IDEA下基于Maven的Java和Scala混合编程
开发Spark项目时，有时候需要用到Java和Scala进行混合编程，比如Java类中调用Scala，或者Scala中调用Java
1. 创建Java Maven工程
首先，创建一个空的Java Maven工程java-scala-program
在src/main/java目录下新建JavaTest类，输出"Hello Java!"
2. 将Scala混合到Java Meavn项目中
为了能够在Java Maven工程中使用Scala，我们需要使用一个Maven插件：scala-maven-plugin，把下面的代码加入到pom.xml文件中
<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><execution><id>scala-test-compile</id><phase>process-test-resources</phase><goals><goal>testCompile</goal></goals></execution></executions></plugin>
因为我们需要使用Scala代码，所以我们还需要加入scala-library依赖，如下：
<dependency><groupId>org.scala-lang</groupId><artifactId>scala-library</artifactId><version>2.11.8</version></dependency>
在src/main目录下，新建scala目录，并右键-->Make Directory as --> Source Root, 并新建 ScalaTest类：
3. 在Java中调用Scala
4. 在Scala中调用Java
5. 添加maven打包工具进行打包
这里我们使用 maven plugin：maven-assembly-plugin对工程进行打包，在pom文件添加如下：
<plugin><artifactId>maven-assembly-plugin</artifactId><configuration><descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs><archive><manifest><mainClass>JavaTest</mainClass></manifest></archive></configuration><executions><execution><phase>package</phase><goals><goal>single</goal></goals></execution></executions></plugin>
mainClass: 是主函数所在的类，如果运行Java，则为JavaTest, 如果运行Scala，则为ScalaTest
打包Java程序：
打包Scala程序：
6. 完整代码
JavaTest.java
public class JavaTest {public static void main(String[] args) {System.out.println("Hello Java!");ScalaTest.output();}public void output(){System.out.println("JavaTest");}}
ScalaTest.scala
object ScalaTest {def main(args: Array[String]): Unit = {println("Hello Scala!")val javaTest = new JavaTest()javaTest.output()}def output(): Unit = {println("Scala Test")}}
pom.xml
<?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>cn.unicom</groupId><artifactId>java-scala-program</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source.version>1.8</maven.compiler.source.version><maven.compiler.target.version>1.8</maven.compiler.target.version><encoding>UTF-8</encoding><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><java.version>1.8</java.version><scala.version>2.11.8</scala.version></properties><dependencies><dependency><groupId>org.scala-lang</groupId><artifactId>scala-library</artifactId><version>${scala.version}</version></dependency></dependencies><build><plugins><!-- This plugin compiles Scala files --><plugin><groupId>net.alchim31.maven</groupId><artifactId>scala-maven-plugin</artifactId><executions><execution><id>scala-compile-first</id><phase>process-resources</phase><goals><goal>add-source</goal><goal>compile</goal></goals></execution><execution><id>scala-test-compile</id><phase>process-test-resources</phase><goals><goal>testCompile</goal></goals></execution></executions><configuration><scalaVersion>${scala.version}</scalaVersion></configuration></plugin><!-- This plugin compiles Java files --><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><configuration><source>${java.version}</source><target>${java.version}</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><configuration><descriptorRefs><descriptorRef>jar-with-dependencies</descriptorRef></descriptorRefs><archive><manifest><mainClass>JavaTest</mainClass></manifest></archive></configuration><executions><execution><phase>package</phase><goals><goal>single</goal></goals></execution></executions></plugin></plugins></build></project>
注意：Scala plugin一定要位于Java plugin前面，即先编译Scala在编译Java；
否则，会出现找不到Scala类的情况