"java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/ObjectMapper" when using gradle

Question

I am writing a simple test program to convert json into java objects using jackson 2.

My code is,

package test;

import com.fasterxml.jackson.databind.ObjectMapper;
import java.net.URL;

public class UseJson{

    public static void main(String[] args){

        ObjectMapper mapper = new ObjectMapper();
        try{
            SomeClass obj = mapper.readValue(new URL("http://someurl"), SomeClass.class);
        }
        catch(Exception ex){
            System.out.println(ex.toString());
        }
    }
}

And the build.gradle file is

repositories {
    mavenCentral()
}

apply plugin: 'java'

dependencies{
    compile('com.fasterxml.jackson.core:jackson-databind:2.8.6')
    compile('com.fasterxml.jackson.core:jackson-core:2.8.6')
    compile('com.fasterxml.jackson.core:jackson-annotations:2.8.6')
}

jar {
        manifest {
                attributes 'Main-Class': 'test.UseJson'
        }
}

But I am getting an exception when trying to execute the program

java -jar ./build/libs/JsonTest.jar
Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/ObjectMapper
        at test.UseJson.main(UseJson.java:10)
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.ObjectMapper
        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

The related posts java.lang.ClassNotFoundException / NoClassDefFoundError for com/fasterxml/jackson/databind/ObjectMapper with Maven and Correct set of dependencies for using Jackson mapper don't solve the problem.

---

Edit: When I tried to compile the program manually using javac and the jar files of the dependencies, it worked. The issue must be with the gradle build file.

Answer 1

You will need to pack your libraries with your app.

jar {
archiveName = 'Name.jar'

manifest {
    attributes 'Main-Class': 'Main',
            'Class-Path': configurations.runtime.files.collect { "lib/$it.name" }.join(' '),
            'Implementation-Version': project.version (if any)
}

from(configurations.compile.collect { it.isDirectory() ? it : zipTree(it) })
}

Other solution would be using Shadow jar plugin.

The most recommended solution is to use application plugin. Why ? it's supported, it's Gradle, it's used by most developers.