如何将Scala库组装到Java7Maven项目中？

Question

我在通过sbt程序集构建Scala库时遇到了困难，这样它就能够被合并到Java项目中。然而，我成功地将Scala库导入到另一个Scala项目中，因此从Scala/SBT的角度来看，它至少是一个有效的JVM二进制文件。

当我打包Scala库时，我使用命令sbt assembly，然后通过以下方式在本地发布它：

╰─$ mvn install:install-file \
-Dfile=/full/path/to/develop/hello/test-library/target/scala-2.11/test-library-assembly-0.1.0-SNAPSHOT.jar \
-DgroupId="com.example" \
-DartifactId="test-library" \
-Dversion="0.1.0-SNAPSHOT" \
-DgeneratePom=true \
-Dpackaging=jar

当我尝试使用Java库时，我看到的错误消息如下：

(在通过mvn clean package打包后，mvn的版本为3.3.9)

╰─$ java -jar target/my-app-1.0-SNAPSHOT.jar
Exception in thread "main" java.lang.NoClassDefFoundError: example/hello/Hello
        at com.mycompany.app.App.main(App.java:19)
Caused by: java.lang.ClassNotFoundException: example.hello.Hello
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 1 more

我的Scala项目如下所示：

build.sbt

import Dependencies._

lazy val root = (project in file(".")).
  settings(
    inThisBuild(List(
      organization := "com.example",
      scalaVersion := "2.11.11",
      version      := "0.1.0-SNAPSHOT",
      scalacOptions += "-target:jvm-1.7"
    )),
    name := "test-library",
    libraryDependencies += scalaTest % Test
  )

project/assembly.sbt

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.5")

project/build.properties

sbt.version=0.13.16

src/main/scala/example/hello/Hello.scala

package example.hello

object Hello {
  def main(args: Array[String]): Unit = {
    println("Hello!!!")
  }
}

Java项目如下所示

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.mycompany.app</groupId>
  <artifactId>my-app</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>my-app</name>
  <url>http://maven.apache.org</url>
  <properties>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
    <encoding>UTF-8</encoding>
  </properties>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.0.2</version>
        <configuration>
          <archive>
            <manifest>
              <addClasspath>true</addClasspath>
              <classpathPrefix>lib/</classpathPrefix>
              <mainClass>com.mycompany.app.App</mainClass>
            </manifest>
          </archive>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.0.2</version>
      </plugin>
    </plugins>
  </build>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>com.example</groupId>
      <artifactId>test-library</artifactId>
      <version>0.1.0-SNAPSHOT</version>
    </dependency>
  </dependencies>
</project>

src/main/java/com/mycompany/app/App.java

package com.mycompany.app;

import example.hello.*;

/**
 * Hello world!
 *
 */
public class App //extends URLClassLoader
{

    public static void main( String[] args ) {
        Hello.main(null);
    }
}

库是否安装在test-library_2.11**?** 下？

不，不需要。下面是mvn install:install-file命令的相关输出。

[INFO] Installing /full/path/to/develop/hello/test-library/target/scala-2.11/test-library-assembly-0.1.0-SNAPSHOT.jar to /home/<my-name>/.m2/repository/com/example/test-library/0.1.0-SNAPSHOT/test-library-0.1.0-SNAPSHOT.jar
[INFO] Installing /tmp/mvninstall9208544268925838468.pom to /home/<my-name>/.m2/repository/com/example/test-library/0.1.0-SNAPSHOT/test-library-0.1.0-SNAPSHOT.pom

Answer 1

问题是test-library是uberjar，但my-app-1.0-SNAPSHOT.jar不是。在建立后，后者作为uberjar以及解决了问题。