java - 同时具有java和scala的maven项目

Question

我想构建一个包含java和scala源代码的maven项目。我已经在 eclipse 中安装了 scala IDE 插件，并在 pom.xml 中添加了 "scala-maven-plugin" ，但是 scala 文件中 java 类的导入出现了编译错误。哪个是构建此类混合项目的最佳 IDE？

项目结构是

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/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.apache.spark</groupId>
  <artifactId>spark-examples_2.11</artifactId>
  <version>0.0.1-SNAPSHOT</version>


<dependencies>
    <dependency>
        <groupId>org.scala-lang</groupId>
        <artifactId>scala-library</artifactId>
        <version>2.11.7</version>
    </dependency>
</dependencies>
<build>
<pluginManagement>
    <plugins>
<!-- This plugin compiles Scala files -->
        <plugin>
            <groupId>net.alchim31.maven</groupId>
            <artifactId>scala-maven-plugin</artifactId>
            <executions>
                <execution>
                    <id>scala-compile-first</id>
                    <phase>process-resources</phase>
                    <goals>
                        <goal>add-source</goal>
                        <goal>compile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
<!-- This plugin compiles Java files -->
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
            <executions>
                <execution>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
<!-- This plugin adds all dependencies to JAR file during 'package' command.
Pay EXTRA attention to the 'mainClass' tag. 
You have to set name of class with entry point to program ('main' method) -->
        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <version>2.5.3</version>
            <configuration>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
                <archive>
                    <manifest>
                        <mainClass>ScalaRunner</mainClass>
                    </manifest>
                </archive>
            </configuration>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
  </pluginManagement>  
</build>
</project>

Answer 1

从您的代码结构看来，您的 Scala 类依赖于 Java，而不是相反。然而在你的 Maven 配置中，Scala 首先被编译。将其更改为在 Java 类之后编译。

以下插件序列适用于我的项目:

<build>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>net.alchim31.maven</groupId>
            <artifactId>scala-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <artifactId>maven-assembly-plugin</artifactId>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>