar and they need to give me back an implementation. They would need to implement a ParserFactory, and a couple of Parsers. They might look something like this
public class SoByCommaParser implements Parser {
#Override
public String[] parse(String s) {
return s.split("\\s+,\\s+");
}
}
public class SoBySpaceParser implements Parser {
#Override
public String[] parse(String s) {
return s.split("\\s+");
}
}
public class SoParserFactory implements ParserFactory {
#Override
public Parser getBySpaceParser() {
return new SoBySpaceParser();
}
#Override
public Parser getByCommaParser() {
return new SoByCommaParser();
}
}
Now Stack Overflow gives me back a jar (say so-myparsers-impl.jar) with these three classes and the required META-INF/services file (per the ServiceLoader pattern), and now when I add the so-myparsers-impl.jar to my project and try to run it again, the program now works, because now it has an implementation.
This is exactly how the JAX-RS spec works. It only defines the high level design of how it should work. The classes, interfaces, and annotations that are part of that design are placed in an "API jar" just like my high level parsers are put into a jar. Implementations cannot alter these classes. All the classes that are part of the JAX-RS specification (version 2.x) are put into one single jar javax.ws.rs-api. You can code against that jar, and your code will compile just fine. But there is nothing to make it "work".
You check out both the written specification and the classes defined by the specification and you will notice that the only classes included in the source code are those mentioned in the specification. But what you should notice is that the written specification doesn't mention anything at all about how it is supposed to be implementation. Take for example the following code
#Path("/test")
public class TestResource {
#GET
public String get() {
return "Testing";
}
}
#ApplicationPath("/api")
public class MyApplication extends Application {
#Override
public Set<Class<?>> getClasses() {
Set<Class<?>> classes = new HashSet<>();
classes.add(TestResource.class);
return classes;
}
}
Now the specification states that this is all we need to run a JAX-RS application in a servlet container. And that's all it says. It says nothing about how it all supposed to work. This is just how it is designed to work.
So what, is there some magic voodoo in Java that we don't know about that will make this Application class start a server, and some hocus pocus that will make a #Path annotated class automatically accept requests. No. Some body needs to provide the engine. The engine might be 20,000 lines of code just to make the above code work as specified.
That being said, Jersey is just the name of an implementation. It's like when I outsourced my parser implementation to Stack Overflow; The name Jersey itself is just the name of the project, just like Hadoop is a name of the project. In this case, what the project is, is an implementation of the JAX-RS specification. And because JAX-RS is just a specification, it means that anyone can implement it. If you wanted to, you could write your own implementation. As long as it works how it is defined to work in the written specification, then you can say that your code is an implementation of JAX-RS. There's more than just Jersey out there; you also have RESTEasy, which is another implementation.
As far as how Jersey implements the engine, that is way too broad. What I can do, is give you a high level overview of what happens behinds the scenes.
A JAX-RS application is defined to run inside of a servlet container. If you understand servlet containers and the servlet spec, then you'll know that the only way to handle requests is either by writing a HttpServlet or Filter. So if you want to implement JAX-RS then you need to able to handle requests either through a HttpServlet or a Filter. The ServletContainer you mentioned, is actually both. So for Jersey, this is the "entry point" into the Jersey application, as far as request processing is concerned. It can be configured in a number of ways (I've leave that research to you).
And if you understand how to write your own servlet, then you know all you get is an HttpServletRequest and HttpServletResponse. You need to figure out what to do from there; get request info from the request, and send response info back out in the response. Jersey handles all of this.
If you really want to get into the gory details of what is going on under the hood, you will just need to to dig into the source code, starting from the entry point, the ServletContainer. Be prepared to spend months on this to get a really good understanding of how it all works. It's not something that can be explained in one Stack Overflow post, if that's what you're expecting.
You already pointed that JAX-RS is a specification and Jersey is the implementation which is how is Java especially Java EE work, maybe this article can explain more better.
To summarize JAX-RS is just a specification, there is no real implementation. The real implementation was done by Jersey and other library that following JAX-RS specification.
Related
How can we force developer to write Developed Custom-annotation on rest api
Example :
We Developed annotation Called : ValidatePermission
what we need to do , displaying runtime error for developer that he missing annotation #ValidatePermission on API , when he tried to write new api
#ValidatePermission
#GetMapping("/details")
#PreAuthorize("hasAuthority('902')")
public ResponseEntity<CustDtlsInqDto> getCustomerDetails(#CurrentUser UserPrincipal currentUser,
#RequestParam(name = "poiNumber", required = false) String poiNumber,
#RequestParam(name = "cif", required = false) String cif) {
return ResponseEntity.ok(customerService.getCustomerDetailsByPoiOrCif(currentUser.getId(), poiNumber, cif));
}
Annotations usage cannot be forced in any way before or on compilation (at least I am not aware of any technique, feel free to correct me).
The only way to go is to perform a check-up during the unit testing phase. Simply write an unit test that scans through the REST API definition beans and its public methods (or annotated) to check up using teh Reflection API whether an annotation from a particular category (implementation details up to you) is present within the formal parameters of methods.
Gits Github: Find all annotated classes in a package using Spring
Baeldung: A Guide to the Reflections Library
Something looks to me weird in this approach.
So you say:
...displaying runtime error for developer that he missing annotation #ValidatePermission on API
Based on this phrase, let me suggest an alternative:
So the developer that runs the project locally (during the debugging session or maybe tests) should see an error if he/she didn't put the annotation on the methods of rest controller, right?
If so, Why don't you need the developers to put this annotation?
The main idea of my suggestion is: Why not letting spring to do it for you automatically?
You could implement some kind of aspect or if you don't want to use a spring aop and prefer 'raw plain spring', BeanPostProcessor, that would 'wrap' all the methods of class annotated with RestContoller (by creating a run-time proxy) and before running a controller method will executed the logic that was supposed to be supported by the annotation?
In the case of Web MVC, another approach is to implement an interceptor that will be invoked automatically by spring mvc engine and you'll be able to execute any custom logic you want there, you'll also be able to inject other beans (like auxiliary services) into the interceptor.
Read this article in case you're not familiar with these interceptors, you'll need preHandle methods as far as I understand.
Is there any way to use soap-rpc web services such that the client is generated via a shared interface? Restful web services do it this way, but what about soap based? Do you always have to use a tool like Axis or CXF to generate your stubs and proxies, or is there something out there that will set it up dynamically?
Thanks.
EDIT #1:
To clarify, I'm looking to do something like this:
Common interface:
#WebService
public interface MyWebService {
#WebMethod
String helloWorld();
}
This common interface can already be used to create the server side component. My question is: can this type of common interface be used on the client side to generate dynamic proxies? Restful web services do it this way (Restlets & CXF) and it seems the .Net world has this type of functionality too.
I would see this tutorial of JAX-WS useful for your purposes:
In the example code the Web Services Client is configured by adding an annotation #WebServiceRef with a property pointing to the WSDL location to the client implementation class and no tools are needed to access the stuff from the Web Service that is referenced.
Was this the way you would like to have it, or did this even answer to right question?
Not exactly sure what you're looking for, but if you don't want to rely on JAX-WS/JAXB-generated artifacts (service interfaces and binding objects), you can make use of the Service and Dispatch APIs. For example:
QName serviceName = new QName(...);
Service service = Service.create(serviceName);
QName portName = new QName(...);
String endpointAddress = "...";
service.addPort(portName, SOAPBinding.SOAP11HTTP_BINDING, endpointAddress);
Dispatch<SOAPMessage> dispatch = service.createDispatch(portName, SOAPMessage.class, Service.Mode.MESSAGE);
SOAPMessage request = ...;
SOAPMessage response = dispatch.invoke(request);
Check Apache CXF. Configuring a Spring Client (Option 1).
When you want to call a webservice, you must have knowledge of methods implemented on it. For that, We need to make stubs OR we can read it from WSDL.
I have created a WS client, using AXIS2 libraries, which is without stubs. The thing is, for each diff. WS we need to create response handles.
You can call any WS method using SOAP envelops and handle the response.
//common interface for response handlers...
//implement this for diff. web service/methods
public interface WSRespHandler{
public Object getMeResp(Object respData);
}
//pass particular handler to client when you call some WS
public class WebServiceClient {
public Object getResp(WSRespHandler respHandler) {
...
return repHandler.getMeResp(xmlData);
}
}
Please check the link below, which shows the example interface for WS client.
http://javalibs.blogspot.com/2010/05/axis2-web-service-client-without.html
For every diff. WS method we can have diff. implementation for WSRespHandler interface, which will help parsing the response.
Not knowing java so well, but being forced to learn some to accomplish a task that I was given, I needed to consume a .Net service that I have already written, I had to do a little research.
I found that 99% of the examples/samples/problems with invoking a method call against a .Net service, or any service for that matter involved using J2EE (ServiceManager) or build classes and a proxy that reflect the service being invoked. Unfortunately for me, none of this would work. I was working "in a box". I could not add new classes, could not WSDL references, did not have J2EE, but DID have access to the standard java libs.
I am used to doing this sort of thing in pretty much every other language but java, but now there was no choice, and java it was.
A lot of digging and figuring out all new terminology, methods, classes, etc, I knew I was getting close, but was having issues with some small items to complete the task.
Then I came across this post: http://www.ibm.com/developerworks/xml/library/x-jaxmsoap/
As long as you have some sort of idea of what you need to send the soap service in term of the soap envelope, the above link will give you the information you need to be able to invoke a service without the classes, wsdl class generators and J2EE, apache or other dependencies.
In an hour from the time I read the mentioned article, I had a class working and about 10 minutes later, converted the code to the "in the box" solution.
Hope this helps
Apache Tuscany might help you, although it may be heavier than you want
http://tuscany.apache.org/
I'm writing a very simple web framework using Java servlets for learning purposes. I've done this before in PHP, and it worked by consulting the request URI, then instantiating the appropriate class and method.
This worked fine in PHP, as one can do something like $c = new $x; $x->$y;. I'm unsure however of how to translate this to Java, or even if this is an appropriate way to go about it.
So far, I've tried:
Router router = new Router(request.getPathInfo());
String className = router.route(); //returns com.example.controller.Foo
Class c = Class.forName(className);
Object x = c.newInstance();
Foo y = (Foo) x;
y.doSomething();
This seems fine for a couple of routes, but doesn't seem like it would scale well, nor would it allow for sourcing routes from a configuration file.
How should I make it work?
Get hold of actions in a Map<String, Action> where the String key represents less or more a combination of request method and request pathinfo. I've posted similar answer before here: Java Front Controller
You can fill such a map either statically (hardcoding all actions) or dynamically (convention over configuration, looking up classes in a certain package, or scanning the entire classpath for classes with a certain annotation or implementing a certain interface).
And just stick to Servlet. The Filter isn't there for. At highest use it to forward the request to the controller Servlet. In the Servlet, just implement HttpServlet#service().
I would use a Servlet Filter as Front Controller. The router would connect paths with request dispatchers. In the doFilter method you would convert ServletRequest to HttpServletRequest, extract the request path and match it against the registered mappings. The result of this mapping is a request dispatcher you would dispatch the request with.
In pseudo code:
doFilter(ServletRequest request, ServletResponse response) {
httpServletRequest = (HttpServletRequest) request;
path = httpServletRequest.getRequestURI();
dispatcher = router.getTarget(path);
dispatcher.dispatch(request, response);
}
Depending on your need the default routing mechanism of the Servlet API could be sufficient.
Not quite sure what you're after but you might want to take a look at Java servlets. Granted many web frameworks are abstracted above plain servlets, but it's a jolly good place to start learning about Java web apps if you ask me (which indirectly you did ;) )
Download the Java servlet specification here: Java Servlet Spec - it's quite interesting.
How should you make it work? However you want it to. If you're just doing it for learning purposes, whatever you do will be fine.
I would suggest having all your actions implement the same interface though (maybe extend Servlet) so that you don't have to compile in all different classes.
Then you can essentially do what you're doing, except that your cast to Foo becomes a cast to Servlet and then you don't have to have a special case for all your different classes.
You can then also load up the routes from configuration (maybe an XML file).
Essentially what you're doing is implemented by the Struts 1 framework so it might be worthwhile reading up on that (it's open-source so you can also look at the source if you want).
For the last couple of years I've had my head in Python, where there are numerous choices for simple, minimal frameworks that allow me to stand up a website or service easily (eg. web.py). I'm looking for something similar in Java.
What is the simplest, least-moving-parts way of standing up simple services using Java these days? I'm looking for something as simple as:
the ability to receive HTTP requests
the ability to dispatch those requests to handlers (preferably a regular expression based url to handler mapping facility)
the ability to set HTTP headers and generally fully control the request/response
Bonus points if the framework plays well with Jython.
[Update] Thanks for the responses, some of these look quite interesting. I'm not seeing the url dispatch capability in these, however. I'm looking for something similar to Django's url.py system, which looks like:
urlpatterns = patterns('',
(r'^articles/2003/$', 'news.views.special_case_2003'),
(r'^articles/(\d{4})/$', 'news.views.year_archive'),
(r'^articles/(\d{4})/(\d{2})/$', 'news.views.month_archive'),
(r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'news.views.article_detail'),
)
Where you specify a url regular expression along with the handler that handles it.
I liked to worth the Simple HTTP Server from the Simple Framework. It offers a nice Tutorial about how to start as well.
there are several alternatives:
servlets
restlet: lightweight REST framework
jax-rs: using jersey or the restlet module implementing the jax-rs specs
grizzly: NIO based server (with HTTP support + handlers)
apache mina: event-driven, async server (with HTTP support)
all these frameworks come with a built-in server.
EDIT
jax-rs has a similar approach using url templates:
#Path("/users/{username}")
public class UserResource {
#GET
#Produces("text/xml")
public String getUser(#PathParam("username") String userName) {
}
}
then put your handlers in an Application object:
public class MyApplicaton extends Application {
public Set<Class> getClasses() {
Set<Class> s = new HashSet<Class>();
s.add(UserResource.class);
return s;
}
}
another example with JAX-RS:
#GET
#Produces("application/json")
#Path("/network/{id: [0-9]+}/{nid}")
public User getUserByNID(#PathParam("id") int id, #PathParam("nid") String nid) {
}
EDIT 2
Restlet supports a centralized configurations like Django, in your Application object:
// Attach the handlers to the root router
router.attach("/users/{user}", account);
router.attach("/users/{user}/orders", orders);
router.attach("/users/{user}/orders/{order}", order);
Servlets might be the way to go. To do very simple things you only need to override one method of one class. More complicated stuff is of course possible, but you can go a long way with a little work.
Investigate Tomcat or Jetty - both are open source and well supported.
public class HelloWorldServlet extends HttpServlet {
public void doGet( HttpServletRequest request, HttpServletResponse response )
throws ServletException, IOException
{
response.setContentType( "text/plain" );
PrintWriter out = response.getWriter();
out.print( "hello world!" );
}
}
Note: This is more general discussion than answer.
I'm having similar issues coming from Python for 10+ years and diving, as it were, back into Java. I think one thing I'm learning is that the "simplicity" factor of Python is very different from that of Java. Where Python abounds with high-level framework-- things like web.py, Java seems much more lower level. Over the past few months, I've gone from saying "What's the Java way to do this easy in Python thing" to "How does one build up this thing in Java." Subtle, but seems to bring my thoughts around from a Python-centric view to a more Java-centric one.
Having done that, I've realized that standing up a website or service is not simple for a Java outsider, that's because there's a large amount of info I have to (re)grok. It's not as simple as python. You still need a webserver, you need to build a "container" to drop your Java code into, and then you need the Java code (am I wrong on this, everyone? Is there a simpler way?).
For me, working with Scala and Lift has helped- and not even those, but this one thread by David Pollack. This was what I needed to build a Jetty server. Take that, follow the directions (somewhat vague, but might be good enough for you) and then you have a servlet container ready to accept incoming traffic on a port (or 3 ports, in his case). Then you can write some Java code using HTTPServlet or something to go the rest of the way.
Again, this is just what I did to get past that barrier, but I'm still not a Java guru. Good luck.
I've hard about: Apache Mina
But quite frankly I don't even know if it is what you need.
:-/
:)
Jetty is a pretty nice embedded http server - even if it isn't possible to do the mapping like you describe, it should be pretty easy to implement what you are going for.
I'm trying to start Jersey on a preconfigured port/url with a preconfigured resource instance. I can't quite figure out how to correctly do it.
Here is a snippet of a code. Help me, please, fill in the blanks:
#Component
#PerRequest
#Path("/svc")
#Consumes({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML})
#Produces({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML})
public class MyService
{
// This piece is known
}
public class JSONMessageBodyWriter implements MessageBodyWriter<Object>
{
// This piece is known
}
public class XMLMessageBodyWriter implements MessageBodyWriter<Object>
{
// This piece is known
}
// This is where I need help
MyService service = new MyService();
...
HttpHandler handler = ???
...
HttpServer server = ???
server.createContext("/services", handler);
...
server.start();
In the snippet above, I'm trying to expose the MyService via the http://localhost:8080/services/svc url. If the JSONMessageBodyWriter and the XMLMessageBodyWriter will be plugged in - the service will work vis XML and JSON accordingly.
If you know how to do this on Jetty or Grizzly, let me know too. Can Spring help here?
Jersey itself provides an entire set of examples, and specifically the simplest helloworld example shows how to start a server on a port to either just run it or test against in JUnits. If you look at that, you'll get example for how to setup and start a server.
Now, on configuring MessageBodyReaders and MessageBodyWriters as part of a jersey application, you'll find that this is covered by the JAX-RS spec itself (which jersey implements). First off, your reader and writer need the #Provider annotation. Additionally, the reader should get the #Consumes annotation, and the writer should get the #Produces annotation, so you can specify what mime-type(s) they consume and produce, respectively.
Next is activating them. The helloworld example above won't show that, because it doesn't use custom readers or writers (another example might, I didn't look). So instead of supplying the package to find resources (as they do; you'll know what I speak of when you see the helloworld example), you'll code a subclass of Application, where you specify your resource class and the reader/writer classes. With the reader and writer you have the option of specifying either a class (that you return from getClasses), or providing an already created instance yourself (that you return from getSingletons).
Finally, specify the name of your Application sub-class as the value of init-parameter "javax.ws.rs.Application". The init-params can be passed to GrizzlyWebContainerFactory.create (again, you'll see this used in the example) when you start the server.
Hope this helps.