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# Kafka Connect MaskField SMT Usage Reference for Confluent Cloud

The following provides usage information for the Apache Kafka® SMT `org.apache.kafka.connect.transforms.MaskField`.

## Description

Can be used for the following scenarios:

* Replace any string or numeric field using the `replacement` property.
* Mask specified fields with a valid null value for the following field types:
  - Boolean: Boolean.FALSE
  - Byte: (byte) 0
  - Short: (short) 0
  - Integer: 0
  - Long: 0L
  - Float: Of
  - Double: 0d
  - BigInteger: BigInteger.ZERO
  - BigDecimal: BigDecimal.ZERO
  - Date: new Date(0)
  - String: “”

Use the concrete transformation type designed for the record key (`org.apache.kafka.connect.transforms.MaskField$Key`) or value (`org.apache.kafka.connect.transforms.MaskField$Value`).

## Examples

### Mask value

This configuration snippet shows how to use `MaskField` to mask the value of a
field.

```json
"transforms": "MaskField",
"transforms.MaskField.type": "org.apache.kafka.connect.transforms.MaskField$Value",
"transforms.MaskField.fields": "string_field"
```

This masks `string_field`, transforming the original message as seen
here:

`{"integer_field":22, "string_field":"foo"}`

into the result here:

`{"integer_field":22, "string_field":""}`

### Replace value

This configuration snippet shows how to use `MaskField` to replace the value of a field. There are three transformations in the example. The first and second replace a value in a single field. The third is applied to both `office` and `mobile` phone number fields.

```json
"transforms": "SSNMask", "IPMask", "PhoneMask",

"transforms.SSNMask.type": "org.apache.kafka.connect.transforms.MaskField$Value",
"transforms.SSNMask.fields": "SSN",
"transforms.SSNMask.replacement": "***-***-****",

"transforms.IPMask.type": "org.apache.kafka.connect.transforms.MaskField$Value",
"transforms.IPMask.fields": "IPAddress",
"transforms.IPMask.replacement": "xxx.xxx.xxx.xxx",

"transforms.PhoneMask.type": "org.apache.kafka.connect.transforms.MaskField$Value",
"transforms.PhoneMask.fields": "office,mobile",
"transforms.PhoneMask.replacement": "+0-000-000-0000"
```

## Properties

| Name          | Description                                              | Type   | Default   | Valid Values                                                                             | Importance   |
|---------------|----------------------------------------------------------|--------|-----------|------------------------------------------------------------------------------------------|--------------|
| `fields`      | Names of fields to mask.                                 | list   |           | non-empty list                                                                           | high         |
| `replacement` | Custom value replacement applied to all `fields` values. | string | null      | Non-empty string with a numeric or text value that can be converted to `fields` type(s). | low          |

## Predicates

Transformations can be configured with *predicates* so that the transformation
is applied only to records which satisfy a condition. You can use predicates in
a transformation chain and, when combined with the [Kafka Connect Filter (Kafka) SMT Usage Reference for Confluent Cloud](filter-ak.md#ak-filter), predicates
can conditionally filter out specific records. For details and examples, see [Predicates](filter-ak.md#predicates).