We're developing warehouse app for picking items which sends requests to a web service on every item scan, e. g. to update the quantity scanned in DB. From the log files I saw thet every now and then the connection on android scanners is lost and that leads to item quantity not being updated or in worst case an app crash.
What would be the best way to handle such connection failures so that I can ensure that the call to web method was successul before continuing code execution? Should I define some variable which accepts response from the web method and repeat the call until success is returned? Or is there some smarter way?
we are moving from monolithic to microservice architecture application, we're still in planning phase and we want to know what is the best practices of building it.
suppose we have two services :
User
Device
getUserDevices(UserId)
addDevice(DeviceInfo, UserId)
...
Each user has multiple devices
what is the most common, cleaner and proper way of asking the server to get all user devices ?
1- {api-url}/User/{UserId}/devices
needs another HTTP request to communicate with Device service.
for user X, get linked devices from User service.
// OR
2- {api-url}/Device/{UserId}/devices
for user X, get linked devices from Device service.
There are a lot of classic patterns available to solve such problems in Microservices. You have 2 microservices - 1 for User (Microservice A) and 1 for Device (Microservice B). The fundamental principle of a microservice is to have a separate database for each of the microservice. If any microservice wants to talk to each other (or to get data from another microservice), they can but they would do it using an API. Another way for communication between 2 microservices is by events. When something happens in Microservice A, it will raise an event and push it to a central event store or a message queue and Microservice B would subscribe to some or all of the events emitted by A.
I guess in your domain, A would have methods like - Add/Update/Delete a User and B would have Add/Update/Delete a device. Each user can have its own unique id and other data fields like Name, Address, Email etc. Each device can have its own unique id, a user id, and other data fields like Name, Type, Manufacturer, Price etc. Whenever you "Add" a device, you can send a POST request or a command (if you use CQRS) to Device Microservice with the request containing data about device + user-id and it could raise an event called "DeviceAdded". It can also have events corresponding to Update and Delete like "DeviceUpdated" and "DeviceRemoved". The microservice A can subscribe to events - "DeviceAdded", "DeviceRemoved", and "DeviceUpdated" events emitted by B and whenever any such event is raised, it will handle that event and denormalize that event into its own little database of Devices (Which you can call UserRelationships). In future, it can listen to events from other microservices too (so your pattern here would be extensible and scalable).
So now to get all devices owned by a user, all you have to do is make an end-point in User Microservice like "http://{microservice-A-host}:{port}/user/{user-id}/devices" and it will return you a list of the devices by querying for user-id in its own little database of UserRelationships which you must have been maintaining through events.
Good Reference is here: https://www.nginx.com/blog/event-driven-data-management-microservices/
it may really be either way, but to my liking, I would choose to put it under /Devices/{userId}/devices as you are looking for the devices given the user id. I hope this helps. Have a nice one!
You are requesting a resource from a service, resource being a device and service being a device service.
From a rest standpoint, you are looking for a resource and your service is providing various methods to manipulate that resource.
The following url can be used.
[GET] ../device?user_id=xyz
And device information can be fetched via ../device/{device_id}
Having said that, if you had one service that is providing for both user and device data than the following would have made sense.
[GET] ../user/{userId}/device
Do note that this is just a naming convention and you can pick what suits best for you, thing is pick one and hold onto it.
When exposing the api consistency is more important.
One core principle of the microservice architecture is
defining clear boundaries and responsibilities of each microservice.
I can say that it's the same Single Responsibility Principle from SOLID, but on macro level.
Сonsidering this principle we get:
Users service is responsible for user management/operations
Devices service is responsible for operations with devices
You question is
..proper way of asking the server to get all user devices
It's 100% responsibility of the Devices service and Users service nothing know about devices.
As I can see you thinking only in routing terms (yes API consistency is also important).
From one side the better and more logical URL is /api/users/{userId}/devices
- you try to get user's devices, these devices belong to user.
From other side you can use the routes like /api/devices/user/{userId} (/api/devices/{deviceId}) and that can be more easily processed
by the routing system to send a request to the Devices service.
Taking into account other constraints you can choose the option that is right for your design.
And also small addition to:
needs another HTTP request to communicate with Device service.
in the architecture of your solution you can create an additional special and separate component that routes the requests to the desired microservice, not only direct calls are possible from one microservice to another.
You should query the device service only.
And treat the user id like a filter in the device service. For eg: you should search on userid similar to how you would search device based on device type. Just another filter
Eg : /devices?userid=
Also you could cache some basic information of user in device service, to save round trips on getting user data
With microservices there is nothing wrong with both the options. However the device api makes more sense and further I'll prefer
GET ../device/{userId}/devices
over
GET ../device?user_id=123
There are two reasons:
As userId should already be there with devices service you'll save one call to user service. Otherwise it'll go like Requester -> User service -> Device Service
You can use POST ../device/{userId}/devices to create new device for particular user. Which looks more restful then parameterized URL.
I have SOAP service which is deployed on a server , which has two Operation
1 ) Send_Message
2 ) Recieve_Message
and now i want to add new Operation i.e Send_Message_Report
the question is what will be affect on my clients that are consuming my Wsdl ,
do they need to Re-import WSDL ?
You need to configure again the project calling your web service to make the web reference become updated because i know the project calling of that webservice has only two function working then you've said that you have to add another one to become three functions. Just update the reference on it so that your project has three functions and become updated.
I have a client server application (desktop app having 4 users and installed on different machines) on 4D. I have written an SOAP web service whose primary role is to read data from another database of SQL Server and insert those one into 4D.
All is working fine if no-one using the application. Now issue was that if someone using the application then my SOAP service is unable to write the data into 4D.
Another issue was in my mind that if there is any locking feature is applied on 4D then this should be applicable for all the 4 user who are communicating with centralized 4D.
Can anyone please help me what was the exact issue? Is it in 4D or something needed to incorporate in my SOAP service.
Generally you should use UNLOAD RECORD after you modified a record.
But a record can be locked for a lot of time for example if a customer open a dialog to modify it, for example, and keep it open. You should avoid to modify directly the records that are often used and modified by users, but if you need to do it the more general way is to wait until the record is writeable:
READ WRITE([Table]) //Change state to writeable
Repeat
DELAY PROCESS(Current Process; 30) //just wait 30 ticks (= half second)
LOAD RECORD([Table]) //Try to load record
Until(Not(Locked([Table])))
// --> here you can make changes to record
SAVE RECORD([Table])
UNLOAD RECORD([Table]) //this free the record lock
READ ONLY([Table]) // Change state to read-only
I am currently working on a project that uses JAX-WS webservices in Java.
The global topic is this : the user creates locally an object, let's say an Agent. He calls a first webservice and passes its Agent to the webservice. The webservice treats the Agent (modifies its properties : e.g. lifepoints), and passes it to another webservice. This call is made from the first webservice, so the user has nothing to do in the process.
After a chain of several webservices, the user retrieves the Agent that has been modified.
The aim of my project is to design 2 parts:
a framework that specifies the behaviour previously described : webservices, Agents and the process of migration
a demo application using my framework. The main difference is the addition of a GUI and a new class Avatar, that extends Agent. So the migration process is still being done "by the framework", with Agent objects.
The following code shows a simple example of how I call my webservice, host my Avatar, then retrieves the agent from the service :
// connection to the server
URL endpoint= new URL("http://SERVER/tomcat/KiwiBidonDynamique/ServiceWebBidonDeDadou?wsdl");
QName serviceName=new QName("http://avatar/","ServeurKiwiBidonService");
Service service = Service.create(endpoint, serviceName);
WebService port = service.getPort(WebService.class);
Avatar myAvatar = new Avatar(1, "Jack the Ripper");
port.hostAgent(myAvatar);
// some process on the service...
Avatar myAvatarTransformed = (Avatar) port.getAgent("AgentNumberOne");
When I do that, I get an exception on the final line :
Exception in thread "main" java.lang.ClassCastException: agent.Agent cannot be cast to avatar.Avatar
After a lot of log reading, I guess the reason is the way the webservice works. When being called, my Avatar given in parameter is marshalled in my JVM then unmarshalled on the service, but the service only constructs an Agent when it unmarshalles. Doing so, it truncates the data specific to the Avatar. Then when I try to retrieve my Agent from the service, it cannot be cast to an Avatar.
Is there a way to keep the Avatar information while processing as an Agent on the service ?
Can I write my own marshalling/unmarshalling somehow ?
Thanks a lot.
If your webservice has Agent element defined as incoming data, then no it is not possible to unmarshall it into an inherited class. I guess it would be possible to write your own marshaller but it is not as easy as it sounds (I would advise against it). Either write a separate WS for each class (messy) or make the incoming data have an element that can store additional structures, like type:any (also messy). The truth is WS are not exactly OO.