请问：如何优雅依赖多个版本的jar包？

问题现状

由于是一个迭代比较久的项目，项目中已经存在poi-tl 1.5.x的依赖，poi-tl v1.5.x是构建在Apache poi3.16上的版本，而我们现在要使用到easyexcel来处理导出，而easyexcel最低的Apache poi版本要求是4.1.2，将项目中已有poi的3.16升级到4.12时，旧代码出错，但是不升级就无法使用easyexcel。

解决思路

解决问题思路无非就是两种：

将项目中已有的poi3.16升级到4.12，解决升级后代码出错的地方；

优点：jar包依赖清晰，在代码改动量可控的情况下，推荐使用该方式；

缺点：代码改动量大，工作量大，而且容易对之前的功能带来不稳定因素；
使用maven-shade-plugin插件来解决，让项目依赖多个版本的poi版本；

优点：对原来的功能无影响，代码改动量小；

缺点：jar依赖变大，因为依赖了同一个依赖的2个版本；jar包依赖不那么清晰优雅；

今天文章主角就是第2种方式。

它的核心思路就是把easyexcel中的高版本poi包改个名字，同时easyexcel中引用的地方也改名（自动），并且代码中用高本版的地方也改个名（手动）。

解决问题

创建一个空maven项目，项目名称为jarjar，引入easyexcel的依赖；
```
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>easyexcel</artifactId>
    <version>3.1.1</version>
</dependency>
```
查看其依赖的poi版本

easyexcel poi版本

引入插件并且配置好修改的方式；

<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>
                                <!-- <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>
                                    <!-- 改名前 -->
                                    <pattern>org.apache.poi</pattern>
                                    <!-- 改名后 -->
                                    <shadedPattern>shaded.org.apache.poi</shadedPattern>
                                </relocation>

                                <!-- 可以配置多个 -->
                                <relocation>
                                    <!-- 改名前 -->
                                    <pattern>com.deepoove.poi.XWPFTemplate</pattern>
                                    <!-- 改名后 -->
                                    <shadedPattern>shaded.com.deepoove.poi.XWPFTemplate</shadedPattern>
                                </relocation>
                            </relocations>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>改名前 -->
                                <pattern>org.apache.poi</pattern>
                                <!-- 改名后 -->
                                <shadedPattern>shaded.org.apache.poi</shadedPattern>
                            </relocation>
                        </relocations>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

较为完整的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>org.example</groupId>
    <artifactId>jarjar</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>easyexcel</artifactId>
            <version>3.1.1</version>
        </dependency>
    </dependencies>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <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>
                                    <!-- 改名前 -->
                                    <pattern>org.apache.poi</pattern>
                                    <!-- 改名后 -->
                                    <shadedPattern>shaded.org.apache.poi</shadedPattern>
                                </relocation>

                                <!-- 可以配置多个 -->
                                <relocation>
                                    <!-- 改名前 -->
                                    <pattern>com.deepoove.poi.XWPFTemplate</pattern>
                                    <!-- 改名后 -->
                                    <shadedPattern>shaded.com.deepoove.poi.XWPFTemplate</shadedPattern>
                                </relocation>
                            </relocations>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

打出jar包；

执行mvn package，如果是IDEA直接双击Lifecycle中的package就行了。

打出jar包

这时target目录中会有两个包，一个是original开头的原本包，因为我们没有新建类，所以这个包是空的。另一个是和artifactId-version.jar的包，artifactId和version是本项目创建时填写的坐标。

如图，我的这个maven项目叫jarjar，版本是1.0：

找到指定的jar包

依赖本地jar，运行项目；

<dependency>
            <groupId>org.example</groupId>
            <artifactId>jarjar</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>system</scope>
            <systemPath>${project.basedir}/src/main/java/lib/jarjar-1.0-SNAPSHOT.jar</systemPath>
</dependency>

 <build>
   <resources>
    <resource>
      <directory>lib</directory>
      <targetPath>/BOOT-INF/lib/</targetPath>
      <includes>
        <include>**/*.jar</include>
      </includes>
    </resource>
   </resources>
 </build>