dropwizard exception: java.lang.NoClassDefFoundError

Question

I have a sample dropwizard application. I am getting following exception:

>java -jar target/order-service-1.0.0-SNAPSHOT.jar

Exception in thread "main" java.lang.NoClassDefFoundError: org/hibernate/engine/jdbc/connections/spi/ConnectionProvider
    at io.dropwizard.hibernate.HibernateBundle.<init>(HibernateBundle.java:20)
    at com.blurb.order.OrderApplication$1.<init>(OrderApplication.java:61)
    at com.blurb.order.OrderApplication.<init>(OrderApplication.java:52)
    at com.blurb.order.OrderApplication.main(OrderApplication.java:133)
Caused by: java.lang.ClassNotFoundException: org.hibernate.engine.jdbc.connections.spi.ConnectionProvider
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 4 more

How do I resolve this exception?

EDIT

Following is config for maven shade plugin:

<plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>1.6</version>
                <configuration>
                    <createDependencyReducedPom>true</createDependencyReducedPom>
                    <filters>
                        <filter>
                            <artifact>*:*</artifact>
                            <excludes>
                                <exclude>META-INF/*.SF</exclude>
                                <exclude>META-INF/*.DSA</exclude>
                                <exclude>META-INF/*.RSA</exclude>
                            </excludes>
                        </filter>
                    </filters>
                </configuration>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.*.order.OrderApplication</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>

Answer 1

The way to resolve this kind of issue is as follows:

1. Find out where the missing class (in this case: org/hibernate/engine/jdbc/connections/spi/ConnectionProvider) should be. Often you can tell from the package name. This one seems to come from hibernate, all the specialized, find the jar for this class services failed me, but a google search turned up this: https://docs.jboss.org/hibernate/orm/4.3/javadocs/org/hibernate/engine/jdbc/connections/spi/class-use/ConnectionProvider.html, so you should check hibernate-*.jar for this class.

2. If you hadn't that jar downloaded/specified for inclusion in your app you obviously have to add it now and you are done.

3. Often you think you have it in the classpath, but for some reason you don't. In that case start by getting you're classpath. Depending on your environment this can be tricky. In a simple desktop application you can use the System property java.class.path for that. In application servers and similar environments this is a little more complicated. You might have to debug the classloader, to find where they are actually looking. Often you can take a short cut on this step by using the classpath you assume you are using, but if the class in question is in the assumed classpath and still doesn't show up, this step will help.

4. Make sure that your jar really gets added to the classpath. Also be aware of tiny differences. Some libs have changed their package name, so a wrong version of a jar might have a class very similar to the one you want to load, but just in the wrong package.