Zipkin Server 無法啓動的問題

加入 Zipkin Server

由於需要收集 Spring Cloud 系統的跟蹤信息，以便及時地發現系統中出現的延遲升高問題並找出系統性能瓶頸的根源，所以在 Spring Cloud 項目中創建 Zipkin Server。
在 zipkin-server 模塊中引入瞭如下依賴：

<dependency>
     <groupId>io.zipkin.java</groupId>
     <artifactId>zipkin-server</artifactId>
     <version>2.12.9</version>
 </dependency>
 <dependency>
     <groupId>io.zipkin.java</groupId>
     <artifactId>zipkin-autoconfigure-ui</artifactId>
     <version>2.12.9</version>
 </dependency>

Multiple SLF4J Bindings

在 Spring Boot 啓動類加上 @EnableZipkinServer 註解，啓動項目，控制檯報錯：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/jake/respository/org/apache/logging/log4j/log4j-slf4j-impl/2.11.2/log4j-slf4j-impl-2.11.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/jake/respository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
Exception in thread "main" java.lang.StackOverflowError
	at org.apache.logging.log4j.util.StackLocator.getCallerClass(StackLocator.java:108)

谷歌搜索了一下，需要排除 zipkin-server 中依賴的 SLF4j

<dependency>
    <groupId>io.zipkin.java</groupId>
    <artifactId>zipkin-server</artifactId>
    <version>2.12.9</version>
    <exclusions>
        <exclusion>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j-impl</artifactId>
        </exclusion>
    </exclusions>
</dependency>

armeriaServer 版本衝突

再次啓動項目，報錯：

Caused by: java.lang.NullPointerException: null
	at zipkin2.autoconfigure.ui.ZipkinUiAutoConfiguration.lambda$uiServerConfigurator$0(ZipkinUiAutoConfiguration.java:179) ~[zipkin-autoconfigure-ui-2.12.9.jar:na]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration.lambda$armeriaServer$0(ArmeriaAutoConfiguration.java:111) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at java.util.ArrayList.forEach(ArrayList.java:1257) ~[na:1.8.0_211]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration.lambda$armeriaServer$1(ArmeriaAutoConfiguration.java:110) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at java.util.Optional.ifPresent(Optional.java:159) ~[na:1.8.0_211]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration.armeriaServer(ArmeriaAutoConfiguration.java:109) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration$$EnhancerBySpringCGLIB$$2d84b2a7.CGLIB$armeriaServer$0(<generated>) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration$$EnhancerBySpringCGLIB$$2d84b2a7$$FastClassBySpringCGLIB$$4c907816.invoke(<generated>) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:363) ~[spring-context-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	at com.linecorp.armeria.spring.ArmeriaAutoConfiguration$$EnhancerBySpringCGLIB$$2d84b2a7.armeriaServer(<generated>) ~[armeria-spring-boot-autoconfigure-0.83.0.jar:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_211]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_211]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_211]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_211]
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
	... 20 common frames omitted

根據搜索結果，得到
錯誤原因：
Zipkin最新版本爲 2.12.9，從 2.12.6 開始有一個較大的更新：遷移使用了 Armeria HTTP 引擎，存在版本衝突。
解決方法：
將版本降低到 2.12.3 就可以正常啓動了。
於是把 Zipkin 的依賴版本修改爲 2.12.3：

<dependency>
    <groupId>io.zipkin.java</groupId>
    <artifactId>zipkin-server</artifactId>
    <version>2.12.3</version>
    <exclusions>
        <exclusion>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j-impl</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>io.zipkin.java</groupId>
    <artifactId>zipkin-autoconfigure-ui</artifactId>
    <version>2.12.3</version>
</dependency>

訪問 Zipkin UI

再次啓動，成功！訪問 localhost:9411：