使用marven实现java和scala的互相调用

1. Java调用Scala类

整个工程的目录结构如下：

java-call-scala/
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── hank
        │           └── java
        │               └── main
        │                   └── App.java
        └── scala
            └── com
                └── hank
                    └── scala
                        └── main
                            └── MyScala.scala

App.java为主程序，由Java语言实现，MyScala.scala为被调用的类，由Scala语言实现。

App.java的代码如下：

package com.hank.java.main;

import com.hank.scala.main.MyScala;
public class App {
    public static void main(String[] args) {
        System.out.println("Hello, I am JAVA, I will call Scala");
                MyScala.print();
    }
}

MyScala.scala的代码如下：

package com.hank.scala.main

object MyScala {
  def print() : Unit = {
        println("Hello, I am SCALA")
  }
}

程序的内容很简单，要在marven中实现Java调用Scala最关键的是编写pom文件，它的内容如下：

<?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.hank.mvn</groupId>
    <artifactId>java-call-scala</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>java-call-scala</name>
    <url>http://maven.apache.org</url>

    <!-- 运行scala库时要依赖的库文件 -->
    <dependencies>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.12.1</version>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <!-- 该插件用于在marven中编译scala程序 -->
            <plugin>
                <!-- see http://davidb.github.com/scala-maven-plugin -->
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.2.2</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

            <!-- 该插件用于打包 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.4.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.hank.java.main.App</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

        </plugins>
        </build>
</project>

编译运行：

# mvn clean scala:compile compile package
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] Building java-call-scala 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ java-call-scala ---
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default-cli) @ java-call-scala ---
[INFO] /home/hank/Study/Java/java-call-scala/src/main/java:-1: info: compiling
[INFO] /home/hank/Study/Java/java-call-scala/src/main/scala:-1: info: compiling
[INFO] Compiling 2 source files to /home/hank/Study/Java/java-call-scala/target/classes at 1507437522083
[INFO] prepare-compile in 0 s
[INFO] compile in 2 s
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/java-call-scala/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ java-call-scala ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /home/hank/Study/Java/java-call-scala/target/classes
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/java-call-scala/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/java-call-scala/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ java-call-scala ---
[INFO] No sources to compile
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ java-call-scala ---
[INFO] No tests to run.
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ java-call-scala ---
[INFO] Building jar: /home/hank/Study/Java/java-call-scala/target/java-call-scala-1.0-SNAPSHOT.jar
[INFO] 
[INFO] --- maven-shade-plugin:2.4.1:shade (default) @ java-call-scala ---
[INFO] Including org.scala-lang:scala-library:jar:2.12.1 in the shaded jar.
[INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing /home/hank/Study/Java/java-call-scala/target/java-call-scala-1.0-SNAPSHOT.jar with /home/hank/Study/Java/java-call-scala/target/java-call-scala-1.0-SNAPSHOT-shaded.jar
[INFO] Dependency-reduced POM written at: /home/hank/Study/Java/java-call-scala/dependency-reduced-pom.xml
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.016 s
[INFO] Finished at: 2017-10-08T12:38:47+08:00
[INFO] Final Memory: 18M/189M
[INFO] ------------------------------------------------------------------------
root@hank-Vostro-270s:/home/hank/Study/Java/java-call-scala# cd target/
root@hank-Vostro-270s:/home/hank/Study/Java/java-call-scala/target# java -jar java-call-scala-1.0-SNAPSHOT.jar 
Hello, I am JAVA, I will call Scala
Hello, I am SCALA

这里要注意的是先编译Scala的类，然后再编译Java的类，最后在target目录下生成了jar文件，可以直接运行。

2. Scala调用Java类

整个工程的结构如下：

scala-call-java/
├── pom.xml
└── src
    └── main
        ├── java
        │   └── com
        │       └── hank
        │           └── java
        │               └── main
        │                   └── MyJava.java
        └── scala
            └── com
                └── hank
                    └── scala
                        └── main
                            └── App.scala

App.scala的代码如下：

package com.hank.scala.main

import com.hank.java.main.MyJava

object App {
  def main(args: Array[String]) : Unit = {
        println("Hello, I am Scala, I will call Java")

        val myObj = new MyJava()
        myObj.print()
  }
}

MyJava.java的代码如下：

package com.hank.java.main;

public class MyJava {
        public void print() {
                System.out.println("Hello, I am Java");
        }
}

pom.xml的文件内容如下：

<?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.hank.mvn</groupId>
    <artifactId>java-call-scala</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>java-call-scala</name>
    <url>http://maven.apache.org</url>

    <!-- 运行scala库时要依赖的库文件 -->
    <dependencies>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.12.1</version>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <!-- 该插件用于在marven中编译scala程序 -->
            <plugin>
                <!-- see http://davidb.github.com/scala-maven-plugin -->
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.2.2</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

            <!-- 该插件用于打包 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.4.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.hank.scala.main.App</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

        </plugins>
        </build>
</project>

编译并运行：

# mvn clean compile scala:compile  package          
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] Building java-call-scala 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ java-call-scala ---
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/scala-call-java/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ java-call-scala ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /home/hank/Study/Java/scala-call-java/target/classes
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default) @ java-call-scala ---
[INFO] /home/hank/Study/Java/scala-call-java/src/main/java:-1: info: compiling
[INFO] /home/hank/Study/Java/scala-call-java/src/main/scala:-1: info: compiling
[INFO] Compiling 2 source files to /home/hank/Study/Java/scala-call-java/target/classes at 1507438404427
[INFO] prepare-compile in 0 s
[INFO] compile in 2 s
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default-cli) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/scala-call-java/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- scala-maven-plugin:3.2.2:compile (default) @ java-call-scala ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ java-call-scala ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/hank/Study/Java/scala-call-java/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ java-call-scala ---
[INFO] No sources to compile
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ java-call-scala ---
[INFO] No tests to run.
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ java-call-scala ---
[INFO] Building jar: /home/hank/Study/Java/scala-call-java/target/java-call-scala-1.0-SNAPSHOT.jar
[INFO] 
[INFO] --- maven-shade-plugin:2.4.1:shade (default) @ java-call-scala ---
[INFO] Including org.scala-lang:scala-library:jar:2.12.1 in the shaded jar.
[INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing /home/hank/Study/Java/scala-call-java/target/java-call-scala-1.0-SNAPSHOT.jar with /home/hank/Study/Java/scala-call-java/target/java-call-scala-1.0-SNAPSHOT-shaded.jar
[INFO] Dependency-reduced POM written at: /home/hank/Study/Java/scala-call-java/dependency-reduced-pom.xml
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.788 s
[INFO] Finished at: 2017-10-08T12:53:28+08:00
[INFO] Final Memory: 18M/169M
[INFO] ------------------------------------------------------------------------
root@hank-Vostro-270s:/home/hank/Study/Java/scala-call-java# ls
dependency-reduced-pom.xml  pom.xml  src  target
root@hank-Vostro-270s:/home/hank/Study/Java/scala-call-java# cd target/
root@hank-Vostro-270s:/home/hank/Study/Java/scala-call-java/target# java -jar ./java-call-scala-1.0-SNAPSHOT.jar 
Hello, I am Scala, I will call Java
Hello, I am Java

这里在编译的时候要先编译Scala的类。

3. Marven的源

默认的Marven源在国外，下载插件的时候会非常慢，找了一个国内的镜像，速度非常快。

<mirror>
        <id>nexus-aliyun</id>  
        <mirrorOf>central</mirrorOf>    
        <name>Nexus aliyun</name>  
        <url>http://maven.aliyun.com/nexus/content/groups/public</url>  
</mirror>

将上面的内容加入到marven的配置文件中，我的机器上对应的文件是/opt/apache-maven-3.5.0/conf/settings.xml，注意要放在<mirrors></mirrors>之间。

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