Cannot invoke "String.length()" because "apiDocsUrl" is null

[Marco-Sulla]

I have two Spring Boot 3.3.11 application, with springdoc-openapi-starter-webmvc-ui 2.6.0.

I tried to upgrade, for security reasons, org.webjars:swagger-ui to version 5.20.7. The first app works, even if I can access the swagger only at URL myhost:XXXX/swagger-ui/5.20.7/index.html.

The second no. It shows me the error Fetch error response status is 500 /v3/api-docs. In the console I get the error message:

java.lang.NullPointerException: Cannot invoke "String.length()" because "apiDocsUrl" is null

springdoc config:

springdoc:
  api-docs:
    path: /v3/api-docs
  swagger-ui:
    path: /swagger-ui.html

Full stack trace:

{timestamp=2025-05-05T15:50:15.730+0200, level=ERROR, thread=http-nio-6060-exec-3, logger=org.apache.catalina.core.ContainerBase.[Tomcat].[localhost].[/].[dispatcherServlet], message=Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed: java.lang.NullPointerException: Cannot invoke "String.length()" because "apiDocsUrl" is null] with root cause, context=default, exception=java.lang.NullPointerException: Cannot invoke "String.length()" because "apiDocsUrl" is null
    at org.springdoc.webmvc.api.OpenApiWebMvcResource.getServerUrl(OpenApiWebMvcResource.java:148)
    at org.springdoc.webmvc.api.OpenApiResource.calculateServerUrl(OpenApiResource.java:247)
    at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:124)
    at org.springdoc.webmvc.api.OpenApiWebMvcResource.openapiJson(OpenApiWebMvcResource.java:114)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:255)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:188)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:926)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:831)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.springframework.web.filter.ServerHttpObservationFilter.doFilterInternal(ServerHttpObservationFilter.java:113)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:164)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:483)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:116)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:398)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:903)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1740)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1189)
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:658)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63)
    at java.base/java.lang.Thread.run(Thread.java:842)
}

[Marco-Sulla]

I tried also to upgrade the second app to Spring Boot 3.4.5 and springdoc-openapi-starter-webmvc-ui 2.8.6, but I get always the same error.

[Mattias-Sehlstedt]

Hi,

Could you please provide either a HelloController or a test-case so that the issue can be reproduced?

See this issue for a good example of how such a controller might look.

[bnasslahsen]

@Marco-Sulla,

Not reproducible.
Feel free to provide a Minimal, Reproducible Example - with HelloController that reproduces the problem.

This ticket will be closed, but can be reopened if your provide the reproducible sample.