陈旧的项目导出excel时用的POI3.14，现在引入easyexcel2.2.6，报错。

Caused by: java.lang.NoClassDefFoundError: org/apache/poi/util/DefaultTempFileCreationStrategy
 at com.alibaba.excel.util.FileUtils.createPoiFilesDirectory(FileUtils.java:138)
 at com.alibaba.excel.write.ExcelBuilderImpl.<clinit>(ExcelBuilderImpl.java:30)
 at com.alibaba.excel.ExcelWriter.<init>(ExcelWriter.java:47)
 at com.alibaba.excel.write.builder.ExcelWriterBuilder.build(ExcelWriterBuilder.java:130)
 at com.alibaba.excel.write.builder.ExcelWriterBuilder.sheet(ExcelWriterBuilder.java:146)
 at com.alibaba.excel.write.builder.ExcelWriterBuilder.sheet(ExcelWriterBuilder.java:134)

easyexcel依赖POI3.17+，POI版本冲突。POI3.14之前用的地方很多，提升版本代价太大。

现使用maven-shade-plugin来保证POI多版本共存。原理是将POI3.17中的类换一个包名，从而和POI3.14中的类区分开。

1. 重新编译easyexcel源码包，使用maven-shade-plugin替换poi包名

2. 将打好的easyexcel.jar放入项目中，添加到本地依赖

   项目中也用到了asm3.3.1，easyexcel引用了asm4.2，也将asm包名替换

   <!--easyexcel打包时的插件-->
   <build>
       <plugins>
           <plugin>
               <groupId>org.apache.maven.plugins</groupId>
               <artifactId>maven-shade-plugin</artifactId>
               <version>3.2.4</version>
               <executions>
                   <execution>
                       <phase>package</phase>
                       <goals>
                           <goal>shade</goal>
                       </goals>
                       <configuration>
                           <createDependencyReducedPom>true</createDependencyReducedPom>
                           <relocations>
                               <relocation>
                                   <!-- poi包替换 -->
                                   <pattern>org.apache.poi</pattern>
                                   <shadedPattern>shade.org.apache.poi</shadedPattern>
                               </relocation>
                               <relocation>
                                   <pattern>org.objectweb.asm</pattern>
                                   <shadedPattern>shade.org.objectweb.asm</shadedPattern>
                               </relocation>
                           </relocations>
                       </configuration>
                   </execution>
               </executions>
           </plugin>
       </plugins>
   </build>
   
   <!-- 项目引用easyexcel -->
   
   <!-- poi3.14和poi3.17共存，asm3.3.1和asm4.2共存，重新打包easyexcel   -->
   <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>easyexcel</artifactId>
       <version>2.2.6</version>
       <systemPath>${basedir}/src/main/webapp/WEB-INF/lib/easyexcel-2.2.6.jar</systemPath>
       <scope>system</scope>
   </dependency>