[Spring] only the last one will be generated in multiple inputSpec

I am using the following pom configuration to generate Controllers:

		<plugin>
		    <groupId>io.swagger</groupId>
		    <artifactId>swagger-codegen-maven-plugin</artifactId>
		    <version>2.3.1</version>
		    <executions>
		        <execution>
        			<id>first-service-api</id>
		            <goals>
		                <goal>generate</goal>
		            </goals>
		            <configuration>
		                <inputSpec>${project.basedir}/src/main/resources/api/administration.yaml</inputSpec>
		                <language>spring</language>
		                <configOptions>
		                   <sourceFolder>src/gen/java/main</sourceFolder>
		                </configOptions>
		                <apiPackage>${default.package}.controller</apiPackage>
		                <modelPackage>${default.package}.model</modelPackage>
		                <generateSupportingFiles>false</generateSupportingFiles>
		                <skip>false</skip>
		            </configuration>
		        </execution>
		        <execution>
        			<id>second-service-api</id>
		            <goals>
		                <goal>generate</goal>
		            </goals>
		            <configuration>
		                <inputSpec>${project.basedir}/src/main/resources/api/receiver.yaml</inputSpec>
		                <language>spring</language>
		                <configOptions>
		                   <sourceFolder>src/gen/java/main</sourceFolder>
		                </configOptions>
		                <apiPackage>${default.package}.controller</apiPackage>
		                <modelPackage>${default.package}.model</modelPackage>
		                <generateSupportingFiles>false</generateSupportingFiles>
		                <skip>false</skip>
		            </configuration>
		        </execution>
		    </executions>
		</plugin>

I use eclipse as my IDE, and trigger the generation via 'run as' --> 'maven generate-sources'.
I can only found one controller in target folder, which generated from the second 'execution'.

Reproduce the issue with the shown Maven configuration, using administration.yaml and receiver.yaml as the two input specifications, then run Maven generate-sources and inspect the target folder. Trace why only the second execution's controller is present; done means both executions generate their controllers without overwriting or suppressing the first.