Why Does Gson Throw an 'Expected BEGIN_OBJECT but was STRING' Error?

Gson Parsing Issue: Understanding the "Expected BEGIN_OBJECT" Error

Gson, a popular Java library for JSON parsing, can encounter errors when processing invalid JSON structures. One such error is "Expected BEGIN_OBJECT but was STRING." To resolve this error, it is essential to understand the issue and the expected JSON structure.

The Problem

In the given code, the parseStringToObject method attempts to parse a JSON string into an instance of the Object class. However, the JSON string does not comply with the expected object structure and begins with a string.

"Invalid JSON structure"

Gson Expectations

Gson expects JSON strings to start with an object opening brace ({) to parse them into an object. It then expects key-value pairs followed by an object closing brace (}).

{
  "name": "John Doe",
  "age": 30
}

Error Explanation

The error message "Expected BEGIN_OBJECT but was STRING" indicates that the JSON string provided does not begin with an object opening brace. Instead, it starts with a string wrapped in double quotes, "Invalid JSON structure".

Resolution

To resolve the error, ensure that the JSON string passed to parseStringToObject is a valid JSON object. It should start with an opening brace, contain key-value pairs, and end with a closing brace.

{
  "name": "John Doe",
  "age": 30
}

Alternatively, if the expected structure is a string, the JSON string should begin with a string without double quotes.

Invalid JSON structure

By adhering to the correct JSON structure, you can prevent the "Expected BEGIN_OBJECT" error when using Gson for JSON parsing.

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