SAP and Kotlin

The SAP Java Connector is used to develop SAP-compatible software components which are executed on the JVM.
Using the connector you can call ABAP from Java and vice versa. In this talk I show how the use of Kotlin helps to develop these components. Coroutines are used for scalability and a DSL is used to create a simplified version of the Connector API.

by Cord Jastram
presented on April 10, 2018 @codecentric

Transcript

1. SAP and Kotlin Cord Jastram, SAP Consultant cord.jastram@gmail.com
2. Agenda • SAP • Extending SAP Systems • Using a Kotlin DSL to access SAP Systems • Using Coroutines to create scalable components • Q and A
3. Caution • Creating a DSL and using Coroutines worked out of the box • I did not get a deeper understanding of the internals
4. SAP • Enterprise Resource Planning (ERP) System • Financials and Controlling FI CO • Production Planning PP • Human Resources HR • Sales and Distribution SD • Archiving, Customs Management (Zoll) and XXX, XXXX • Uses ABAP as the main programming language Allgemeiner Berichtsaufbereitungsprozessor Advanced Business Application Programming
5. SAP Pros and Cons Pros • Market share leadership: too big to fail in the near future • A global solution for more than 40 countries including legal requirements • Software scope and industry expertise • ABAP for writing business logic and interacting with modules written in Java and .NET Cons • Complex pricing, high TCO and recurring upgrades • New technologies only available for new releases after long ramp up phases • ABAP for developing infrastructure code like connecting mobile devices to SAP • Limited number of Open Source libraries for ABAP, commercial libraries are expensive
6. What can we do? Use Java libraries to pimp your SAP
7. Use case for a Java extension (1) • Customer wants to create predictions for sales volumes using Neural Networks • Customer wants to optimize the distribution of pallets on trucks using Constraint Logic Programming (CLP) • No ABAP libraries available • .NET and JAVA libraries available
8. Use case for Java extension (2) • Customer uses an old SAP release • Service technicians use a mobile client based on Lotus Notes • Customer wants to send push Notifications to technicians from the SAP system • Customer wants to send basic informations to technicians from the SAP system • Google Firebase provides a sync layer for free / small amount • No ABAP libraries available • JAVA libraries available
9. First Task Connect SAP to a Java program running on a JVM
10. SAP Java Connector JCo The SAP Java Connector (SAP JCo) is a middleware component that enables the development of SAP-compatible components and applications in Java. SAP JCo supports communication with the SAP Server in both directions: Inbound: Java calls an ABAP Function Module Outbound: ABAP calls Java a Function Module implemented in JAVA
11. SAP Java Connector JCo Pros • Free of charge for SAP customers • Rock solid software • Excellent APIs for SAP Busines Objects Cons • Complicated API • Verbose coding SAP System RFC Library JNI Layer RFC Middleware Middleware Interface JCo Java API Java Application
12. Second Task Call asynchronous Firebase methods Call lots of methods
13. Connect a mobile device to SAP Firebase SAP Connector
14. Challenges Firebase SAP Connector
15. What can we do? KOTLIN !
16. Solution Firebase SAP Connector
17. An internal DSL for the SAP JCo
18. SAP Function Modules • A Function Module in ABAP is similar to a public static method in JAVA • The APIs of an SAP System are defined by Function Modules • You can write your own Function Modules
19. Definition
20. Import Parameters
21. Export Parameters
22. Tables Parameter
23. Exceptions
24. ABAP DATA: ls_option TYPE rfc_db_opt, lt_options TYPE TABLE OF rfc_db_opt, lt_fields TYPE TABLE OF rfc_db_fld, ls_tab512 TYPE tab512, lt_tab512 TYPE TABLE OF tab512. ls_option-text = 'MSGNR = ''100'''. APPEND ls_option TO lt_options. CALL FUNCTION 'RFC_READ_TABLE' EXPORTING query_table = 'T100' rowcount = 5 TABLES options = lt_options fields = lt_fields data = lt_tab512 EXCEPTIONS table_not_available = 1 … OTHERS = 0. IF sy-subrc = 0. LOOP AT lt_tab512 INTO ls_tab512. WRITE / ls_tab512-wa. ENDLOOP. ENDIF.
25. Java JCoDestination destination = JCoDestinationManager.getDestination("NPL_DEMO"); JCoFunction function = destination.getRepository().getFunction("RFC_READ_TABLE"); function.getImportParameterList().setValue("QUERY_TABLE", "T100"); function.getImportParameterList().setValue("ROWCOUNT", 5); JCoTable optionsTable = function.getTableParameterList().getTable("OPTIONS"); optionsTable.appendRow(); optionsTable.setValue("TEXT", "MSGNR = '100'"); try { function.execute(destination); JCoTable table = function.getTableParameterList().getTable("DATA"); for ( int i=0; i < table.getNumRows(); i++) { table.setRow(i); System.out.println( table.getValue("WA")); } } catch (AbapException e ) { System.out.println("ERROR: " + e.getMessage() ); }
26. Kotlin DSL sapCall("FIREBASE") { rfcFunction("RFC_READ_TABLE") { importing { this["QUERY_TABLE"] = "T100" this["ROWCOUNT"] = 5 } table("OPTIONS") { this.appendRow() this["TEXT"] = "MSGNR = '100'" } execute() onSuccess { table("DATA").forEach { println(it["WA"]) } } onAbapException { e -> println("ERROR ABAP Exception: ${e.message}") } } }
27. How does it work? • Use functions having a lambda with a receiver as an argument • Inside the body of the function literal, the receiver object passed to a call becomes an implicit this, so that you can access the members of that receiver object without any additional qualifiers, or access the receiver object using a this expression. • This behavior is similar to extension functions, which also allow you to access the members of the receiver object inside the body of the function.
28. How To (Rule of thumb) • Write an example of your DSL in pseudo code • Describe the class and the methods you need in each lambda • Implement the classes and functions top down
29. Step 1 sapCall("FIREBASE") { Destination.rfcFunction("RFC_READ_TABLE") { importing { this["QUERY_TABLE"] = "T100" this["ROWCOUNT"] = 5 } table("OPTIONS") { this.appendRow() this["TEXT"] = "MSGNR = '100'" } execute() onSuccess { table("DATA").forEach { println(it["WA"]) } } onAbapException { e -> println("ERROR ABAP Exception: ${e.message}") } } }
30. The code (simplified) fun sapCall(name : String, block : Destination.() -> Unit ) { Destination(name).block() } class Destination(destinationName: String, val destination : JCoDestination = JCoDestinationManager.getDestination(destinationName)) { fun rfcFunction(name : String, block: RfcFunction.() -> Unit) { RfcFunction(this.destination, name).block() } }
31. Step 2 sapCall("FIREBASE") { rfcFunction("RFC_READ_TABLE") { RfcFunction.importing { this["QUERY_TABLE"] = "T100" this["ROWCOUNT"] = 5 } RfcFunction.table("OPTIONS") { this.appendRow() this["TEXT"] = "MSGNR = '100'" } RfcFunction.execute() RfcFunction.onSuccess { table("DATA").forEach { println(it["WA"]) } } RfcFunction.onAbapException { e -> println("ERROR ABAP Exception: ${e.message}") } } }
32. The code (simplified) class RfcFunction(val destination: JCoDestination, name: String) { protected val importingParameters: ImportingParameters protected val exportingParameters: ExportingParameters private val tableParameters: JCoParameterList init { importingParameters = ImportingParameters(function.importParameterList) exportingParameters = ExportingParameters(function.exportParameterList) tableParameters = function.tableParameterList } fun onSuccess(init: () -> Unit) { ... } fun execute(): RfcFunction { try { this.successfull = false function.execute(destination) this.successfull = true }catch(e: AbapException) { this.abapException = e } catch (e: Throwable) { this.throwable = e } return this } fun onAbapException(init: (e: AbapException) -> Unit) { ... } fun exporting(init: ExportingParameters.() -> Unit): ExportingParameters { exportingParameters.init() return exportingParameters } fun importing(init: ImportingParameters.() -> Unit): ImportingParameters { importingParameters.init() return importingParameters } }
33. Kotlin DSL sapCall("FIREBASE") { rfcFunction("RFC_READ_TABLE") { importing { ImportingParameter.this["QUERY_TABLE"] = "T100" ImportingParameter.this["ROWCOUNT"] = 5 } table("OPTIONS") { this.appendRow() this["TEXT"] = "MSGNR = '100'" } execute() onSuccess { table("DATA").forEach { println(it["WA"]) } } onAbapException { e -> println("ERROR ABAP Exception: ${e.message}") } } }
34. The code class ImportingParameters(private val parameters: JCoParameterList?, private val writeonlyStructure: WriteonlyStructure = WriteonlyStructure(parameters)) { fun structure(structureName: String, init: WriteonlyValues.() -> Unit): WriteonlyValues { var writeonlyStructure = WriteonlyStructure(this.parameters!!.getStructure(structureName)) writeonlyStructure.init() return writeonlyStructure } operator fun set(name: String, value: String) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: BigInteger) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Boolean) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Char) { writeRecord!!.setValue(name, value)} operator fun set(name: String, value: CharArray) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Short) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Int) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Long) { writeRecord!!.setValue(name, value) } operator fun set(name: String, value: Float) { writeRecord!!.setValue(name, value) } ... }
35. Kotlin DSL in IntelliJ Editor
36. DSL Code Completion Importing Parameter • Writeonly Interface • Minimal API
37. Java Code Completion Importing Parameter • Full API • Useless methods
38. Real Life SD_SALESDOCUMENT_CREATE
39. Real Life: 14 Input Parameters
40. Real Life: 39 Table Parameters
41. Real Life: 130 Fields for a Structure
42. Coroutines
43. Why do I use Coroutines? • Coroutines help me to execute functions in parallel • Coroutines help to call asynchronous functions in a deterministic order
44. Kotlin Coroutines • Coroutines are experimental in Kotlin 1.1+ • The API is defined in kotlin.coroutines.experimental as the API might change in the future • The API will move to kotlin.coroutines when the API is finished • Warnings on experimental status are disabled via Gradle apply plugin: 'kotlin' kotlin { experimental { coroutines 'enable' } } apply plugin: 'kotlin' kotlin { experimental { coroutines 'enable' } }
45. Coroutines From the documentation • “Basically, coroutines are computations that can be suspended without blocking a thread” • “.. coroutines can not be suspended at random instructions, but rather only at so called suspension points, which are calls to specially marked functions” • “Coroutine suspension is almost free”
46. Coroutines Implementation 1. Extension to the Kotlin compiler • New Keyword: suspend for function • Compilation of coroutines to State Machines 2. Library • Functions to create coroutines: Coroutine Builder • Functions to wrap existing asynchronous APIs with coroutines • Functions to resume a suspended coroutine 3. Runtime • Dispatching of coroutines to Threads
47. Coroutines versus Threads
48. 2 Asynchronous Calls + 1 Thread Time call first service callback from service Blocking Blocking call next service with result from first service callback from service
49. 12 Asynchronous Calls + 6 Threads • Threads are expensive • Upper limit of threads
50. 2 Asynchronous Calls with Coroutine Time call a service callback from service to resume Suspend Suspend call next service callback from service
51. 12 Asynchronous Calls + 6 Coroutines + 1 Thread • Coroutines are light-weight • You can create lots of coroutines
52. Simple Benchmark Threads versus Coroutines Thread val time = measureTimeMillis { val n = AtomicInteger() val jobs = List(N) { thread(start=true ) { n.addAndGet(1) } } jobs.forEach { it.join() } } println(time) Coroutine val time = measureTimeMillis { val n = AtomicInteger() val jobs = List(N) { launch { n.addAndGet(1) } } jobs.forEach { it.join() } } println(time)
53. Coroutines versus Threads -2000 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 1 10 100 1000 10000 100000 1000000 10000000 Threads /Coroutines Coroutine ST Coroutine MT Threads 1 50 19 10 10 44 23 5 100 52 24 46 1000 70 34 175 10000 120 88 1367 100000 192 179 12972 1000000 782 785 10000000 16026 14586 Time (ms) Number ofThreads/Coroutines
54. An Example suspension point from IDE coroutine builder
55. Helper Functions
56. An Example
57. An Example
58. An Example
59. An Example
60. An Example
61. An Example
62. An Example
63. An Example
64. An Example
65. An Example
66. An Example
67. An Example
68. An Example
69. • Use coroutines to perform computations in parallel • Use suspending functions to execute async calls in a deterministic order Rule of thumb
70. Wrapping existing APIs Reading values from Firebase in Java final CountDownLatch latch = new CountDownLatch(1); final List fcmInfoList = new ArrayList<TestItem>(); FirebaseDatabase.getInstance().getReference("fcm/info").addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot snapshot) { for(DataSnapshot childSnapshot : snapshot.getChildren() ){ fcmInfoList.add(childSnapshot.getValue(TestItem.class)); } latch.countDown(); } @Override public void onCancelled(DatabaseError error) { latch.countDown(); throw error.toException(); } }); latch.await(); ... Further Processing
71. Wrapping existing APIs Writing a Kotlin adapter for Coroutines for Firebase suspend fun <T> DatabaseReference.readList(clazz: Class<T>): List<T> = suspendCoroutine { continuation -> val list = ArrayList<T>() addListenerForSingleValueEvent(object : ValueEventListener { override fun onDataChange(snapshot: DataSnapshot) { try { for (ds in snapshot.children) { list.add(ds.getValue(clazz)) } continuation.resume(list) } catch (e: Throwable) { continuation.resumeWithException(e) } } override fun onCancelled(error: DatabaseError) { continuation.resumeWithException(error.toException()) } }) }
72. Wrapping existing APIs Now you can write val job = launch{ val list = FirebaseDatabase.getInstance().getReference("fcm/info").readList(TestItem::class.java) ... Further Processing } job.join()
73. Wrapping existing APIs Some Firebase functions return an ApiFuture: Wrap It! suspend fun <T> ApiFuture<T>.await(): T = suspendCoroutine { continuation -> ApiFutures.addCallback(this, object : ApiFutureCallback<T> { override fun onFailure(t: Throwable) { continuation.resumeWithException(t) } override fun onSuccess(result: T) { continuation.resume(result) } }) }
74. Wrapping existing APIs Now you can write val job = launch{ val list = FirebaseDatabase.getInstance().getReference("fcm/info").readList(TestItem::class.java) ... Further Processing } job.join()
75. Summary • Kotlin is easy to use • Kotlin DSLs help to simplify the use of APIs, which are not easy to use • Coroutines help to execute code in parallel and suspending functions and coroutines help to execute asynchronous calls in a synchronous fashion.