具有Maven依赖项的Java项目可以编译，但在运行时会失败 [英] Java project with Maven dependency compiles but fails at runtime

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问题描述

绝对不应关闭此问题.我不是在问如何创建可执行jar.jar不需要是可执行文件即可从终端运行.例如，如果我有以下代码:包com.dogzilla.maven.quickstart;

This question should absolutely not be closed. I'm NOT asking how to create an executable jar. A jar doesn't need to be executable to be run from the terminal. For example, if I have have this code: package com.dogzilla.maven.quickstart;

public class App 
{
    public static void main( String[] args )
    {
        System.out.println( "Hello World" );
    }
}

...然后Maven构建它，它创建quickstart-0.0.1-SNAPSHOT.jar.哎呀，那不是可执行文件".

...and Maven builds it, it creates quickstart-0.0.1-SNAPSHOT.jar. Which is not, ahem, 'executable'.

我可以在终端上非常成功地运行它:

I can run it from the terminal quite successfully with this:

java -cp /opt/workspace/eclipse/java/quickstart/target/quickstart-0.0.1-SNAPSHOT.jar com.dogzilla.maven.quickstart.App

使用外部依赖项时，我会在下面写到这个问题.</结束编辑>

The problem, as I have written below, is experienced when using an external dependency. </end edit>

我在Eclipse(2020-6)中有一个简单的Maven项目.它是通过在Eclipse中执行以下操作来设置的:

I have a simple Maven project in Eclipse (2020-6). It was set up by doing the following in Eclipse:

1.  File -> New -> Other... Maven -> Maven Project
2.  Used the maven-archetype-quickstart archetype

    Group ID:  com.dogzilla.maven
    Artifact ID:  quickstart

右键单击pom文件->选择添加依赖关系->输入:

Right click the pom file -> select Add Dependency -> enter:

Group ID: com.google.code.gson
Artifact ID: gson
Version: 2.8.6

我在 https://search.maven.org/

这是POM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>com.dogzilla.maven</groupId>
  <artifactId>quickstart</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <name>quickstart</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <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>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.8.6</version>
    </dependency>
  </dependencies>

  <build>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-jar-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
        <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
        <plugin>
          <artifactId>maven-site-plugin</artifactId>
          <version>3.7.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-project-info-reports-plugin</artifactId>
          <version>3.0.0</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

这是源代码:

package com.dogzilla.maven.quickstart;

import com.google.gson.Gson;

public class App 
{
    public static void main( String[] args )
    {
        Gson gson = new Gson();
        System.out.println(gson.toJson("Hello World!") );
    }
}

然后我右键单击POM文件->运行方式->Maven构建...

I then right-clicked on the POM file -> Run As -> Maven Build...

这是输出:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/opt/eclipse/java/plugins/org.eclipse.m2e.maven.runtime.slf4j.simple_1.16.0.20200610-1735/jars/slf4j-simple-1.7.5.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [file:/opt/eclipse/java/configuration/org.eclipse.osgi/5/0/.cp/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.SimpleLoggerFactory]
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/opt/eclipse/java/plugins/org.eclipse.m2e.maven.runtime.slf4j.simple_1.16.0.20200610-1735/jars/slf4j-simple-1.7.5.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [file:/opt/eclipse/java/configuration/org.eclipse.osgi/5/0/.cp/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.SimpleLoggerFactory]
[INFO] Scanning for projects...
[INFO] 
[INFO] -------------------< com.dogzilla.maven:quickstart >--------------------
[INFO] Building quickstart 0.0.1-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:3.1.0:clean (default-clean) @ quickstart ---
[INFO] Deleting /opt/workspace/eclipse/java/quickstart/target
[INFO] 
[INFO] --- maven-resources-plugin:3.0.2:resources (default-resources) @ quickstart ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /opt/workspace/eclipse/java/quickstart/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ quickstart ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /opt/workspace/eclipse/java/quickstart/target/classes
[INFO] 
[INFO] --- maven-resources-plugin:3.0.2:testResources (default-testResources) @ quickstart ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /opt/workspace/eclipse/java/quickstart/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ quickstart ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /opt/workspace/eclipse/java/quickstart/target/test-classes
[INFO] 
[INFO] --- maven-surefire-plugin:2.22.1:test (default-test) @ quickstart ---
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.dogzilla.maven.quickstart.AppTest
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.022 s - in com.dogzilla.maven.quickstart.AppTest
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] 
[INFO] --- maven-jar-plugin:3.0.2:jar (default-jar) @ quickstart ---
[INFO] Building jar: /opt/workspace/eclipse/java/quickstart/target/quickstart-0.0.1-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.967 s
[INFO] Finished at: 2020-12-13T20:00:27-07:00
[INFO] ------------------------------------------------------------------------

但是如果我跑步:

java -cp /opt/workspace/eclipse/java/quickstart/target/quickstart-0.0.1-SNAPSHOT.jar com.dogzilla.maven.quickstart.App

它失败并显示:

Exception in thread "main" java.lang.NoClassDefFoundError: com/google/gson/Gson
        at com.dogzilla.maven.quickstart.App.main(App.java:13)
Caused by: java.lang.ClassNotFoundException: com.google.gson.Gson
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        ... 1 more

问题是，如果我更改System.out.println(gson.toJson("H​​ello World！")))；到普通的'ol System.out.println("H​​ello World")；有用.因此，我知道问题不在于我的java命令，也不在于我如何在解决依赖项之外设置项目.

The thing is if I change System.out.println(gson.toJson("Hello World!") ); to plain 'ol System.out.println("Hello World"); it works. So I know the porblem isn't with my java command or how I set the project up outside of the dependency getting resolved.

所以问题是，我不确定这是如何导致依赖关系失败的.我的印象是Maven为您完成了所有这些工作.为什么无法运行?

So the question is, I'm not sure how this is failing on the dependency. I was under the impression Maven managed all that for you. Why is this failing to run?

推荐答案

从您的项目创建的jar文件仅包含您编写的类.如果需要运行应用程序，则需要在类路径中包括所有必需的依赖项(直接或传递).

The jar file that created from your project only contains classes that written by you. If you need to run the application, you need to include all the necessary dependencies (either direct or transitive) in your classpath.

如果您需要一个无需其他依赖项即可执行的jar文件，请遵循创建胖子.

If you need a single jar file that you can execute without other dependencies, Please follow this to create a fatjar.

这篇关于具有Maven依赖项的Java项目可以编译，但在运行时会失败的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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