Kotlin + Java与Maven混合，未解决的参考 [英] Mixed Kotlin + Java with Maven, unresolved reference
问题描述
我有一个带有Kotlin代码hello.kt的Maven项目，该项目调用Java代码JavaFoo.java，后者调用Kotlin代码KotlinFoo.kt. hello.kt也直接调用KotlinFoo.kt.我正在尝试使用
I have a Maven project with Kotlin code hello.kt which calls Java code JavaFoo.java which calls Kotlin code KotlinFoo.kt. hello.kt also calls KotlinFoo.kt directly. I'm trying to build this with mvn clean install using exactly the Maven settings described in kotlinlang's Maven docs.
如果hello.kt不调用JavaFoo(但是我将JavaFoo留在项目中)，则此构建就可以了.
If hello.kt doesn't call JavaFoo (but I leave JavaFoo in the project) then this builds just fine.
文档说Kotlin编译器应在Java编译器之前调用，这向我暗示所有Kotlin代码都需要在任何Java代码之前进行编译，即，通过这种设置，您可以从Java调用Kotlin，反之则不行.但是，文档将这种设置描述为混合代码应用程序"，而不是从Java调用Kotlin".
The docs say that the Kotlin compiler should be invoked before the Java compiler, which suggests to me that all Kotlin code needs to compile before any Java code, i.e. with this setup you can call Kotlin from Java but not vice versa. However, the docs describe this setup as just "mixed code applications", not "calling Kotlin from Java".
换句话说，这种失败似乎与文档所暗示的含义一致，但与他们直接说的不一致，或者我只是误解了一些东西.
In other words, this failure seems consistent with what the docs seem to imply but not with what they directly say -- or I'm just misunderstanding something.
我想用另一种语言来称呼对方.请问有Maven配置可以做到这一点吗?
I want to call each language from the other. Is there a Maven configuration that will do this, please?
(我研究了关于混合代码设置的各种StackExchange问题，但没有一种解决方案适合我.)
(I looked at various StackExchange questions on mixed code settings and none of the solutions works for me.)
根据要求添加代码: pom.xml:
Adding the code as requested: pom.xml:
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example.kotlindemo</groupId>
<artifactId>kotlin-demo</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>kotlin-demo</name>
<properties>
<kotlin.version>1.1.2-2</kotlin.version>
<kotlin.compiler.incremental>true</kotlin.compiler.incremental>
<main.class>com.example.kotlindemo.HelloKt</main.class>
</properties>
<dependencies>
<dependency>
<groupId>org.jetbrains.kotlin</groupId>
<artifactId>kotlin-stdlib</artifactId>
<version>${kotlin.version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>kotlin-maven-plugin</artifactId>
<groupId>org.jetbrains.kotlin</groupId>
<version>${kotlin.version}</version>
<executions>
<execution>
<id>compile</id>
<phase>process-sources</phase>
<goals> <goal>compile</goal> </goals>
<configuration>
<sourceDirs>
<sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
<sourceDir>${project.basedir}/src/main/java</sourceDir>
</sourceDirs>
</configuration>
</execution>
<execution>
<id>test-compile</id>
<goals> <goal>test-compile</goal> </goals>
<configuration>
<sourceDirs>
<sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
<sourceDir>${project.basedir}/src/test/java</sourceDir>
</sourceDirs>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<executions>
<!-- Replacing default-compile as it is treated specially by maven -->
<execution>
<id>default-compile</id>
<phase>none</phase>
</execution>
<!-- Replacing default-testCompile as it is treated specially by maven -->
<execution>
<id>default-testCompile</id>
<phase>none</phase>
</execution>
<execution>
<id>java-compile</id>
<phase>compile</phase>
<goals> <goal>compile</goal> </goals>
</execution>
<execution>
<id>java-test-compile</id>
<phase>test-compile</phase>
<goals> <goal>testCompile</goal> </goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.6</version>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals> <goal>single</goal> </goals>
<configuration>
<archive>
<manifest>
<mainClass>${main.class}</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
src/main/kotlin/hello.kt:
package com.example.kotlindemo
fun main(args : Array<String>) {
println("Hello, world!")
var kfoo = KotlinFoo()
kfoo.printFooString()
kfoo.fooString = "init2"
kfoo.printFooString()
var foo2 = JavaFoo("abcd")
foo2.printString()
}
src/main/kotlin/KotlinFoo.kt:
package com.example.kotlindemo
class KotlinFoo {
var fooString = "init"
fun printFooString() {
println(this.fooString)
}
}
src/main/java/JavaFoo.java:
package com.example.kotlindemo;
class JavaFoo {
private KotlinFoo k;
JavaFoo(String initializer) {
k = new KotlinFoo();
k.setFooString(initializer);
}
void printString() {
this.k.printFooString();
}
}
错误:
[ERROR] .../src/main/kotlin/hello.kt: (12, 14) Unresolved reference: JavaFoo
推荐答案
编译失败，因为您的Java类不在与其package语句匹配的目录中.尽管Kotlin允许您将类放在任何目录中，而不管它们所在的包是什么，但是Java要求您将每个文件都放在与其目录相对应的包中.此要求也适用于混合语言项目.
The compilation fails because your Java class is not in a directory that matches its package statement. While Kotlin allows you to put classes in any directories regardless of the package they're in, Java requires you to put each file in a package that corresponds to its directory. This requirement applies to mixed-language projects as well.
要解决该错误，请将JavaFoo.java移至src/main/java/com/example/kotlindemo.
To fix the error, move JavaFoo.java to src/main/java/com/example/kotlindemo.
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