Variables

The Data Migrator automatically handles the transformation of Camunda 7 variables to Camunda 8 compatible formats during migration.

info

The handling and intercepting of variables described on this page is currently only supported for the Runtime Data Migrator.

About variables

This section documents which variable types are supported and how they are transformed.

For complete details on Camunda 7 variable types, see the official Camunda 7 documentation.

Supported Types

The following table shows how different Camunda 7 variable types are handled during migration:

Camunda 7 Type	Example Value	Migration Behavior	Camunda 8 Result
String	"hello world"	Direct migration	String value
Boolean	true, false	Direct migration	Boolean value
Integer	42, 1234	Direct migration	Number value
Long	123456789L	Direct migration	Number value
Double	3.14159	Direct migration	Number value
Short	(short) 1	Direct migration	Number value
Null	null	Direct migration	Null value
Date	new Date()	Converted to ISO format	String (ISO 8601)
Java Object serialized as JSON	Serialized JSON	Converted to Map	JSON object
Spin JSON	SpinJsonNode	Converted to Map	JSON object
Spin XML	SpinXmlElement	Converted to String	String (raw XML)
Java Object serialized as XML	XML serialized object	Converted to String	String (raw XML)

Unsupported Types

When a process instance contains unsupported variable types, the migrator will:

• Skip the entire process instance.
• Log a detailed error message indicating the variable type that caused the skip.
• Mark the instance as skipped for potential retry after manual intervention.

The following Camunda 7 variable types are not supported and will cause the process instance migration to be skipped:

Camunda 7 Type	Example
Byte Array	"hello".getBytes()
File	FileValue objects.
Java Serialized Objects	Java objects serialized as application/x-java-serialized-object like List, Set, Map, float, byte, char or custom types.

Transformation

Variable transformations are handled by built-in transformers.

Date

• Input: Java Date objects from Camunda 7.
• Output: ISO 8601 formatted strings (yyyy-MM-dd'T'HH:mm:ss.SSSZ).
  • Example: 2024-07-25T14:30:45.123+0200
• Timezone: Uses the JVM's default timezone setting.

JSON

JSON variables are handled differently depending on their origin:

Spin JSON Variables and JSON Object Variables (serialized with application/json):

• Deserialized into Map structures for Camunda 8.
• Maintains nested object structure.
• Example: {"name": "John", "age": 30} becomes a Map object.

Invalid JSON: If JSON cannot be parsed, the process instance is skipped.

XML

Spin XML Variables and XML Object Variables (serialized with application/xml):

• Raw XML string content is preserved.
• No parsing or transformation applied.

Name Compatibility

The migrator handles variable names that are invalid in FEEL expressions:

• Names starting with numbers (for example, 1stVariable).
• Names with spaces (for example, my variable).
• Names with special characters (for example, var/name, var-name).
• Reserved keywords (for example, null).

These variables are migrated as-is, but may require special handling in FEEL expressions using bracket notation.

Built-in Transformers

The following transformers are automatically applied during migration:

1. BuiltInVariableTransformer (Order: 0)

   • Handles all basic variable type transformations.
   • Converts JSON objects to Map structures.
   • Handles Spin JSON/XML variables.
   • Rejects unsupported variable types.
   • Runs first to ensure proper type handling.

2. BuiltInDateVariableTransformer (Order: 10)

   • Converts Camunda 7 Date variables to ISO 8601 format.
   • Uses JVM default timezone settings.
   • Runs after the main transformer to handle Date-specific formatting.

Custom Transformation

The VariableInterceptor interface allows you to define custom logic that executes whenever a variable is accessed or modified during migration. This is useful for auditing, transforming, or validating variable values.

How to Implement a VariableInterceptor

1. Create a new Maven project with the provided pom.xml structure.
2. Add a dependency on camunda-7-to-8-data-migrator-core (scope: provided).
3. Implement the VariableInterceptor interface.
4. Add setter methods for any configurable properties.
5. Package as JAR and deploy to the configuration/userlib folder.
6. Configure in configuration/application.yml.

# Variable interceptor plugins configuration
# These plugins can be packaged in JARs and dropped in the userlib folder
camunda:
  migrator:
    interceptors:
      - class-name: com.example.MyCustomVariableInterceptor
      - class-name: com.example.AnotherVariableInterceptor

Example: See ./examples/variable-interceptor directory for an example custom variable interceptor.

Execution Order

• If multiple interceptors are present, their execution order is determined by the @Order annotation (lower values run first).
• When the interceptor is not a Spring bean, the default order is used and added to last in the list.

Error Handling

When variable transformation fails:

• The entire process instance is skipped.
• Detailed exception messages are logged with the specific variable name and exception cause.
• The instance is marked for potential retry after fixing the underlying issue.
• You can use --list-skipped and --retry-skipped commands to manage failed migrations.