Running spring boot with multiple main classes

Spring Boot gives several ways:

• specify main class as system property:

java -cp app.jar -Dloader.main=com.company.MyAppMain1 org.springframework.boot.loader.PropertiesLauncher 

• configure main class in Maven pom.xml <properties> section:

<properties> <start-class>com.company.MyAppMain1</start-class> </properties> 

Note that this property will only be evaluated if you use spring-boot-starter-parent as <parent> in your pom.xml.

• configure main class for spring-boot-maven-plugin:

<build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>${start-class}</mainClass> </configuration> </plugin> </plugins> </build> 

Note: plugin configuration can be performed in Maven profile, so by activating different profiles, you'll run app with different main class.

Following are the different way to run Spring Boot main class:

1. Single main class in the Spring Boot Application

A. via <properties> section

<properties> <start-class>com.company.MyAppMain1</start-class> </properties> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> 

Note:

1. When we use start-class property in properties section of pom.xml, we don't need to pass explicit value to plugin spring-boot-maven-plugin

B. via Custom property <custom-mainClass>

<properties> <custom-mainClass>com.company.MyAppMain1</custom-mainClass> </properties> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>${custom-mainClass}</mainClass> </configuration> </plugin> </plugins> </build> 

Note:

1. Custom property custom-mainClass can be hard coded inside the property file as mentioned above 1.B

2. Pass by maven property using build as mentioned below:

   mvn -U clean install -Dcustom-mainClass=com.company.MyAppMain1

C. via Hard coded value in plugin spring-boot-maven-plugin section

<build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>com.company.MyAppMain1</mainClass> </configuration> </plugin> </plugins> </build> 

2. Multiple main class in the Spring Boot Application

A. via org.springframework.boot.loader.PropertiesLauncher

Step 1:

<build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass> org.springframework.boot.loader.PropertiesLauncher </mainClass> </configuration> </plugin> </plugins> </build> 

Step 2: Use below command to start application

java -Dloader.main=com.company.MyAppMain1 -jar myapp.jar 

OR

java -cp myapp.jar -Dloader.main=com.company.MyAppMain1 org.springframework.boot.loader.PropertiesLauncher 

Note:

1. Use -Dloader.main as Java VM arguments to pass dynamic main-class during start of application as shown in step 2
2. org.springframework.boot.loader.PropertiesLauncher has moved to org.springframework.boot.loader.launch.PropertiesLauncher

B. via Custom property <custom-mainClass>

<properties> <custom-mainClass>com.company.MyAppMain1</custom-mainClass> </properties> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>${custom-mainClass}</mainClass> </configuration> </plugin> </plugins> </build> 

Note:

1. Pass by maven property using build as mentioned below:

   mvn -U clean install -Dcustom-mainClass=com.company.MyAppMain1

This also a dynamic main-class but its good only during maven build. Not applicable during application startup as shown in step 2 of section 2.A

With Spring boot 3.2.x (Release Notes)

<properties> <start-class>org.springframework.boot.loader.launch.PropertiesLauncher</start-class> </properties> ... <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>${start-class}</mainClass> </configuration> </plugin> 

To run the jar with dynamic main class names

java -jar -Dloader.main=com.myapp.Main1 -jar myapp.jar java -jar -Dloader.main=com.myapp.Main2 -jar myapp.jar