Maven 阴影插件警告 : we have a duplicate - how to fix?

Question

这是我的项目 POM (link to the paste, so you can right click > save as pom.xml)

<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.zybnet</groupId>
    <artifactId>excel-reporter</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>mvn1</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>3.8</version>
        </dependency>
        <dependency>
            <groupId>net.sf.jasperreports</groupId>
            <artifactId>jasperreports</artifactId>
            <version>4.6.0</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-all</artifactId>
            <version>2.0.0</version>
        </dependency>
    </dependencies>

    <build>
        <resources>
            <resource>
                <directory>${project.build.sourceDirectory}</directory>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <finalName>${artifactId}-${version}-tmp</finalName>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>1.7.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <filters>
                                <filter>
                                    <artifact>*:*</artifact>
                                    <excludes>
                                        <exclude>META-INF/*.SF</exclude>
                                        <exclude>META-INF/*.DSA</exclude>
                                        <exclude>META-INF/*.RSA</exclude>
                                    </excludes>
                                </filter>
                            </filters>
                            <transformers>
                                <transformer
                                    implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.zybnet.Main</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

我遵循了 the FAQ 中宣传的配置默认 jar 插件的建议。 ，但仍然在我运行时 mvn package发出了大约 20K 个警告。运行 mvn clean也没有帮助。

根据 this answer ，我可以手动排除一些依赖项。然而，我不知道这是否是正确的方法，而且依赖树相当复杂，所以很难争论从哪里开始。

我知道这些问题无害，但我习惯于将警告视为必须解决的问题。此外，我是Maven的初学者，所以我想了解我的理解有什么问题，以及如何解决问题。

(使用 Maven 程序集插件不是这里的选项)

Answer 1

有时会在两个或多个 JAR 文件(通常这些是依赖 JAR)中找到相同的类定义。在这种情况下，开发人员只能尝试找出从依赖项或最终 Artifact 中手动排除的内容(也许在 mvn dependency:tree -Ddetail=true 的帮助下)。我opened an issue and submitted a patch , 以帮助开发人员提供稍微漂亮的输出，例如

[WARNING] xml-apis-1.3.02.jar, xmlbeans-2.3.0.jar define 4 overlappping classes:
[WARNING]   - org.w3c.dom.TypeInfo
[WARNING]   - org.w3c.dom.DOMConfiguration
[WARNING]   - org.w3c.dom.DOMStringList
[WARNING]   - org.w3c.dom.UserDataHandler
[WARNING] maven-shade-plugin has detected that some .class files
[WARNING] are present in two or more JARs. When this happens, only
[WARNING] one single version of the class is copied in the uberjar.
[WARNING] Usually this is not harmful and you can skip these
[WARNING] warnings, otherwise try to manually exclude artifacts
[WARNING] based on mvn dependency:tree -Ddetail=true and the above
[WARNING] output
[WARNING] See http://docs.codehaus.org/display/MAVENUSER/Shade+Plugin

使用此输出和来自 mvn dependency:tree 的输出我添加了像

<dependency>
    <groupId>net.sf.jasperreports</groupId>
    <artifactId>jasperreports</artifactId>
    <version>4.7.0</version>
    <exclusions>
        <exclusion>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
        </exclusion>
        <exclusion>
            <groupId>bouncycastle</groupId>
            <artifactId>bcmail-jdk14</artifactId>
        </exclusion>
        <exclusion>
            <groupId>bouncycastle</groupId>
            <artifactId>bcprov-jdk14</artifactId>
        </exclusion>
        <exclusion>
            <groupId>org.bouncycastle</groupId>
            <artifactId>bctsp-jdk14</artifactId>
        </exclusion>
    </exclusions>
</dependency>

并设法将警告数量从数千个减少到几十个。尽管如此，这并不完美。尽管如此，他们仍然继续复制粘贴导致名称冲突的类(我不明白为什么)。尽管如此，这个解决方案是特定于这个特定项目的，不能轻易移植到任何其他项目上。