如何使用Maven编译Java + Kotlin项目？

Question

我正在尝试编译maven项目,该项目包含引用Java类的Kotlin类.这是我父POM的一部分:

...

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
    <version>${kotlin.version}</version>
</dependency>

...

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>${compiler-plugin-version}</version>
    <configuration>
        <source>${java-version}</source>
        <target>${java-version}</target>
        <encoding>${project.build.sourceEncoding}</encoding>
    </configuration>
</plugin>

<plugin>
    <artifactId>kotlin-maven-plugin</artifactId>
    <groupId>org.jetbrains.kotlin</groupId>
    <version>${kotlin.plugin.version}</version>

    <executions>
        <execution>
            <id>compile</id>
            <phase>process-sources</phase>
            <goals>
                <goal>compile</goal>
            </goals>
        </execution>

        <execution>
            <id>test-compile</id>
            <phase>process-test-sources</phase>
            <goals>
                <goal>test-compile</goal>
            </goals>
        </execution>
    </executions>

    <configuration>
        <scanForAnnotations>false</scanForAnnotations>
    </configuration>
</plugin>

和孩子POM的相关部分:

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
</dependency>

...

<plugin>
    <artifactId>kotlin-maven-plugin</artifactId>
    <groupId>org.jetbrains.kotlin</groupId>
    <configuration>
        <sourceDirs>
            <source>${project.basedir}/src/main/kotlin</source>
        </sourceDirs>
    </configuration>
</plugin>

和Kotlin类:

Stateless
open class DummyServiceImpl : DummyService {

    PersistenceContext(unitName = Consts.UNIT_NAME)
    private val em: EntityManager? = null

    override fun get(id: Long?): Dummy {
        return em!!.find<Dummy>(javaClass<Dummy>(), id)
    }

    override fun sayHi(): String {
        return "Dummy service says \"Hi!\"."
    }
}

DummyService和Consts类是驻留在同一模块中的Java类DummyServiceImpl.所以当我编译包含DummyServiceImplMaven 的模块时,它是这样的:

[error] C:\somepath\service\DummyServiceImpl.kt: (14, 31) Unresolved reference: DummyService
[error] C:\somepath\service\DummyServiceImpl.kt: (16, 35) Unresolved reference: Consts

如果我将Kotlin插件执行切换phase到compile那时它可以预测会失败,如果有从Java到Kotlin类的引用:

[ERROR] /C:/somepath/service/impl/DummyServiceClientImpl.java:[5,27] cannot find symbol
[ERROR] symbol:   class DummyServiceImpl

那么,要做些什么呢？请注意,使用IDEA构建make完全没问题.

Answer 1

确保你<build>的pom.xml中有这个声明

    <plugins>
        <plugin>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-plugin</artifactId>
            <version>${kotlin.version}</version>
            <executions>
                <execution>
                    <id>compile</id>
                    <phase>process-sources</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <source>src/main/java</source>
                            <source>src/main/kotlin</source>
                            <source>src/main/resources</source>
                        </sourceDirs>
                    </configuration>
                </execution>
                <execution>
                    <id>test-compile</id>
                    <phase>process-test-sources</phase>
                    <goals>
                        <goal>test-compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <source>src/test/java</source>
                            <source>src/test/kotlin</source>
                            <source>src/test/resources</source>
                        </sourceDirs>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>

确保配置中提到的所有文件夹(src/main中的3x和src/test中的3x)实际存在,即使它们不包含任何类/资源.一旦它适合您,您仍然可以微调配置.

还要注意使用与我上面提到的完全相同的顺序让编译器首先编译Java代码.

Answer 2

从此Kotlin + Java演示应用程序引荐

您必须执行mvn kotlin:compile之前mvn package。mvn kotlin:compile会将Kotlin文件编译为类文件。

<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.wffweb</groupId>
    <artifactId>kotlinminimalproductionsample</artifactId>
    <version>0.0.1</version>
    <packaging>war</packaging>

    <!--
    To package as war:- mvn clean kotlin:compile package
    -->

    <properties>
        <maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <kotlin.version>1.2.21</kotlin.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.websocket</groupId>
            <artifactId>javax.websocket-api</artifactId>
            <version>1.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>com.webfirmframework</groupId>
            <artifactId>wffweb</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-jdk8</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-test</artifactId>
            <version>${kotlin.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                </includes>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.4.0</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
                <executions>
                    <execution>
                        <id>compile</id>
                        <phase>compile</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>test-compile</id>
                        <phase>test-compile</phase>
                        <goals>
                            <goal>test-compile</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <jvmTarget>1.8</jvmTarget>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>