Maven 依赖项上的 NoClassDefFoundError [英] NoClassDefFoundError on Maven dependency
问题描述
我第一次使用 Maven 时遇到了依赖关系.
My first use of Maven and I'm stuck with dependencies.
我使用 Eclipse 创建了一个 Maven 项目并添加了依赖项，它运行没有问题.
I created a Maven project with Eclipse and added dependencies, and it was working without problems.
但是当我尝试通过命令行运行它时:
But when I try to run it via command line:
$ mvn package # successfully completes
$ java -cp target/bil138_4-0.0.1-SNAPSHOT.jar tr.edu.hacettepe.cs.b21127113.bil138_4.App # NoClassDefFoundError for dependencies
它下载依赖项，成功构建，但是当我尝试运行它时，出现 NoClassDefFoundError:
It downloads dependencies, successfully builds, but when I try to run it, I get NoClassDefFoundError:
Exception in thread "main" java.lang.NoClassDefFoundError: org/codehaus/jackson/JsonParseException
at tr.edu.hacettepe.cs.b21127113.bil138_4.db.DatabaseManager.<init>(DatabaseManager.java:16)
at tr.edu.hacettepe.cs.b21127113.bil138_4.db.DatabaseManager.<init>(DatabaseManager.java:22)
at tr.edu.hacettepe.cs.b21127113.bil138_4.App.main(App.java:10)
Caused by: java.lang.ClassNotFoundException: org.codehaus.jackson.JsonParseException
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
... 3 more
我的 pom.xml 是这样的:
My pom.xml is like this:
<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>tr.edu.hacettepe.cs.b21127113</groupId>
<artifactId>bil138_4</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>bil138_4</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.codehaus.jackson</groupId>
<artifactId>jackson-core-asl</artifactId>
</dependency>
<dependency>
<groupId>org.codehaus.jackson</groupId>
<artifactId>jackson-mapper-asl</artifactId>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.codehaus.jackson</groupId>
<artifactId>jackson-core-asl</artifactId>
<version>1.9.6</version>
</dependency>
<dependency>
<groupId>org.codehaus.jackson</groupId>
<artifactId>jackson-mapper-asl</artifactId>
<version>1.9.6</version>
</dependency>
</dependencies>
</dependencyManagement>
</project>
有人可以帮我吗?
推荐答案
当我尝试运行它时，出现 NoClassDefFoundError
when I try to run it, I get NoClassDefFoundError
如何运行?您可能试图在没有正确导入 Maven 类路径的情况下使用 Eclipse 运行它.请参阅 m2eclipse 插件以将 maven 与 eclipse 集成.
Run it how? You're probably trying to run it with eclipse without having correctly imported your maven classpath. See the m2eclipse plugin for integrating maven with eclipse for that.
要验证您的 maven 配置是否正确，您可以使用 exec 插件 运行您的应用程序，使用:
To verify that your maven config is correct, you could run your app with the exec plugin using:
mvn exec:java -D exec.mainClass=<your main class>
更新: 首先，关于你在运行 exec:java 时的错误，你的主类是 tr.edu.hacettepe.cs.b21127113.bil138_4.App.在谈论类名时，它们(几乎)总是以点分隔.简单的类名只是最后一部分:App 在你的情况下.完全限定名称是完整的包加上简单的类名，这就是当您想要运行某些东西时提供给 maven 或 java 的名称.您尝试使用的是源文件的文件系统路径.那是完全不同的野兽.与文件系统中的源文件相比，类名通常直接转换为在类路径中找到的类文件.在您的特定情况下，有问题的类文件可能位于 target/classes/tr/edu/hacettepe/cs/b21127113/bil138_4/App.class 因为 maven 编译为 target/classes，而java传统上为每个级别的打包创建一个目录.
Update: First, regarding your error when running exec:java, your main class is tr.edu.hacettepe.cs.b21127113.bil138_4.App. When talking about class names, they're (almost) always dot-separated. The simple class name is just the last part: App in your case. The fully-qualified name is the full package plus the simple class name, and that's what you give to maven or java when you want to run something. What you were trying to use was a file system path to a source file. That's an entirely different beast. A class name generally translates directly to a class file that's found in the class path, as compared to a source file in the file system. In your specific case, the class file in question would probably be at target/classes/tr/edu/hacettepe/cs/b21127113/bil138_4/App.class because maven compiles to target/classes, and java traditionally creates a directory for each level of packaging.
您最初的问题只是您没有将 Jackson jars 放在类路径上.当您从命令行运行 java 程序时，您必须设置类路径以使其知道可以从何处加载类.您添加了自己的 jar，但没有添加其他必需的 jar.您的评论让我觉得您不了解如何手动构建类路径.简而言之，类路径可以有两个东西:包含类文件的目录和包含类文件的 jar.包含 jar 的目录将不起作用.有关构建类路径的更多详细信息，请参阅设置类路径" 和 java 和 javac 工具文档.
Your original problem is simply that you haven't put the Jackson jars on your class path. When you run a java program from the command line, you have to set the class path to let it know where it can load classes from. You've added your own jar, but not the other required ones. Your comment makes me think you don't understand how to manually build a class path. In short, the class path can have two things: directories containing class files and jars containing class files. Directories containing jars won't work. For more details on building a class path, see "Setting the class path" and the java and javac tool documentation.
您的类路径至少需要是，并且没有换行符:
Your class path would need to be at least, and without the line feeds:
target/bil138_4-0.0.1-SNAPSHOT.jar:
/home/utdemir/.m2/repository/org/codehaus/jackson/jackson-core-asl/1.9.6/jackson-core-asl-1.9.6.jar:
/home/utdemir/.m2/repository/org/codehaus/jackson/jackson-mapper-asl/1.9.6/jackson-mapper-asl-1.9.6.jar
请注意，Windows 上的分隔符是分号 (;).
Note that the separator on Windows is a semicolon (;).
我很抱歉没有早点注意到它.问题出在你原来的帖子里，但我错过了.
I apologize for not noticing it sooner. The problem was sitting there in your original post, but I missed it.
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