How do I convert a JSON array to an ArrayList?

Question

I am grabbing a string from a database that looks like this

[{"messageContent":"Good morning Christine! My name is Oso, it\u0027s 
beary nice to meet you 
:3","msgType":"MSG_TYPE_RECEIVED","statusCode":0,"timeString":"10:31"}, 
{"messageContent":"Good morning Christine! My name is Oso, it\u0027s 
beary nice to meet you 
:3","msgType":"MSG_TYPE_RECEIVED","statusCode":0,"timeString":"10:31"}

It began as an ArrayList but I had to convert it into a string to store in in the database.

I need to convert it back. I had was going to use this function but it doesn't seem to work.

public static ArrayList<ChatMessage> fromString(String value) {
    Type listType = new TypeToken<ArrayList<String>>() {}.getType();
    return new Gson().fromJson(value, listType);
}

I get this error when I try to run the function.

 com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 3 path $[0]

Vucko · Accepted Answer · 2018-04-20 23:02:08Z

1

It's because you're trying to create an ArrayList of String, but you have OBJECTS, not strings in your JSON. Try changing this line:

Type listType = new TypeToken<ArrayList<String>>() {}.getType();

To something like this:

Type listType = new TypeToken<ArrayList<ChatMessage>>() {}.getType();

Assuming Gson knows how to deserialize your ChatMessage class, that should work.

answered Apr 20, 2018 at 23:02

Vucko

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2 Comments

OneCricketeer Over a year ago

You would think it would at least attempt to do Object.toString

Jason Smyth Over a year ago

thank you. I had played arround with the function and forgot to change String back to ChatMessage

Anik Raj C · Accepted Answer · 2018-04-20 23:11:00Z

0

Your database string is missing a JSON array closing bracket ] at the end.
gson type parameter is wrong. You require a ArrayList<ChatMessage> but you used ArrayList<String>.

Replace

Type listType = new TypeToken<ArrayList<String>>() {}.getType();

With

Type listType = new TypeToken<ArrayList<ChatMessage>>() {}.getType();

answered Apr 20, 2018 at 23:11

Anik Raj C

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