spring-boot-starter-parent in independent module causes its beans not be seen in dependent modules

Question

I've an aggregator POM which references 2 modules 'appA' and 'appB'. 'appB' depends on 'appA' as a dependency 'appB' has 'spring-boot-starter-parent' as the parent POM 'appA' has a bean ('hwBean') defined in package "com.multipom.config"

when 'appB' application runs, it sees 'hwBean' only if 'appA' does NOT use 'spring-boot-starter-parent' as parent POM. When 'appA' uses 'spring-boot-starter-parent' as parent POM, 'hwBean' bean defined in 'appA' is not available in 'appB'. Is this a spring-boot bug?

in AppA module

---- com.multipom.App_A.java ------

package com.multipom;

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

---- com.multipom.config.ApplicationConfig.java

package com.multipom.config;
@Configuration
public class ApplicationConfig {
    @Bean
    public String hwBean () {
        return "Hello World";
    }
}

in AppB module

---- com.multipom.App_B.java ------

package com.multipom;

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

root/pom.xml

<groupId>com.splitpom</groupId>
<artifactId>root</artifactId>
<version>1.0.0</version>
<packaging>pom</packaging>
<modules>
    <module>./appA</module>
    <module>./appB</module>
</modules>

appB/pom.xml

<groupId>com.multipom</groupId>
<artifactId>appB</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>

<name>appB</name>
<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>1.5.2.RELEASE</version>
  <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
  <dependency>
    <groupId>com.multipom</groupId>
    <artifactId>appA</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </dependency>
</dependencies>

appA/pom.xml (CASE 1)

<groupId>com.multipom</groupId>
<artifactId>appA</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>

<name>appA</name>
<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>1.5.2.RELEASE</version>
  <relativePath/> <!-- lookup parent from repository -->
</parent>

appA/pom.xml (CASE 2)

<groupId>com.multipom</groupId>
<artifactId>appA</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>

<name>appA</name>
<parent>
  <groupId>com.splitpom</groupId>
  <artifactId>root</artifactId>
  <version>1.0.0</version>
</parent>

$ java -jar appA-0.0.1-SNAPSHOT.jar

2017-03-18 11:23:23.340 TRACE 26149 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appA/target/appA-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/config/ApplicationConfig.class]
2017-03-18 11:23:23.415 DEBUG 26149 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Identified candidate component class: URL [jar:file:/multipom/appA/target/appA-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/config/ApplicationConfig.class]
2017-03-18 11:23:23.416 TRACE 26149 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appA/target/appA-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_A.class]
2017-03-18 11:23:23.430 TRACE 26149 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Ignored because not matching any filter: URL [jar:file:/multipom/appA/target/appA-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_A.class]
2017-03-18 11:23:24.084 DEBUG 26149 --- [           main] a.ConfigurationClassBeanDefinitionReader : Registering bean definition for @Bean method com.multipom.config.ApplicationConfig.hwBean()

CASE 1: if 'appA' uses 'spring-boot-starter-parent' as parent POM (notice here that 'appB' doesn't find 'hwBean' from 'appA'

$ java -jar appB-0.0.1-SNAPSHOT.jar

2017-03-18 11:24:31.461 TRACE 26203 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]
2017-03-18 11:24:31.546 TRACE 26203 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Ignored because not matching any filter: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]

CASE 2: if 'appA' does NOT use 'spring-boot-starter-parent' as parent POM (notice here that 'appB' does find 'hwBean' from 'appA' .

$ java -jar appB-0.0.1-SNAPSHOT.jar   
2017-03-18 12:03:28.261 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]
2017-03-18 12:03:28.316 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Ignored because not matching any filter: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]
2017-03-18 12:03:28.316 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/App_A.class]
2017-03-18 12:03:28.324 DEBUG 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Identified candidate component class: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/App_A.class]
2017-03-18 12:03:28.325 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/config/ApplicationConfig.class]
2017-03-18 12:03:28.330 DEBUG 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Identified candidate component class: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/config/ApplicationConfig.class]
2017-03-18 12:03:28.348 DEBUG 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning
2017-03-18 12:03:28.373 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]
2017-03-18 12:03:28.384 DEBUG 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Identified candidate component class: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/com/multipom/App_B.class]
2017-03-18 12:03:28.385 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/App_A.class]
2017-03-18 12:03:28.388 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Ignored because not matching any filter: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/App_A.class]
2017-03-18 12:03:28.389 TRACE 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Scanning URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/config/ApplicationConfig.class]
2017-03-18 12:03:28.390 DEBUG 27097 --- [           main] o.s.c.a.ClassPathBeanDefinitionScanner   : Identified candidate component class: URL [jar:file:/multipom/appB/target/appB-0.0.1-SNAPSHOT.jar!/BOOT-INF/lib/appA-0.0.1-SNAPSHOT.jar!/com/multipom/config/ApplicationConfig.class]
2017-03-18 12:03:29.123 DEBUG 27097 --- [           main] a.ConfigurationClassBeanDefinitionReader : Registering bean definition for @Bean method com.multipom.config.ApplicationConfig.hwBean()

mpprdev mpprdev · Accepted Answer · 2017-03-19T01:09:21

The problem is the way spring-boot-maven-plugin packages the dependency jar. In the default settings this plugin packages the jar in a special executable jar format that puts all of your classes under /BOOT-INF/classes/.... If your jar is used as a dependency in another module, you don't want that. Instead your jar has to be a normal flat jar so that all of contained beans can be discoverable by the dependent app. The solution is to add the following to the spring-boot-maven-plugin section (in appA/pom.xml):

    <executions>
            <execution>
                <goals>
                    <goal>repackage</goal>
                </goals>
                <configuration>
                    <classifier>exec</classifier>
                </configuration>
            </execution>
        </executions>

spring-boot-starter-parent in independent module causes its beans not be seen in dependent modules

1 Answers