groovy: LazyMap class cast exception

Question

I have a code to parse a huge JSON:

static <T> List<T> parseJSON(String json) {
   Map<String, T> result = jsonSlurper.parseText(json)
   List<T> list = result.result
   return list
}

the String json = {result:[{obj1},{obj2}....]}

I am getting a proper List at the end with the variable list but in Java when I get the value it throws an exception java.lang.ClassCastException: groovy.json.internal.LazyMap cannot be cast to {MyPOJO}

here is how I receive the data

List<MYClass> list = MyClass.parseJSON(someString);
for(MyClass i : list) {
  System.out.println(i.someValue());
}

how can I resolve this?

You need to tell your JSON parser what type to deserialize as. — SLaks, Aug 15 '17 at 21:23
@user3519456 I doubt this will work even there is no type erasure in JVM. List of LazyMap just cannot be used as list of MyClass if there is no explicit conversion. — aristotll, Aug 16 '17 at 00:57
This could help https://stackoverflow.com/questions/41305311/jsonslurper-execution-failure — CodeRunner, May 27 '21 at 15:25

score 0 · Answer 1 · answered Aug 16 '17 at 01:17

Your generic does not make much sense. When having such json string in your question, parseJSON always return a list of groovy.json.internal.LazyMap. You have to convert explicitly from LazyMap to MyClass. Otherwise just a cast exception.

Here is my code:

class MyClass {
    MyClass(Map map) {
        this.a = map.a as int
        this.b = map.b
    }
    int a
    String b

}

    List<Map> jSON = parseJSON("""{"result":[{"a":2,"b":"b"},{"a":2,"b":"b"}]}""")
    for (def item in jSON) {
        def myClass = new MyClass(item)
        println myClass.a
    }

groovy: LazyMap class cast exception

1 Answers1