ClassCastException when trying to parse a JSONArray

Question

When trying to parse the following JSON string using the json.simple library:

[
    {"id" : "6d7662a9.f8ba04"},
    {"id" : "2da98cc2.145ba4"},
    {"id" : "45492640.a17d68"}
]

I get this exception:

java.lang.ClassCastException: org.json.simple.JSONArray cannot be cast to org.json.simple.JSONArray

This is how I'm doing it:

JSONArray json = (JSONArray) new JSONParser().parse(jsonString);

The JSON string is an array so not sure why that exception is thrown.

There are several similar questions here but in their cases, they were trying to cast a JSONObject to a JSONArray so it makes sense that an exception is thrown but in this case, it looks correct.

-----------------EDITS-----------------

I added a line to print the class of the object, like this:

Object json = new JSONParser().parse(jsonString);
System.out.println(json.getClass());

That prints the following line:

class org.json.simple.JSONArray

and in the next line, I have this if:

if(json instanceof JSONArray) {
    System.out.println("This is a JSONArray");
}

But it does not access the if, so it is really weird, because first I check that the object is a JSONArray but it does not print "This is a JSONArray"

Possible duplicate of [How to parse JSON in Java](https://stackoverflow.com/questions/2591098/how-to-parse-json-in-java) — Manoj Perumarath, Mar 16 '19 at 03:33
Please explain the downvote, the question marked as duplicate is not the same, my question is specific to a weird situation where a clearly JSON array cannot be casted to a JSONArray object — CIOC, Mar 16 '19 at 03:37
parse it to `JSONObject` and then check is it a `JSONArray` by using `instanceof` @CJ1 — Ryuzaki L, Mar 16 '19 at 03:44
Object is not the instance of JSONArray. Check the edited edited answer of mine — Vigneshwaran, Mar 16 '19 at 04:07
This error did not occur while trying to parse. The parse was successful. The cast was not. — user207421, Mar 16 '19 at 04:17

Stephen C · Accepted Answer · 2019-03-16T05:03:44.377

You say you are getting this:

java.lang.ClassCastException: org.json.simple.JSONArray cannot be cast 
    to org.json.simple.JSONArray

Note that the fully qualified class names look identical. If that message was transcribed accurately, and the names are identical¹, it means that you have two versions of the JSONArray class loaded into your JVM!

This is possible in a JVM where the application or the framework has multiple class loaders, and you have managed to load the class in more than one class loader. For example, this could happen if you have the JSON library JAR file BOTH in a web container's shared library directory AND in a webapp's WAR file.

The thing is that the runtime type of a class is identified by the classes FQN and the classloader. Two classes with the same FQN loaded in different class loaders are different types, even if the bytecodes are identical. This means that they are not assignment compatible, and it leads to weird (but correct!) class cast failures.

Solution:

Look at the web container file tree on your execution platform to find multiple copies of the JSON JAR file.
Remove the problematic copy(s) from either the shared lib directory or all of the WAR files.

^{1 - A really obscure alternative explanation is that the names look the same due to "homoglyphs" but are actually different. But in this context, I think we can discount that explanation as implausible.}

I think this might be it, looks like there are other places in the application where the library jar is loaded, I will investigate this route and update the question — CIOC, Mar 16 '19 at 04:08
Yes, that fixed the issue, the library was loaded in two different places, so I just removed one of the jars, to confirm I also printed `json.getClass().getClassLoader()` and they were different, thanks! — CIOC, Mar 16 '19 at 05:25

Vigneshwaran · Answer 2 · 2019-03-16T04:02:59.490

-2

It should be like

    Object obj = new JSONParser().parse(jsonString);
    JSONArray json = new JSONArray();
json.add(obj);

edited Mar 16 '19 at 04:02

answered Mar 16 '19 at 03:51

Vigneshwaran

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Same result, it throws the exception in the second line – CIOC Mar 16 '19 at 03:54
Are you sure the input is exactly the same as you provided – Vigneshwaran Mar 16 '19 at 03:58
Check the edited answer. If it works, please upvote – Vigneshwaran Mar 16 '19 at 04:03

ClassCastException when trying to parse a JSONArray

2 Answers2