Using Java Spring Server with oas2 doesn't compile due error in @ApiResponse annotation (content field not array)

How to reproduce

Using programmatically approach to create Java Spring Server with oas2 generates code:

new OpenApiGenerator(new v3.SpringCodegen() {
    setJava8(true)
    setInterfaceOnly(true)
    setDateLibrary("java8")
    //  setUseOas2(false)
    typeMapping.put("binary", "MultipartFile")
  })

The generated API interface code looks like this:

package smsgw.api.openapi.generated.api;

import smsgw.api.openapi.generated.model.ArrayOfCodewordAvailableResponse;
import smsgw.api.openapi.generated.model.CodewordReservationResponse;
import smsgw.api.openapi.generated.model.CodewordReserve;
import smsgw.api.openapi.generated.model.InternalServerResponse;
import smsgw.api.openapi.generated.model.UnauthorizedResponse;
import smsgw.api.openapi.generated.model.ValidationResponse;
import com.fasterxml.jackson.databind.ObjectMapper;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.Parameter;
import io.swagger.v3.oas.annotations.enums.ParameterIn;
import io.swagger.v3.oas.annotations.responses.ApiResponses;
import io.swagger.v3.oas.annotations.responses.ApiResponse;
import io.swagger.v3.oas.annotations.media.ArraySchema;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.security.SecurityRequirement;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.bind.annotation.CookieValue;

import javax.servlet.http.HttpServletRequest;
import javax.validation.Valid;
import javax.validation.constraints.*;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Optional;

@javax.annotation.Generated(value = "SwaggerCodegenPluginX$$anon$3", date = "2022-03-13T23:19:15.833689+01:00[Europe/Oslo]")
@Validated
public interface CodewordApi {

    Logger log = LoggerFactory.getLogger(CodewordApi.class);

    default Optional<ObjectMapper> getObjectMapper(){
        return Optional.empty();
    }

    default Optional<HttpServletRequest> getRequest(){
        return Optional.empty();
    }

    default Optional<String> getAcceptHeader() {
        return getRequest().map(r -> r.getHeader("Accept"));
    }

    @Operation(summary = "Check if codewords are available", description = "Check if codewords are available.", security = {
        @SecurityRequirement(name = "tokenAuth")    }, tags={ "Codeword" })
    @ApiResponses(value = { 
        @ApiResponse(responseCode = "200", description = "The availability of the codewords", content = @Content(mediaType = "application/json", schema = @Schema(implementation = ArrayOfCodewordAvailableResponse.class))),
        
        @ApiResponse(responseCode = "400", description = "Validation error", content = @Content(mediaType = "application/json", schema = @Schema(implementation = ValidationResponse.class))),
        
        @ApiResponse(responseCode = "401", description = "Authentication error", content = @Content(mediaType = "application/json", schema = @Schema(implementation = UnauthorizedResponse.class))) })
    @RequestMapping(value = "/codeword",
        produces = { "application/json" }, 
        method = RequestMethod.GET)
    default ResponseEntity<ArrayOfCodewordAvailableResponse> availableCodeword(@NotNull @Size(min=1) @Parameter(in = ParameterIn.QUERY, description = "Comma seperated value (csv) list of codewords the organization wants to reserve. At least one codeword is required. Example: ?codeword=company,trademark " ,required=true,schema=@Schema()) @Valid @RequestParam(value = "codeword", required = true) List<String> codeword, @NotNull @Parameter(in = ParameterIn.QUERY, description = "Comma seperated value (csv) list of codewords the organization wants to reserve. At least one codeword is required. Example: ?moDestination=45345345 " ,required=true,schema=@Schema()) @Valid @RequestParam(value = "moDestination", required = true) String moDestination) {
 // More generated code......

But the problem is that this code doesn't compile due to

@ApiResponse(content = @Content(mediaType = "application/json", schema = @Schema(implementation = UnauthorizedResponse.class))) }

Reason

The thing is that content is an array:

public @interface ApiResponse {
    /**
     * An array containing descriptions of potential response payloads, for different media types.
     *
     * @return array of content
     **/
    Content[] content() default {};

Solution

Adding brackets around the content solves the problem:

        @ApiResponse(responseCode = "200", description = "The availability of the codewords", content = {@Content(mediaType = "application/json", schema = @Schema(implementation = ArrayOfCodewordAvailableResponse.class))}),

Fix

The problem can be fixed in src/main/resources/handlebars/JavaSpring/api.mustache
by changing the following line:

@ApiResponse(responseCode = "{{{code}}}", description = "{{{message}}}"{{^vendorExtensions.x-java-is-response-void}}{{#baseType}}, content = {@Content({{#schema.extensions.x-content-type}}mediaType = "{{schema.extensions.x-content-type}}", {{/schema.extensions.x-content-type}}{{^containerType}}schema = @Schema(implementation = {{{baseType}}}.class))}{{/containerType}}{{#containerType}}array = @ArraySchema(schema = @Schema(implementation = {{{baseType}}}.class)))

Sidenote

For some reason it doesn't make any difference if setUseOas2() is true or false... It's expected that the problematic code should be ignored when useOas2=false due to {{^useOas2}}in the mustache file

Start in src/main/resources/handlebars/JavaSpring/api.mustache and inspect the ApiResponse content generation shown in the issue. Regenerate a Java Spring server from an OAS2 definition using the programmatic setup, then confirm the generated annotations compile with content represented as an array.