How to Fix the \'Expected BEGIN_OBJECT but was NAME\' Error When Parsing Nested JSON with GSON in Android?

JSON Parsing with GSON in Android

How can you simplify JSON parsing with GSON in Android? Let's explore a common issue when using GSON and delve into a step-by-step solution.

Problem Statement:

When using GSON to parse a JSON string, you may encounter an "Expected BEGIN_OBJECT but was NAME" error. This typically occurs when you attempt to parse a JSON object that is nested within an array.

JSON Example:

Consider the following JSON data:

<code class="json">{
    "count": "12",
    "colbreak": 1,
    "name": "unary rels",
    "score": "9090",
    "Words": [
        {
            "count": 6,
            "word": "prp_għaċ-",
            "name": "prp_għaċ-",
            "score": 9.1,
            "Words": "kol",
            "seek": 2231297
        }
    ],
    "seek": 0
}</code>

Code:

Your code using GSON for parsing:

<code class="java">public static <T> ArrayList<T> JsonParse(T t, String response) {
    // ...
    while (reader.hasNext()) {
        T cse = (T) gson.fromJson(reader, t.getClass());
        lcs.add(cse);
    }
    // ...
}</code>

Error:

Running this code may result in an error like:

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was NAME at line 1 column 73

Solution:

To resolve this error, you need to modify the way you read the JSON value. Instead of looping through the entire JSON string, you should skip to the specific object you want to parse and then decode it.

Revised Method:

Here's a corrected version of the JsonParse method:

<code class="java">public static <T> ArrayList<T> JsonParse(T t, String response) {
    // ...
    while (reader.hasNext()) {
        String name = reader.nextName();
        if (name.equals("Words")) {
            reader.beginArray();
            while (reader.hasNext()) {
                T cse = (T) gson.fromJson(reader, t.getClass());
                lcs.add(cse);
            }
            reader.endArray();
        } else {
            reader.skipValue();
        }
    }
    // ...
}</code>

Explanation:

In this revised method, the code checks if the current JSON name is "Words" and if so, begins reading the array. It then loops through each object in the array, parsing them using GSON and adding them to the list. For any other JSON names, such as "count" or "score," the method simply skips over them.

Additional Considerations:

• Ensure that your model classes (GsonParse and Words) have getters and setters for all the JSON fields.
• If you're reading JSON from a file in the assets folder, make sure to use InputStreamReader instead of JsonReader.
• To support UTF-8 characters, convert the JSON string to UTF-8 before parsing it.

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