I'm converting a list of Foo objects to a JSON string. I need to parse the JSON string back into a list of Foos. However in the following example, parsing gives me a list of JSONObjects instead of Foos.
Example
List list = [new Foo("first"), new Foo("second")]
def jsonString = (list as JSON).toString()
List parsedList = JSON.parse(jsonString) as List
println parsedList[0].getClass() // org.codehaus.groovy.grails.web.json.JSONObject
How can I parse it into Foos instead? Thanks in advance.
I had a look at the API docs for JSON and there doesn't appear to be any way to parse to a JSON string to a specific type of object.
So you'll just have to write the code yourself to convert each JSONObject to a Foo. Something like this should work:
import grails.converters.JSON
import org.codehaus.groovy.grails.web.json.*
class Foo {
def name
Foo(name) {
this.name = name
}
String toString() {
name
}
}
List list = [new Foo("first"), new Foo("second")]
def jsonString = (list as JSON).toString()
List parsedList = JSON.parse(jsonString)
// Convert from a list of JSONObject to a list of Foo
def foos = parsedList.collect {JSONObject jsonObject ->
new Foo(name: jsonObject.get("name"))
}
A more general solution would be to add a new static parse method such as the following to the JSON metaClass, that tries to parse the JSON string to a List of objects of a particular type:
import grails.converters.JSON
import org.codehaus.groovy.grails.web.json.*
class Foo {
def name
Foo(name) {
this.name = name
}
String toString() {
name
}
}
List list = [new Foo("first"), new Foo("second")]
def jsonString = (list as JSON).toString()
List parsedList = JSON.parse(jsonString)
// Define the new method
JSON.metaClass.static.parse = {String json, Class clazz ->
List jsonObjs = JSON.parse(json)
jsonObjs.collect {JSONObject jsonObj ->
// If the user hasn't provided a targetClass read the 'class' proprerty in the JSON to figure out which type to convert to
def targetClass = clazz ?: jsonObj.get('class') as Class
def targetInstance = targetClass.newInstance()
// Set the properties of targetInstance
jsonObj.entrySet().each {entry ->
if (entry.key != "class") {
targetInstance."$entry.key" = entry.value
}
}
targetInstance
}
}
// Try the new parse method
List<Foo> foos = JSON.parse(jsonString, Foo)
// Confirm it worked
assert foos.every {Foo foo -> foo.class == Foo && foo.name in ['first', 'second'] }
You can try out the code above in the groovy console. A few warnings
.properties is only writeable for Grails domain objects. For regular Groovy objects, I think .properties is read-only.
If you are doing this in a Grails controller, and Foo IS indeed a domain object, don't forget that armed with your JSON map, you can also do:
List list = [new Foo("first"), new Foo("second")]
def jsonString = (list as JSON).toString()
List parsedList = JSON.parse(jsonString) as List
Foo foo = new Foo()
bindData(foo, parsedList[0]);
I've taken this code and extended it to work with nested structures. It relies on a 'class' attribute existing in the JSON. If there's a better way by now in Grails please let me know.
// The default JSON parser just creates generic JSON objects. If there are nested
// JSON arrays they are not converted to theirs types but are left as JSON objects
// This converts nested JSON structures into their types.
// IT RELIES ON A PROPERTY 'class' that must exist in the JSON tags
JSON.metaClass.static.parseJSONToTyped = {def jsonObjects ->
def typedObjects = jsonObjects.collect {JSONObject jsonObject ->
if(!jsonObject.has("class")){
throw new Exception("JSON parsing failed due to the 'class' attribute missing: " + jsonObject)
}
def targetClass = grailsApplication.classLoader.loadClass(jsonObject.get("class"))
def targetInstance = targetClass.newInstance()
// Set the properties of targetInstance
jsonObject.entrySet().each {entry ->
// If the entry is an array then recurse
if(entry.value instanceof org.codehaus.groovy.grails.web.json.JSONArray){
def typedSubObjects = parseJSONToTyped(entry.value)
targetInstance."$entry.key" = typedSubObjects
}
else if (entry.key != "class") {
targetInstance."$entry.key" = entry.value
}
}
targetInstance
}
return typedObjects
}
As of Grails 2.5, this is possible:
Period test = new Period()
test.periodText = 'test'
String j = test as JSON
def p = JSON.parse(j)
test = p.asType(Period)
println(test.periodText)
Output:
test
I am unsure of when it became an option.
