java - 为什么我在 POM 中包含正确的依赖项后仍会出现 NoClassDefFoundError？

Question

我正在尝试构建我的应用程序并将 jar 文件发送给用户。它很好地构建，但是当我试图运行 jar 时它出现了问题。

我正在尝试运行从 mvn package 命令编译的 jar 文件。之后，我正在运行 java -jar ApplicationRunner.jar，但我遇到了以下异常。 请注意，当我通过 Intellij Idea IDE 运行时 - 它工作正常

Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/core/JsonProcessingException
    at cs550.pa3.ApplicationRunner.<init>(ApplicationRunner.java:27)
    at cs550.pa3.ApplicationRunner.main(ApplicationRunner.java:39)
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.core.JsonProcessingException
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

我的 pom.xml 文件 -

<?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>FileSharingSystem</groupId>
    <artifactId>FileSharingSystem-1</artifactId>
    <version>3.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <!-- Make this jar executable -->
            <plugin>

                <groupId>org.apache.maven.plugins</groupId>

                <artifactId>maven-jar-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>cs550.pa3.ApplicationRunner</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
            </plugin>
        </plugins>

    </build>
    <dependencies>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.5</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.mockito/mockito-all -->
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-all</artifactId>
            <version>1.9.5</version>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>RELEASE</version>
        </dependency>
        <!--<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.6.1</version>
        </dependency>-->

        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
        <!--<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.8.4</version>
        </dependency>-->

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.8.0</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.8.0</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.8.0</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
            <version>2.6.5</version>
        </dependency>


    </dependencies>

</project>

Answer 1

如果你想为客户端提供一个可执行的jar，你应该在jar中添加所需的依赖。
您可以使用 maven-assembly-plugin 创建一个包含依赖项的 jar:

<build>
  <plugins>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <archive>
          <manifest>
            <mainClass>cs550.pa3.ApplicationRunner</mainClass>
          </manifest>
        </archive>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
      </configuration>
    </plugin>
  </plugins>
</build>