升级到 spring boot 2.1.3 到 2.1.4 在启动时给出 tomcat 异常答案

【问题标题】：Upgrading to spring boot 2.1.3 to 2.1.4 giving tomcat exception while starting升级到 spring boot 2.1.3 到 2.1.4 在启动时给出 tomcat 异常
【发布时间】：2019-05-16 17:19:51
【问题描述】：

我已将我的 spring 父级从 2.1.3 更新到 2.1.4 版本，因此在启动应用程序时遇到了一些异常。有版本问题吗？

用于运行的命令：mvn spring-boot:run

java 版本：11

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.sample.business</groupId>
    <artifactId>sample-order-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>sample-order-service</name>
    <description>sample Order Service</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent> 

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>11</java.version>
        <jaxb-runtime.version>2.4.0-b180830.0438</jaxb-runtime.version>
        <spring-cloud.version>Greenwich.M1</spring-cloud.version>
        <sample.version>1.0</sample.version>
        <swagger.version>2.9.2</swagger.version>
        <jjwt.version>0.9.1</jjwt.version>
        <json.version>20180813</json.version>
        <mysql.version>8.0.11</mysql.version>
        <commons-io.version>2.6</commons-io.version>
        <commons-lang.version>2.6</commons-lang.version>
        <commons-pool2.version>2.5.0</commons-pool2.version>
        <redis.version>2.9.1</redis.version>
        <velocity.version>1.7</velocity.version>
        <velocity-tools.version>2.0</velocity-tools.version>
        <logstash-logback-encoder.version>5.3</logstash-logback-encoder.version>
        <httpclient.version>4.5.6</httpclient.version>
        <env>dev</env>
    </properties>   

    <dependencies>
        <!-- Start: Spring Libraries -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-mongodb</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-oauth2</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-oauth2-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.kafka</groupId>
            <artifactId>spring-kafka</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-sleuth</artifactId>
        </dependency>
        <!-- End: Spring Libraries -->

        <!-- Adding JAXB Runtime since it is not shipped with JDK 9+ -->
        <dependency>
            <groupId>org.glassfish.jaxb</groupId>
            <artifactId>jaxb-runtime</artifactId>
            <version>${jaxb-runtime.version}</version>
        </dependency>

        <!-- Start: Swagger Libraries -->
        <!-- https://mvnrepository.com/artifact/io.springfox/springfox-swagger2 -->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>${swagger.version}</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/io.springfox/springfox-swagger-ui -->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>${swagger.version}</version>
        </dependency>
        <!-- End: Swagger Libraries -->


        <!-- https://mvnrepository.com/artifact/org.json/json -->
        <dependency>
            <groupId>org.json</groupId>
            <artifactId>json</artifactId>
            <version>${json.version}</version>
        </dependency>

        <!-- Json Web Token Binary -->
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt</artifactId>
            <version>${jjwt.version}</version>
        </dependency>

        <!-- Logstash Log Encoder -->
        <dependency> 
            <groupId>net.logstash.logback</groupId> 
            <artifactId>logstash-logback-encoder</artifactId> 
            <version>${logstash-logback-encoder.version}</version> 
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>${mysql.version}</version><!--$NO-MVN-MAN-VER$-->
        </dependency>

        <!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>${commons-io.version}</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-pool2 -->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-pool2</artifactId>
            <version>${commons-pool2.version}</version><!--$NO-MVN-MAN-VER$-->
        </dependency>

        <!-- https://mvnrepository.com/artifact/redis.clients/jedis -->
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
            <version>${redis.version}</version><!--$NO-MVN-MAN-VER$-->
        </dependency>       

        <!-- velocity -->
        <dependency>
            <groupId>org.apache.velocity</groupId>
            <artifactId>velocity</artifactId>
            <version>${velocity.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.velocity</groupId>
            <artifactId>velocity-tools</artifactId>
            <version>${velocity-tools.version}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>${httpclient.version}</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.4</version>
        </dependency>


        <!-- Start: Spring Boot and Security Test Libraries -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- End: Spring Boot and Security Test Libraries -->

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <finalName>sample-order-service</finalName>
        <filters>
            <filter>${env}-build.properties</filter>
        </filters>
        <resources>
            <resource>
                <filtering>true</filtering>
                <directory>${project.basedir}/src/main/resources</directory>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <release>${java.version}</release>
                </configuration>
            </plugin>
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-jar-plugin</artifactId>
              <configuration>
                <archive>
                  <manifestEntries>
                    <Automatic-Module-Name>com.sample.business.order</Automatic-Module-Name>
                  </manifestEntries>
                </archive>
              </configuration>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories> 
</project>

日志：

2019-05-14 18:40:30.277  INFO [sample-order-service,,,] 10916 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8083 (http)
2019-05-14 18:40:30.494 ERROR [sample-order-service,,,] 10916 --- [           main] org.apache.catalina.core.ContainerBase   : A child container failed during start

java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [NonLoginAuthenticator[StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[]]]
        at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
        at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909)
        at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:831)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1377)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1367)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
        at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:140)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:902)
        at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardService.startInternal(StandardService.java:423)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:928)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.startup.Tomcat.start(Tomcat.java:455)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:106)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.<init>(TomcatWebServer.java:86)
        at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getTomcatWebServer(TomcatServletWebServerFactory.java:427)
        at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:180)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:181)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:154)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142)
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775)
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:316)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248)
        at com.sample.business.order.OrderServiceApplication.main(OrderServiceApplication.java:30)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.springframework.boot.maven.AbstractRunMojo$LaunchRunner.run(AbstractRunMojo.java:558)
        at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [NonLoginAuthenticator[StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[]]]
        at org.apache.catalina.util.LifecycleBase.handleSubClassException(LifecycleBase.java:441)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:198)
        at org.apache.catalina.core.StandardPipeline.startInternal(StandardPipeline.java:181)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5060)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1377)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1367)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
        at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:140)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:902)
        ... 35 common frames omitted
Caused by: java.lang.NoSuchMethodError: javax.servlet.ServletContext.getVirtualServerName()Ljava/lang/String;
        at org.apache.catalina.authenticator.AuthenticatorBase.startInternal(AuthenticatorBase.java:1178)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        ... 45 common frames omitted

2019-05-14 18:40:30.579 ERROR [sample-order-service,,,] 10916 --- [           main] org.apache.catalina.core.ContainerBase   : A child container failed during start

java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: A child container failed during start
        at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
        at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909)
        at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:262)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardService.startInternal(StandardService.java:423)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:928)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.startup.Tomcat.start(Tomcat.java:455)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:106)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.<init>(TomcatWebServer.java:86)
        at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getTomcatWebServer(TomcatServletWebServerFactory.java:427)
        at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:180)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:181)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:154)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142)
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775)
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:316)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248)
        at com.sample.business.order.OrderServiceApplication.main(OrderServiceApplication.java:30)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.springframework.boot.maven.AbstractRunMojo$LaunchRunner.run(AbstractRunMojo.java:558)
        at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:921)
        at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:831)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1377)
        at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1367)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
        at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:140)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:902)
        ... 27 common frames omitted
Caused by: java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [NonLoginAuthenticator[StandardEngine[Tomcat].StandardHost[localhost].TomcatEmbeddedContext[]]]
        at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
        at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
        at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:909)
        ... 35 common frames omitted

我尝试使用 clean build 和 maven repos 仍然没有运气。有版本问题吗？

【问题讨论】：

有一个java.lang.NoSuchMethodError。检查您的依赖项，是否存在缺失或错误的版本依赖项。
您的类路径似乎包含一个太旧的 servlet-api 版本。执行mvn dependency:tree 来查看拉入了哪些依赖项，看看它们是否依赖于旧的servlet API 版本。
感谢@Gimby 的帮助。 java servlet 之间存在冲突。所以我从velocity-tools中排除了java-servlet，然后它对我有用
你可能有一个非常旧版本的速度工具，2.0 版本声明了 servlet-api 作为提供，这意味着它不应该被自动转储到你的应用程序的类路径中。也许升级依赖项也可以。

标签： spring-boot

【解决方案1】：

这样的问题通常意味着你对你的类路径的依赖太旧了。当使用像 Maven 这样的工具时会发生这种情况，因为它具有 传递依赖项 的概念，这意味着依赖项被拉入，因为另一个依赖项指示您需要它们。它很方便……而且容易出错。

从异常堆栈跟踪中可以清楚地看出它与 servlet 类有关，这意味着它是 servlet-api.jar（谷歌搜索类名通常是找出类是什么 jar 的简单方法如果你碰巧没有通过经验知道它的一部分）。

知道可能是哪个jar，就可以执行maven命令了

mvn dependency:tree

让 Maven 生成所有依赖项、它们的版本和作用域的列表。通过这个搜索你可以找到那个罐子被拉进去的地方。

因此，在 cmets 中提到的这种情况下，依赖速度工具正在拉入 servlet-api，它是一个较旧的版本（通过查看 pom of that dependency 来猜测是 2.3 版）。了解这一点后，您可以采取一些基本步骤来纠正这种情况。以下是我常用的三个，一个是个坏主意。

1.删除有问题的依赖项（在这种情况下为速度工具）

这只有在你实际上并不需要这种依赖时才有意义。这实际上比 Maven pom 更常见，我们都喜欢不小心复制/粘贴。

2。升级依赖

可能需要根依赖，但仍在使用非常旧的版本。依赖问题可以在较新的更新中解决（这似乎也是速度工具的情况）。从历史上看，maven Central 中的依赖项并没有过多地关注为其传递依赖项声明正确的范围，并且可能会在编译范围上产生比实际需要的更多的依赖项。这在最近几年有了很大的改进，但是在包含非常旧的依赖版本时仍然会遇到问题。

3。自己声明传递依赖的正确版本和范围

说 servlet-api 在编译范围内被拉入 - 这是错误。 Servlet-api 绝不能与您的应用程序一起部署，服务器 (Tomcat) 提供它。这是一个依赖，其目的只是为了让您可以编译使用 servlet API 的代码。

因此，如果您确实发现自己处于必须包含依赖项进行编译但从部署中排除的情况，您可以在 pom（或您的父 pom）中自己管理它，这将具有优先权。

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>3.1</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

4.添加排除项（不推荐）

如果您确实需要根依赖项，则可能仍然是引入的传递依赖项（在这种情况下为 servlet-api）与您的代码完全无关。在这种情况下，您可以添加排除项。

<dependency>
    <groupId>org.apache.velocity</groupId>
    <artifactId>velocity-tools</artifactId>
    <version>1.3</version>
    <exclusions>
      <exclusion>
        <groupId>javax.servlet</groupId>
        <artifactId>servlet-api</artifactId>
      </exclusion>
    </exclusions>
</dependency>

排除应该是最后的手段，因为它们很难维护；他们本质上是一个黑客。将排除项添加到一个依赖项并不能保证该依赖项消失，因为它也可能被拉入其他地方。尽可能通过其他三个选项之一管理依赖项，尽量避免使用排除项。

【讨论】：