Code generation where '@' prefix used in attribute names

Description

When generating Java code from a swagger definition, if there are any variables prefixed with a '@' character, the code generator strips this character.

However, if you have a swagger where you have two attributes, one called @type and another just called type, this results in two attributes being generated in the resulting code both called type, resulting in a compilation error.

Swagger-codegen version

2.3.1

Swagger declaration file content or url

Try generating a from a swagger definition containing the following:

{
  "swagger": "2.0",
  "definitions": {
    "DuplicateAt": {
      "type": "object",
      "properties": {
        "@type": {
          "type": "string"
        },
        "type": {
          "type": "string"
        }
      }
    }
  }
}

A full Maven project can be uploaded if required.

Command line used for generation

Will provide on request if needed.

Steps to reproduce

Generate the model code.

Related issues/PRs

Very are numerous issues which relate to duplicate variable declarations in Java, but I'm not sure if they relate directly to this issue.

Suggest a fix/enhancement

I would suggest that when striping the any special characters from an attribute name, the code generator checks to see if this would could a duplicate to be created, and, if it is, cause the generation to fail, or, rename the attribute name by adding a prefix and/or suffix.

Reproduce generation with the provided Swagger 2.0 definition containing both @type and type properties, using the Java generator; the issue does not name a source file, test, or command. Trace where attribute names lose the @ prefix and establish a handling rule that prevents duplicate Java attributes, then verify the generated model compiles.