Could not find or load main class using both Java Class and Jar files

Question

I am new to java and facing same old issue while executing the Class/Jar file, i.e. getting error which says "Could not find or load main class com.finance.LoanProcessor", where com.finance.LoanProcessor is my fully qualified class name. I have created many other sample projects, and I can execute both class/jar file in them. Only this project is causing the issue.

Here is what I understand from Java tutorials and StackOverflow solutions for this issue:

1. While executing the class file directly using 'Java' command, I need to use this syntax: java com.finance.LoanProcessor

Note: I should not use '.class' suffix. In command prompt, I should be in the parent folder which has the 'com' folder, so that the java command can navigate inside the com/finance directory and execute the LoanProcessor class.

2. While executing the jar file directly using the 'Java' command, I need to use this syntax: java -jar LoanOnboardingSystem-1.0-SNAPSHOT.jar

Note: I should be in the same directory where this jar file is located. Also, the jar should have the META-INF/MANIFEST.MF file, which should have the Main-Class: com.finance.LoanProcessor attribute defined.

I have kept all above notes in mind and tried executing my main class and jar both, but both are failing. While other sample projects are getting executed in same fashion on my same laptop, only this project is giving error. I have asked a few java experts in my office, but they are not able to figure out issue too.

Hence, I have uploaded the whole project on following git repository now: LoanOnboardingProject

Could the community kindly help to check the project and suggest what I am missing?

Few other things which I have done:

1. I am using IntelliJ IDE. I have built jar with IDE's out of box options, and it gives same error. [This jar is under the 'out' folder in above repository.]

2. I have created above project as Maven project. I used 'mvn package' command to build the jar, but it gives the same error. [This jar is under the 'target' folder in above repository.]

3. When I run the program within IntelliJ itself, it works just fine. No issues with that.

Thanks a lot in advance. Any help is much appreciated.

Answer 1

The problem is, that you main class LoanProcessor implements CommandLineRunner interface. This class is not included in the resulting jar (when built by maven). Therefore it is not on the classpath. And that is the reason, why java can't load the main class (because it references another class that it can't find).

To run the app, you need to add all required classes to the classpath (using -cp parameter of java command). This would be quite complicated in your case, because you would need to add all of your dependencies specified in your pom.xml file. And all jars that these dependencies require. That would probably be a lot of jar files.

You could you maven-shade-plugin to build a jar with all dependencies included.

Here is an example config (add to your pom to the section):

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-shade-plugin</artifactId>
  <version>2.3</version>
  <executions>
    <execution>
      <phase>package</phase>
      <goals>
        <goal>shade</goal>
      </goals>
      <configuration>
        <transformers>
          <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
            <manifestEntries>
              <Main-Class>com.finance.LoanProcessor</Main-Class>
            </manifestEntries>
          </transformer>
          <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
        </transformers>
      </configuration>
    </execution>
  </executions>
</plugin>

Then you will be able to execute the class (when standing in the directory containing the pom.xml):

java -cp target/LoanOnboardingSystem-1.0-SNAPSHOT.jar com.finance.LoanProcessor

or by:

java -jar target/LoanOnboardingSystem-1.0-SNAPSHOT.jar 

Answer 2

In you pom.xml replace build with given below. Using maven-shade-plugins.

<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.3</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <keepDependenciesWithProvidedScope>false</keepDependenciesWithProvidedScope>
                            <promoteTransitiveDependencies>false</promoteTransitiveDependencies>
                            <createDependencyReducedPom>false</createDependencyReducedPom>
                            <minimizeJar>false</minimizeJar>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>



To Execute:

java -cp LoanOnboardingSystem-1.0-SNAPSHOT.jar com.finance.LoanProcessor

Answer 3

The answer provided by Jan above is definitely going to solve many people's problems, and it solved my problem too. However, since I was using the spring boot, I got another error while running the shaded jar: "No auto configuration classes found in META-INF/spring.factories".

Hence, I came across this link on StackOverflow itself, which solved above problem.

The interesting thing is that now when I use the 'spring-boot-maven-plugin' only in the pom.xml, and not the 'maven-shade-plugin', then also the project jar gets executed just fine. Spring-boot-maven-plugin also includes all the required dependencies in jar file and creates a smaller jar than the one created by 'maven-shade-plugin.'

Just in case that link goes down some day, I am posting the same answer here too:

   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>1.5.2.RELEASE</version>
      <executions>
       <execution>
        <goals>
         <goal>repackage</goal>
        </goals>
       </execution>
     </executions>
   </plugin>