Problem with Webservice returning invalid JSON

Question

could you please point out my error? I have a very simple class and a webservice:

public class JSONFactory {
public Integer id;
public String name;
public String lastName;
public JSONFactory(Integer a, String b, String c){
    this.id = a;
    this.name = b;
    this.lastName = c;
    }
}



@RestResource(urlMapping='/Johnny')
global class WebServiceFactory {
    @HttpGet
    global static String getRecord() {
        List<JSONFactory> JSONs = new List<JSONFactory>();
        for(integer i = 0; i<4; i++){
            JSONs.add(new JSONFactory(i, 'Jan' + i, 'Test' + i));
        
            }
        return JSONs.toString();
    }
}

The web service should return a JSON made of a list of objects. According to the documentation, this happens automatically:

The response is either the serialized form of the method return value or it's the value of the responseBody property based on the following rules:

• If the method returns void, then Apex REST returns the response in the responseBody property. If the method returns a value, then Apex
• REST serializes the return value as the response.

After calling the getRecord method, the system debugs:

14:45:08:352 USER_DEBUG [43]|DEBUG|"(JSONFactory:[id=0, lastName=Test0, name=Jan0], JSONFactory:[id=1, lastName=Test1, name=Jan1], JSONFactory:[id=2, lastName=Test2, name=Jan2], JSONFactory:[id=3, lastName=Test3, name=Jan3])"

This is not a valid JSON and I am having trouble deserializing it into a list of Objects:

List<Object> objs = (List<Object>)JSON.deserializeUntyped(res.getBody());

I'm getting an exception:

FATAL_ERROR System.TypeException: Invalid conversion from runtime type String to List<ANY>

Answer 1

To allow automatic serialization, use the return type of any serializable type:

@HttpGet
global static List<JSONFactory> getRecord() {
    List<JSONFactory> JSONs = new List<JSONFactory>();
    for(integer i = 0; i<4; i++){
        JSONs.add(new JSONFactory(i, 'Jan' + i, 'Test' + i));
    
        }
    return JSONs;
}

Salesforce will automatically serialize the results for you, in XML or JSON, depending on the Accept header.

You can read more in the docs.

Answer 2

This error occurs because the toString method does not return valid json. To convert the list object to valid json you can use the Apex JSON class provided by Salesforce - https://developer.salesforce.com/docs/atlas.en-us.apexref.meta/apexref/apex_class_System_Json.htm

@RestResource(urlMapping='/Johnny')
global class WebServiceFactory {
    @HttpGet
    global static String getRecord() {
        List<JSONFactory> JSONs = new List<JSONFactory>();
        for(integer i = 0; i<4; i++){
            JSONs.add(new JSONFactory(i, 'Jan' + i, 'Test' + i));
        
            }
        return System.JSON.serialize(JSONs); 
    }
}

Answer 3

The return type .toString() does not generate a JSON formatted String.

You will have to change that to :

@RestResource(urlMapping='/Johnny')
global class WebServiceFactory {
    @HttpGet
    global static String getRecord() {
        List<JSONFactory> JSONs = new List<JSONFactory>();
        for(integer i = 0; i<4; i++){
            JSONs.add(new JSONFactory(i, 'Jan' + i, 'Test' + i));

        }
        return JSON.serialize(JSONs);
    }
}

Only then you will receive a JSON formatted String.

20:24:05.199 (202088269)|USER_DEBUG|[17]|DEBUG|[{"name":"Jan0","lastName":"Test0","id":0},{"name":"Jan1","lastName":"Test1","id":1},{"name":"Jan2","lastName":"Test2","id":2},{"name":"Jan3","lastName":"Test3","id":3}]

After this your List<Object> objs = (List<Object>)JSON.deserializeUntyped(res.getBody()); would work as expected.