java.lang.ClassNotFoundException / NoClassDefFoundError for com/fasterxml/jackson/databind/ObjectMapper with Maven
classpath, fasterxml, java, maven
Solution
The default maven plugin doesn't build a fat jar with dependencies.
To build a jar bundled with its dependencies so that we can execute it with `java -jar`, we can use maven-assembly-plugin, which packages the jar with the name `xxx-jar-with-dependencies.jar`.
Here is a sample `pom.xml`
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>com.example.yourMain</mainClass>
</manifest>
</archive>
</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>
Now you should be able to run your jar with
java -jar xxx-jar-with-dependencies.jar
Problem
I get the following error when trying to run a java program that uses jackon's ObjectMapper class: ``` Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/ObjectMapper at com.inin.dynamotransfer.DynamoTransfer.importData(DynamoTransfer.java:133) at com.inin.dynamotransfer.DynamoTransfer.main(DynamoTransfer.java:67) Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.ObjectMapper at java.net.URLClassLoader$1.run(URLClassLoader.java:366) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ... 2 more ``` I have the Jackson annotations, databind (which contains ObjectMapper), and core JARs in my Maven repository under ~/.m2/repository/com/fasterxml/jackson/core/jackson-[packagename]/2.4.0. here's the dependencies section of my pom.xml: ``` <dependencies> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-annotations</artifactId> <version>2.4.0</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.4.0</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>2.4.0</version> </dependency> </dependencies> ``` here's my CLASSPATH: ``` :/Users/myusername/Library/Java/Extensions:/Library/Java/Extensions:/Users/myusername/.m2/repository ``` so Maven knows all about these JARs - where to get em, where to put em, etc. - but java itself can't seem to find the classes I need. what am I doing wrong?? thanks!