JSON

This extension converts JSON messages to/from stream processor events.

Features

  • json (Sink Mapper)

    This extension is an Event to JSON output mapper. Transports that publish messages can utilize this extension to convert Stream events to JSON messages. You can either send a pre-defined JSON format or a custom JSON message.

  • json (Source Mapper)

    This extension is a JSON-to-Event input mapper. Transports that accept JSON messages can utilize this extension to convert an incoming JSON message into a Stream event. Users can either send a pre-defined JSON format, where event conversion happens without any configurations, or use the JSON path to map from a custom JSON message. In default mapping, the JSON string of the event can be enclosed by the element "event", though optional.

json (Sink Mapper)

This extension is an Event to JSON output mapper. Transports that publish messages can utilize this extension to convert Stream events to JSON messages. You can either send a pre-defined JSON format or a custom JSON message.

Syntax

@sink(..., @map(type="json", validate.json="<BOOL>", enclosing.element="<STRING>")

QUERY PARAMETERS

Name Description Default Value Possible Data Types Optional Dynamic
validate.json If this property is set to true, it enables JSON validation for the JSON messages generated. When validation is carried out, messages that do not adhere to proper JSON standards are dropped. This property is set to false by default. false BOOL Yes No
enclosing.element This specifies the enclosing element to be used if multiple events are sent in the same JSON message. Stream treats the child elements of the given enclosing element as events and executes JSON expressions on them. If an enclosing.element is not provided, the multiple event scenario is disregarded and JSON path is evaluated based on the root element. $ STRING Yes No

EXAMPLE 1

@sink(type='inMemory', topic='stock', @map(type='json'))
define stream FooStream (symbol string, price float, volume long);

Above configuration does a default JSON input mapping that generates the output given below.

{    
"event":{        
    "symbol":GDN,        
    "price":55.6,        
    "volume":100    
    }
}

EXAMPLE 2

@sink(type='inMemory', topic='{{symbol}}', @map(type='json', enclosing.element='$.portfolio', validate.json='true', @payload( """{"StockData":{"Symbol":"{{symbol}}","Price":{{price}}}}""")))
define stream BarStream (symbol string, price float, volume long);

The above configuration performs a custom JSON mapping that generates the following JSON message as the output.

{
    "portfolio":{    
        "StockData":{        
            "Symbol":GDN,        
            "Price":55.6      
        }
    }
}

json (Source Mapper)

This extension is a JSON-to-Event input mapper. Transports that accept JSON messages can utilize this extension to convert an incoming JSON message into a Stream event. Users can either send a pre-defined JSON format, where event conversion happens without any configurations, or use the JSON path to map from a custom JSON message.In default mapping, the JSON string of the event can be enclosed by the element "event", though optional.

Syntax

@source(..., @map(type="json", enclosing.element="<STRING>", fail.on.missing.attribute="<BOOL>")

QUERY PARAMETERS

Name Description Default Value Possible Data Types Optional Dynamic
enclosing.element This is used to specify the enclosing element when sending multiple events in the same JSON message. Mapper treats the child elements of a given enclosing element as events and executes the JSON path expressions on these child elements. If the enclosing.element is not provided then the multiple-event scenario is disregarded and the JSON path is evaluated based on the root element. $ STRING Yes No
fail.on.missing.attribute This parameter allows users to handle unknown attributes.The value of this can either be true or false. By default it is true.  If a JSON execution fails or returns null, mapper drops that message. However, setting this property to false prompts mapper to send an event with a null value to Stream, where users can handle it as required, ie., assign a default value.) true BOOL Yes No

EXAMPLE 1

@source(type='inMemory', topic='stock', @map(type='json'))
define stream FooStream (symbol string, price float, volume long);

This configuration performs a default JSON input mapping. For a single event, the input is required to be in one of the following formats:

{    
    "event":{        
        "symbol":"GDN",        
        "price":55.6,        
        "volume":100    
    }
}

or

{    
    "symbol":"GDN",    
    "price":55.6,    
    "volume":100
}

EXAMPLE 2

@source(type='inMemory', topic='stock', @map(type='json'))
define stream FooStream (symbol string, price float, volume long);

This configuration performs a default JSON input mapping. For multiple events, the input is required to be in one of the following formats:

[
    {"event":
        {"symbol":"GDN","price":55.6,"volume":100}
    },
    {"event":
        {"symbol":"GDN","price":56.6,"volume":99}
    },
    {"event":
        {"symbol":"GDN","price":57.6,"volume":80}
    }
]

or

[
    {"symbol":"GDN","price":55.6,"volume":100},
    {"symbol":"GDN","price":56.6,"volume":99},
    {"symbol":"GDN","price":57.6,"volume":80}
]

EXAMPLE 3

@source(type='inMemory', topic='stock', @map(type='json', enclosing.element="$.portfolio", @attributes(symbol = "company.symbol", price = "price", volume = "volume")))

This configuration performs a custom JSON mapping.For a single event, the expected input is similar to the one shown below:

{ 
 "portfolio":{     
        "stock":{
            "volume":100,        
            "company":{           
                "symbol":"GDN"          
            },        
            "price":55.6       
        }   
    }
}

EXAMPLE 4

@source(type='inMemory', topic='stock', @map(type='json', enclosing.element="$.portfolio", @attributes(symbol = "stock.company.symbol", price = "stock.price", volume = "stock.volume")))
define stream FooStream (symbol string, price float, volume long);

The configuration performs a custom JSON mapping.For multiple events, expected input looks as follows..

{"portfolio":   
    [
        {"stock":{
            "volume":100,
            "company":{
                "symbol":"GDN"
            },
            "price":56.6
            }
        },
        {"stock":{
            "volume":200,
            "company":{
                "symbol":"GDN"
            },
            "price":57.6
            }
        }
    ]
}
Top