"expected BEGIN_OBJECT but was STRING at line 1 column 1"

java

json-validation

exception-handling

retrofit

byAlex Kataev·Feb 6, 2025

When you encounter the error "Expected BEGIN_OBJECT but was STRING at line 1 column 1", it's an indication of a mismatch in JSON parsing. The code anticipates a JSON object ({...}), but finds a string instead. Ensure the JSON string begins with a left curly brace {.

Valid JSON object format:

{ "key": "value" }

Invalid string format:

"this error isn't as fun as a horcrux hunt"

Solution: Use Gson to parse your JSON strings correctly. This works:

Gson gson = new Gson();
MyClass result = gson.fromJson(jsonString, MyClass.class);

Remember to check if jsonString starts with { — and wave your magic wand, er, I mean, check your MyClass.

JSON Sanity Check

Ensuring JSON follows proper structure and format is crucial. A single misplaced bracket or quote could break the entire JSON object. [Harry Potter couldn't kill Voldemort with a drumstick, nor can we parse JSON with wrong brackets!]

JSON String Validation

Implement StringEscapeUtils.unescapeJava(jsonString) to unescape any additional escape characters:

String correctedJson = StringEscapeUtils.unescapeJava(jsonString); 
// Frodo should have had this in his ring

Abra Kadabra: Exception Handling

JsonSyntaxException, the metaphorical crouching tiger, hidden dragon in JSON parsing, can be handled using a try/catch block:

try {
    MyClass result = gson.fromJson(jsonString, MyClass.class);
} catch (JsonSyntaxException e) {
    // Handle your malformed JSON here, Mario!
}

Retrofit Framework: Friend or Foe

When working with Retrofit, ensure to:

Add ScalarsConverterFactory to handle raw strings.
Set headers correctly, "Content-Type" should be "application/json".
Handle JSONException.

Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://your.api.url/")
    .addConverterFactory(ScalarsConverterFactory.create())
    // Gson converter factory joining the party
    .build();

Remember, Retrofit's @Body aren't just bodybuilders, they offer more.

The Magic Dust: Preprocessing JSON

Like Arthur Weasley trying to understand muggles, sometimes JSON can be tricky too. Excess quotes might sneak in. Use this to sanitize:

jsonString = jsonString.replaceAll("^\"|\"$", ""); // Dobby is free!

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JSON Sanity Check JSON String Validation Abra Kadabra: Exception Handling Retrofit Framework: Friend or Foe The Magic Dust: Preprocessing JSON