com.ibm.streamsx.topology.json

Class JSONStreams

java.lang.Object

com.ibm.streamsx.topology.json.JSONStreams

public class JSONStreams
extends java.lang.Object

Utilities for JSON streams. A JSON stream is a stream of JSON objects represented by the class com.ibm.json.java.JSONObject. When a JSON value that is an array or value (not an object) needs to be present on the stream, the approach is to represent it as a object with the key payload containing the array or value.
A JSON stream can be published so that IBM Streams applications implemented in different languages can subscribe to it.

See Also:

http://www.json.org - JSON (JavaScript Object Notation) is a lightweight data-interchange format.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	JSONStreams.DeserializeJSON Function to deserialize a String to a JSONObject.
static class	JSONStreams.SerializeJSON Function to serialize a JSONObject to a String.
static class	JSONStreams.ToJSON<T extends JSONAble> Function to convert a JSONAble tuple to a JSONObject, using JSONAble.toJSON().

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	PAYLOAD JSON key for arrays and values.

Constructor Summary

Constructors

Constructor and Description
JSONStreams()

Method Summary

Modifier and Type	Method and Description
static TStream<com.ibm.json.java.JSONObject>	deserialize(TStream<java.lang.String> stream) Declare a stream of JSON objects from a stream of serialized JSON tuples.
static TStream<com.ibm.json.java.JSONObject>	flattenArray(TStream<com.ibm.json.java.JSONObject> stream, java.lang.String arrayKey, java.lang.String... additionalKeys) Declare a stream that flattens an array present in the input tuple.
static TStream<java.lang.String>	serialize(TStream<com.ibm.json.java.JSONObject> stream) Create a stream of serialized JSON objects as String tuples.
static <T extends JSONAble> TStream<com.ibm.json.java.JSONObject>	toJSON(TStream<T> stream) Declare a stream of JSON objects from a stream of Java objects that implement JSONAble.
static SPLStream	toSPL(TStream<com.ibm.json.java.JSONObject> stream) Convert a JSON stream to an SPLStream.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

PAYLOAD

public static final java.lang.String PAYLOAD

JSON key for arrays and values. When JSON is an array or a value (not an object) it is represented as a JSONObject tuple with an attribute (key) "payload" containing the array or value.

See Also:

Constant Field Values

Constructor Detail

JSONStreams

public JSONStreams()

Method Detail

toSPL

public static SPLStream toSPL(TStream<com.ibm.json.java.JSONObject> stream)

Convert a JSON stream to an SPLStream.

Parameters:

stream - JSON stream to be converted.

Returns:

SPLStream with schema JSONSchemas.JSON.

serialize

public static TStream<java.lang.String> serialize(TStream<com.ibm.json.java.JSONObject> stream)

Create a stream of serialized JSON objects as String tuples.

Parameters:

stream - Stream containing the JSON objects.

Returns:

Stream that will contain the serialized JSON values.

deserialize

public static TStream<com.ibm.json.java.JSONObject> deserialize(TStream<java.lang.String> stream)

Declare a stream of JSON objects from a stream of serialized JSON tuples. If the serialized JSON is a simple value or an array, then a JSON object is created, with a single attribute payload containing the deserialized value.

Parameters:

stream - Stream containing the JSON serialized values.

Returns:

Stream that will contain the JSON objects.

toJSON

public static <T extends JSONAble> TStream<com.ibm.json.java.JSONObject> toJSON(TStream<T> stream)

Declare a stream of JSON objects from a stream of Java objects that implement JSONAble.

Parameters:

stream - Stream containing JSONAble tuples.

Returns:

Stream that will contain the JSON objects.

flattenArray

public static TStream<com.ibm.json.java.JSONObject> flattenArray(TStream<com.ibm.json.java.JSONObject> stream,
                                                                 java.lang.String arrayKey,
                                                                 java.lang.String... additionalKeys)

Declare a stream that flattens an array present in the input tuple. For each tuple on stream the key arrayKey and its value are extracted and if it is an array then each element in the array will be present on the returned stream as an individual tuple.
If an array element is a JSON object it will be placed on returned stream, otherwise a JSON object will be placed on the returned stream with the key payload containing the element's value.
If arrayKey is not present, is not an array or is an empty array then no tuples will result on the returned stream.

Any additional keys (additionalKeys) that are specified are copied (with their value) into each JSON object on the returned stream from the input tuple, unless the flattened tuple already contains a value for the key.
If an addition key is not in the input tuple, then it is not copied into the flattened tuples.

For example, with a JSON object input tuple of:

 
 {"ts":"13:28:07", "sensors":
   [
     {"temperature": 34.2},
     {"rainfall": 12.96}
   ]
 }
 
 

and a call of flattenArray(stream, "sensors", "ts") would result in two tuples:

 
 {"temperature": 34.2, "ts": "13:28:07"}
 {"rainfall": 12.96, "ts": "13:28:07"}
 
 

With a JSON input tuple containing an array of simple values:

 
 {"ts":"13:43:09", "unit": "C", "readings":
   [
     33.9,
     33.8,
     34.1
   ]
 }
 
 

and a call of flattenArray(stream, "readings", "ts", "unit") would result in three tuples:

 
 {"payload": 33.9, "ts": "13:43:09", "unit":"C"}
 {"payload": 33.8, "ts": "13:43:09", "unit":"C"}
 {"payload": 34.1, "ts": "13:43:09", "unit":"C"}
 
 

Parameters:

stream - Steam containing tuples with an array to be flattened.

arrayKey - Key of the array in each input tuple.

additionalKeys - Additional keys that copied from the input tuple into each resultant tuple from the array

Returns:

Stream containing tuples flattened from input tuple.