NoClassDefFoundError occurs even if dependency was added to pom.xml

Question

So I would like to build my maven project with

mvn clean package

But once I try to run my built jar file in target folder like

java -jar app-1.0-SNAPSHOT.jar

It shows error:

Error: A JNI error has occurred, please check your installation and try again Exception in thread "main" java.lang.NoClassDefFoundError: net/sourceforge/jdatepicker/DateModel at java.lang.Class.getDeclaredMethods0(Native Method) at java.lang.Class.privateGetDeclaredMethods(Class.java:2701) at java.lang.Class.privateGetMethodRecursive(Class.java:3048) at java.lang.Class.getMethod0(Class.java:3018) at java.lang.Class.getMethod(Class.java:1784) at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544) at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526) Caused by: java.lang.ClassNotFoundException: net.sourceforge.jdatepicker.DateModel 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) ... 7 more

Pom DataPicker dependency:

<!-- https://mvnrepository.com/artifact/net.sourceforge.jdatepicker/jdatepicker -->
        <dependency>
            <groupId>net.sourceforge.jdatepicker</groupId>
            <artifactId>jdatepicker</artifactId>
            <version>1.3.2</version>
        </dependency>

Why even though dependency was added, exception occurs?

Answer 1

You need to ensure all your dependencies are available to java runtime by adding them to your classpath. Adding a dependency in pom will help only in compiling and packaging the project.

Answer 2

try delete and redownload the jar in your local maven repo.

If your are using idea, try update local repo in the maven setting.

Answer 3

try adding maven plugin so that it copies all your dependencies with the jar file and it does not have to look any further. Do this by adding:

<plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-dependency-plugin</artifactId>
        <version>2.4</version>
        <executions>
            <execution>
                <id>copy-dependencies</id>
                <phase>package</phase>
                <goals><goal>copy-dependencies</goal></goals>
            </execution>
        </executions>
    </plugin>