Data extraction-ApsaraMQ for Kafka(Kafka)-阿里云帮助中心

When you route events through EventBridge, you may need to reshape or filter the event payload before it reaches the target. EventBridge provides four transformation methods that convert events from the standard CloudEvents format into the structure the target expects:

Method	Use case	What gets routed
Complete event	Route the full event payload without changes	The entire CloudEvents-format event
Partial event	Extract a single field from the event	The value at the specified JSONPath
Fixed value	Use the event as a trigger only	A predefined constant value
Template	Reshape the event into a custom format	A string or JSON structure with variable substitution

Transformation pipeline

EventBridge receives events in the standard CloudEvents 1.0 format. When an event matches a rule, EventBridge applies the transformation method you configured, then delivers the result to the event target:

Event source  -->  EventBridge  -->  Transform  -->  Event target
               (CloudEvents 1.0)   (your method)

The following sample event is used throughout this topic to demonstrate each method:

{
    "id": "7adc8c1a-645d-4476-bdef-5d6fb57f****",
    "source": "acs.oss",
    "specversion": "1.0",
    "type": "oss:ObjectCreated:PostObject",
    "datacontenttype": "application/json",
    "dataschema": "http://example.com/test.json",
    "subject": "acs:oss:cn-hangzhou:1234567:xls-papk/game_apk/123.jpg",
    "time": "2020-08-17T16:04:46.149Asia/Shanghai",
    "aliyuneventbusname": "demo-bus",
    "aliyunregionid": "Shanghai",
    "data": {
        "name": "test",
        "scope": 100
    }
}

Complete event

Route the full CloudEvents-format event to the target without any transformation. The event target receives the exact payload shown in the sample event above.

Partial event

Extract a single field from the event by using a JSONPath expression. Only the extracted value is routed to the event target.

Constraints:

Parameter	Constraint
JSONPath expression	Only one expression per transformation
Extracted value	Up to 1,024 characters

Example: Extract the name field from the data object in the sample event.

JSONPath	`$.data.name`
Output	`test`

Fixed value

Use the event purely as a trigger. EventBridge ignores the event content and routes a predefined constant value to the event target.

Constraints:

Parameter	Constraint
Fixed value	Up to 1,024 characters

Example: Set test1 as the fixed value. Regardless of the event content, the event target receives:

test1

Template

Build a custom output by extracting event fields into named variables with JSONPath, then substituting those variables into a template. The rendered result is routed to the event target.

Constraints:

Parameter	Constraint
Variable value (JSONPath or fixed)	Up to 1,024 characters
Template body	Up to 10,240 characters
Variable definitions	Nested structures not supported

Define variables

Map variable names to JSONPath expressions or fixed strings in the Parameters field:

{
    "name": "$.data.name",
    "constant": "Please deal with it timely."
}

Each variable value can be either:

A JSONPath expression that extracts a value from the event (for example, $.data.name)
A fixed string (for example, "Please deal with it timely.")

Example: Using the parameters above with the sample event:

Template:

The instance is broken, which name is ${name}, ${constant}

Output:

The instance is broken, which name is test, Please deal with it timely.

Reference variables in the template

Use ${variable_name} syntax in the Template field. EventBridge resolves each variable at runtime before routing the output.

Three output formats are supported:

Note

The following examples assume the event data field contains {"name": "test", "state": "RUNNING"}.

Simple string

Parameters:

{
    "name": "$.data.name",
    "state": "$.data.state"
}

Template:

"name ${name} is in ${state}"

Output:

"name test is in RUNNING"

Simple JSON

Parameters:

{
    "name": "$.data.name",
    "state": "$.data.state"
}

Template:

{
    "name": "${name}",
    "state": "${state}"
}

Output:

{
    "name": "test",
    "state": "RUNNING"
}

JSON with variables and fixed values

Parameters:

{
    "name": "$.data.name",
    "state": "$.data.state"
}

Template:

{
    "name": "${name}",
    "state": [
        9,
        "${state}",
        true
    ],
    "Transformed": "Yes"
}

Output:

{
    "name": "test",
    "state": [
        9,
        "RUNNING",
        true
    ],
    "Transformed": "Yes"
}