maven快速入门第六讲——在maven中安装tomcat8-maven-plugin插件，并使用它来运行maven工程

在前几讲中，我都是使用tomcat7插件来运行maven项目的，这只需要我们在pom.xml文件中添加tomcat7插件的依赖即可。

我靠！这个tomcat7插件是不是有点太老了，因为我本地tomcat服务器使用的都是apache-tomcat-8.5.38这个版本了。我不禁就想了，何不在maven中安装tomcat8-maven-plugin插件，并使用它来运行maven项目呢？

你不禁想问了，如何找到这样一个tomcat8-maven-plugin插件的坐标呢？首先，打开浏览器，访问https://mvnrepository.com/artifact/org.apache.tomcat.maven/tomcat8-maven-plugin这样一个url地址，这时你就可以看到所有版本的tomcat8-maven-plugin插件了。

这里，我们不妨选择3.0-r1655215这个版本的tomcat8-maven-plugin插件。点击3.0-r1655215，就能看到这个版本的tomcat8-maven-plugin插件的坐标了。

如果把上面的依赖加入到pom.xml文件中，那么要么就是提示找不到该依赖，要么就是下载不下来。我找了半天终于找到了一个解决方法，那就是使用maven中的<pluginRepositories>标签（该标签是用来配置插件地址的）。因为maven中的所有功能都是使用插件来实现的，所以需要从特定的地址下载插件包。

于是，首先要在pom.xml文件中加入如下内容：

<!-- 配置tomcat8插件下载地址 -->
<pluginRepositories>
    <pluginRepository>
        <id>alfresco-public</id>
        <url>https://artifacts.alfresco.com/nexus/content/groups/public</url>
    </pluginRepository>
    <pluginRepository>
        <id>alfresco-public-snapshots</id>
        <url>https://artifacts.alfresco.com/nexus/content/groups/public-snapshots</url>
        <snapshots>
            <enabled>true</enabled>
            <updatePolicy>daily</updatePolicy>
        </snapshots>
    </pluginRepository>
    <pluginRepository>
        <id>beardedgeeks-releases</id>
        <url>http://beardedgeeks.googlecode.com/svn/repository/releases</url>
    </pluginRepository>
</pluginRepositories>

然后，再在pom.xml文件中加入tomcat8-maven-plugin插件的依赖。

<!-- 配置tomcat8插件 -->
<plugin>
    <groupId>org.apache.tomcat.maven</groupId>
    <artifactId>tomcat8-maven-plugin</artifactId>
    <version>3.0-r1655215</version>
    <configuration>
        <server>tomcat8</server>
        <!-- 配置访问端口 -->
        <port>8080</port>
        <!-- 访问的项目路径 -->
        <path>/hellomaven</path>
        <!-- 
                编码，为什么加这个编码呢？大家都知道，我们使用网络传输的时候，默认情况下使用的是iso8859-1编码
                （提交请求的时候，特别是使用get请求的时候），所以要进行一个编码转换！ 
        -->
        <uriEncoding>utf-8</uriEncoding>
    </configuration>
</plugin>

接下来，就要使用tomcat8-maven-plugin插件来运行maven项目了，大家可以按照下图所示的步骤进行操作。

然后，在弹出的窗口中输入tomcat8:run命令，点击Run即可运行maven项目了。

这时，eclipse控制台打印出了如下内容。

从中可以发现使用maven里面带有的tomcat8插件来运行maven项目已经运行成功了。紧接着，打开Google Chrome浏览器，并访问http://localhost:8080/hellomaven/HelloServlet这样一个url地址，发现报错了，错误提示信息如下：

而且，eclipse控制台也打印出了如下错误提示信息：

严重: Servlet.service() for servlet jsp threw exception
java.lang.LinkageError: loader constraint violation: when resolving method "org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(Ljavax/servlet/ServletConfig;)Lorg/apache/tomcat/InstanceManager;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for the method's defining class, org/apache/jasper/runtime/InstanceManagerFactory, have different Class objects for the type org/apache/tomcat/InstanceManager used in the signature
	at org.apache.jsp.index_jsp._jspInit(index_jsp.java:32)
	at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:49)
	at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:180)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:721)
	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
	at com.meimeixia.web.HelloServlet.doGet(HelloServlet.java:13)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
	at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Unknown Source)

十二月 21, 2019 9:13:01 下午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [HelloServlet] in context with path [/hellomaven] threw exception [java.lang.LinkageError: loader constraint violation: when resolving method "org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(Ljavax/servlet/ServletConfig;)Lorg/apache/tomcat/InstanceManager;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for the method's defining class, org/apache/jasper/runtime/InstanceManagerFactory, have different Class objects for the type org/apache/tomcat/InstanceManager used in the signature] with root cause
java.lang.LinkageError: loader constraint violation: when resolving method "org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(Ljavax/servlet/ServletConfig;)Lorg/apache/tomcat/InstanceManager;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/codehaus/plexus/classworlds/realm/ClassRealm) for the method's defining class, org/apache/jasper/runtime/InstanceManagerFactory, have different Class objects for the type org/apache/tomcat/InstanceManager used in the signature
	at org.apache.jsp.index_jsp._jspInit(index_jsp.java:32)
	at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:49)
	at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:180)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:721)
	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:466)
	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:391)
	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:318)
	at com.meimeixia.web.HelloServlet.doGet(HelloServlet.java:13)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
	at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Unknown Source)

尼玛的，使用tomcat8插件来运行maven项目，有这么难吗？我也在网上翻阅了好多篇文章，但也没找到一个解决办法，我的心真的好痛啊！但不管怎么样，还是把这个问题记录在这儿吧！如果大家知道一个好的解决办法，那么请告知我一下，万分感谢！！！