如何告诉 Maven 项目在目标文件夹中包含依赖项？

Question

我正在学习使用 Maven。所以，我创建了一个简单的程序，它只解析一些 JSON 文本。为此，我使用了一个外部库“jackson”，并将其作为依赖项包含在 pom.xml 文件中，以及“jackson”本身所需的依赖项，如下所示。

<?xml version="1.0"?>

<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>alex</groupId>

  <artifactId>test</artifactId>

  <version>0.0.1-SNAPSHOT</version>

  <packaging>jar</packaging>

  <name>test</name>

  <url>http://maven.apache.org</url>

  <properties>

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

    <jackson.version>2.9.5</jackson.version>

    <maven.compiler.source>1.8</maven.compiler.source>

    <maven.compiler.target>1.8</maven.compiler.target>

  </properties>

  <dependencies>

    <dependency>

      <groupId>junit</groupId>

      <artifactId>junit</artifactId>

      <version>3.8.1</version>

      <scope>test</scope>

    </dependency>

    <dependency>

      <groupId>com.fasterxml.jackson.core</groupId>

      <artifactId>jackson-databind</artifactId>

      <version>${jackson.version}</version>

    </dependency>

    <dependency>

当我输入时mvn clean package，程序编译正常，我可以看到在文件target夹中创建的 jar 文件。但是，当我尝试通过java -jar test-0.0.1-SNAPSHOT.jar从那里键入来运行该 jar 文件时，它抱怨找不到依赖项。它给了我这样的错误。

    Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/ObjectMapper

        at alex.test.App.main(App.java:20)

Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.ObjectMapper

        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)

        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190)

        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)

        ... 1 more

所以，我的问题是，我需要进行哪些更改，以确保所有依赖项最终都在目标文件夹中，并且我不再收到此错误。

Answer 1

尝试将此添加到您的pom.xml：<project>...&nbsp; &nbsp; <build>&nbsp; &nbsp; &nbsp; &nbsp; <plugins>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <plugin>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <artifactId>maven-assembly-plugin</artifactId>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <version>3.0.0</version>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <configuration>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <archive>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <manifest>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <mainClass>com.yourpackage.MainClass</mainClass>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <addDefaultImplementationEntries>true</addDefaultImplementationEntries>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </manifest>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </archive>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <descriptorRefs>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <descriptorRef>jar-with-dependencies</descriptorRef>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </descriptorRefs>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </configuration>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <executions>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <execution>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <id>make-assembly</id> <!-- this is used for inheritance merges -->&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <phase>package</phase> <!-- bind to the packaging phase -->&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <goals>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <goal>single</goal>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </goals>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </execution>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </executions>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; </plugin>&nbsp; &nbsp; &nbsp; &nbsp; </plugins>&nbsp; &nbsp; </build></project>它将在您的目标中生成一个可运行的 jar 文件，其中包含所有依赖项。请务必设置主类的路径。