I'm creating a web-application and decided to use micro-services approach. Would you please tell me what is the best approach or at least common to organize access to the database from all web-services (login, comments and etc. web-services). Is it well to create DAO web-service and use only it to to read/write values in the database of the application. Or each web-service should have its own dao layer.
Each microservice should be a full-fledged application with all necessary layers (which doesn't mean there cannot be shared code between microservices, but they have to run in separate processes).
Besides, it is often recommended that each microservice have its own database. See http://microservices.io/patterns/data/database-per-service.html https://www.nginx.com/blog/microservices-at-netflix-architectural-best-practices/ Therefore, I don't really see the point of a web service that would only act as a data access facade.
Microservices are great, but it is not good to start with too many microservices right away. If you have doubt about how to define the boundaries between microservices in your application, start by a monolith (all the time keeping the code clean and a good object-oriented with well designed layers and interfaces). When you get to a more mature state of the application, you will more easily see the right places to split to independently deployable services.
The key is to keep together things that should really be coupled. When we try to decouple everything from everything, we end up creating too many layers of interfaces, and this slows us down.
I think it's not a good approach.
DB operation is critical in any process, so it must be in the DAO layer inside de microservice. Why you don't what to implement inside.
Using a service, you loose control, and if you have to change the process logic you have to change DAO service (Affecting to all the services).
In my opinion it is not good idea.
I think that using Services to expose data from a database is ideal due to the flexibility it provides. Development of a REST service to expose some or all of your data as a service provides flexibility to consume the data directly to the UI via AJAX or by other services which can process the data and generate new information. These consumers do not need to implement a DAO and can be in any language. While a REST Service of your entire database is probably not a Micro-Service, a case could be made for breaking this down as Read only for Students, Professors and Classes for exposing on the School Web site(s), with different services for Create, Update and Delete (CUD) available only to the Registrars office desktop applications.
For example building a Service to exposes a statistical value on data will protect the data from examination by a user/program who only needs a statistical value without the requirement of having the service implement an entire DAO for the components of that statistic. Full function databases like SQL Server or Oracle provide a lot of functionality that application developers can use, including complex queries(using indexes), statistics the application of set operations on data.
Having a database service is a completely valid pattern. In fact, this is one of the key examples of where to start to export aspects of a monolith to a micro service in the Building Microservices book.
How to organize your code around such idea is a different issue. Yes, from the db client programmer's stand point, having the same DAO layer on each DB client makes a lot of sense.
The DAO pattern may be suitable to bind your DB to one programming language that you use. But then you need to ask yourself why you are exposing your database as a web service if all access to it will be mediated by the same DAO infrastructure. Or are you going to create one DAO pattern for each client programming language binding?
If all database clients are going to be written on the same programming language, then are you sure you really need to wrap your DB as a microservice? After all, the DB is usually already a remote service with a well-defined network protocol optimized to transfer data fast and reliably. Why adding HTTP on top of it? What are you expecting to gain from adding such complexity?
Another problem with using the DAO pattern is that the DAO structure does not necessarily follow the evolution of the web service. The web service may evolve in a way that does not make old clients incompatible. You may have different clients using different features of the micro service. In this case you are not sharing the same DAO layer structure on each client.
Make sure you are not using RPC-style programming over web services, which does not make much sense. You will be basically throwing away one of the key advantages of micro services, which is the decoupling between service and client.
com Developer and working on an integration app that links an external system with Salesforce.com. The external system exposes its service through SOAP API and provides a WSDL which I have imported and classes are created under a namespace. I need help in developing the overall architecture of the application.
What should be the architecture of the system? Should I develop model and service classes for different entities for fetching data from external app and converting response into my own model classes?
Treat the external system as you would a typical data layer (DBMS, Web services, etc). This means encapsulating the data fetching logic in such a way that the business layer has no idea where the data is coming from. The Repository Pattern is one technique for doing this.
Once you have abstracted your data layer away, you would handle the translation of Data to Entities in whatever way you see fit. You could use a tool such as AutoMapper to do this or write your own custom translation layer where the Data is translated into objects that your application works with.
I am going to develop a webservice which will expose two operations. These operation will query/update data from database.
Please suggest do i use EJB for database operation and what advantage i will get?
or
in my webservice i use JPA directly like following, and create my entities and persist them
#PersistenceUnit private EntityManagerFactory emf;
#Resource
private UserTransaction utx;
Please answer with advantages/disadvantages.
Regards,
imran
Both approaches are valid and supported by Java EE, so this is only a design recommendation based on my experience:
Do never directly expose EJB operations as Web Services, it only increases runtime complexity. If you publish an EJB as a Web Service the container must still wrap it by using an internal Web Services servlet which (implicitly) tightly couples your WAR containing the internal Web Service mapping to your ejb-jar (depends on app server product). Furthermore, it's hard to debug in day-to-day operations.
My recommendation using only standard Java EE features without any additional libraries:
POJO defines the Web Service interface, aka its operations (#WebService annotation). It delegates to a functional implementation. Let's call this POJO WS-POJO.
Two options to implement the functionality:
WS-POJO calls stateless Session Beans which provide the required functionality. Pro: All EJB features available (dependency injection, declarative transaction mgmt, etc.). Con: "Heavyweight"
WS-POJO calls custom POJOs following e.g. the Command Pattern. Pro: "Lightweight". Con: Dependency injection not possible; Entity Manager etc. to be passed.
Today, I'd go with option #1... my 2 cent
Interoperability comes to mind (MS/Java).
Also, with EJB you need to distribute EJB interface, with WS you got WSLD (I know there's EJB extension for WSDL, but I'm not sure it's used).
Anything else?
EJB is mostly about a programming model for how you implement callable Business Logic. You code is running in a container which looks after management, clustering, transactions and security. Your component can be called by and number of different mechansims including local Java Calls, RMI/IIOP for remote invocation and also Web Services, so yes your EJB can indeed have a WSDL and be callable fro other non-Java envrionments.
If you start instead from the point of view of having a WSDL, which probably will specify SOAP/HTTP, then you are free to implement that in many different technologies, and of cource invoke it via that specified protocol, which very many different clients can use. The big question is how easily you can deal with those quality of implementation issues - your chosen implementation environment may give a lot of help or leave a lot to you.
Summary: you're not really comparing like-with-like. Web Services is very about the interface, EJB very much about the implementation.
I'm using BizUnit to unit-tests my Biztalk orchestrations, but some orchestrations consume a WebService,and testing these seems more like integration testing than unit testing.
I'm familiar with using a mocking framework to mock the generated proxy objects, in order to test a web service from a Windows Forms application, but I would like to be able to do it in a more integrated way in a request-response port?
How would you approach this problem?
This goes to the heart of one of my main irritations as a BizTalk developer - BizTalk does not lend it self to unit testing. From the fact the 99% of your interfaces into BizTalk applications are message based and have a huge number of possible inputs, through to the opaque nature of orchestrations, BizTalk offers no real way of testing units of functionality as... well... units.
For BizTalk, integration tests are sadly often the only game in town.
That results in, due to no fault on the part of Kevin Smith, BizUnit being (IMO) a misnomer. A better name would perhaps be BizIntegrationIt. BizUnit offers a range of tools that assist in integration testing, the majority of its tests, like checking if a file has been written to a given directory or sending an HTTPRequest to a BizTalk HTTPReceive location are all strictly speaking, testing integration.
Now that I've gotten that rant out, what you are asking for is something I've been thinking about for a long time, the ability to create automated unit tests that give some real confidence that my making a small change to a map won't suddenly break something else downstream, as well as a way to remove dependance on external services.
I've never thought of any nice way of doing this but below is a solution that should work, I've done variations of each part of this in isolation but never tried to but them all together in this specific form.
So given the desire to mock a call to some external service (that may not even exist yet) without needing to actually make any external call and wanting to have the ability to set expectations for that service call and to specify the nature of the response, the only method I can think of is to develop a custom adapter.
Mock webservice using custom adapter
If you build a custom request-response adapter you can plug it into your send port in place of the SOAP adapter. You can then specify properties for the adapter that allow it to behave as a mock of your webservice. The adapter would be similar in concept to a loopback adapter but would allow internal mocking logic.
Things that you might want to include as adapter properties:
Expected document (perhaps a disk location that specifies an example of what you expect your BizTalk applicaiton to send to the webservice).
Response document - the document that the adapter will send back to the messaging engine.
Specific expectations for the test such as lookup values in document elements.
You could also have the custom adapter write to disk and setup a BizUnit step to validate the file that was written out.
Building a custom adapter is non-trivial, but possible, you can get a good start from the BizTalk Adapter Wizard and there is an article on deploying custom adapters here.
There is a bug in the code generated by the wizard, you will need to change new Guid(""), to new Guid().
There are also some examples of building custom adapters in the BizTalk SDK.
Another option is to use a plain http page and the HTTP solicit response as discussed here, all your logic goes in the http page. This is probably simpler if you are happy having an http call, and setting up an IIS port to listen for your test.
Initialising unit tests
You can import binding files into a BizTalk application using a .bat file.
If you make a new binding file for each test you run, as well as for your standard applicaiton set up, you can then run the appropriate batch file to apply the right binding.
Each binding file would change your webservice sendport to use the mock custom adapter and set the specific properties for that test.
You could then even make a custom BizUnit step that (perhaps) generated binding settings based on settings in the test step and then ran the shell commands to update the bindings.
Testing Message Contents
A final thing that you might want to consider, to really tie all this together, is some way of testing the contents of messages. You could do this in your mock adapter, but that would get tedious very quickly for large messages, or for a large range of possible input messages.
One option is to make a custom pipeline that calls Schematron to validate files that it receives. Schematron is a schema language that allows a much richer level of file inspection that xsd, so you can check things like "If element x contains this content, I expect element y to be present".
If you built a custom pipeline that took a schematron schema as a parameter, you could then swap in a testing file for a specific unit test, validating that for this test, when you call the webservice you get a file that actually matches what you want (and doesn't just match the xsd)
As a co-author of BizUnitExtensions (www.codeplex.com/bizunitextensions) i agree that the name "unit" in BizUnit can be confusing but for Biztalk, the 'integration test' is the unit test. Some Biztalk folk have successfully used mocks to test pipeline components and other test harnesses (+ BizUnit/Extensions) to test schemas and maps.
Orchestrations unfortunately are opaque. But theres are good reasons for that.
(a) Because of the huge subscription system in the message box - that orchestrations use when being activated etc, it is not possible to fire up some "virtual" process to host the orchestration (which can be done for pipelines. Tomas Restrepo has done something along these lines).
(b) Also, how would this virtual process handle persistence and dehydration?. I'd wager that people using WF would have the same problem in trying to test the workflow fully.
(c) we dont work with the C# directly, so there is no way we can "inject" a mock
interface into the orchestration code.
(d) An orchestration is not really a "unit". its a composite element. The units are the messages going to and from the message box and the external components called through expression shapes.So even if you could inject a mock webservice interface you cannot inject mock message boxes and correlation sets and other things.
One thing that can be done for orchestrations (and i've been considering an addition to the BizUnitExtensions library to do this) is to link in with the OrchestrationProfiler tool as that tool gives a pretty detailed report of all the shapes and somehow check that individual steps were executed (and perhaps the time it took for execution). This could go quite far in making the orchestration a bit more of a white box.Also considering that the orchestration debugger shows a lot of the variable values, surely it must be possible to get that info via an API to show what the values of variables were at a given point for a given instance.
Back to Richard's question though, my previous dev team had a solution. Basically what we did was to write a generic configurable HttpHandler that parsed incoming service requests and returned pre-set responses. The response sent back was configurable based on conditions such as XPath. In the BUILD and DEV binding files, the webservice end point was the mock. This worked brilliantly in isolating the BUILD and DEV environments from the actual third party webservices. This also helped in a "contract first" approach where we built the mock and the orch developer used it while the webservice author went ahead and built the actual service.
[Update:17-FEB-09: this tool is now on codeplex : http://www.codeplex.com/mockingbird.
If this approach sounds interesting check it out and let me know what you think of the tool ]
Now, before someone throws the old "WHAT ABOUT MOCK OBJECT FRAMEWORKS" chestnut in, let me say that the utility above was used for both Biztalk 'consumers' as well as non Biztalk consumers, BUT i have also worked with NMock2 and found that to be an excellent way to mock interfaces and set expectations when writing CLR consumers. (I'm going to be looking into MoQ and TypeMock etc soon). However, it wont work with orchestrations for the reasons described above.
Hope this helps.
Regards,
Benjy
Don't.
Don't test against arbitrary interfaces, and don't create mocks for them.
Most people seem to see developer (unit) testing as intended for testing nontrivial, individual units of functionality such as a single class. On the other hand, it is also important to perform customer (acceptance/integration) testing of major subsystems or the entire system.
For a web service, the nontrivial unit of functionality is hidden in the classes that actually perform the meaningful service, behind the communication wiring. Those classes should have individual developer test classes that verify their functionality, but completely without any of the web-service-oriented communication wiring. Naturally, but maybe not obviously, that means that your implementation of the functionality must be separate from your implementation of the wiring. So, your developer (unit) tests should never ever see any of that special communication wiring; that is part of integration and it can be viewed (appropriately) as a "presentation" issue rather than "business logic".
The customer (acceptance/integration) tests should address a much bigger scale of functionality, but still not focused on "presentation" issues. This is where the use of the Facade pattern is common--exposing a subsystem with a unified, coarse-grained, testable interface. Again, the web service communication integration is irrelevant and is implemented separately.
However, it is very useful to implement a separate set of tests that actually do include the web service integration. But I strongly recommend against testing only one side of that integration: test it end-to-end. That means building tests that are web service clients just like the real production code; they should consume the web services exactly the way that the real application(s) do(es), which means that those tests then serve as examples to anyone who must implement such applications (like your customers if you are selling a library).
So, why go to all that trouble?
Your developer tests verify that your functionality works in-the-small, regardless of how it is accessed (independent of presentation tier since it is all inside the business logic tier).
Your customer tests verify that your functionality works in-the-large, again regardless of how it is accessed, at the interface boundary of your business logic tier.
Your integration tests verify that your presentation tier works with your business logic tier, which is now managable since you can now ignore the underlying functionality (because you separately tested it above). In other words, these tests are focused on a thin layer of a pretty face (GUI?) and a communication interface (web services?).
When you add another method of accessing your functionality, you only have to add integration tests for that new form of access (presentation tier). Your developer and customer tests ensure that your core functionality is unchanged and unbroken.
You do not need any special tools, such as a test tool specifically for web services. You use the tools/components/libraries/techniques that you would use in production code, exactly as you would use them in such production code. This makes your tests more meaningful, since you are not testing someone else's tools. It saves you lots of time and money, since you are not buying, deploying, developing for, and maintaining for a special tool. However, if you are testing through a GUI (don't do that!), you might need one special tool for that part (e.g., HttpUnit?).
So, let's get concrete. Assume that we want to provide some functionality for keeping track of the cafeteria's daily menu ('cause we work in a mega-corp with its own cafe in the building, like mine). Let's say that we are targeting C#.
We build some C# classes for menus, menu items, and other fine-grained pieces of functionality and its related data. We establish an automated build (you do that, right?) using nAnt that executes developer tests using nUnit, and we confirm that we can build a daily menu and look at it via all these little pieces.
We have some idea of where we are going, so we apply the Facade pattern by creating a single class that exposes a handful of methods while hiding most of the fine-grained pieces. We add a separate set of customer tests that operate only through that new facade, just as a client would.
Now we decide that we want to provide a web page for our mega-corp knowledge workers to check today's cafeteria menu. We write an ASP.NET page, have it invoke our facade class (which becomes our model if we are doing MVC), and deploy it. Since we have already thoroughly tested the facade class via our customer tests, and since our single web page is so simple, we forego writing automated tests against the web page--a manual test using a few fellow knowledge workers will do the trick.
Later, we start adding some major new functionality, like being able to preorder our lunch for the day. We extend our fine-grained classes and the corresponding developer tests, knowing that our pre-existing tests guard us against breaking existing functionality. Likewise, we extend our facade class, perhaps even splitting off a new class (e.g., MenuFacade and OrderFacade) as the interface grows, with similar additions to our customer tests.
Now, perhaps, the changes to the website (two pages is a website, right?) make manual testing unsatisfactory. So, we bring in a simple tool comparable to HttpUnit that allows nUnit to test web pages. We implement a battery of integration/presentation tests, but against a mock version of our facade classes, because the point here is simply that the web pages work--we already know that the facade classes work. The tests push and pull data through the mock facades, only to test that the data successfully made it to the other side. Nothing more.
Of course, our grand success prompts the CEO to request (demand) that we expose the web application to mega-corp's BlackBerrys. So we implement some new pages and a new battery of integration tests. We don't have to touch the developer or customer tests, because we have added no new core functionality.
Finally, the CTO requests (demands) that we extend our cafeteria application to all of mega-corp's robotic workers--you did notice them over the last few days? So, now we add a web services layer that communicates through our facade. Again, no changes to our core functionality, our developer tests, or our customer tests. We apply the Adapter/Wrapper pattern by creating classes that expose the facade with an equivalent web service API, and we create client-side classes to consume that API. We add a new battery of integration tests, but they use plain nUnit to create client-side API classes, which communicate over the web service wiring to the service-side API classes, which invoke mock facade classes, which confirm that our wiring works.
Note that throughout this whole process, we did not need anything significant beyond our production platform and code, our chosen development platform, a few open-source components for automated building and testing, and a few well-defined batteries of tests. Also note that we didn't test anything that we don't use in production, and we didn't test anything twice.
We ended up with a solid core of functionality (business logic tier) that has proven itself mature (hypothetically). We have three separate presentation tier implementations: a website targeted to desktops, a website targeted to BlackBerrys, and a web service API.
Now, please forgive me for the long answer--I tire of inadequate answers and I did not want to provide one. And please note that I have actually done this (though not for a cafeteria menu).
This is a very interesting question that I still haven't seen a good generic answer to. Some people suggest using SoapUI but I haven't had time to actually test that yet. This page might be interesting on that.
Another way might be to somehow wrap the WebDev.WebHost.dll and use that ... Phil Hakkck discusses that in this post.
It's also be discussed before on SO here.
Please let us know if you find another solution to this!
This is the way to do it:
Back to Richard's question though, my
previous dev team had a solution.
Basically what we did was to write a
generic configurable HttpHandler that
parsed incoming service requests and
returned pre-set responses. The
response sent back was configurable
based on conditions such as XPath
I haven't had to do this in a while, but when I would test my Biztalk Apps I always used either soap ui or web service studio. I was able to test different input values without effort.