IDEA解决maven包冲突

maven包冲突虽然在工作遇到不是特别多，但是遇到了也是很挠头的，下面介绍一种解决方式，妈妈再也不用担心我的maven冲突了。

包冲突显现出来的问题有：某些类找不到。
原因：工程中引入了一个需要的依赖，但工程中其他依赖的包内部也可能会有相同的依赖，如果版本不同maven可能取了一个低的版本，然后可能造成某个类找不到。
比如：
在工程中引入了easypoi jar，要使用Excel导出功能。

<dependency>
 <groupId>cn.afterturn</groupId>
 <artifactId>easypoi-spring-boot-starter</artifactId>
 <version>4.1.2</version>
</dependency>
上述jar 内部依赖 apache-poi 版本 4.1.0
<dependency>
 <groupId>org.apache.poi</groupId>
 <artifactId>poi</artifactId>
 <version>4.1.0</version>
</dependency>

我的工程中有个公司的公用的jar，内部依赖了apache-poi 3.x
编写代码时没问题，运行调用相关接口报错如下
java.lang.NoClassDefFoundError: org/apache/poi/hssf/util/HSSFColor$HSSFColorPredefined

org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/poi/hssf/util/HSSFColor$HSSFColorPredefined
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at cn.huimin100.account.manager.main.filters.RequestWrapperFilter.doFilterInternal(RequestWrapperFilter.java:24)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:109)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1594)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

发现找不到是个内部类，搜索主类发现主类所在的jar版本为3.9而不是4.1.0，这就是jar版本冲突造成的问题。

解决步骤：

1.在IDEA中右键项项目的pom文件，选择Maven->Show Dependencies，会打开一个maven的依赖树窗口，如下：

2.打开窗口我们可以看到完整的依赖树,小技巧：左上角有几个小工具，比较常用的1显示冲突项，2显示从root到被选择的jar包路径，3显示实际大小。要选择冲突项的话可以直接点击1，然后在点击3，显示的会更清楚一些，因为jar包比较多，jar依赖比较复杂会让图变得很小。之后如果你需要看这个jar的引用路径可以点击这个jar包再点击2，就回显示从pom文件的根路径的包到被选择的包的单条路线，很方便；

3.找到冲突的包后，选择需要的那个jar包，右键要去除的那个jar包，点击exclude。
红色虚线代表冲突，而且标了相应版本。

就会在pom文件中被剔除（就是对应的pom中的exclusion）

重启，调用，正常。这样，就解决了jar版本冲突问题。