Question

I’m writing a library that wraps around a REST API. The wrapper I’m creating uses GSON to deserialize the json into my object. Basically, something like this…

public Post getPost(url) throws IOException {
  String jsonString = httpClient.get(url);
  Post p = gson.fromJson(jsonString, Post.class);
  // return Post to client and let client do something with it.
}

If I understand correctly, IOException is a checked exception. I’m telling my client: Hey, buddy – you better watch out and recover from this exception. Now my client can wrap the call in a try/catch and determine what to do if there is some network failure.

The GSON fromJson() method throws a JsonSyntaxException. I believe this is unchecked in the Java world, as one of its super classes is RuntimeException, and also because I am not required to add a try/catch or another “throws” like IOException.

Assuming what I have said so far is correct – how exactly should the API and client handle this situation? If the json string is garbage, my client is going to fail miserably due to the JsonSyntaxException because it’s unchecked.

// Client
PostService postService = new PostService();
try{
  Post p = postService.getPost(urlString);
  // do something with post
}catch (IOException){
   // handle exception
}
// ok, what about a JsonSyntaxException????

What’s the best way to handle these situations?

Answer 1

You are allowed to catch unchecked exceptions. Just add catch(JsonSyntaxException e) to your try-catch block. After you catch the JsonSyntaxException, you can either handle it or rethrow it as a checked exception.

Ex:

try{
    //do whatever
}catch(JsonSyntaxException e){
    e.printStackTrace();
    // throw new Exception(e); //checked exception
}catch(IOException e){
    e.printStackTrace();
}