SpringBoot 2.6.x整合springfox 3.0報錯問題及解決方案
一、問題現(xiàn)象
SpringBoot版本：2.6.4
springfox swagger版本：
<dependency> <groupId>io.springfox</groupId> <artifactId>springfox-boot-starter</artifactId> <version>3.0.0</version> </dependency>
啟動之后報錯：
org.springframework.context.ApplicationContextException: Failed to start bean 'documentationPluginsBootstrapper'; nested exception is java.lang.NullPointerException
at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:181) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356) ~[spring-context-5.3.16.jar:5.3.16]
at java.lang.Iterable.forEach(Iterable.java:75) ~[na:1.8.0_202]
at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586) ~[spring-context-5.3.16.jar:5.3.16]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.6.4.jar:2.6.4]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) [spring-boot-2.6.4.jar:2.6.4]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) [spring-boot-2.6.4.jar:2.6.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) [spring-boot-2.6.4.jar:2.6.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) [spring-boot-2.6.4.jar:2.6.4]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) [spring-boot-2.6.4.jar:2.6.4]
at com.mycan.cplatform.CplatformApplication.main(CplatformApplication.java:12) [classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.6.4.jar:2.6.4]
Caused by: java.lang.NullPointerException: 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$3(Orderings.java:89) ~[springfox-spi-3.0.0.jar:3.0.0]
at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469) ~[na:1.8.0_202]
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355) ~[na:1.8.0_202]
at java.util.TimSort.sort(TimSort.java:220) ~[na:1.8.0_202]
at java.util.Arrays.sort(Arrays.java:1512) ~[na:1.8.0_202]
at java.util.ArrayList.sort(ArrayList.java:1462) ~[na:1.8.0_202]
at java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:387) ~[na:1.8.0_202]
at java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:1.8.0_202]
at java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:1.8.0_202]
at java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:1.8.0_202]
at java.util.stream.Sink$ChainedReference.end(Sink.java:258) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[na:1.8.0_202]
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_202]
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[na:1.8.0_202]
at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81) ~[springfox-spring-webmvc-3.0.0.jar:3.0.0]
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[na:1.8.0_202]
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[na:1.8.0_202]
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_202]
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_202]
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[na:1.8.0_202]
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-5.3.16.jar:5.3.16]
... 19 common frames omitted
二、問題排查
查看異常堆棧的頂部，發(fā)現(xiàn)是此處報空指針異常：springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper#getPatterns，
跟蹤condition變量，發(fā)現(xiàn)是從springfox.documentation.spring.web.WebMvcRequestHandler#getPatternsCondition方法返回的WebMvcPatternsRequestConditionWrapper類的對象返回的。
找到類org.springframework.web.servlet.mvc.method.RequestMappingInfo，發(fā)現(xiàn)有兩個很相近的方法，查看方法注釋可以知道當(dāng)其中一個起作用時，另外一個則返回null。
所以，springfox的代碼似乎不應(yīng)該這樣寫，而是應(yīng)該加上一個判斷。
實際上，SpringBoot 2.6.0開始，請求路徑與Spring MVC處理映射匹配的默認策略已從AntPathMatcher更改為PathPatternParser。
但是可以通過設(shè)置spring.mvc.pathmatch.matching-strategy為ant-path-matcher來改變。
所以我們在application.properties文件中加上一行配置：
spring.mvc.pathmatch.matching-strategy=ant_path_matcher
啟動項目，發(fā)現(xiàn)還是報錯。
繼續(xù)看，發(fā)現(xiàn)還是有HandlerMethod的patternsCondition為空。
那么為了不報空指針異常，只能把這些HandlerMethod過濾掉，這些HandlerMethod是從RequestMappingInfoHandlerMapping獲取的，那么通過過濾RequestMappingInfoHandlerMapping就可以達到目標(biāo)，通過判斷條件getPatternParser() == null進行判斷，這樣過濾之后，所有的HandlerMethod的getPatternsCondition()都不是為空的了。
于是，我們對WebMvcRequestHandlerProvider類型的Bean進行改造，添加代碼：
@Bean
public BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
return new BeanPostProcessor() {
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
}
return bean;
}
private <T extends RequestMappingInfoHandlerMapping> void customizeSpringfoxHandlerMappings(List<T> mappings) {
List<T> copy = mappings.stream()
.filter(mapping -> mapping.getPatternParser() == null)
.collect(Collectors.toList());
mappings.clear();
mappings.addAll(copy);
}
@SuppressWarnings("unchecked")
private List<RequestMappingInfoHandlerMapping> getHandlerMappings(Object bean) {
try {
Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
field.setAccessible(true);
return (List<RequestMappingInfoHandlerMapping>) field.get(bean);
} catch (IllegalArgumentException | IllegalAccessException e) {
throw new IllegalStateException(e);
}
}
};
}三、解決方案
1. 添加配置文件：
spring.mvc.pathmatch.matching-strategy=ant_path_matcher
2. 添加代碼配置：
@Bean
public BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
return new BeanPostProcessor() {
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof WebMvcRequestHandlerProvider || bean instanceof WebFluxRequestHandlerProvider) {
customizeSpringfoxHandlerMappings(getHandlerMappings(bean));
}
return bean;
}
private <T extends RequestMappingInfoHandlerMapping> void customizeSpringfoxHandlerMappings(List<T> mappings) {
List<T> copy = mappings.stream()
.filter(mapping -> mapping.getPatternParser() == null)
.collect(Collectors.toList());
mappings.clear();
mappings.addAll(copy);
}
@SuppressWarnings("unchecked")
private List<RequestMappingInfoHandlerMapping> getHandlerMappings(Object bean) {
try {
Field field = ReflectionUtils.findField(bean.getClass(), "handlerMappings");
field.setAccessible(true);
return (List<RequestMappingInfoHandlerMapping>) field.get(bean);
} catch (IllegalArgumentException | IllegalAccessException e) {
throw new IllegalStateException(e);
}
}
};
}四、其他
Spring fox 已經(jīng)大半年沒有更新了，為了使用swagger折騰的費勁，其實現(xiàn)在也有其他的api文檔方案，比如Spring doc和Apifox，可以考慮更換。
總結(jié)
以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。
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