spring-boot-start-web依赖
启动报错
第一次启动网关项目项目时报错，错误信息如下：
***************************
APPLICATION FAILED TO START
***************************
Description:
Parameter 0 of method modifyRequestBodyGatewayFilterFactory in org.springframework.cloud.gateway.config.GatewayAutoConfiguration required a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' that could not be found.
Action:
Consider defining a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' in your configuration.
错误分析
根据上面描述（Description）中信息了解到GatewayAutoConfiguration这个配置中找不到ServerCodecConfig这个Bean。
而网关项目是一个spring boot项目，在启动的时候会去加载它的配置，其中有一个叫做GatewayClassPathWarningAutoConfiguration的配置类中有这么一行代码：
@Configuration
@ConditionalOnClass(name = "org.springframework.web.servlet.DispatcherServlet")
protected static class SpringMvcFoundOnClasspathConfiguration {
public SpringMvcFoundOnClasspathConfiguration() {
log.warn(BORDER+"Spring MVC found on classpath, which is incompatible with Spring Cloud Gateway at this time. " + "Please remove spring-boot-starter-web dependency."+BORDER);
}
}
log.warn中翻译一下意思就是“在类路径上找到的Spring MVC，此时它与Spring Cloud网关不兼容。请删除spring-boot-start-web依赖项。”。
解决方案
排除spring-boot-starter-web依赖。
再次启动，果然成功了。O(∩_∩)O哈哈~
非spring-boot-start-web依赖
添加数据库相关依赖后启动报错
昨天在整合OAuth2.0时，因为需要保存token到数据库，于是添加了以下依赖：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
<!-- druid -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
</dependency>
启动项目时报错：
05-06 11:57:08.590 ERROR o.s.boot.SpringApplication [826] Application run failed
java.lang.NoClassDefFoundError: javax/servlet/Servlet
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:2671)
at java.lang.Class.getDeclaredConstructors(Class.java:2020)
at org.springframework.boot.context.properties.ConfigurationPropertiesBindConstructorProvider.findConstructorBindingAnnotatedConstructor(ConfigurationPropertiesBindConstructorProvider.java:62)
at org.springframework.boot.context.properties.ConfigurationPropertiesBindConstructorProvider.getBindConstructor(ConfigurationPropertiesBindConstructorProvider.java:48)
at org.springframework.boot.context.properties.ConfigurationPropertiesBean$BindMethod.forType(ConfigurationPropertiesBean.java:311)
at org.springframework.boot.context.properties.ConfigurationPropertiesBeanDefinitionValidator.validate(ConfigurationPropertiesBeanDefinitionValidator.java:63)
at org.springframework.boot.context.properties.ConfigurationPropertiesBeanDefinitionValidator.postProcessBeanFactory(ConfigurationPropertiesBeanDefinitionValidator.java:45)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:286)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:174)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:706)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:532)
at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.refresh(ReactiveWebServerApplicationContext.java:66)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
at com.ileadtek.gateway.CpGatewayApplication.main(CpGatewayApplication.java:18)
Caused by: java.lang.ClassNotFoundException: javax.servlet.Servlet
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
... 19 common frames omitted
发现是因为Druid依赖于javax.servlet-api
但在我添加servlet依赖后又报错：
接着添加tomcat-embed-core依赖来解决以上错误，再次启动后发现又出现了之前遇到过的jar包冲突问题：
***************************
APPLICATION FAILED TO START
***************************
Description:
Parameter 0 of method modifyRequestBodyGatewayFilterFactory in org.springframework.cloud.gateway.config.GatewayAutoConfiguration required a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' that could not be found.
Action:
Consider defining a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' in your configuration.
好嘞，排除spring-boot-starter-web依赖肯定行的啦(￣▽￣)／ 但是。。。我好想没发现哪个项目有依赖spring-boot-starter-web呀！
是它！Druid的问题
我又排除了好几个依赖项，最终才定位到是Druid的问题，最根本的原因是它间接依赖了tomcat-embed-core，无奈之下只好换数据源了：
再次启动，果然成功了。O(∩_∩)O哈哈~
总结
看来spring-cloud-starter-gateway并非是spring-boot-starter-web的原因，我发现spring-boot-starter-web也依赖了tomcat-embed-core。
所以我认为最根本的还是因为项目中tomcat-embed-core依赖包(*￣︶￣)
参考
www.codeleading.com/article/651…
如果大家也遇到了这个问题，欢迎一起交流哦(#^.^#)
