Maven没有正确设置依赖关系的类路径 [英] Maven not setting classpath for dependencies properly

问题描述

操作系统名称：linux版本：2.6.32-27-genericarch：i386系列：unix

OS name: "linux" version: "2.6.32-27-generic" arch: "i386" Family: "unix"

Apache Maven 2.2.1 （r801777; 2009-08-06 12：16：01-0700）

Apache Maven 2.2.1 (r801777; 2009-08-06 12:16:01-0700)

Java版本：1.6.0_20

Java version: 1.6.0_20

我试图在ubuntu中使用maven中的mysql依赖关系。如果我将maven下载到我的$ JAVA_HOME / jre / lib / ext /文件夹中的mysql-connector-java-5.1.14.jar文件，我运行jar时一切都很好。

I am trying to use the mysql dependency in with maven in ubuntu. If I move the "mysql-connector-java-5.1.14.jar" file that maven downloaded into my $JAVA_HOME/jre/lib/ext/ folder, everything is fine when I run the jar.

我想我应该能够在pom.xml文件中指定依赖关系，并且maven应该自动设置依赖关系jar的类路径。这是不正确的吗？

I think I should be able to just specify the dependency in the pom.xml file and maven should take care of setting the classpath for the dependency jars automatically. Is this incorrect?

我的pom.xml文件如下所示：

My pom.xml file looks 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>com.ion.common</groupId>
  <artifactId>TestPreparation</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>TestPrep</name>
  <url>http://maven.apache.org</url>

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

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>

        <configuration>
          <archive>
            <manifest>
              <addClasspath>true</addClasspath>
              <mainClass>com.ion.common.App</mainClass>
            </manifest>
          </archive>
        </configuration>

      </plugin>
    </plugins>
  </build>

  <dependencies>

    <!-- JUnit testing dependency -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>

    <!-- MySQL database driver -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.14</version>
      <scope>compile</scope>
    </dependency>

  </dependencies>
</project>

命令mvn package构建它没有任何问题，我可以运行它，但是当应用程序尝试访问数据库时，会显示此错误：

The command "mvn package" builds it without any problems, and I can run it, but when the application attempts to access the database, this error is presented:

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
        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)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:186)
        at com.ion.common.Functions.databases(Functions.java:107)
        at com.ion.common.App.main(App.java:31)

它的行失败的是：

Class.forName("com.mysql.jdbc.Driver");

任何人都可以告诉我我在做错什么或如何解决？

Can anyone tell me what I'm doing wrong or how to fix it?

推荐答案

Raghuram给了我一个正确的方向。让maven自动处理复制jar的方法是在pom.xml文件的标签内添加这个代码：

Raghuram gave me a push in the right direction. The way to get maven to take care of copying the jars automatically is to add this code inside the tag in the pom.xml file:

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <executions>
      <execution>
        <id>copy-dependencies</id>
        <phase>package</phase>
        <goals>
          <goal>copy-dependencies</goal>
        </goals>
        <configuration>
          <outputDirectory>${project.build.directory}</outputDirectory>
          <overWriteReleases>false</overWriteReleases>
          <overWriteSnapshots>true</overWriteSnapshots>
        </configuration>
      </execution>
    </executions>
  </plugin>

可以在这里找到更多细节：
http://maven.apache.org/plugins/maven-dependency-plugin/howto.html

More details on this can be found here: http://maven.apache.org/plugins/maven-dependency-plugin/howto.html

将maven打包在一起将会很好，但这是足够好的回答这个问题。关于stackoverflow的相关答案：

Getting maven to package the jars together would be nice, but this is good enough to answer this question. Related answers on stackoverflow:

使用maven构建可执行jar的问题

如何使用Maven创建具有依赖关系的可执行JAR？

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