One page to cover most commonly found errors for fat jar in SpringBoot

Kill time, or kiss time!

Summary

As you know, fat jar is the jar file can be executed via java -jar abc.jar, because all configuration and dependencies included by default.

However, there are few errors found working with fat jar. This is a page to summarize and show how to get the point to fix it directly.

Errors

no main manifest attribute, in xxx.jar

The error looks like below:

no main manifest attribute, in your-dummy-service-1.0-SNAPSHOT.jar

Error: Could not find or load main class

Error: Could not find or load main class com.dummy.hr.WorkflowServiceRunner
Caused by: java.lang.NoClassDefFoundError: org/springframework/boot/CommandLineRunner

troubleshooting

Those errors indicate your fat-jar don’t work propperly. You can try following steps for troubleshooting:

Open generated jar file under folder /targer

Firstly run command to generate the file, e.g. mvn clean install then check your target folder within IDE. As below screenshot:

(1) The fat-jar jar file will be saved to target folder. (2) There should be two files one in your-name.jar and another is your-name.jar.original. (3) The difference is your-name.jar.original is the original file from your code, then sprint-boot hijacked it to injected several logis, such as setup SpringBootApplication annotated main-class , spring-boot guessed dependencies, etc. (4) Open the file MANIFEST.MF, this is the file contains metadata for this fat-jar (5) The Main class should be updated to org.springframework.boot.loader.JarLauncher in step #3. (6) Then the varaible Start-Class: com.xxxservice.xxxServiceApplicationMain is your main class annoted with @SpringBootApplication

Solution

There are several possible reasonse to cause the fat jar failed to generate. While here are some note-worthy points for fix.

(1) To add parent element spring-boot-starter-parent in front of your applicationo defintiona in pom.xml

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.5.3</version>
    <relativePath/> 
</parent>

<groupId>com.dummy</groupId>
<artifactId>abc-workflow-service</artifactId>
<version>1.0-SNAPSHOT</version>

(2) To add build/plugins at bottom of pom.xml, be advised its NOT build/pluginManagement/plugins

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>2.6.6</version>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>11</source>
                <target>11</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-resources-plugin</artifactId>
            <version>2.4</version>
        </plugin>
    </plugins>
</build>

–HTH–