Add Swagger to Spring Boot in 1 minute (Without Spring Fox)

Recently, I needed to add swagger (openAPI) to my Spring boot app. However, with recent changes, it is almost impossible to use the infamous springfox implementation. When added the maven dependency to the project, I got errors that many others had:

2022-08-23 09:07:05.941 ERROR 265704 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException: Cannot invoke "org.springframework.web.servlet.mvc.condition.PatternsRequestCondition.getPatterns()" because "this.condition" is null
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.20.jar:5.3.20]
	at java.base/java.lang.Iterable.forEach(Iterable.java:75) ~[na:na]
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.20.jar:5.3.20]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.0.jar:2.7.0]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.0.jar:2.7.0]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.0.jar:2.7.0]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.0.jar:2.7.0]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.0.jar:2.7.0]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.0.jar:2.7.0]
	at com.binarycarpenter.license_server.LicenseServerApplication.main(LicenseServerApplication.java:11) ~[classes/:na]
Caused by: java.lang.NullPointerException: Cannot invoke "org.springframework.web.servlet.mvc.condition.PatternsRequestCondition.getPatterns()" because "this.condition" is null
	at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56) ~[springfox-spring-webmvc-3.0.0.jar:3.0.0]
	at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:113) ~[springfox-core-3.0.0.jar:3.0.0]
	at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89) ~[springfox-spi-3.0.0.jar:3.0.0]
	at java.base/java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:473) ~[na:na]
	at java.base/java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[na:na]
	at java.base/java.util.TimSort.sort(TimSort.java:220) ~[na:na]
	at java.base/java.util.Arrays.sort(Arrays.java:1307) ~[na:na]
	at java.base/java.util.ArrayList.sort(ArrayList.java:1721) ~[na:na]
	at java.base/java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:392) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:510) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[na:na]
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682) ~[na:na]
	at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81) ~[springfox-spring-webmvc-3.0.0.jar:3.0.0]
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197) ~[na:na]
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) ~[na:na]
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921) ~[na:na]
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:na]
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682) ~[na:na]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.withDefaults(AbstractDocumentationPluginsBootstrapper.java:107) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.buildContext(AbstractDocumentationPluginsBootstrapper.java:91) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.bootstrapDocumentationPlugins(AbstractDocumentationPluginsBootstrapper.java:82) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:100) ~[springfox-spring-web-3.0.0.jar:3.0.0]
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178) ~[spring-context-5.3.20.jar:5.3.20]
	... 14 common frames omitted

This is a known bug of the Spring fox open API implementation. Many people have tried to fix it and there are some workarounds. However, why settle for a workaround when you can have a much better, cleaner solution?

Add Swagger(OpenAPI) to Spring Boot application with Spring Doc

In my case, I completely removed spring fox’s dependencies. Instead, I used this:

<!-- https://mvnrepository.com/artifact/org.springdoc/springdoc-openapi-ui -->
<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-ui</artifactId>
    <version>1.6.11</version>
</dependency>

The current version at the time of this post is 1.6.11. However, you should check the official repository to get the latest versions.

After adding this dependency and removing all annotations required by spring fox previously, I got the open API (swagger) page up at http://myhost/myapp/swagger-ui.html

Actually, your app will redirect you to the other URL: http://myhost/myapp/swagger-ui/index.html

adding swagger (open api) to spring boot application successfully
adding swagger (open api) to spring boot application successfully

Conclusion

In this post, I’ve shown you how to quickly add open API (swagger) documentation to your spring boot application without using spring fox. This post is not to bash spring fox. That library has been one of the best solutions to add swagger to java web applications for a long time. However, with recent bugs, it’s better to use spring doc.


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