log4j2 java.lang.NoClassDefFoundError:org/apache/logging/log4j/LogManager

Question

我在我的java应用程序中使用log4j 2.3.我通过maven添加了依赖项.
在eclipse中运行程序时一切正常,但是当我用maven打包并尝试运行jar时,我得到以下错误:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache logging/log4j/LogManager
    at main.myclass.<clinit>(myclass.java:11)
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager 


    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 1 more

为什么从jar运行它时无法找到类？

添加log4j 1.2也不起作用.该程序在eclipse中正常运行,因此不应缺少依赖项.

Answer 1

从命令行运行应用程序jar时,依赖jar在运行时不可用.您需要将这两个插件中的任何一个包含到pom.xml中,以便在运行时使用您的依赖项.

使用:maven-shade-plugin

<plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>2.4.1</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals>
              <goal>shade</goal>
            </goals>
            <configuration>
              <transformers>
                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                  <mainClass>org.sonatype.haven.HavenCli</mainClass>
                </transformer>
              </transformers>
            </configuration>
          </execution>
        </executions>
      </plugin>

使用:Maven的依赖关系的插件

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <version>2.8</version>
    <executions>
        <execution>
             <id>copy-dependencies</id>
             <phase>package</phase>
             <goals>
                 <goal>copy-dependencies</goal>
             </goals>
             <configuration>
                 <outputDirectory>${project.build.directory}/lib</outputDirectory>
             </configuration>
        </execution>
     </executions>
</plugin>

当你执行mvn package它时,它将生成uber jar /或将依赖项复制到outputDirectory.我更喜欢maven-shade-plugin生成一个jar将所有依赖项.