sbt-assembly打包Scala项目缺失PostgreSQL JDBC驱动解决方案

我有一个Scala项目，通过JDBC连接PostgreSQL数据库取数，使用IntelliJ配合SBT构建，借助sbt-assembly插件打包成包含所有依赖的单JAR包。在IntelliJ内运行程序完全正常，但执行以下命令时抛出异常：

java -jar /opt/service/sample.jar

异常信息：

Exception in thread "main" java.sql.SQLException: java.sql.SQLException: No suitable driver found for jdbc:postgresql://

解压生成的JAR包后，未找到PostgreSQL驱动相关文件，推测是sbt-assembly未将该依赖打包进JAR。本地通过指定额外依赖的方式执行命令，程序能正常运行：

java -cp sampl.jar:/Users/x/.m2/repository/org/postgresql/postgresql/42.2.7/postgresql-42.2.7.jar com.abc.main

以下是项目中build.sbt的assembly相关配置，需要修改配置让单JAR包无需额外依赖即可运行：

ThisBuild / libraryDependencies ++= Seq(
  "com.typesafe.scala-logging" %% "scala-logging" % "3.9.2",
  "org.postgresql" % "postgresql" % "42.2.14"
)

import sbtassembly.MergeStrategy
assemblyMergeStrategy in assembly := {
  case PathList("org", "apache", xs @ _*) => MergeStrategy.first
  case PathList("org", "slf4j", xs @ _*) => MergeStrategy.first
  case PathList("org", "aopalliance", xs @ _*) => MergeStrategy.first
  case PathList("jersey", "repackaged", xs @ _*) => MergeStrategy.first
  case PathList("javax", xs @ _*) => MergeStrategy.first
  case PathList("io", "netty", xs @ _*) => MergeStrategy.first
  case PathList("com", "amazonaws", xs @ _*) => MergeStrategy.first
  case PathList("META-INF", xs @ _*) =>
    (xs map {_.toLowerCase}) match {
      case ("manifest.mf" :: Nil) | ("index.list" :: Nil) | ("dependencies" :: Nil) => MergeStrategy.discard
      case _ => MergeStrategy.first
    }
  case PathList("com", "sun", xs @ _*) => MergeStrategy.first
  case PathList("git.properties", xs @ _*) => MergeStrategy.first
  case PathList("mozilla", xs @ _*) => MergeStrategy.first
  case x =>
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    oldStrategy(x)
}

修改后的build.sbt配置如下，主要调整两点：确保PostgreSQL驱动被纳入打包范围，以及正确处理驱动的服务注册文件避免丢失：

ThisBuild / libraryDependencies ++= Seq(
  "com.typesafe.scala-logging" %% "scala-logging" % "3.9.2",
  // 显式声明compile范围，确保驱动被打包进最终JAR
  "org.postgresql" % "postgresql" % "42.2.14" % Compile
)

import sbtassembly.MergeStrategy
assemblyMergeStrategy in assembly := {
  // 新增PostgreSQL路径的合并策略，避免驱动文件被意外排除
  case PathList("org", "postgresql", xs @ _*) => MergeStrategy.first
  case PathList("org", "apache", xs @ _*) => MergeStrategy.first
  case PathList("org", "slf4j", xs @ _*) => MergeStrategy.first
  case PathList("org", "aopalliance", xs @ _*) => MergeStrategy.first
  case PathList("jersey", "repackaged", xs @ _*) => MergeStrategy.first
  case PathList("javax", xs @ _*) => MergeStrategy.first
  case PathList("io", "netty", xs @ _*) => MergeStrategy.first
  case PathList("com", "amazonaws", xs @ _*) => MergeStrategy.first
  case PathList("META-INF", xs @ _*) =>
    (xs map {_.toLowerCase}) match {
      case ("manifest.mf" :: Nil) | ("index.list" :: Nil) | ("dependencies" :: Nil) => MergeStrategy.discard
      // 合并JDBC驱动的服务注册文件，保证自动加载生效
      case ("services" :: "java.sql.Driver" :: Nil) => MergeStrategy.concat
      case _ => MergeStrategy.first
    }
  case PathList("com", "sun", xs @ _*) => MergeStrategy.first
  case PathList("git.properties", xs @ _*) => MergeStrategy.first
  case PathList("mozilla", xs @ _*) => MergeStrategy.first
  case x =>
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    oldStrategy(x)
}

额外注意：如果你的JDBC连接代码没有显式加载驱动类Class.forName("org.postgresql.Driver")，则必须确保META-INF/services/java.sql.Driver文件被正确打包（上面的配置已经通过MergeStrategy.concat处理了该文件的合并，避免被其他依赖的同名文件覆盖）。

修改完成后，重新执行sbt assembly生成新的JAR包，再运行java -jar /opt/service/sample.jar即可正常连接数据库。

内容的提问来源于stack exchange，提问作者Siddarth