...

Asynchronous execution
Stage execution in sequence
Stage execution in parallel
Complex flow execution, including execution of nested flows in parallel
Dynamic stage generation based on context data
Stage cancellation of one of the upstream stages failed
Stage execution observability
- methods to observe critical moments of stage execution
- explicit logging, including flow engine reports in logs
Java-friendly context management using the Decorator pattern

Expand

title	Java code example

Code Block

language	java

import java.util.concurrent.Executors;
import org.folio.flow.api.Flow;
import org.folio.flow.api.FlowEngine;
import org.folio.flow.api.Stage;
import org.folio.flow.api.StageContext;
import org.folio.flow.model.FlowExecutionStrategy;

public class FlowEngineExample {

  public static void main(String[] args) {
    var sampleFlow = Flow.builder()
      .id("sample flow")
      .stage(new Stage1())
      .stage(new Stage2())
      .executionStrategy(FlowExecutionStrategy.IGNORE_ON_ERROR)
      .build();

    var flowEngine = FlowEngine.builder()
      .executor(Executors.newFixedThreadPool(4))
      .build();

    flowEngine.execute(sampleFlow);
  }

  public static class Stage1 implements Stage<StageContext> {

    @Override
    public void execute(StageContext context) {
      System.out.println("Stage1 executed");
    }

    @Override
    public void cancel(StageContext context) {
      System.out.println("Stage1 cancelled");
    }

    @Override
    public void recover(StageContext context) {
      System.out.println("Stage1 recovered");
    }
  }

  public static class Stage2 implements Stage<StageContext> {

    @Override
    public void execute(StageContext context) {
      throw new RuntimeException("Stage2 failed");
    }

    @Override
    public void cancel(StageContext context) {
      System.out.println("Stage2 cancelled");
    }

    @Override
    public void recover(StageContext context) {
      System.out.println("Stage2 recovered");
    }
  }
}

Sequence Task Execution

Description

...

Info

Data can be transferred between stages using StageContext model.

Stage context store data with key as String and value as Object. There is a way to make context more Java-friendly using AbstractStageContextWrapper

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...

When one of the stages in flow fails - the flow manager stops the execution and calls onFlowErrorStage (if defined)

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...

Simple flow execution (failed stage with cancellation)

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Code Block

language	java

Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(task2)
  .stage(task3)
  .stage(task4)
  .onFlowCancellation(onFlowCancellationStage)
  .onFlowError(onFlowErrorStage)/ta
  .executionStrategy(CANCEL_ON_ERROR | IGNORE_ON_ERROR)
  .build();

Parallel Task Execution

...

Define tasks that can be executed in parallel.
The Flow Engine will manage the concurrent execution of these tasks.
- parallelism is configured in the FlowEngine component
If one task fails, all running parallel tasks will be canceled except failed ones (if the strategy is CANCEL_ON_ERROR).

Parallel Stage execution

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...

Parallel Stage execution(stage failed)

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Code Block

language	java

Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(ParallelStage.of(task2_1, task2_2, task2_3))
  .stage(task3)
  .onFlowError(onFlowErrorStage)
  .build();

Models

Stage

Flow

...

Parallel Stage execution (stage failed with cancellation)

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Code Block

language	java

Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(ParallelStage.of(task2_1, task2_2, task2_3))
  .stage(task3)
  .onFlowCancellation(onFlowCancellationStage)
  .executionStrategy(CANCEL_ON_ERROR)
  .build();

Nested flow execution

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Code Block

language	java

var flow1 = Flow.builder()
  .id("Flow 1")
  .stage(task2_1_1)
  .stage(task2_1_2)
  .build();

var flow2 = Flow.builder()
  .id("Flow 1")
  .stage(task2_2_1)
  .stage(task2_2_2)
  .build();
  
Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(ParallelStage.of(flow1, flow2))
  .stage(task3)
  .build();

Interfaces and models

Flow / Flow Builder

Provides a Flow object, containing a sequence of stages and flows to be executed

Sucessfull flow executions are always finished without exceptions

If error is occurred during flow execution and executionStrategy is IGNORE_ON_ERROR - then FlowExecutionException will be raised with a reason in cause
If error is occurred during flow execution and executionStrategy is CANCEL_ON_ERROR - then
- FlowCancelledException will be raised with a reason of cancellation in cause
- FlowCancellationException will be raised with a reason of cancellation failure in cause

Flows can be executed in async mode using flowEngine.executeAsync method. In this case result in CompletableFuture will contain an exception in the body.

Method

Description

id

Used to define flow identifier that will be used for report and in the trace logs

stage

Allows to define a Stage or StageExecutor to be executed in the flow

flowParameter

Allows to define a general flow parameter that will be available for all stages in the flow

flowParameters

Allow to define a map with flow parameters that will be available for all stages in the flow

executionStrategy

Allows to define flow execution strategy:

CANCEL_ON_ERROR : on stage error – all executed stage will be cancelled by calling cancel method (if defined) in reverse order
IGNORE_ON_ERROR : on stage error – the flow will be stopped by skipping execution of upstream stage and calling onFlowError stage (if defined)

onFlowError

Allows to define a Stage or StageExecutor that will be always executed if flow is failed

onFlowCancellation

Allows to define a Stage or StageExecutor that will be always executed if flow is cancelled

onFlowCancellationError

Allows to define a Stage or StageExecutor that will be always executed if flow is cancelled and one if cancel method is failed

onFlowSkip

Allows to define a Stage or StageExecutor that will be executed if flow is skipped by previous stage failure

Info
This stage is only usable for nested flow, main flow cannot be skipped

Flow Engine

A flow engine is an object that is used to execute a flow defined by a developer

Method	Description
`execute`	Executes flow using executor and timeout from `FlowEngineBuilder` synchronously
`executeAsync`	Executes flow using executor and timeout from `FlowEngineBuilder` asynchronously, returning `Future<Void` as a result
`getFlowStatus`	Allows to get flow status from `FlowEngine` using flow identifier Posible flow statuses: `IN_PROGRESS` `SUCCESS` `FAILED` `CANCELLED` `CANCELLATION_FAILED` `UNKNOWN` (if flow by id is not found)
`builder`	Provides a `FlowEngineBuilder` to create a `FlowEngine` object

Builder

Flow engine builder allows to customize a FlowEngine object

Method	Description
`name`	Allows to define flow engine name
`lastExecutionsStatusCacheSize`	Allows to define how much history preserve in memory for latest flow executions
`executor`	Allows to define custom executor for the `FlowEngine`, by default is common `ForkJoinPool` is used
`printFlowResult`	Defines if flow result must be printed in logs
`stageReportProvider`	Allows to define custom stage report provider instead of custom one

Stage Report Provider

Stage report is a useful way to customize intends and stage execution messages

Default stage report example:

Code Block

language	java

var flowEngine = FlowEngine.builder()
    .printFlowResult(true)
    .executor(newSingleThreadExecutor())
    .executionTimeout(FIVE_SECONDS)
    .name("single-thread-flow-engine")
    .lastExecutionsStatusCacheSize(10)
    .build();
    
var flow = Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(task2)
  .stage(task3)
  .onFlowCancellationError(onFlowCancellationErrorStage)
  .build();
  
flow.execute(flow);

Code Block

17:06:51.051 INFO  FlowEngineImpl       [l-2-thread-1] Flow 'Simple Flow' execution report:
  -> Stage: task1 |> CANCELLED
  -> Stage: task2 |> CANCELLATION_FAILED with [RuntimeException]: error
  -> Stage: onFlowCancellationErrorStage |> SUCCESS

Custom stage report example:

Code Block

language	java

var flowEngine = FlowEngine.builder()
    .printFlowResult(true)
    .executor(newSingleThreadExecutor())
    .executionTimeout(FIVE_SECONDS)
    .name("single-thread-flow-engine")
    .stageReportProvider(StageReportProvider.builder()
      .template("[${flowId}] -> [${stageId}] is ${statusName}")
      .errorTemplate("[${flowId}] -> [${stageId}] is ${statusName} with [${errorType}]: ${shortErrorMessage}")
      .build())
    .lastExecutionsStatusCacheSize(10)
    .build();

var flow = Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(task2)
  .stage(task3)
  .onFlowCancellationError(onFlowCancellationErrorStage)
  .build();

flowEngine.execute(flow);

Code Block

17:04:15.015 INFO  FlowEngineImpl       [l-2-thread-1] Flow 'Simple Flow' execution report:
  [flow-tc9s82] -> [task1] is CANCELLED
  [flow-tc9s82] -> [task2] is CANCELLATION_FAILED with [RuntimeException]: error
  [flow-tc9s82] -> [onFlowCancellationErrorStage] is SUCCESS

Stage

This interface is functional, which means that it can be used as lambda for stage definition

Code Block

language	java

var stage1 = new Stage<>() {

  @Override
  public void execute(StageContext context) {
    System.out.println("Stage executed");
  }
};

var stage2 = (Stage<StageContext>) context -> System.out.println("Stage2 executed");

Flow.builder()
  .id("Simple Flow")
  .stage(stage1)
  .stage(stage2)
  .stage(context -> System.out.println("Stage3 executed"))
  .build();

Note
The limitation of using lambdas - it’s their nature in Java and this approach won’t allow to determine in information about generic type, so context customization is not working with this case, and raw StageContext will be passed

Flow Methods

The flow engine uses flow methods to determine, what capabilities the stage provides:

Stage cancellation
Stage recovery

Method	Description
`execute`	Main method, which is must be defined for stage with business logic
`getId`	Returns stage identifier, which will be printed in the final report or in listenable methods
`recover`	Provides the ability to recover a stage after fail in `execute` method
`cancel`	Provides an ability to revert changed, done in `execute` and `recover` methods, if flow is failed by upstream stage
`shouldCancelIfFailed`	Defines execution of `cancel` method using `StageContext`, by default - it’s `false`

Listenable Methods

Listenable methods provided at crucial points of stage execution to provide better observability for the stage execution status

Method	Description
`onStart`	This method is called before stage execution
`onSuccess`	This method is called after successful stage execution including successful execution of `recover` method, if `execute` failed
`onError`	This method is called after unsuccessful stage execution (`execute` and `recover` methods)
`onCancel`	This method is called after successful execution of `cancel` method
`onCancelError`	This method is called after unsuccessful execution of `cancel` method

Parallel Stage

A parallel stage is used to specify a group of stages that need to be executed simultaneously.

Code Block

var flowEngine = FlowEngine.builder().build();
var parallelStage = ParallelStage.of(task1, task2, task3);

var flow = Flow.builder()
  .id("Simple Flow")
  .stage(parallelStage)
  .build();

flowEngine.execute(flow);

Parallel Stage Builder

`id`	Used to define flow identifier that will be used for report and in the trace logs
`stage`	Allows to define a `Stage` or `StageExecutor` to be executed in the parallel
`stages`	Allows to define a list of `Stage` objects to be executed in parallel
`shouldCancelIfFailed`	Defines if parallel stage must call `cancel` method for inner stages if failed

Dynamic Stage

A dynamic stage generates a stage, flow, or parallel stage based on the data within StageContext.

Code Block

language	java

var flowEngine = FlowEngine.builder().build();
var stage1 = (Stage<StageContext>) ctx -> ctx.put("values", List.of("v1", "v2"));
var parallelStage = DynamicStage.of("dynamicStageId", ctx -> {
  var flowBuilder = Flow.builder().id("Generated flow by dynamicStageId");
  var listValues = ctx.<List<String>>get("values");
  for (var value : listValues) {
    flowBuilder.stage(c -> System.out.println(value));
  }
  return flowBuilder.build();
});

var flow = Flow.builder()
  .id("Simple Flow")
  .stage(stage1)
  .stage(parallelStage)
  .build();

flowEngine.execute(flow);

Stage Context

Stage context is generated before execution of the stage and it will contain the following data

Current flow identifier
Previous stage context data
Flow parameters (nested flow parameters will always override main flow parameters until exiting the nested flow)

Stage executor

A StageExecutor is an interface that allows developers to implement a custom stage execution method. It has already been implemented as follows:

DefaultStageExecutor - used to execute all stages implementing Stage interface
FlowExecutor - used to execute all Flow objects
ParallelStageExecutor - used to execute stages in parallel
DynamicStageExecutor - used to execute DynamicStage objects

`id`	Used to define flow identifier that will be used for report and in the trace logs
`stage`	Allows to define a `Stage` or `StageExecutor` to be executed in the parallel
`stages`	Allows to define a list of `Stage` objects to be executed in parallel
`shouldCancelIfFailed`	Defines if parallel stage must call `cancel` method for inner stages if failed

Logging

flow engine provides a general logger with the name folio-flow-engine, and the log level can be customized

Code Block
logger.flow-engine.name=folio-flow-engine logger.flow-engine.level=debug

By default - all execution logs appear at the DEBUF level, and flow engine reports at the INFO level

Code Block

language	java

var flowEngine = FlowEngine.builder()
    .printFlowResult(true)
    .executor(newSingleThreadExecutor())
    .executionTimeout(FIVE_SECONDS)
    .name("single-thread-flow-engine")
    .lastExecutionsStatusCacheSize(10)
    .build();
    
var flow = Flow.builder()
  .id("Simple Flow")
  .stage(task1)
  .stage(task2)
  .stage(task3)
  .onFlowCancellationError(onFlowCancellationErrorStage)
  .build();
  
flow.execute(flow);

Code Block

17:06:51.051 DEBUG FlowExecutor         [l-2-thread-1] [Simple Flow] Initializing flow...
17:06:51.051 DEBUG DefaultStageExecutor [l-2-thread-1] [Simple Flow] Stage 'task1' executed with status: SUCCESS
17:06:51.051 DEBUG DefaultStageExecutor [l-2-thread-1] [Simple Flow] Stage 'task2' executed with status: FAILED
java.lang.RuntimeException: error
	at org.folio.flow.api.models.CancellableTestStage.execute(CancellableTestStage.java:11) ~[test-classes/:?]
	at org.folio.flow.impl.DefaultStageExecutor.tryExecuteStage(DefaultStageExecutor.java:129) ~[classes/:?]
	at java.base/java.util.concurrent.CompletableFuture.uniApplyNow(CompletableFuture.java:684) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture.uniApplyStage(CompletableFuture.java:662) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture.thenApply(CompletableFuture.java:2168) ~[?:?]
	at org.folio.flow.impl.DefaultStageExecutor.execute(DefaultStageExecutor.java:95) ~[classes/:?]
	at org.folio.flow.impl.FlowExecutor.tryExecuteStageOrSkip(FlowExecutor.java:85) ~[classes/:?]
	at org.folio.flow.impl.FlowExecutor.lambda$execute$1(FlowExecutor.java:74) ~[classes/:?]
	at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1150) [?:?]
	at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:482) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) [?:?]
	at java.base/java.lang.Thread.run(Thread.java:840) [?:?]
17:06:51.051 DEBUG FlowExecutor         [l-2-thread-1] [Simple Flow] Flow is finished with status: FAILED
17:06:51.051 DEBUG FlowExecutor         [l-2-thread-1] [Simple Flow] Initializing flow cancellation...
17:06:51.051 DEBUG DefaultStageExecutor [l-2-thread-1] [Simple Flow] Stage 'task2' cancellation failed
java.lang.RuntimeException: error
	at org.folio.flow.api.models.CancellableTestStage.cancel(CancellableTestStage.java:15) ~[test-classes/:?]
	at org.folio.flow.impl.DefaultStageExecutor.tryCancelStage(DefaultStageExecutor.java:163) ~[classes/:?]
	at java.base/java.util.concurrent.CompletableFuture.uniApplyNow(CompletableFuture.java:684) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture.uniApplyStage(CompletableFuture.java:662) ~[?:?]
	at java.base/java.util.concurrent.CompletableFuture.thenApply(CompletableFuture.java:2168) ~[?:?]
	at org.folio.flow.impl.DefaultStageExecutor.cancel(DefaultStageExecutor.java:117) ~[classes/:?]
	at org.folio.flow.utils.StageUtils.cancelStageAsync(StageUtils.java:36) ~[classes/:?]
	at org.folio.flow.impl.FlowExecutor.lambda$cancel$8(FlowExecutor.java:116) ~[classes/:?]
	at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1150) [?:?]
	at java.base/java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:482) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) [?:?]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) [?:?]
	at java.base/java.lang.Thread.run(Thread.java:840) [?:?]
17:06:51.051 DEBUG DefaultStageExecutor [l-2-thread-1] [Simple Flow] Stage 'task1' is cancelled
17:06:51.051 DEBUG DefaultStageExecutor [l-2-thread-1] [Simple Flow] Stage 'onFlowCancellationError' executed with status: SUCCESS
17:06:51.051 DEBUG FlowExecutor         [l-2-thread-1] [Simple Flow] Flow is cancelled with status: CANCELLATION_FAILED

Versions Compared

Old Version 1

New Version Current

Key

Sequence Task Execution

Simple flow execution (failed stage with cancellation)

Parallel Task Execution

Parallel Stage execution

Parallel Stage execution(stage failed)

Models

Stage

Flow

Parallel Stage execution (stage failed with cancellation)

Nested flow execution

Interfaces and models

Flow / Flow Builder

Flow Engine

Builder

Stage Report Provider

Stage

Flow Methods

Listenable Methods

Parallel Stage

Parallel Stage Builder

Dynamic Stage

Stage Context

Stage executor

Logging

Page Comparison

Versions Compared

Old Version 1

New Version Current

Key

Sequence Task Execution

Simple flow execution (failed stage with cancellation)

Parallel Task Execution

Parallel Stage execution

Parallel Stage execution(stage failed)

Models

Stage

Flow

Parallel Stage execution (stage failed with cancellation)

Nested flow execution

Interfaces and models

Flow / Flow Builder

Flow Engine

Builder

Stage Report Provider

Stage

Flow Methods

Listenable Methods

Parallel Stage

Parallel Stage Builder

Dynamic Stage

Stage Context

Stage executor

Logging