解决WebMvcPatternsRequestConditionWrapper.getPatterns NullPointerException 启动失败

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已于 2022-03-13 03:28:44 修改

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分类专栏： Spring Spring Boot 解决方案文章标签： spring java spring boot NPE

于 2022-03-13 03:04:59 首次发布

本文链接：https://blog.csdn.net/qq_35425070/article/details/123453752

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本文档介绍了在SpringBoot 2.6之后，使用Swagger遇到的NPE异常，该异常源于SpringBoot的路径解析策略变更。分析了问题原因并提出了四种解决方案，包括修改Spring配置、切换到SpringDoc、自建分支修复SpringFox以及通过BeanPostProcessor拦截处理。详细探讨了每种方案的成本和适用场景。

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Spring Boot2.6之后，swagger的包，WebMvcPatternsRequestConditionWrapper.getPatterns NPE 异常

文章目录

Spring Boot2.6之后，swagger的包，WebMvcPatternsRequestConditionWrapper.getPatterns NPE 异常
报错现象
- 堆栈
- 截图
排查过程
解决方案
- 劫持SpringFox的方法，避免NPE

报错现象

堆栈

2022-03-13 02:40:28.000 ERROR [16312] --- [           main] o.s.boot.SpringApplication               : Application run failed

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)
	at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:54)
	at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:356)
	at java.base/java.lang.Iterable.forEach(Iterable.java:75)
	at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:155)
	at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:123)
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:935)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:586)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
	at com.example.demo1.Demo1Application.main(Demo1Application.java:22)
Caused by: java.lang.NullPointerException: null
	at springfox.documentation.spring.web.WebMvcPatternsRequestConditionWrapper.getPatterns(WebMvcPatternsRequestConditionWrapper.java:56)
	at springfox.documentation.RequestHandler.sortedPaths(RequestHandler.java:113)
	at springfox.documentation.spi.service.contexts.Orderings.lambda$byPatternsCondition$3(Orderings.java:89)
	at java.base/java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469)
	at java.base/java.util.TimSort.countRunAndMakeAscending(TimSort.java:355)
	at java.base/java.util.TimSort.sort(TimSort.java:234)
	at java.base/java.util.Arrays.sort(Arrays.java:1515)
	at java.base/java.util.ArrayList.sort(ArrayList.java:1750)
	at java.base/java.util.stream.SortedOps$RefSortingSink.end(SortedOps.java:392)
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.base/java.util.stream.Sink$ChainedReference.end(Sink.java:258)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
	at springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider.requestHandlers(WebMvcRequestHandlerProvider.java:81)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.withDefaults(AbstractDocumentationPluginsBootstrapper.java:107)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.buildContext(AbstractDocumentationPluginsBootstrapper.java:91)
	at springfox.documentation.spring.web.plugins.AbstractDocumentationPluginsBootstrapper.bootstrapDocumentationPlugins(AbstractDocumentationPluginsBootstrapper.java:82)
	at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.start(DocumentationPluginsBootstrapper.java:100)
	at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:178)
	... 14 common frames omitted

截图

在这里插入图片描述

排查过程

首先在NPE地方打断点，发现是 this.condition 为 null 导致的，那就看它哪里set了
在这里插入图片描述
Ctrl + F 搜一下发现只有构造方法有赋值语句，那就在这里打断点吧，然后重启debug，再次来到这里

顺着堆栈往上找，发现是springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider在返回 requestHandlers 时赋值的。
我们来看这个值来源是什么，顺着stream的代码，找到了原来时取handlerMappings中的字段，发现是org.springframework.web.servlet.mvc.method.RequestMappingInfo#pathPatternsCondition 字段
这个类是Spring的代码，我们直接看定义处，发现本身就可能为空，说明这是SpringFox代码的一个bug
使用这么广的开源软件居然有bug，怀疑是没及时更新导致，看了一下最新的3.0.0其实是2020.7发布的，怪不得和spring boot最新版不兼容
- 再来看为啥2.6之前就没事呢？去 spring 官网看看2.6的更新，其中有一条

请求路径与 Spring MVC 处理映射匹配的默认策略已从AntPathMatcher更改为PathPatternParser。
你可以设置spring.mvc.pathmatch.matching-strategy为ant-path-matcher来改变它。

原来是默认的 path 解析策略调整了，所以我列了以下几个解决方案

解决方案

方案	成本	对比
设置 application.properties 属性还原成 antMacher`spring.mvc.pathmatch.matching-strategy为ant-path-matcher`	最低	属于临时快速兼容方案，AntPathMatcher性能不如PathPatternParser，功能强大一点，且springfox很久不发新版本，不建议继续使用
将 SpringFox 换成 SpringDoc	中	代码注解将由Swagger配置改为标准的OpenAPI3配置，见另一篇文章
克隆springfox代码，自己拉分支修完发版本，程序中再依赖	较高	springfox很久不发新版本，不建议继续使用，否则会有长期自主维护成本
通过代理，劫持SpringFox的方法，过滤掉为null的接口	低	不建议，antMatch匹配的的接口都是空，会导致所有接口都不出现在接口文档上，相当于没有使用 swagge，不如直接把swagger排除掉

劫持SpringFox的方法，避免NPE

	/**
     * Spring Boot 2.6 与 swagger 不兼容解决
     */
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(WebMvcRequestHandlerProvider.class)
    public static class FixNpeForSpringfoxHandlerProviderBeanPostProcessorConfiguration {

        @Bean
        public static BeanPostProcessor springfoxHandlerProviderBeanPostProcessor() {
            return new BeanPostProcessor() {

                @Override
                public Object postProcessAfterInitialization(@Nonnull Object bean, @Nonnull 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);
                    }
                }
            };
        }
    }