YOUnite Adaptor Guide for Java Developers

Owned by Mark Fitzpatrick (Unlicensed)
Last updated: May 29, 2018 by Former user (Deleted)
16 min read

This page contains content intended for the Adaptor Developer.

What is a YOUnite Adaptor?

YOUnite Adaptors are essentially extensions to the YOUnite Data Hub, allowing access to managed data. Third parties implement these adaptors using the YOUnite Adaptor SDK. Adaptors are a fundamental component to federated data domains.

Additionally, an Adaptor is software located within a system that shares data through the YOUnite Data Hub and acts as the connection point between that system and the Data Hub. An adaptor focuses on ETL (Extract, Transform, and Load) and CRUD functions, ensuring the outbound data from that system meets the format requirements of the Data Hub and transforming the inbound data from the hub into what any other system requires. It may have additional business logic such as filtering for specific data from the Data Hub.


For more information on YOUnite adaptors see:

Introductions to Adaptors can be found on the Introduction to YOUnite page and the Adaptors page.

Managing adaptors can be found on the Managing Adaptors page.

The YOUnite API Documentation can be found at https://younite.us/api

How to Get Started With the YOUnite SDK

To implement an adaptor you use the YOUnite Adaptor SDK (SDK). The SDK handles much of the behind-the-scenes complexity, but developers still need to manage: configuration elements, the life cycle, and the proper use of the SDK Annotations.

  1. Get the actual YOUnite Adaptor SDK. For Java, the most common method is to use the YOUnite-provided Maven artifact. If you don't use Maven, you can optionally download the SDK library directly. <TODO Kevin: Link here to latest sdk jar file>.
  2. Use the following Maven configuration:
<dependencies>
  <dependency>
    <groupId>com.younite</groupId>
    <artifactId>adaptor-sdk</artifactId>
    <version>1.0.0-SNAPSHOT</version>
  </dependency>
</dependencies>

3. Add a server to your project POM to access the YOUnite Maven Repository: <TODO KEVIN: ONCE YOUNITE MAVEN REPO IS WORKING... INSERT INFO BELOW>

<repositories>
  <repository>
    <id>younite-snapshots</id>
    <name>younite</name>
    <url>https://younite.bintray.com/</url>
	<snapshots>
		<enabled>true</enabled>
	</snapshots>
  </repository>
</repositories>

4. Once you have these configurations in place for your project, the YOUnite Adaptor SDK will be available.

Dependencies

The YOUnite Adaptor SDK aims to be a very small, easy-to-use library. It is a product of the design goal to avoid external library dependencies as much as possible. The YOUnite Adaptor SDK depends on only one external library: the Google Reflections library. Using just this one external library minimizes the impact of integrating within existing applications that may use duplicates of the same libraries, possibly of different versions, causing a dependency conflict. The Google Reflections library provides run-time reflection capabilities needed to find and resolve classes and methods.

Use the following configuration in your project's pom.xml file:


<dependency>
  <groupId>org.reflections</groupId>
  <artifactId>reflections</artifactId>
  <!-- use latest version of Reflections -->
  <!-- maintained here: https://github.com/ronmamo/reflections -->
  <version>0.9.11</version>
</dependency>

Adaptor Architecture

Once an adaptor is connected to the YOUnite Data Hub through the YOUnite Message Bus, it is able to send and receive data and ops messages. The SDK has minimal configuration steps, allowing developers to focus on their adaptor's business logic instead of the inner workings of sending and receiving messages, parsing those messages, etc. To facilitate getting your adaptor up and running, the YOUnite Adaptor SDK makes use of  annotations. Developers use these annotations to define the adaptor's capabilities: what their adaptor can produce and/or consume. Capabilities loosely translate into a Pub/Sub configuration on the YOUnite Data Hub.

Capabilities tell the YOUnite Data Hub:

  • the specific domain properties they want to receive changes for
  • which of their adaptor-associated local services' domain properties will be pushed to the YOUnite Data Hub
  • which of their local services' domain properties will be sent when requested by the YOUnite Data Hub

Local services could be direct database data, an FTP server, in-memory data, or a remote service with data. The dynamic nature of YOUnite domains leaves the details to each individual adaptor implementation. You determine how your adaptor accesses and retrieves domain property data and what, if any, transformations get applied to the data.

Connecting Adaptors to the YOUnite Data Hub

To get connected to the YOUnite Data Hub, an adaptor must make use of a dynamic transport layer. YOUnite Adaptor SDK comes bundled with the Active MQ Message Bus transport layer, which requires minimal configuration (described below). The YOUnite Adaptor SDK's flexibility leaves transport layer options open, however, as the SDK agnostically handles Data Hub connectivity and sending and receiving data. 

Configuring 

Because the YOUnite Data Hub runtime engine may be deployed in any number of environments (including, but not limited to, local developer machines, QA, Staging, Production, etc.), you must tell the YOUnite Adaptor SDK how to connect to the YOUnite Data Hub.

  1. Configure the YOUnite Adaptor SDK with the following items:
    • the URL the YOUnite Adaptor SDK will use to connect to the implemented transport layer
    • authentication details that allow the transport layer to identify the specific Adaptor to the YOUnite Data Hub as a legitimate
    • a valid adaptor UUID and Zone UUID (previously registered with the YOUnite Data Hub)
    • possibly the OAuth Server URL used by the transport layer (TODO: Determine if this is necessary.. or can the transport layer which is already configured with the URL details in order to check the validity of the adaptor authentication just use what it has configured)
  2. Create a Config object, provided by the SDK, and provide the configuration properties, such as those mentioned previously and a few others. 
    • The YAML file is turned in to a Config object when that is the configuration option used. Either way is identical to the SDK, though providing a YAML file can present some potential runtime issues if the file is not valid, or not found, etc. On the other hand, it does allow for an external configuration file as opposed to code that has to be recompiled to pick up any configuration changes.

Adaptor Startup

Once the configuration steps above are complete, use the following steps to start your adaptor.

  1. Call the AdaptorSDK.init() method and pass it either the Config object, or the YAML configuration file location. <Add links to example working code here>.  The configuration will attach to the transport layer, authenticate, and set up data and ops listeners for incoming messages.
  2. Behind the scenes, the YOUnite Adaptor SDK attempts to:
    • locate any annotated adaptor classes
    • build the capabilities list from annotated methods within adaptor classes
    • connect to the transport layer
    • send the capabilities list to the YOUnite Data Hub, and
    • build some necessary mappings in memory for the SDK to properly process incoming messages

Mappings

Internally, the YOUnite Adaptor SDK maintains data structures to keep track of your adaptor capabilities and the associated domain version(s) of the YOUnite Data Hub. This is what makes it possible to:

  • respond to incoming data
  • send outgoing data for the purpose of data change detection (implemented by the adaptor developer)

Before diving into more details, it is helpful to understand adaptor capabilities and how they are defined.

Adaptor Capabilities

As mentioned previously, when an adaptor is started (by calling the AdaptorSDK.init() method), it builds the list of capabilities that it must send to the YOUnite Data Hub. The Adaptor Capabilities List consists of the capabilities an adaptor declares to the YOUnite Data Hub upon initialization that 1) link records in the underlying application/service to YOUnite data records, 2) POST entries in the underlying application/service that link to YOUnite data records, and 3) manipulate data in the underlying service.

The capabilities list lets the Data Hub know:

  • what data the adaptor accepts (most notably, from other adaptors)
  • what data the adaptor can provide (most notably to other adaptors)

Capabilities describe:

  • a specific domain name
  • domain version
  • a set of properties that the domain schema defines (that are associated with the domain name/version)

What this means is the Adaptor developer will either:

  • work closely with the Data Steward to define the domains and their properties (as defined by a JSON schema representing the domain)

-OR-

  • use the YOUnite Adaptor SDK's Adaptor Generator tool to quickly build and generate an Adaptor stub (details below).

The purpose of an adaptor is to:

  • get domain/version property data to do something with it (from other adaptors)

-OR-

  • to send domain/version property data the adaptor is responsible for to other adaptors (via the Data Hub)

We are defining which properties of a specified domain/version the adaptor is able to work with. 

The YOUnite Adaptor SDK provides a set of annotations for annotating methods within an annotated Adaptor class. The annotation properties indicate the domain's name, version, and properties names within the domain that the annotated method expects as input or returns as output.

Lets see a simple example, including how we annotate the Adaptor class:


@Adaptor(name = "SimpleAdaptor")
public class MyAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {})
  })
  public Student getStudent() {
    return new Student("Jane Doe");
  }
}


Each annotation has a specific purpose. In the code example above:

  • the @Adaptor annotation specifies the class MyAdaptor is an implementation of an Adaptor
  • a single method, getStudent(), defines the GetFromAdaptor annotation
  • the @GetFromAdaptor is used to define a method that responds to an incoming request to retrieve the specified properties from the local service

From the example above, you can see a new Student object is returned. More examples will provide details on when and how to use the various method annotations. See the list of YOUnite Adaptor SDK supported annotations here: (Insert link to the table of annotations, definitions, etc). 

All annotation have two things in common:

  • they always specify at least one domain by name and version. There is no use case for any of the Action annotations being used without a domain name AND version. In fact, the in-memory mapping mentioned earlier requires that the domain name AND version both be provided at all times. If, during the processing of adaptors, an @Domain annotation is discovered without a name and version, or only having one or the other, a processing exception will occur as the method will be deemed an invalid annotation use.
  • for every @Domain specified, a properties array is required. Unlike the requirement to specify values (such as domain name and version,) the properties array is a hint to the YOUnite Adaptor SDK about which domain properties the properties are associated with, this particular method (and ultimately the Adaptor) has the capability to accept or send (depending on the Action annotation being used).

What does this mean exactly? Simply that whenever a @Domain is specified, the object associated with that Domain definition is passed in as a parameter OR returned from the method, again, depending on the Action annotation being used, regardless of the properties specified.

What is the purpose of specifying properties? Specifying properties lets the YOUnite Data Hub know exactly what properties to send to, or expect from, an adaptor. For example, in the above code sample, the Data Hub knows that this adaptor will return a Student domain object, version 1, back in response to the GetFromAdaptor action. And, because no properties are specified, it is essentially a wild card "*", meaning any-to-all of the properties within the domain may be returned as part of the Student object.

What happens if you define a property?

@Adaptor(name = "SimpleAdaptor")
public class MyAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"})
  })
  public Student getStudent() {
    return new Student("Jane Doe");
  }
}

The code sample above tells the YOUnite Data Hub to only expect the name property of the Student domain (version 1) to be returned. Or, more explicitly, it tells the YOUnite Data Hub that the capability of THIS Adaptor is that it returns the Name property of the Student domain, version 1. This allows the YOUnite Data Hub to use this information to assemble a routing manifest (link to ROUTING details here).

What happens if the adaptor method sets additional properties on the object?

@Adaptor(name = "SimpleAdaptor")
public class MyAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"})
  })
  public Student getStudent() {
    Student student = new Student();
    student.setName("Jane Doe");
    student.setAge("21");
    student.setAddress("Some Address");
    return student;
  }
}

In the example above only the name property is defined, yet we added age and address to the returned object. One of two things will happen:

  • Either the entire object as it is populated in the example above is sent back (in JSON format) and the Data Hub simply ignores the other properties based on the fact that the annotation only indicates it handles the Name property, OR,
  • the YOUnite Adaptor SDK itself may do one of the following:
    • it will do some extensive checking to ensure that only the specified properties contain data and if anything else is set to anything other than null (which results in the JSON string not containing the property name/value), a runtime exception can be thrown, OR,
    • it will modify the structure so that ONLY the properties specified will contain data before the object is sent on its way.

Both of these last two options are possible but, as of version 1 of the YOUnite Adaptor SDK, the entirety of the object is sent with everything filled and is left for the Data Hub to deal with.

What if you want to work with multiple domains in a single Adaptor class?

Perhaps the local service handles students and courses. How do you do this? We could define two @Adaptor classes, each with their own set of annotated methods related to a specific domain:


@Adaptor(name = "StudentAdaptor")
public class StudentAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"})
  })
  public Student getStudent() {
    Student student = new Student();
    student.setName("Jane Doe");
    return student;
  }
}

------------------------------------------------------------------------

@Adaptor(name = "CourseAdaptor")
public class CourseAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Course", version = "1", properties = {})
  })
  public Course getCourse() {
    return new Course();
  }
}

However, one problem that may arise is that you may have a need to work with both objects in one class and may not want to have to set up additional helper methods or other means to use both classes in some manner.

A better approach is to be able to use both domains in a single adaptor:

@Adaptor(name = "StudentAndCourseAdaptor")
public class StudentCourseAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"})
  })
  public Student getStudent() {
    Student student = new Student();
    student.setName("Jane Doe");
    return student;
  }

  @GetFromAdaptor(domains = {
    @Domain(name = "Course", version = "1", properties = {})
  })
  public Course getCourse() {
    return new Course();
  }
}

In the above example both domains are accounted for in separate methods but in just one Adaptor. You can specify as many of these as you want in one class, but best practices indicate it would be best to limit this to situations where you need to use multiple domains in the one class.

As stated above, a capability defines a domain name, version, and a subset of properties defined by the Domain Schema, declared in one of the Action annotations. For each action annotation defined, at least one domain name and version are specified. Remember, there is no point in defining an action without the domain name and version it expects to work with as this will cause an error. Each and every @Domain() becomes a capability.

Same Domain, Different Properties

It is possible to use the same action annotation multiple times on different methods. This allows you to separate your code by domain/version, if desired. Or, you can separate individual properties on a property-per-method basis. For example:

@Adaptor(name = "StudentAndCourseAdaptor")
public class StudentCourseAdaptor {
  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"})
  })
  public Student getStudentName() {
    Student student = new Student();
    student.setName("Jane Doe");
    return student;
  }

  @GetFromAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"address"})
  })
  public Student getStudentAddress() {
    Student student = new Student();
    student.setAddress("address");
    return student;
  }
}

In the example above, the same action is used on two methods for the same domain and version. However, each method's property is different. One returns the Student with the name filled out, the other returns the Student with the address filled out. You may notice they both return a Student object, yet they define different properties.

What is to stop an adaptor developer from filling in other properties in either of the Student objects other than the property(ies) it is declared to manage? Nothing. Any extra data will simply be ignored by the Data Hub <TODO: We MIGHT remove data before it is sent at the SDK layer.. not initially..but in a future version, scrub data not defined so as to avoid the Data Hub having to do that work (e.g. distribute the load of doing that work to the adaptors to limit the processing needed by Data Hub for this menial task). > 

To be clear, the purpose for specifying the same action for domain/version but different properties is code aesthetics. Trying to shoehorn extra data into the object is bad form. Don't do it. Keep the code concise and consistent.

Combining Capabilities

In the previous section, examples showed you could define the same action for the same domain and version, but declare different properties. We reiterated that a capability is nothing more than the domain name, version, and its properties.

What happens when you have two (or more) methods with the same action annotation each having a subset of the domain schema properties? They get combined into one capability. A capability is the domain name/version and the sum of all properties defined, regardless of the number of methods over which the definitions are distributed. 

What About Data Flowing Into Adaptors From YOUnite? 

There are actions to handle those situations too. There is PostOrLinkToAdaptor, and PutToAdaptor, as well as DeleteAtAdaptor. 

The PostOrLinkToAdaptor annotation is used when new data is intended to be stored at the local service. Typically this would mean the entire domain object is provided as the parameter to the method that is annotated with PostOrLinkToAdaptor.

Data changes to individual properties, on the other hand, would fall under the PutToAdaptor action. This is used to update (think overwrite) the local data with data provided from the Data Hub.

Unlike the GetFromAdaptor annotation, which can only return a single Domain object, the various incoming data actions can support multiple domain types for one method:

@Adaptor(name = "StudentAndCourseAdaptor")
public class StudentCourseAdaptor {
  @PutToAdaptor(domains = {
    @Domain(name = "Student", version = "1", properties = {"name"}),
    @Domain(name = "Course", version = "1", properties = {})
  })
  public void updateStudentOrCourse(Student student, Course course) {
    if (null != student && null != course) { // do something that may require both objects to be present at the same time
    } else if (null != student) {  // do something with the student object at the local service
    } else if (null != course) {  // do something with the course object at the local service
    } else 
  }
}

In the example above a single @PutToAdaptor action is defined, yet two domains are specified. It is possible that the method will be called with a Student object OR a Course object OR both. If the message that arrives at the adaptor contains both student data AND course data, the method would be called with BOTH objects provided. This opens up the ability to use both objects at once before working with the local service. It may seem unlikely, but there could very well be use cases where BOTH a student and a course domain must be provided before the local service can be updated.

Another use case scenario: If the local service that creates a student has a NOT NULL column specified to a Course (e.g. course table), the ability to update a student can not occur without the course data being provided as well. Again, this may be unlikely in many cases, but requirements can be unpredictable. Thus, we allow for either or both domain objects to be provided in a single method call. As such, it is best to set up null checks before attempting to use objects (or properties of the object) to avoid null pointer exceptions.

Detecting Changes (rough draft.. implementation not yet in place so this is subject to change)

One SDK feature is, when a local entity change occurs, providing a way to send that change to YOUnite MDM without the developer having to do so in code. There may still need to be some code required on the developer's part in determining how that change is detected. However, as long as the @PutToMdm annotated method is called with a domain object, that object will be sent to YOUnite MDM. This is essentially a PUSH from the adaptor to YOUnite MDM. 

To standalone or integrate...

At some point, you need a way to get your adaptor started. In the above sections you learned how you configure the adaptor to get connected to the transport layer and to apply annotations to describe the capabilities of your adaptor. But your adaptor implementation has to actually call the AdaptorSDK.init() call some how.

You can do this by either:

  • creating a standalone application wrapper (a microservice, if you will), OR,
  • integrating your adaptor implementation into an existing application, such as a web application

Standalone

If you are starting out with a clean slate and need a way to start your adaptor, a simple application framework can be used to get things started. The most important point is to understand that the YOUnite Adaptor SDK does not have a background thread that starts up and keeps it running. If you call the AdaptorSDK.init() call, and your application wrapper does not keep a thread alive and running, the application will abruptly end. It is essential to make sure your application framework maintains a thread to keep it alive in order for the adaptor to be of use.

As described in a previous section on configuration, the AdaptorSDK.init() static method needs the Config object and the String[] packages array passed to it. This is enough to get things rolling, as the Adaptor SDK can look for classes annotated with the @Adaptor annotation.

  • The Config object you know about.
  • The String[] packages is for specifying the package names annotated adaptor classes may reside. The primary purpose of this is to only look for classes within the specified packages, speeding up the process at runtime.

Note: The classpath used to look for classes is specified by two classloaders the scanning process makes use of.

  • The first is the Thread context classloader. This is typically the classloader that loaded the application and the SDK library itself.
  • The second classloader is the classloader owner of the dependent reflections library the SDK makes use of to find classes. This will typically be the same classloader in a standalone application as the thread context classloader.

Integration

Integrating the YOUnite Adaptor SDK into an existing application is similar to the standalone route described above, but with some subtle differences depending on the application being integrated. The primary caveat is to be aware of is the possible differences in classloader hierarchy.

In a standalone application the YOUnite Adaptor SDK library is loaded by the thread context classloader. In some types of applications, such as a web application that executes in a container like Tomcat or Jetty, those containers reorder the classloader hierarchy in order to ensure web applications (and their internal contents) load in specific order to assure dependent-library discovery order.

It is possible the thread context classloader will be different than the second classloader used by the Google Reflections library. While this should pose no problem for the use of the YOUnite Adaptor SDK, it is nevertheless important to be aware of potential scenarios in case a runtime classpath issue arises within the adaptor implementation. In the event that it may be needed to add additional classloaders to the two mentioned above, an overloaded init() method is available that takes in an array of ClassLoader as the middle parameter (e.g. init(Config, ClassLoader[], String...). With this, it is possible to add any additional classloaders, such as specific container loaders, to the list of loaders used to search for annotated adaptor classes.

Other than the items mentioned above, Integration is about the same as the Standalone method. At some point you make the call to the AdaptorSDK.init() method in the same way as the standalone approach (presumably a one-time initialize method). Like the Standalone approach, it is assumed the Integration container framework has some sort of background thread running to keep the process alive. 

Other Caveats (Maybe this should go in to a troubleshooting section at the end?)

The Integration approach may run in to another issue that sometimes arises in applications that make use of third-party libraries: versioning. It is unlikely, but possible, that the integration application would have another version of the Google Reflections library within the classpath (due to the nature of how and why the Google Reflections library is used; namely, for scanning the classpath for classes with specific annotations, signatures, etc). Many developers will be aware of a term "classpath hell". This situation arises when two (or more) of the same libraries are on the application classpath, usually with different versions.

Third-party libraries often bundle a "fat jar" that include classes from yet other libraries that might also be part of other libraries. A common case is logging. Often times log4j or other logging libraries will be bundled via the "fat jar" process, which can lead to runtime classpath issues. This issue is especially difficult to narrow down in integrated platform environments like servlet and JEE containers because of the way they munge the classloader hierarchy. A telltale sign is when you start to see runtime exceptions with ClassNotFoundExceptions showing up in the logs. In the case of the YOUnite Adaptor SDK, it may present as if the SDK is not finding any of your annotated adaptor classes. 

Examples

Here is a list of examples provided via the <portal? sdk.zip outside of maven? link to github projects??> with information on each.

TBD...