Endpoint "/api-docs" doesn't work with custom GsonHttpMessageConverter - spring-boot

Question

I migrated from Springfox Swagger to Springdoc OpenApi. I have added few lines in my configuration about springdoc:
springdoc:
pathsToMatch: /api/**
api-docs:
path: /api-docs
swagger-ui:
path: /swagger-ui.html
In configuration class MainConfig.kt I have following code:
val customGson: Gson = GsonBuilder()
.registerTypeAdapter(LocalDateTime::class.java, DateSerializer())
.registerTypeAdapter(ZonedDateTime::class.java, ZonedDateSerializer())
.addSerializationExclusionStrategy(AnnotationExclusionStrategy())
.enableComplexMapKeySerialization()
.setPrettyPrinting()
.create()
override fun configureMessageConverters(converters: MutableList<HttpMessageConverter<*>>) {
converters.add(GsonHttpMessageConverter(customGson))
}
When I go to http://localhost:8013/swagger-ui.html (in configuration I have server.port: 8013) the page is not redirect to swagger-ui/index.html?url=/api-docs&validatorUrl=. But this is not my main problem :). When I go to swagger-ui/index.html?url=/api-docs&validatorUrl= I got page with this information:
Unable to render this definition
The provided definition does not specify a valid version field.
Please indicate a valid Swagger or OpenAPI version field. Supported version fields are swagger: "2.0" and those that match openapi: 3.0.n (for example, openapi: 3.0.0).
But when I go to http://localhost:8013/api-docs I have this result:
"{\"openapi\":\"3.0.1\",\"info\":{(...)}}"
I tried using default config and I commented configureMessageConverters() method and result of \api-docs now looks like normal JSON:
// 20191218134933
// http://localhost:8013/api-docs
{
"openapi": "3.0.1",
"info": {(...)}
}
I remember when I was using Springfox there was something wrong with serialization and my customGson had additional line: .registerTypeAdapter(Json::class.java, JsonSerializer<Json> { src, _, _ -> JsonParser.parseString(src.value()) })
I was wondering that I should have special JsonSerializer. After debugging my first thought was leading to OpenApi class in io.swagger.v3.oas.models package. I added this code: .registerTypeAdapter(OpenAPI::class.java, JsonSerializer<OpenAPI> { _, _, _ -> JsonParser.parseString("") }) to customGson and nothing changed... So, I was digging deeper...
After when I ran my Swagger tests:
#EnableAutoConfiguration
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
#AutoConfigureMockMvc
#ExtendWith(SpringExtension::class)
#ActiveProfiles("test")
class SwaggerIntegrationTest(#Autowired private val mockMvc: MockMvc) {
#Test
fun `should display Swagger UI page`() {
val result = mockMvc.perform(MockMvcRequestBuilders.get("/swagger-ui/index.html"))
.andExpect(status().isOk)
.andReturn()
assertTrue(result.response.contentAsString.contains("Swagger UI"))
}
#Disabled("Redirect doesn't work. Check it later")
#Test
fun `should display Swagger UI page with redirect`() {
mockMvc.perform(MockMvcRequestBuilders.get("/swagger-ui.html"))
.andExpect(status().isOk)
.andExpect(MockMvcResultMatchers.content().contentTypeCompatibleWith(MediaType.TEXT_HTML))
}
#Test
fun `should get api docs`() {
mockMvc.perform(MockMvcRequestBuilders.get("/api-docs"))
.andExpect(status().isOk)
.andExpect(MockMvcResultMatchers.content().contentTypeCompatibleWith(MediaType.APPLICATION_JSON))
.andExpect(MockMvcResultMatchers.jsonPath("\$.openapi").exists())
}
}
I saw in console this:
MockHttpServletRequest:
HTTP Method = GET
Request URI = /api-docs
Parameters = {}
Headers = []
Body = null
Session Attrs = {}
Handler:
Type = org.springdoc.api.OpenApiResource
Method = org.springdoc.api.OpenApiResource#openapiJson(HttpServletRequest, String)
Next I check openapiJson in OpenApiResource and...
#Operation(hidden = true)
#GetMapping(value = API_DOCS_URL, produces = MediaType.APPLICATION_JSON_VALUE)
public String openapiJson(HttpServletRequest request, #Value(API_DOCS_URL) String apiDocsUrl)
throws JsonProcessingException {
calculateServerUrl(request, apiDocsUrl);
OpenAPI openAPI = this.getOpenApi();
return Json.mapper().writeValueAsString(openAPI);
}
OK, Jackson... I have disabled Jackson by #EnableAutoConfiguration(exclude = [(JacksonAutoConfiguration::class)]) because I (and my colleagues) prefer GSON, but it doesn't explain why serialization go wrong after adding custom GsonHttpMessageConverter. I have no idea what I made bad. This openapiJson() is endpoint and maybe it mess something... I don't know. I haven't any idea. Did you have a similar problem? Can you give some advice or hint?
PS. Sorry for my bad English :).

Answer 1

I had the same issue with a project written in Java, and I've just solved that by defining a filter to format my springdoc-openapi json documentation using Gson. I guess you can easily port this workaround to Kotlin.
#Override
public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
throws IOException, ServletException {
ByteResponseWrapper byteResponseWrapper = new ByteResponseWrapper((HttpServletResponse) response);
ByteRequestWrapper byteRequestWrapper = new ByteRequestWrapper((HttpServletRequest) request);
chain.doFilter(byteRequestWrapper, byteResponseWrapper);
String jsonResponse = new String(byteResponseWrapper.getBytes(), response.getCharacterEncoding());
response.getOutputStream().write((new com.google.gson.JsonParser().parse(jsonResponse).getAsString())
.getBytes(response.getCharacterEncoding()));
}
#Override
public void destroy() {
}
static class ByteResponseWrapper extends HttpServletResponseWrapper {
private PrintWriter writer;
private ByteOutputStream output;
public byte[] getBytes() {
writer.flush();
return output.getBytes();
}
public ByteResponseWrapper(HttpServletResponse response) {
super(response);
output = new ByteOutputStream();
writer = new PrintWriter(output);
}
#Override
public PrintWriter getWriter() {
return writer;
}
#Override
public ServletOutputStream getOutputStream() {
return output;
}
}
static class ByteRequestWrapper extends HttpServletRequestWrapper {
byte[] requestBytes = null;
private ByteInputStream byteInputStream;
public ByteRequestWrapper(HttpServletRequest request) throws IOException {
super(request);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
InputStream inputStream = request.getInputStream();
byte[] buffer = new byte[4096];
int read = 0;
while ((read = inputStream.read(buffer)) != -1) {
baos.write(buffer, 0, read);
}
replaceRequestPayload(baos.toByteArray());
}
#Override
public BufferedReader getReader() {
return new BufferedReader(new InputStreamReader(getInputStream()));
}
#Override
public ServletInputStream getInputStream() {
return byteInputStream;
}
public void replaceRequestPayload(byte[] newPayload) {
requestBytes = newPayload;
byteInputStream = new ByteInputStream(new ByteArrayInputStream(requestBytes));
}
}
static class ByteOutputStream extends ServletOutputStream {
private ByteArrayOutputStream bos = new ByteArrayOutputStream();
#Override
public void write(int b) {
bos.write(b);
}
public byte[] getBytes() {
return bos.toByteArray();
}
#Override
public boolean isReady() {
return false;
}
#Override
public void setWriteListener(WriteListener writeListener) {
}
}
static class ByteInputStream extends ServletInputStream {
private InputStream inputStream;
public ByteInputStream(final InputStream inputStream) {
this.inputStream = inputStream;
}
#Override
public int read() throws IOException {
return inputStream.read();
}
#Override
public boolean isFinished() {
return false;
}
#Override
public boolean isReady() {
return false;
}
#Override
public void setReadListener(ReadListener readListener) {
}
}
You will also have to register your filter only for your documentation url pattern.
#Bean
public FilterRegistrationBean<DocsFormatterFilter> loggingFilter() {
FilterRegistrationBean<DocsFormatterFilter> registrationBean = new FilterRegistrationBean<>();
registrationBean.setFilter(new DocsFormatterFilter());
registrationBean.addUrlPatterns("/v3/api-docs");
return registrationBean;
}