JSON to HashMap with objects using Gson

Question

In my Android app (written in Kotlin), I need to turn some JSON into a string to MainObject hash map. This is what the JSON looks like:

{
    "a": {
        "name": "A",
        "some_int": "2",
        "some_string": "string",
        "some_bool": false,
        "some_string_arr": [
            "str1",
            "str2"
        ],
        "sub_obj_arr": [
            {
                "obj_name": "d",
                "some_obj_string": "s"
            }
        ]
    },
    "b": {
        "name": "B",
        "some_int": "4",
        "some_string": "string",
        "some_bool": false,
        "some_string_arr": [
            "str5",
            "str6"
        ]
    }
}

I created a couple of objects to help with this.

class MainObject {
    @SerializedName("name")
    val name: String? = null

    @SerializedName("some_int")
    val someInt: Int? = null

    @SerializedName("some_string")
    val someString: String? = null

    @SerializedName("some_bool")
    val someBool: Boolean = false

    @SerializedName("some_string_arr")
    val someStringArr: List<String>? = null

    @SerializedName("sub_obj_arr")
    val someObjArr: List<SubObject>? = null
}

class SubObject {
    @SerializedName("obj_name")
    val objName: String? = null

    @SerializedName("some_obj_string")
    val someObjString: String? = null
}

How do I convert this into a type of HashMap<String, MainObject>? I tried using a TypeToken as described here, but I was getting the error "expected begin object but was string".

Any ideas?

UPDATE

I'm also reading in the JSON data locally via the solution described here

Error Log

10-15 20:06:42.771 10328-10328/xxx E/AndroidRuntime: FATAL EXCEPTION: main
    Process: xxx, PID: 10328
    java.lang.RuntimeException: Unable to start activity ComponentInfo{xxx}: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6541)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
     Caused by: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $
        at com.google.gson.Gson.fromJson(Gson.java:900)
        at com.google.gson.Gson.fromJson(Gson.java:853)
        at com.google.gson.Gson.fromJson(Gson.java:802)
        at xxx.onCreate(BottomNavigation.kt:48)
        at android.app.Activity.performCreate(Activity.java:6975)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6541) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
     Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $
        at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:385)
        at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:183)
        at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
        at com.google.gson.Gson.fromJson(Gson.java:888)
        at com.google.gson.Gson.fromJson(Gson.java:853) 
        at com.google.gson.Gson.fromJson(Gson.java:802) 
        at xxx.onCreate(BottomNavigation.kt:48) 
        at android.app.Activity.performCreate(Activity.java:6975) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6541) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Update 2

The actual issue is something wrong with the way I am reading in my local JSON file. The code I use is this:

val input = this.resources.openRawResource(R.raw.json)
val json = try {
    val size = input.available()
    val buffer = ByteArray(size)
    input.read(buffer)
    input.close()
    String(buffer)
} catch (ex: IOException) {
    ex.printStackTrace()
    null
}

Which gives me these weird characters when I print out the json to the console:

10-15 23:55:11.911 3351-3351/xxx I/System.out: ��{��

10-15 23:55:11.911 3351-3351/xxx I/System.out: �� "��a��"��:�� {��

No idea why though.

Please share the whole error log.

Joshua
– Joshua

2017-10-16 01:31:49 +00:00
Commented Oct 16, 2017 at 1:31 — Joshua
– Joshua, Commented Oct 16, 2017 at 1:31
Updated it with the error log

Derek Fredrickson
– Derek Fredrickson

2017-10-16 02:49:35 +00:00
Commented Oct 16, 2017 at 2:49 — Derek Fredrickson
– Derek Fredrickson, Commented Oct 16, 2017 at 2:49

Joshua · Accepted Answer · 2017-10-16 03:10:58Z

10

I don't know why you have any error. I am able to parse the JSON with following code.

val gson = GsonBuilder().create()
val type = object:TypeToken<Map<String, MainObject>>(){}.type
val result = gson.fromJson<Map<String, MainObject>>("{ \"a\": { \"name\": \"A\", \"some_int\": \"2\", \"some_string\": \"string\", \"some_bool\": false, \"some_string_arr\": [ \"str1\", \"str2\" ], \"sub_obj_arr\": [ { \"obj_name\": \"d\", \"some_obj_string\": \"s\" } ] }, \"b\": { \"name\": \"B\", \"some_int\": \"4\", \"some_string\": \"string\", \"some_bool\": false, \"some_string_arr\": [ \"str5\", \"str6\" ] } }", type)

answered Oct 16, 2017 at 3:10

Joshua

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2 Comments

Derek Fredrickson Over a year ago

Hmm, interesting. Thanks for running that test for me. That makes me think there is something wrong with the way I'm reading in the JSON file itself.

android developer Over a year ago

This doesn't seem to work for me, when I use object:TypeToken<Map<LocalDate, Int>>(){}.type . It causes IllegalStateException: Expected BEGIN_OBJECT but was STRING at line ... . Any idea why? Asked here: stackoverflow.com/q/77741719/878126

Derek Fredrickson · Accepted Answer · 2017-10-16 04:06:00Z

0

Okay, with the help of others I figured out that the issue wasn't with Gson or my JSON or anything. It was in the way I was reading it into memory. The code I was using was:

val input = this.resources.openRawResource(R.raw.json)
val json = try {
    val size = input.available()
    val buffer = ByteArray(size)
    input.read(buffer)
    input.close()
    String(buffer)
} catch (ex: IOException) {
    ex.printStackTrace()
    null
}

However, String(buffer) defaults to using UTF_8 charset. In order for mine to work, I needed to use a UTF_16 charset. The working change was using String(buffer, Charsets.UTF_16).

answered Oct 16, 2017 at 4:06

Derek Fredrickson

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