编译无效标志时出错--模块路径

Question

我有一个项目。最初是一个单一模块的项目，结构是这样的

java-cloud-sample\
    src\
        main\
            java
    pom.xml

我决定把它做成多模块结构——反正我用的是< code>java 9。所以我这样分开了

java-cloud-sample\
    java-cloud-rest-api\
        src\
        pom.xml
    pom.xml

哪里根 pom.xml看起来像这样

<?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>pom</packaging>

    <modules>
        <module>java-cloud-rest-api</module>
    </modules>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.6.RELEASE</version>
    </parent>

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.2</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <version>3.0.0</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>3.0.1</version>
                <executions>
                    <execution>
                        <id>copy-dependencies</id>
                        <phase>package</phase>
                        <goals><goal>copy-dependencies</goal></goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>


</project>

以及模块＜代码＞pom。xml如下所示

<?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>

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

    <artifactId>java-cloud-rest-api</artifactId>
    <description>Demo project for Spring Boot</description>
    <packaging>jar</packaging>

    <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-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</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>
        </plugins>
    </build>
</project>

但当我尝试运行＜code＞mvn clean package

INFO] java-cloud-rest-api ................................ FAILURE [  1.060 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.104 s
[INFO] Finished at: 2017-09-08T17:15:46+03:00
[INFO] Final Memory: 27M/331M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.2:compile (default-compile) on project java-cloud-rest-api: Fatal error compiling: invalid flag: --module-path -> [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/MojoExecutionException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :java-cloud-rest-api

问题是什么？（也许我应该将＜code＞maven

Answer 1

当一个项目正在定义一个< code>module-info.java并且Java 8与Maven一起使用来编译该项目时，我在Maven编译器插件3.8.1中遇到了这个错误。似乎只要Maven编译器插件看到< code>module-info.java,它就会在命令行中添加< code> - module-path标志，这对于Java 8编译器来说是未知的。排除此文件并在没有模块支持的情况下编译项目的一种方法是根据Maven概要文件从编译中排除< code>module-info.java:

    <profiles>
        <profile>
            <id>java8</id>
            <activation>
                <jdk>1.8</jdk>
            </activation>
            <build>
                <plugins>
                    <plugin>
                        <groupId>org.apache.maven.plugins</groupId>
                        <artifactId>maven-compiler-plugin</artifactId>
                        <version>3.8.1</version>
                        <configuration>
                            <excludes>
                                <exclude>module-info.java</exclude>
                            </excludes>
                        </configuration>
                    </plugin>
                </plugins>
            </build>
        </profile>

Answer 2

当机器上安装的maven配置为java8作为默认java版本时，会发生此故障。您可以通过执行

mvn -version

并检查配置中声明的Java版本。

要将版本解析为目前支持的更新版本，例如java9，您可以在您的机器上创建/编辑mavenrc（在MacOS上）文件：

vi ~/.mavenrc

包括这些

export PATH
export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/
export PATH=${PATH}:$JAVA_HOME/bin

保存此配置后，您可以使用相同的命令确认maven应该使用Java版本9，然后您的项目将在没有声明错误的情况下构建。