Function

The JSON format allows you to read and write JSON data based on a JSON schema. Currently, the JSON schema is derived from table schema. For details, see JSON Format.

Supported Connectors

Kafka
Upsert Kafka
Elasticsearch

Parameters

**Table 1**
Parameter	Mandatory	Default Value	Type	Description
format	Yes	None	String	Format to be used. Set this parameter to json.
json.fail-on-missing-field	No	false	Boolean	Whether missing fields and rows will be skipped or failed. The default value is false, indicating that an error will be thrown.
json.ignore-parse-errors	No	false	Boolean	Whether fields and rows with parse errors will be skipped or failed. The default value is false, indicating that an error will be thrown. Fields are set to null in case of errors.
json.timestamp-format.standard	No	'SQL'	String	Specify the input and output timestamp format for TIMESTAMP and TIMESTAMP_LTZ type. Currently supported values are SQL and ISO-8601: Option SQL will parse input TIMESTAMP values in "yyyy-MM-dd HH:mm:ss.s{precision}" format, e.g "2020-12-30 12:13:14.123", parse input TIMESTAMP_LTZ values in "yyyy-MM-dd HH:mm:ss.s{precision}'Z'" format, e.g "2020-12-30 12:13:14.123Z", and output timestamp in the same format. Option ISO-8601 will parse input TIMESTAMP in "yyyy-MM-ddTHH:mm:ss.s{precision}" format, e.g "2020-12-30T12:13:14.123", parse input TIMESTAMP_LTZ in "yyyy-MM-ddTHH:mm:ss.s{precision}'Z'" format, e.g "2020-12-30T12:13:14.123Z", and output timestamp in the same format.
json.map-null-key.mode	No	'FALL'	String	Handling mode when serializing null keys for map data. Available values are as follows: FAIL will throw exception when encountering map value with null key. DROP will drop null key entries for map data. LITERAL replaces the empty key value in the map with a string constant. The string literal is defined by json.map-null-key.literal option.
json.map-null-key.literal	No	'null'	String	String literal to replace null key when json.map-null-key.mode is LITERAL.
json.encode.decimal-as-plain-number	No	false	Boolean	Encode all decimals as plain numbers instead of possible scientific notations. For example, 0.000000027 is encoded as 2.7E-8 by default, and will be written as 0.000000027 if set this parameter to true.

Data Type Mapping

Currently, the JSON schema is always derived from table schema. Explicitly defining a JSON schema is not supported yet.

Flink JSON format uses jackson databind API to parse and generate JSON string.

The following table lists the type mapping from Flink type to JSON type.

**Table 2** Data type mapping
Flink SQL Type	JSON Type
CHAR/VARCHAR/STRING	String
BOOLEAN	Boolean
BINARY/VARBINARY	string with encoding: base64
DECIMAL	Number
TINYINT	Number
SMALLINT	Number
INT	Number
BIGINT	Number
FLOAT	Number
DOUBLE	Number
DATE	string with format: date
TIME	string with format: time
TIMESTAMP	string with format: date-time
TIMESTAMP_WITH_LOCAL_TIME_ZONE	string with format: date-time (with UTC time zone)
INTERVAL	Number
ARRAY	array
MAP / MULTISET	object
ROW	object

Example

In this example, data is read from a topic and written to another using a Kafka sink.

Create a datasource connection for the communication with the VPC and subnet where Kafka locates and bind the connection to the queue. Set an inbound rule for the security group to allow access of the queue and test the connectivity using the Kafka address. If the connection is successful, the datasource is bound to the queue. Otherwise, the binding fails.

Create a Flink OpenSource SQL job, select Flink 1.15, and allow DLI to save job logs in OBS. Use the following statement in the job and submit it:

CREATE TABLE kafkaSource (
  order_id string,
  order_channel string,
  order_time string, 
  pay_amount double,
  real_pay double,
  pay_time string,
  user_id string,
  user_name string,
  area_id string
) WITH (
  'connector' = 'kafka',
  'topic' = 'kafkaTopic',
  'properties.bootstrap.servers' = 'KafkaAddress1:KafkaPort,KafkaAddress2:KafkaPort',
  'properties.group.id' = 'GroupId',
  'scan.startup.mode' = 'latest-offset',
  'format' = 'json'
);

CREATE TABLE printSink (
  order_id string,
  order_channel string,
  order_time string, 
  pay_amount double,
  real_pay double,
  pay_time string,
  user_id string,
  user_name string,
  area_id string
) WITH (
  'connector' = 'print'
);
insert into printSink select * from kafkaSource;

Insert the following data into the source Kafka topic:

{"order_id":"202103241000000001","order_channel":"webShop","order_time":"2021-03-24 10:00:00","pay_amount":100.0,"real_pay":100.0,"pay_time":"2021-03-24 10:02:03","user_id":"0001","user_name":"Alice","area_id":"330106"}

{"order_id":"202103241606060001","order_channel":"appShop","order_time":"2021-03-24 16:06:06","pay_amount":200.0,"real_pay":180.0,"pay_time":"2021-03-24 16:10:06","user_id":"0001","user_name":"Alice","area_id":"330106"}

Perform the following operations to view the data result in the taskmanager.out file:
1. Log in to the DLI console. In the navigation pane, choose Job Management > Flink Jobs.
2. Click the name of the corresponding Flink job, choose Run Log, click OBS Bucket, and locate the folder of the log you want to view according to the date.
3. Go to the folder of the date, find the folder whose name contains taskmanager, download the .out file, and view result logs.
```
+I[202103241000000001, webShop, 2021-03-24 10:00:00, 100.0, 100.0, 2021-03-24 10:02:03, 0001, Alice, 330106]
+I[202103241606060001, appShop11, 2021-03-24 16:06:06, 200.0, 180.0, 2021-03-24 16:10:06, 0001, Alice, 330106]
```