Spring Boot allow Square brackets for nested objects in Request Parameters - spring

Question

I'm using Spring Boot 2.6.7 and org.springdoc:springdoc-openapi-ui:1.6.7 to run swagger ui with OpenApi 3 definition along with my backend.
My Setup
#GetMapping(value = "/hello", produces = MediaType.APPLICATION_JSON_VALUE)
public String getHello(HelloInput input) {
return "";
}
public class HelloInput {
public NestedInput nested;
// getter setter omitted
}
public class NestedInput {
public boolean a = true;
// getter setter omitted
}
This produces the following request when trying it out in swagger ui:
curl -X 'GET' \
'http://localhost:8080/api/hello?nested[a]=true' \
-H 'accept: application/json'
The Problem
However, when I execute this call I get the following Exception:
org.springframework.beans.InvalidPropertyException: Invalid property 'nested[a]' of bean class [com.proj.App.rest.explore.HelloInput]: Property referenced in indexed property path 'nested[a]' is neither an array nor a List nor a Map; returned value was [com.proj.App.rest.explore.NestedInput#68d1c7c4]
What do I need
The square braces notation causes this issue. The same call with dot notation does not cause exceptions:
curl -X 'GET' \
'http://localhost:8080/api/hello?nested.a.=true' \
-H 'accept: application/json'
Is there a way to either:
A: Configure Spring Boot in a way that it accepts the square brackets notation also for object properties and not just maps, lists etc.
OR
B: Configure Swagger UI in a way that it uses the dot notation when constructing the calls?
What did I already try
I already did a lot of research, but could not find other people with this problem.
I found a feature request for Spring to support squared brackets, but it was rejected: https://github.com/spring-projects/spring-framework/issues/20052
I found basically the same question, but the answers seem to be outdated, since the RelaxedDataBinder does not seem to be a part of Spring Boot 2.6.7 anymore: Customize Spring #RequestParam Deserialization for Maps and/or Nested Objects
Other than that, no one else seems to have this problem. Am I completely misunderstanding how Spring Boot handles Request Parameters and this problem occurs because I'm breaking some convention on how to handle GET Requests with many parameters?

Answer 1

I have the same problem and can't find any good solution. I have found only one more hack. So you can reformat request param json with dot-separated fields. It is a little bit inconvenient but works for me.
For example, by default for the controller in question, the request param input form will have json that will look like this:
{
"nested": {
"a": true
}
}
But you can use
{
"nested.a": true
}
to get what you want without any even more hacky changes(as I see this) to swagger-ui or spring components.

Answer 2

CAUTION: Hacky workaround for making swagger ui use dots instead of squared braces (probably breaks in a lot of scenarios)
Swagger Ui offers to define a requestInterceptor, that takes outbound requests and offers the user to change them.
When using Springdoc, swagger ui downloads a swagger-initializer.js for configuration of swagger ui.
This file is generated by an instance of a SwaggerIndexPageTransformer. The default instance already creates a requestInterceptor for CORS requests. I took that code and adapted it to change all requests with the squared braces notation to the dot notation.
For reference see AbstractSwaggerIndexTransformer#addCRSF
Workaround
First define a Configuration that offers a SwaggerIndexTransformer Bean:
#Configuration
public class OpenApiConfig {
#Bean
public SwaggerIndexTransformer swaggerIndexTransformer(
SwaggerUiConfigProperties a,
SwaggerUiOAuthProperties b,
SwaggerUiConfigParameters c,
SwaggerWelcomeCommon d) {
return new CustomSwaggerIndexTransformer(a, b, c, d);
}
}
Next implement the CustomSwaggerIndexTransformer, that now edits the swagger-initializer.js to add a requestInterceptor function, that replaces every [ with a . and removes all ].
public class CustomSwaggerIndexTransformer extends SwaggerIndexPageTransformer {
private static final String PRESETS = "presets: [";
...
#Override
protected String defaultTransformations(InputStream inputStream) throws IOException {
String html = super.defaultTransformations(inputStream);
html = addDottedRequests(html);
return html;
}
protected String addDottedRequests(String html) {
String interceptorFn = """
requestInterceptor: (request) => {
request.url = request.url.replaceAll("[", ".").replaceAll("]", "");
return request;
},
""" + PRESETS;
return html.replace(PRESETS, interceptorFn);
}
}
Limitations
This probably breaks working behavior when swagger ui uses squared braces for Maps, Arrays and Lists
This does not work when CORS is enabled for springdoc, since it also defines a requestInterceptor, in that case the javascript should somehow be incorporated into the CORS requestInterceptor function.