Java：Maven项目中的NoClassDefFoundError？

Question

我已经开始使用Maven在Codenvy IDE中使用OpenGL开发3D Java游戏引擎。我配置了运行Java 8，并且我已经设置了所需的pom.xml的依赖关系。但是，当我运行测试窗口时，我得到一个NoClassDefFoundError。我不确定为什么发生这种情况，考虑到Maven被配置为将所有.Jar依赖关系存储到一个文件中，因此访问它们不应该成为问题。所有文件已正确下载到我的Codenvy项目的External Packages目录中。

这里是pom.xml：

<?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>engineTester.First3DEngine</groupId> 
    <artifactId>First3DEngine</artifactId> 
    <version>1.5.7</version> 
    <packaging>jar</packaging> 

    <dependencies> 
    <dependency> 
     <groupId>org.lwjgl.lwjgl</groupId> 
     <artifactId>lwjgl</artifactId> 
     <version>2.8.4</version> 
    </dependency> 

    <dependency> 
     <groupId>org.lwjgl.lwjgl</groupId> 
     <artifactId>lwjgl_util</artifactId> 
     <version>2.8.4</version> 
    </dependency> 

    <dependency> 
     <groupId>org.lwjgl.lwjgl</groupId> 
     <artifactId>lwjgl_util_applet</artifactId> 
     <version>2.8.4</version> 
    </dependency> 

    <dependency> 
     <groupId>com.typesafe.slick</groupId> 
     <artifactId>slick_2.10</artifactId> 
     <version>3.1.1</version> 
    </dependency> 
    <dependency> 
     <groupId>java3d</groupId> 
     <artifactId>vecmath</artifactId> 
    <version>1.3.1</version> 
    </dependency> 
    <dependency> 
     <groupId>junit</groupId> 
     <artifactId>junit</artifactId> 
     <version>4.12</version> 
    </dependency> 
    </dependencies> 
    <build> 
    <plugins> 
     <plugin> 
     <!-- Build an executable JAR --> 
     <groupId>org.apache.maven.plugins</groupId> 
     <artifactId>maven-jar-plugin</artifactId> 
     <version>2.6</version> 
     <configuration> 
      <argLine>-Xmx1024m</argLine> 
      <archive> 
      <manifest> 
      <addDefaultImplementationEntries>true</addDefaultImplementationEntries> 
     <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries> 
       <addClasspath>true</addClasspath> 
       <classpathPrefix>lib/</classpathPrefix> 
       <mainClass>engineTester.MainGameLoop</mainClass> 
      </manifest> 
      </archive> 
     </configuration> 
     </plugin> 
    </plugins> 
    </build> 
</project> 

这里是哪里，我发现了问题：

package engineTester; 

import org.lwjgl.opengl.Display; 

import renderEngine.DisplayManager; 
import util.Console; 

public class MainGameLoop { 
    public static void main(String[] args){ 
     new Console(); 
     DisplayManager.createDisplay(); <-- line which throws the error 
     while(!Display.isCloseRequested()){ 
      //game logic 
      //render 
      DisplayManager.updateDisplay(); 
     } 

     DisplayManager.closeDisplay(); 

    } 
} 

DisplayManager.createDisplay()方法：

public static void createDisplay(){ 
    ContextAttribs attribs = new ContextAttribs(3,2); 
    attribs.withForwardCompatible(true); 
    attribs.withProfileCore(true); 

    try{ 
     Display.setDisplayMode(new DisplayMode(WIDTH,HEIGHT)); 
     Display.create(new PixelFormat(), attribs); 
    } catch (LWJGLException e){ 
     e.printStackTrace(); 
    } 

    GL11.glViewport(0,0,WIDTH,HEIGHT); 
} 

最后完整的错误：

Exception in thread "main" java.lang.NoClassDefFoundError:  org/lwjgl/LWJGLException 
    at engineTester.MainGameLoop.main(MainGameLoop.java:11) 
Caused by: java.lang.ClassNotFoundException: org.lwjgl.LWJGLException 
    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 

感谢您的帮助！

Answer 1

你可以使用maven-assembly-plugin来制作一个可以自行运行的fat jar，或者你可以使用maven运行你的程序，这样编译时jar就会被添加到你的classpath中。

要使用maven运行：

mvn exec:java -Dexec.mainClass="engineTester.MainGameLoop" 

要使用Assembly插件：

<build> 
    <plugins> 
     <plugin> 
      <artifactId>maven-assembly-plugin</artifactId> 
      <version>2.5.5</version> 
      <configuration> 
       <archive> 
        <manifest> 
         <mainClass>engineTester.MainGameLoop</mainClass> 
        </manifest> 
       </archive> 
       <descriptorRefs> 
        <descriptorRef>jar-with-dependencies</descriptorRef> 
       </descriptorRefs> 
      </configuration> 
      <executions> 
       <execution> 
        <id>make-assembly</id> <!-- this is used for inheritance merges --> 
        <phase>package</phase> <!-- bind to the packaging phase --> 
        <goals> 
         <goal>single</goal> 
        </goals> 
       </execution> 
      </executions> 
     </plugin> 
    </plugins> 
</build> 

这将创建一个罐子-jar-with-depencencies添加到名称在目标目录中。那可以使用java -jar jarfile运行。