SpringBoot: Unable to find a single main class from the following candidates

Question

I've generated a Spring Boot web application using Spring Initializer, embedded Tomcat, Thymeleaf template engine.Technologies used: Spring Boot 1.4.2.RELEASE, Spring 4.3.4.RELEASE, Thymeleaf 2.1.5.RELEASE, Tomcat Embed 8.5.6, Maven 3, Java 8

I have an SpringBoot app. with these 2 classes:

@Profile("!war")
@SpringBootApplication
@Import({SecurityConfig.class ,PersistenceConfig.class, ServiceConfig.class})
public class BookApplication {

    public static void main(String[] args) {
        SpringApplication.run(BookApplication.class, args);
    }
}

@Profile("war")
@Import({SecurityConfig.class ,PersistenceConfig.class})
@SpringBootApplication
public class BookApplicationWar extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(BookApplicationWar.class);
    }

    public static void main(String[] args) throws Exception {
        SpringApplication.run(BookApplicationWar.class, args);
    }

}

I generate the war with this command

 mvn clean package -DskipTests -Dspring.profiles.active=pebloc,war -DAPP-KEY=pebloc

But I got this error:

[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage (default) on project book: Execution default of goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage failed: Unable to find a single main class from the following candidates [com.tdk.BookApplication, com.tdk.BookApplicationWar] -> [Help 1]

This happens because you may have 2 main methods – Java Main Feb 12 '20 at 14:21 — Java Main, Feb 12 '20 at 14:21

Eugene Maysyuk · Answer 1 · 2022-06-28T10:29:35.747

Define single main class via start-class property

<properties>
      <start-class>com.may.Application</start-class>
</properties>

Alternatively, define the main class in the spring-boot-maven-plugin

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <mainClass>com.may.Application</mainClass>
            </configuration>
        </plugin>
    </plugins>
</build>

Or via profiles

<profiles>
        <profile>
            <id>profile1</id>
            <properties>
                <spring.boot.mainclass>com.may.Application1</spring.boot.mainclass>
            </properties>
        </profile>
        <profile>
            <id>profile2</id>
            <properties>
                <spring.boot.mainclass>com.may.Application2</spring.boot.mainclass>
            </properties>
        </profile>
</profiles>

<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <mainClass>${spring.boot.mainclass}</mainClass>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

Adding the mainClass tag to configuration had no effect, but setting the property did. — user515655, Jun 25 '22 at 14:45
@user515655 here is the official doc for spring-boot-maven-plugin configuration and it still says that mainClass tag should work https://docs.spring.io/spring-boot/docs/3.0.x-SNAPSHOT/maven-plugin/reference/htmlsingle/#packaging. don't know why it didn't work for you. — Eugene Maysyuk, Jun 28 '22 at 10:26

score 54 · Accepted Answer · answered Mar 16 '17 at 17:22

54

If you have more than one main class, you need to explicitly configure the main class in each profile:

<profiles>
    <profile>
        <id>profile1</id>
        <properties>
          <spring.boot.mainclass>com.SomeClass</spring.boot.mainclass>
        </properties>
    </profile>
    <profile>
        <id>profile2</id>
        <properties>
          <spring.boot.mainclass>com.SomeOtherClass</spring.boot.mainclass>
        </properties>
    </profile>
</profiles>

...

<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>
        <configuration>
          <mainClass>${spring.boot.mainclass}</mainClass>
        </configuration>
      </execution>
    </executions>
    ...
</plugin>

See spring-boot:repackage

answered Mar 16 '17 at 17:22

Sean Patrick Floyd

292,901
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and the tag @Profile I use is useless ? – Nuñito Calzada Mar 16 '17 at 18:22
Maven profiles and Spring profiles are two different concepts. – Nuñito Calzada Mar 16 '17 at 20:06
@NuñitodelaCalzada I know, but Maven is causing the trouble, so you will have to solve it there – Sean Patrick Floyd Mar 16 '17 at 20:30
1

@NuñitodelaCalzada the problem is not Spring, but the Jar itself. A Jar manifest can only have one main class defined. Spring Profiles only get activated inside the main class. – Sean Patrick Floyd Mar 16 '17 at 20:36
1

Still same error, this solution does not work – fsalazar_sch Aug 31 '22 at 17:19
I'm trying the described approach and it doesn't work: https://stackoverflow.com/q/76807834/283837 Perhaps someone could tell me if I'm doing something wrong? – Simeon Leyzerzon Aug 01 '23 at 03:26

score 19 · Answer 3 · answered May 21 '20 at 20:52

19

To disambiguate the entry point of a spring boot application, you can add the following directive to your Gradle build file

springBoot {
    mainClassName = 'your.org.bla.TestKt'
}

answered May 21 '20 at 20:52

Holger Brandl

10,634
3
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5

Thanks for the pointer. Seems this has changed to `mainClass` only. See the docs: https://docs.spring.io/spring-boot/docs/current/gradle-plugin/reference/htmlsingle/#packaging-executable.configuring.main-class – Florian Waibel Aug 17 '22 at 09:13

score 14 · Answer 4 · answered Jun 20 '18 at 14:20

14

Sometimes this error is given when you do mvn install without doing mvn clean.

answered Jun 20 '18 at 14:20

yılmaz

1,818
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2

Diddo for Gradle. This may happen when changing the package name when the project was already build once. In that case the clean does wonders. – Claus Oct 15 '19 at 17:33
1

Worked like a charm. Package refactoring was done, but didn't clean it. – Francis Raj Mar 10 '20 at 06:15

score 12 · Answer 5 · answered Jun 25 '18 at 13:16

or simply hard code the main class in plugin configuration.

        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                    <configuration>
                        <mainClass>your.main.class.MainClass</mainClass>
                    </configuration>
                </execution>
            </executions>
        </plugin>

This doesn't work at least for me i think must be at the same level as and . @EugeneMaysyuk answer is the most concise and complete so far — Adel Ben Hamadi, May 20 '23 at 12:56

score 10 · Answer 6 · answered May 22 '19 at 08:37

10

From the command line you can use

... -Dstart-class=com.your.package.application.BookApplication

answered May 22 '19 at 08:37

Matteo Gaggiano

1,254
15
28

That's what I was looking for. Where did you find this ? – YogendraR Aug 20 '22 at 09:02

vaquar khan · Answer 7 · 2017-08-17T15:47:38.623

[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage (default) on project book: Execution default of goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage failed: Unable to find a single main class from the following candidates [com.tdk.BookApplication, com.tdk.BookApplicationWar]

One possible reason to getting following error is more than one main methods in your code, Spring boot allow only one main method across all class in same project.

score 3 · Answer 8 · answered Jan 10 '20 at 17:08

If you have a Spring Boot Application generally there is only one main class that has @SpringBootApplication , If you add another main method in the application some where , the gradle build process gets confused . So add the following at the root level of your build.gradle file

apply plugin: 'application'
mainClassName = 'packageNameAfter.srcMainJavaFolder.YourClassName'

score 2 · Answer 9 · answered Jan 11 '21 at 13:19

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <mainClass>your.main.class.MainClass</mainClass>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>repackage</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Element configuration must be inside the plugin one!

score 1 · Answer 10 · answered Jan 28 '19 at 11:25

1

I had the same error. I had renamed my Application class containing main from foo.java to bar.java, cleaned and updated. So I only ever had one main.

The error went away when I deleted the old generated class, foo.class under the target folder.

answered Jan 28 '19 at 11:25

schoon

2,858
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1

A similar solution worked for me -- I'm using Grails on a Mac, so just `./gradlew clean` did the trick. – Tracy Logan Aug 06 '21 at 21:20

score 0 · Answer 11 · answered Oct 15 '18 at 01:28

Check your application if you have multiple classes with public static void main(String[] args). Remove the one that you do not need. Specially if you generate the project with https://start.spring.io/ it comes with a class with main method in it.

If you do need all of the classes with main method just explicitly mention which one would to be boos-trapped up on application start up by mentioning it in the pom.

score 0 · Answer 12 · answered Jan 05 '20 at 14:28

I was building a spring boot library project, so I don't need a main starter class, so I faced the same issue while building the project with maven, so I removed the maven plugin to compile successfully

<!--
    <build>
      <plugins>
        <plugin>
          <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
      </plugins>
    </build>
-->

For a more detailed example. find it here https://spring.io/guides/gs/multi-module/

score 0 · Answer 13 · answered Feb 15 '22 at 15:50

You don't need to use profiles to avoid the error. You can configure the spring-boot-maven-plugin like this:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>2.6.3</version> <!-- use the corresponding version of your spring boot -->
        <executions>
            <execution>
                <id>repackage-application1</id>
                <phase>package</phase>
                <goals>
                    <goal>repackage</goal>
                </goals>
                <configuration>
                    <mainClass>com.yourpackage1.Application1</mainClass>
                    <finalName>app1</finalName>
                    <outputDirectory>target/apps</outputDirectory>
                </configuration>
            </execution>
            <execution>
                <id>repackage-application2</id>
                <phase>package</phase>
                <goals>
                    <goal>repackage</goal>
                </goals>
                <configuration>
                    <mainClass>com.yourpackage2.Application2</mainClass>
                    <finalName>app2</finalName>
                    <outputDirectory>target/apps</outputDirectory>
                </configuration>
            </execution>
        </executions>
    </plugin>

This will create app1.jar and app2.jar in your target folder.

Important note: if you inherit from spring-boot-starter-parent, it executes by default the spring-boot-maven-plugin with a default configuration that expects only one spring application. If you have two apps in a module, that default configuration will fail with the error "Unable to find a single main class" error. To fix your build you need to deactivate the default plugin execution in your parent pom. One way to do it could be to exclude a plugin in the parent pom you can take a look at maven exclude plugin defined in parent pom (did not try it myself)

score 0 · Answer 14 · answered Feb 01 '23 at 14:02

I defined two @SpringBootApplication on purpose. To avoid conflicts in Gradle I defined additional tasks with alternative mainClass:

tasks.named("bootRun", BootRun.class).configure {
    mainClass = "com.evil.App"
}
tasks.named("bootJar", BootJar.class).configure {
    mainClass = "com.evil.App"
}

tasks.register("bootRunH2", BootRun.class) {
    group = bootRun.group
    description = bootJar.description
    mainClass = "com.evil.H2App"
}
tasks.register("bootJarH2", BootJar.class) {
    group = bootJar.group
    description = bootJar.description
    targetJavaVersion = bootJar.targetJavaVersion
    classpath = bootJar.classpath
    mainClass = "com.evil.H2App"
}

This way you can have as many different bootRun/bootJar tasks as you wish.

SpringBoot: Unable to find a single main class from the following candidates

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