compilation failure for spring boot application with java 9 and maven

Question

I am trying to build spring-boot application that uses java-9 and would be deployed to heroku. As a build tool I use maven.

I generated spring boot 1.5 application using initializr. I added heroku specific files and added toolchains.xml to .m2 repository for maven-compiler-plugin.

My pom.xml looks like this

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.lapots.breed.platform.cloud</groupId>
    <artifactId>java-cloud-sample</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>java-cloud-sample</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.9</java.version>
        <maven.compiler.source>1.9</maven.compiler.source>
        <maven.compiler.target>1.9</maven.compiler.target>
        <maven.compiler.release>9</maven.compiler.release>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <goals>
                            <goal>build-info</goal>
                        </goals>
                        <configuration>
                            <additionalProperties>
                                <encoding.source>${project.build.sourceEncoding}</encoding.source>
                                <encoding.reporting>${project.reporting.outputEncoding}</encoding.reporting>
                                <java.source>${maven.compiler.source}</java.source>
                                <java.target>${maven.compiler.target}</java.target>
                            </additionalProperties>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.6.0</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-toolchains-plugin</artifactId>
                <version>1.1</version>
                <configuration>
                    <toolchains>
                        <jdk>
                            <version>1.9</version>
                            <vendor>oracle</vendor>
                        </jdk>
                    </toolchains>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>toolchain</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>


</project>

When I try to compiler project using mvn clean package I get the error

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] javac: invalid flag: -Xmodule:null
Usage: javac <options> <source files>
use --help for a list of possible options

[INFO] 1 error
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.031 s
[INFO] Finished at: 2017-08-30T21:08:25+03:00
[INFO] Final Memory: 20M/309M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.0:testCompile (default-testCompile) on
 project java-cloud-sample: Compilation failure
[ERROR] javac: invalid flag: -Xmodule:null
[ERROR] Usage: javac <options> <source files>
[ERROR] use --help for a list of possible options
[ERROR]
[ERROR]
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

module-info looks like this

module com.lapots.breed.platform.cloud.javacloudsample {
    requires spring.boot;
}

What is the problem? Project available here github repository

Answer 1

maven-compiler-plugin 3.6.0 is based on the first signature of module-info.class, which has changed a couple of times. It is not compatible with current Java 9 signature. You should use 3.6.2 when using most recent versions of JDK 9.