Introduction to Activiti Workflow Engine and Its Usage

Before explaining Activiti, we first look at what a workflow is.

Workflow is the automation of a business process, either partially or wholly, within a computer application environment, enabling predefined rules to automatically pass documents, information, or tasks among participants to achieve a business goal.

In my view, a workflow breaks a large business logic into segments and centrally controls their execution conditions, order, and communication, achieving decomposition and decoupling of business logic.

Activiti is an open‑source workflow engine that implements the BPMN 2.0 specification, allowing you to publish designed process definitions and schedule them via API.

BPMN (Business Process Model and Notation) defines the basic symbols for process diagrams and how they combine to form a Business Process Diagram.

Activiti 5.13 uses 23 tables to support the entire workflow framework, with MyBatis handling database operations. The tables are:

1) ACT_RE_*: repository tables storing static resources such as images and rules. 2) ACT_RU_*: runtime tables containing process instances, tasks, variables, asynchronous tasks, etc.; records are deleted after the process ends. 3) ACT_ID_*: identity tables holding user and group information. 4) ACT_HI_*: history tables storing historical process instances, variables, tasks, etc. 5) ACT_GE_*: generic tables, e.g., bytearray for binary data.

The basic workflow process is: define the process (outside the framework) → deploy the process definition → start a process instance (framework moves to task 1) → claim a group task → complete a personal task (framework moves to task 2) → repeat. Group tasks can be claimed by multiple users and must be claimed before they become personal tasks.

2. Activiti Usage

2.1 Create ProcessEngine

The ProcessEngine controls the entire workflow.

It can also be integrated with Spring; the applicationContext.xml configuration is shown in the following image.

2.2 Deploy Process Definition

A process is defined by the user through BPMN (XML) files, as illustrated by the BPMN diagram above.

The defined process must be deployed to Activiti before it can be used.

2.3 Start Process Instance

2.4 Handle Task

2.5 Other Operations

Through JavaBeans you can access fields such as: processInstance.getActivityId() – the current task name processDefinition.getDiagramResourceName() – the name of the diagram image in the definition file

2.6 Process Variables

Multiple tasks can communicate via process variables, which are stored as key‑value pairs in the act_ru_variable table; within the same process instance, setting a variable with an existing key overwrites the previous value.

Variables can also be referenced in process definitions using expressions like ${variableName}, which the engine resolves from act_ru_variable before executing the corresponding task.

There is an overloaded method for starting a process instance that also accepts a business key:

processEngine.getRuntimeService().startProcessInstanceByKey(processDefinitionKey, businessKey, variables);

The businessKey is usually set to the primary key of a business table, making it easy to retrieve the latest business state when using Activiti.

2.7 Group Tasks

Group Task 1

Group Task 2

2.8 Exclusive Gateway

Setting branch conditions.

3. Some Usage Experience

1) Consider mapping each workflow task to a business segment and set taskDefinitionKey to the corresponding Struts action method for better reusability.

2) Two ways to query process definitions; the latter provides more detailed information:

repositoryService.createProcessDefinitionQuery().processDefinitionId(id).singleResult()

and

(ProcessDefinitionEntity) repositoryService.getProcessDefinition(id)

.

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