JavaScriptSerializer.Deserialize() skip property if cannot parse it

Question

I am deserializing JSON strings into using Person objects using this code:

JavaScriptSerializer serializer = new JavaScriptSerializer();
Person person = serializer.Deserialize<Person>(jsonString);

The Person class has an Age property:

int Age {get;set;}

The JSON string has a value like:

{age: 'not valid int'}

and I am getting an exception as follows:

Cannot cast string to Int32

Is there any way to tell the JavaScriptSerializer to skip on error and continue with the other properties?

Answer 1

Yes, it is possible to control the deserialization process by writing a custom JavaScriptConverter class:

public class PersonConverter : JavaScriptConverter
{
    public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
    {
        Person person = new Person();

        foreach (string key in dictionary.Keys)
        {
            var value = dictionary[key];

            switch (key)
            {
                case "Name":
                    person.Name = (string)value;
                    break;

                case "Age":
                    {
                        if (value is int)
                        {
                            person.Age = (int)value;
                        }
                        else
                        {
                            int age;
                            if (int.TryParse((string)dictionary[key], out age))
                            {
                                person.Age = age;
                            } // else leave Age as null (or if int, leave as 0); alternatively put an else block here to set to value of your choice
                        }
                    }
                    break;
            }
        }

        return person;
    }

    public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override IEnumerable<Type> SupportedTypes
    {
        get
        {
            return new[] { typeof(Person) };
        }
    }
}

I have taken the liberty of making Person.Age nullable, where null indicates that the age is unknown, but if this is not acceptable you could modify the converter to default to 0 or -1 when the age was not parseable:

public class Person
{
    public string Name { get; set; }
    public int? Age { get; set; }
}

Usage:

var serializer = new JavaScriptSerializer();
serializer.RegisterConverters(new[] { new PersonConverter() });
var person = serializer.Deserialize<Person>(jsonString);

Example with output:

    var serializer = new JavaScriptSerializer();
    serializer.RegisterConverters(new[] { new PersonConverter() });

    var jsonStrings = new List<string>
    {
        "{ Name: 'Steve',  Age: 21 }",
        "{ Name: 'Teoman',  Age: 'not valid int'}",
        "{ Name: 'Queen Elizabeth II',  Age: '89'}"
    };

    foreach (var jsonString in jsonStrings)
    {
        var person = serializer.Deserialize<Person>(jsonString);
        Console.WriteLine("Name: {0}, Age: {1}", person.Name, person.Age);
    }

Name: Steve, Age: 21

Name: Teoman, Age:

Name: Queen Elizabeth II, Age: 89

Please note that we have handled here: a literal number, a number inside a string, and a totally invalid value.