“Java error occurred” message while executing a jar built from maven

Question

I am trying to build an executable jar. When i execute the code from the project via eclipse, it runs fine, but not when the jar is executed from CMD line. Looks like some issue with class path, but i am not sure ...I have the following dependencies in my pom file:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.12</version>
    <scope>compile</scope>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.12</version>
    <scope>compile</scope>
</dependency>

and the following maven plugins in the tag of the pom file:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <source>1.5</source>
        <target>1.5</target>
    </configuration>
</plugin>
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <configuration>
        <archive>
            <manifest>
                <mainClass>org.swx.nursing.tools.quicklaunch.executor.QuickLaunch</mainClass>
            </manifest>
        </archive>
    </configuration>
</plugin>

Then I use the following to build the jar: mvn clean install

When i execute the jar, i see the following message i am not sure why:

C:\Workspaces\CCQueryHotkey\quicklaunch\target>java -jar quicklaunch-0.0.1-SNAPSHOT.jar
Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
    at org.swx.nursing.tools.quicklaunch.executor.QuickLaunch.<clinit>(QuickLaunch.java:18)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 1 more

I see that the SLF4j jars are in the project folder pulled by maven.

Please advise!

Thanks

Answer 1

You can use the shade plugin to create an executable jar. Look at this link for example

Answer 2

You will have to set classpath to your .m2 repository. Try to execute

java -cp "Path to your .m2 repository." -jar quicklaunch-0.0.1-SNAPSHOT.jar

Answer 3

You are getting java.lang.NoClassDefFoundError because classes are not available during runtime at classpath location.

You can use maven assembly plugin to fix the issue.

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <source>1.5</source>
        <target>1.5</target>
    </configuration>
</plugin>
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>2.2</version>
    <!-- nothing here -->
</plugin>
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>2.2-beta-4</version>
    <configuration>
        <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>

            <finalName>test</finalName>
            <appendAssemblyId>false</appendAssemblyId>
            <archive>
                <manifest>
                    <mainClass>org.swx.nursing.tools.quicklaunch.executor.QuickLaunch</mainClass>
                </manifest>
            </archive>
    </configuration>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>single</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Update your pom.xml with the configuration given above and run mvn clean install . Then, cd into the target directory and try again:

java -jar test.jar

For reference: maven assembly plugin