Got it! The issue here is that your current shaded JAR doesn’t have the Main-Class entry in its manifest, which is why you have to use java -cp instead of the simpler java -jar command. Let’s fix that by updating your maven-shade-plugin configuration to include this critical manifest attribute.

Here’s how to modify your pom.xml’s build section:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-shade-plugin</artifactId>
      <version>3.5.1</version> <!-- Use the latest stable version available -->
      <executions>
        <execution>
          <phase>package</phase>
          <goals>
            <goal>shade</goal>
          </goals>
          <configuration>
            <!-- This transformer adds the Main-Class to the JAR's manifest -->
            <transformers>
              <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                <mainClass>Weather</mainClass> <!-- Replace with full package path if needed, e.g., com.yourpackage.Weather -->
              </transformer>
            </transformers>
            <!-- Optional: Add additional transformers here if you need to handle duplicate resources or services -->
          </configuration>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

Key Notes: #

• The ManifestResourceTransformer injects the Main-Class entry into the JAR’s META-INF/MANIFEST.MF file—this is what lets Java know which class to run when using java -jar.
• Double-check that the <mainClass> value matches your actual main class (include the full package name if your class isn’t in the root package).
• Specifying a plugin version ensures you’re using a stable, up-to-date release instead of relying on Maven’s default (which might be outdated).

After Updating: #

1. Re-run your build command: mvn clean package
2. Now you can execute the JAR directly on any machine with Java installed using:

   java -jar target/uber-weather-lookup-1.0-SNAPSHOT.jar
   

Quick Verification: #

To confirm the manifest is set correctly, unzip the JAR and check the META-INF/MANIFEST.MF file—you should see a line like:

Main-Class: Weather

That’s all you need to make your shaded JAR fully standalone!

内容的提问来源于stack exchange，提问作者Fat Owl