Maven java project builds, but doesn't run

问题

I am creating a maven project from scratch, first just learn how to use maven. The main project contains no source code file, but it has two modules (app, and util). App depends on util. I would like to have a .jar from app, and have no manifest file if possible. I am able to compile the whole project with mvn clean install, but can not run the app from console.

The main project .pom is

<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.proba</groupId>
  <artifactId>myproject</artifactId>
  <version>0.0.1</version>
<packaging>pom</packaging>


<modules>
  <module>util</module>
  <module>app</module>
</modules>
</project>

Util .pom is

<?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd" 
xmlns="http://maven.apache.org/POM/4.0.0" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.proba</groupId>
    <artifactId>myproject</artifactId>
    <version>0.0.1</version>
  </parent>
  <artifactId>util</artifactId>


 <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
     </dependency>
 </dependencies>

</project>

app pom is

<?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.proba</groupId>
        <artifactId>myproject</artifactId>
        <version>0.0.1</version>
    </parent>
    <artifactId>app</artifactId>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.proba</groupId>
            <artifactId>util</artifactId>
            <version>0.0.1</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <archive>
                        <manifest>
                            <mainClass>com.proba.app.App</mainClass>
                            <addClasspath>true</addClasspath>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.1.1</version>
                <executions>
                    <execution>
                        <phase>site-deploy</phase>
                        <goals>
                            <goal>java</goal>
                        </goals>
                        <configuration>
                            <mainClass>com.proba.app.App</mainClass>
                            <!--<arguments> <argument>myArg1</argument> <argument>myArg2</argument> 
                                </arguments> -->
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

The code doesn't do too much. App.java (that inside the app module) is package com.proba.app;

import com.proba.util.UtilClass;
public class App 
{
    public static void main( String[] args )
    {
        System.out.println( "Hello World!" );
        UtilClass uc = new UtilClass(); 
        System.out.println( "QQQQQ: " + uc.print() );
    }
}

I compile it with

mvn clean install
[INFO] Reactor Summary:
[INFO]
[INFO] myproject .......................................... SUCCESS [  0.406 s]
[INFO] util ............................................... SUCCESS [  2.074 s]
[INFO] app ................................................ SUCCESS [  0.535 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

myproject, util, app is SUCCESS.

I try to run it with

java -jar app/target/app-0.0.1.jar
Hello World!
Exception in thread "main" java.lang.NoClassDefFoundError: com/proba/util/UtilClass
        at com.proba.app.App.main(App.java:17)
Caused by: java.lang.ClassNotFoundException: com.proba.util.UtilClass
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 1 more

As you can see, Hello World! is printed out, but UtilClass is not found. I am able to run the build from eclipse, but not from the console. What I am doing wrong? Do you have any idea?

回答1:

What you missing is the jar of UtilClass. You just need to add shade plugin in your pom. As reference: maven-shade-plugin

回答2:

In the pom.xml of app module,You have writtent the compile thats why at runtime your jar is not getting into the classpath.Remove the compile line.And it will work.

回答3:

Util.jar is added to your app pom.xml as dependency but the scope is compile. So it is not getting added to your Manifest as classpath entry. Remove scope element and then try.

来源：https://stackoverflow.com/questions/39286428/maven-java-project-builds-but-doesnt-run