[NiFi 1.23.2] Validating JSON, against a schema present as a flow file attribute

phadkev — Thu, 06 Nov 2025 12:11:05 GMT

I want to validate my JSON objects against an schema like this:

{ "type": "object", "required": [ "apple", "banana", "orange" ], "properties": { "apple": { "type": "object", "required": [ "header", "enableAlert" ], "properties": { "header": { "type": "string" }, "enableAlert": { "type": [ "boolean", "string" ], "enum": [ true, false, "true", "false" ] } }, "additionalProperties": true }, "orange": { "type": "object", "required": [ "test1", "test2" ], "properties": { "test1": { "type": "string" }, "test2": { "type": "string" } } }, "banana": { "type": "boolean" }, "additionalProperties": true } }

The schema can change per flow file, so I want to derive it from flow file attribute and then use it as ${schema}. In the ValidateJSON 1.23.2 processor, the schema can't be derived from EL.

So I thought of using a script like this:

import org.apache.nifi.processor.io.StreamCallback import java.nio.charset.StandardCharsets import org.json.JSONObject import org.everit.json.schema.loader.SchemaLoader import org.everit.json.schema.ValidationException import org.everit.json.schema.Schema def flowFile = session.get() if (!flowFile) return def schemaStr = flowFile.getAttribute('schema') if (!schemaStr) { log.error("No 'schema' attribute found.") session.transfer(flowFile, REL_FAILURE) return } def isValid = true def errorMsg = "" flowFile = session.write(flowFile, { inputStream, outputStream -> def content = new String(inputStream.bytes, StandardCharsets.UTF_8) try { def jsonData = new JSONObject(content) def jsonSchema = new JSONObject(schemaStr) def schema = SchemaLoader.load(jsonSchema) schema.validate(jsonData) } catch (ValidationException e) { isValid = false errorMsg = e.allMessages.join("; ") } catch (Exception e) { isValid = false errorMsg = e.message } outputStream.write(content.bytes) } as StreamCallback) if (isValid) { log.info("JSON validated successfully.") session.transfer(flowFile, REL_SUCCESS) } else { log.error("JSON validation failed: ${errorMsg}") flowFile = session.putAttribute(flowFile, 'validation.error', errorMsg) session.transfer(flowFile, REL_FAILURE) }

This is my setup:

ls /root/integration_src/workarea/nifi/scripts/lib json-20231013.jar org.everit.json.schema-1.14.3.jar

I am getting this error now:

ExecuteScript[id=58d580dd-019a-1000-4e36-7b54d5c2d161] Processing failed: org.apache.nifi.processor.exception.ProcessException: javax.script.ScriptException: org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
Script5.groovy: 15: unable to resolve class org.everit.json.schema.loader.SchemaLoader
 @ line 15, column 1.
   import org.everit.json.schema.loader.SchemaLoader
   ^

Script5.groovy: 16: unable to resolve class org.everit.json.schema.ValidationException
 @ line 16, column 1.
   import org.everit.json.schema.ValidationException
   ^

Script5.groovy: 17: unable to resolve class org.everit.json.schema.Schema
 @ line 17, column 1.
   import org.everit.json.schema.Schema
   ^

3 errors

Any idea on how to resolve the error?

Re: [NiFi 1.23.2] Validating JSON, against a schema present as a flow file attribute

MattWho — Thu, 06 Nov 2025 17:19:35 GMT

@phadkev

Have you considered using the ValidateRecord processor instead of the ValidateJson?

The ValidateRecord processor can be configured with a JSON reader. The Json readers can be configured to use "Schema Text". The Schema text property support expression language allowing you to extract the Schema you want to use from an inbound FlowFile attribute.

Please help our community grow. If you found any of the suggestions/solutions provided helped you with solving your issue or answering your question, please take a moment to login and click "Accept as Solution" on one or more of them that helped.

Thank you,
Matt

question Re: [NiFi 1.23.2] Validating JSON, against a schema present as a flow file attribute in Support Questions

[NiFi 1.23.2] Validating JSON, against a schema present as a flow file attribute

Re: [NiFi 1.23.2] Validating JSON, against a schema present as a flow file attribute