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Can you change the Type of Java Exception’s error message?

I’m writing an Internal-Facing tool with a very slow runtime. Because of this runtime I’m trying to validate the input for errors and send a JSON object with a detailed list of every missing or failing element to the client before actually running the tool.

I was wondering if there was a way to modify java Exception’s error message return type so that I can throw this HashMap within an error.

The hashmap containing the errors would look something like this:

Error: {
   Message: "Your X is configured improperly, please fill out the required fields before running this tool", 
   formXErrors: {
     Message: "The following fields are missing from formX", 
     Error: {
       field1Name: "field 1", 
       field2Name: "field 2",
       ... 
    },
    formYErrors: {
     Message: "The following fields are missing from formY", 
     Error: {
       field1Name: "field 1", 
       field2Name: "field 2",
       ... 
     }
  } 
}

And then if an error was found I would like to throw it like this (passing a HashMap into the message field instead of a string):

if (errorHashMap != null) {
  throw new ToolXException(errorHashMap);
}

Java is slightly new to me so I was wondering if anyone could point me towards finding a way to achieve this behavior. Is it even possible? Or is the only way to return this HashMap instead of throwing, and send it to the client?

Thanks in advance!

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Answer

You can’t edit the type of a message, but you can certainly add a field of any type you like to a custom Exception type.

class ToolXException extends Exception {
  private final Map<Key, Value> map;
  public Map<Key, Value> getMap() { return map; }
  public ToolXException(Map<Key, Value> map) {
    this.map = map;
  }
} 

…and then you can get it out and display it however you like when you catch it:

try {
  ...
} catch (ToolXException e) {
  doSomethingWith(e.getMap());
}

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