XPRIM_JsonObject and XPRIM_JsonArray is an in-memory representation of JSON objects and JSON arrays. They store their child elements in a tree-like structure in memory, to support random access of elements by member name and array index. XPRIM_JsonObject and XPRIM_JsonArray have a common superclass, XPRIM_JsonElement.
As XPRIM_JsonObject/XPRIM_JsonArray are both readable and modifiable (with random access support), they are useful when you need to create an abstract, in-memory, representation of your JSON data, that you need to pass around, to another routine or any third-party library routines.
Note however that if you just need to construct a JSON string (that is, a string representation of a JSON data), you should use XPRIM_JsonWriter instead as XPRIM_JsonWriter is specifically designed to construct a JSON string, so it does that very efficiently, with a minimum memory footprint. Similarly, if you just need to parse a JSON string and read its values, you'd be better off using XPRIM_RandomAccessJsonReader or XPRIM_JsonReader. XPRIM_JsonWriter and XPRIM_JsonReader will be discussed in the next section.
Here is how you create an XPRIM_JsonObject and an XPRIM_JsonArray:
Define_Com Class(#XPRIM_JsonObject) Name(#RootObject)
Define_Com Class(#XPRIM_JsonArray) Name(#JsonArray)
You can then populate your JSON object or JSON array with values.
JSON data has 6 value types:
- Null
- String
- Number
- Boolean
- Object
- Array
Both XPRIM_JsonObject and XPRIM_JsonArray have the following methods that each correspond to the type of value it inserts to the object or array:
- InsertNull
- InsertString
- InsertNumber
- InsertBoolean
- InsertElement (insert any kind of JSON element, including JSON array and object)
Note however that the XPRIM_JsonObject's Insert methods would have a Key parameter that specifies the property name of the value to be inserted, whereas the XPRIM_JsonArray's Insert methods wouldn't have a Key parameter as it would just append the value to the end of the array.
Examples:
- Insert a string "John" as the "name" property of a JSON object
#RootObject.InsertString Key('name') String('John') - Insert a number 9 into a JSON array
#JsonArray.InsertNumber Number(9) - Insert a NULL value as the "allergies" property of a JSON object
#RootObject.InsertNull Key('allergies')
The following example show how to create an object/array as a property of another object: - Define an XPRIM_JsonObject reference
Define_Com Class(#XPRIM_JsonObject) Name(#ChildObject) - Insert the street & suburb of the address into #ChildObject
#ChildObject.InsertString Key('street') String('122 Arthur St')
#ChildObject.InsertString Key('suburb') String('North Sydney') - Insert #ChildObject into #RootObject as a member with name "address"
#RootObject.InsertElement Key('address') Element(#ChildObject)
If you want to convert your XPRIM_JsonObject (or XPRIM_JsonArray) into a string (for example for debugging purpose), call the SerializeAsString method.
Define_Com Class(#PRIM_DC.UnicodeString) Name(#MyJsonString) - Convert JSON to a string
#MyJsonString := #RootObject.SerializeAsString
You can also serialize your JSON object (or array) into a file, using the SerializeToFile method.
#RootObject.SerializeToFile Path('/home/TestJson.txt')
You can also parse a JSON string and construct an XPRIM_JsonObject or XPRIM_JsonArray from the JSON string, using the ParseString and ParseFile methods. - Define an ErrorInfo object to hold the error details
Define_Com Class(#XPRIM_ErrorInfo) Name(#ErrorInfo) - Call the 'Parse' method
#RootObject.ParseString String(#JsonString) ErrorInfo(#ErrorInfo) - Get the error message if parsing failed
If (*Not #ErrorInfo.OK)
#ErrorMessage := #ErrorInfo.ErrorMessage
EndIf
You can access the values of an object or an array using one of the Get… accessor methods: - GetString
- GetBoolean
- GetNumber
- GetObject
- GetArray
For example, if you have a JSON string like this, stored in a variable called '#String':
{
"name": {
"given": "John",
"surname": "Smith"
},
"age": 45,
"contactNo":
[
{ area: "02", no: "9378 2867", type: "landline" },
{ no: "0468 732 371", type: "mobile" }
]
}
To parse this JSON string and read its values:
Define_Com Class(#XPRIM_JsonObject) Name(#RootObject)
Define_Com Class(#XPRIM_ErrorInfo) Name(#ErrorInfo)
- Parse JSON string
#RootObject.ParseString String(#String) ErrorInfo(#ErrorInfo) - First check thst the JSON string was parsed OK
If (#ErrorInfo.OK)
* Get the values
#GivenName := #RootItem.GetObject('name').GetString('given')
#Surname := #RootItem.GetObject('name').GetString('surname')
#Age := #RootItem.GetNumber('age')
Endif
You can use the ItemCount property to tell how many item an array (or object) contains.
Define_Com Class(#XPRIM_JsonArray) Name(#ContactNumbers) - Get the contactNo value (which is an array), ...
- ... and assign to #ContactNumbers
#ContactNumbers.Refer To(#RootItem.GetArray('contactNo') - Get the array length using the 'ItemCount' property
#ContactCount := #ContactNumbers.ItemCount
To iterate through elements in a JSON array, you can use the FOR-EACH-IN construct: - Use the contactNo array from the previous example
FOR EACH(#Number) IN(#ContactNumbers)
#COM_SELF.ProcessContactNumber Number(#Number)
ENDFOR
You can check the type of a JSON element (XPRIM_JsonElement) by reading its Type property, which will return one of the following values: - NULL
- STRING
- NUMBER
- BOOLEAN
- OBJECT
- ARRAY
If you just want to check if a JSON element is of a certain type, you can use one of the Is… method:
- IsNull
- IsString
- IsNumber
- IsBoolean
- IsObject
- IsArray