How many gateways in Flowable do you know?

Gateway

Gateways are used to control the flow of processes.

1. Exclusive Gateway

An exclusive gateway (also called an XOR gateway, or more professionally, an exclusive data-based gateway) is used to model decision making in a process. When execution reaches this gateway, all outgoing sequence flows are evaluated in the order in which they are defined. The first sequence flow whose condition evaluates to true (a sequence flow is considered true when no condition is set) is chosen to continue the process.

Please note that the meaning of the exit sequence flow here is different from the general case in BPMN 2.0. In general, all sequence flows whose conditions evaluate to true are selected and executed in parallel. When using an exclusive gateway, only one sequence flow is selected. When the conditions of multiple sequence flows all evaluate to true, only the sequence flow defined first in the XML is selected to continue the process. If there are no available sequence flows, an exception is thrown.

An exclusive gateway is represented by a standard gateway (diamond) with an 'X' icon inside it, which stands for exclusive OR. Please note that a gateway without an icon inside is an exclusive gateway by default. The BPMN 2.0 specification does not allow mixing diamonds with and without an X in the same process.

Examples:

 /**
 * Deployment process
 */
 @Test
 public void deploy ( ) {
 ProcessEngine processEngine = ProcessEngines .getDefaultProcessEngine ( ) ;
 RepositoryService repositoryService = processEngine .getRepositoryService ( ) ;

 Deployment deploy = repositoryService .createDeployment ( )
 .addClasspathResource ( "Leave Request Process-Exclusive Gateway.bpmn20.xml" )
 .name ( "Request Flow - Exclusive Gateway" )
 .deploy ( ) ;
 System .out .println ( "deploy.getId() = " + deploy .getId ( ) ) ;
 System .out .println ( deploy .getName ( ) ) ;
 }

 /**
 * Start a process instance
 */
 @Test
 public void runProcess ( ) {
 ProcessEngine processEngine = ProcessEngines .getDefaultProcessEngine ( ) ;
 RuntimeService runtimeService = processEngine .getRuntimeService ( ) ;
 // Assign a value to the UEL expression in the process definition
 Map < String , Object > variables = new HashMap <> ( ) ;
 // variables .put ( "g1" , "group1" ) ;
 variables .put ( "num" , 3 ) ; // Assign a value to the UEL expression in the process definition
 runtimeService .startProcessInstanceById ( "holiday-exclusive:1:4" , variables ) ;
 }


 /**
 * Start a process instance
 */
 @Test
 public void setVariables ( ) {
 ProcessEngine processEngine = ProcessEngines .getDefaultProcessEngine ( ) ;
 RuntimeService runtimeService = processEngine .getRuntimeService ( ) ;
 // Assign a value to the UEL expression in the process definition
 Map < String , Object > variables = new HashMap <> ( ) ;
 // variables .put ( "g1" , "group1" ) ;
 variables .put ( "num" , 4 ) ; // Assign a value to the UEL expression in the process definition
 runtimeService .setVariables ( "12503" , variables ) ;
 }



 /**
 * Complete the task
 */
 @Test
 public void completeTask ( ) {
 ProcessEngine processEngine = ProcessEngines .getDefaultProcessEngine ( ) ;
 TaskService taskService = processEngine .getTaskService ( ) ;
 Task task = taskService .createTaskQuery ( )
 // .processInstanceId ( "2501" )
 .processDefinitionId ( "holiday-exclusive:1:4" )
 .taskAssignee ( "zhangsan" )
 .singleResult ( ) ;
 if ( task != null ) {
 // Complete the task
 taskService .complete ( task .getId ( ) ) ;
 System .out .println ( "Task completed" ) ;
 }
 }

If all conditions of the line out of the gateway are not met, a system exception will be thrown .

But please note that the task has not been introduced, it is still the original task, and we can reset the process variables.

 @Test
 public void setVariables ( ) {
 ProcessEngine processEngine = ProcessEngines .getDefaultProcessEngine ( ) ;
 RuntimeService runtimeService = processEngine .getRuntimeService ( ) ;
 // Assign a value to the UEL expression in the process definition
 Map < String , Object > variables = new HashMap <> ( ) ;
 // variables .put ( "g1" , "group1" ) ;
 variables .put ( "num" , 4 ) ; // Assign a value to the UEL expression in the process definition
 runtimeService .setVariables ( "12503" , variables ) ;
 }

We can define conditions directly on the connection line before, so why do we need an exclusive gateway? In the case of direct connection, if none of the conditions are met, the process ends, and it ends abnormally!

2. Parallel Gateway

The parallel gateway allows the process to be divided into multiple branches, and multiple branches can also be brought together. The functionality of the parallel gateway is based on the incoming and outgoing sequence flows:

• Fork branch: After parallelization, all outgoing sequence flows create a concurrent branch for each sequence flow.
• Join aggregation: All incoming branches that arrive at the parallel gateway and wait here will pass through the convergence gateway until all branches entering the sequential flow have arrived.

Note that if the same parallel gateway has multiple incoming and multiple outgoing sequence flows, it has both branching and converging functions. In this case, the gateway will first converge all incoming sequence flows and then split them into multiple parallel branches.

The main difference from other gateways is that the parallel gateway does not resolve conditions. Even if conditions are defined in the sequence flow, they are ignored.

Examples:

After we execute the creation of the leave request and reach the parallel gateway, there are two records in the ACT_RU_TASK table.

Then there are three records in ACT_RU_EXECUTION at the same time, and one task corresponds to two execution instances.

3. Included Gateway

The Inclusive Gateway can be seen as a combination of the Exclusive Gateway and the Parallel Gateway. Like the Exclusive Gateway, you can define conditions on the outgoing sequence flows and the Inclusive Gateway will resolve them. But the main difference is that the Inclusive Gateway can select more than one sequence flow, just like the Parallel Gateway.

The functionality of the included gateway is based on incoming and outgoing sequence flows:

• Branching: All outgoing sequence flow conditions are resolved, and sequence flows that evaluate to true continue to execute in parallel, creating a branch for each sequence flow.
• Convergence: When all parallel branches reach the inclusive gateway, they enter a waiting state until every branch of the incoming sequence flow containing the process token has arrived. This is the biggest difference from the parallel gateway. In other words, the inclusive gateway only waits for the incoming sequence flow that has been selected for execution. After convergence, the process will continue to execute through the inclusive gateway.

4. Event Gateway

Event gateways allow flow decisions based on events. Each outgoing sequence flow of the gateway is connected to an intermediate catching event. When the process reaches an event-based gateway, the gateway enters a waiting state: execution is suspended. At the same time, a corresponding event subscription is created for each outgoing sequence flow.

The outgoing sequence flows of the event gateway are different from ordinary sequence flows. These sequence flows will not be actually "executed". Instead, they let the process engine decide which events the process executing to the event gateway needs to subscribe to. The following conditions should be considered:

The event gateway must have two or more outgoing sequence flows;

After the event gateway, only the intermediateCatchEvent type can be used (activiti does not support connecting ReceiveTask based on the event gateway);

An intermediate capturing event connected to an event gateway must have only one entry sequence flow.