sbt公布assembly解决jar包冲突 deduplicate: different file contents found in the following

一个、问题定义

近期使用sbt战斗assembly发生故障时，包，在package什么时候，发生jar包冲突/文件冲突，两个相同class来自不同jar包classpath内心冲突。

有关详细信息：我有一个self4j的jar， hadoop-common-hdfs的jar包。当中hadoop-common-hdfs.jar内包括了self4j这个jar包，导致冲突。

此类异常通常是由于打包不规范和打包疏忽引起的。

（个人觉得正确的打包策略是：仅仅打包自己核心功能。不将依赖打包在一起。可是有时为了方便或者有时不得不打在一起。要注意可能会出现上述问题）

异常log例如以下：

[trace] Stack trace suppressed: run last *:assembly for the full output.
[error] (*:assembly) deduplicate: different file contents found in the following:
[error] C:\Users\shengli.victor\.ivy2\cache\org.slf4j\slf4j-api\jars\slf4j-api-1.7.7.jar:org/slf4j/IMarkerFactory.class
[error] C:\Users\shengli.victor\.ivy2\cache\com.xxx.xx.hdfsfile\hdfscommon\jars\hdfscommon-1.1.jar:org/slf4j/IMarkerFactory.class
[error] Total time: 4 s, completed 2014-11-20 19:07:33

异常非常明显，来自2个不同的jar包self4j, hdfscommon-1.1.jar里。在org/slf4j/IMarkerFactory.class这个类冲突了。

例如以下图：

hdfscommon-1.1/jar

watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvb29wc29vbQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt="" />

slf4j-api-1.7.2.jar

二、解决方式

解决jar包冲突有两种方案：

1、删除当中的某个jar,或者说，在打包的时候。不将2个同样的class打在同一个jar包内的classpath内，即exclude jar。

2、合并冲突

1. Excluding JARs and files

% "provided"

将同样的jar中排除一个，由于反复。能够使用"provided"keyword。

比如spark是一个容器类，编写spark应用程序我们须要spark core jar. 可是真正打包提交到集群上运行，则不须要将它打入jar包内。

这是我们使用 % "provided" keyword来exclude它。

libraryDependencies ++= Seq(
  "org.apache.spark" %% "spark-core" % "0.8.0-incubating" % "provided",
  "org.apache.hadoop" % "hadoop-client" % "2.0.0-cdh4.4.0" % "provided"
)

Maven defines "provided" as:

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime. For example, when building a web application for the Java Enterprise Edition, you would set the dependency on the Servlet API and related Java EE APIs to scopeprovided because the web container provides those classes. This scope is only available on the compilation and test classpath, and is not transitive.

2、Merge Strategy

假设在相对路径下，有多个同样的文件或者jar。这时我们能够使用Merge策略。

在build.sbt中对assemblyMergeStrategy 进行定义。

例如以下：

mergeStrategy in assembly <<= (mergeStrategy in assembly) { (old) =>
  {
    case PathList("org", "slf4j", xs @ _*)         => MergeStrategy.first
    case PathList(ps @ _*) if ps.last endsWith "axiom.xml" => MergeStrategy.filterDistinctLines
    case PathList(ps @ _*) if ps.last endsWith "Log$Logger.class" => MergeStrategy.first
    case PathList(ps @ _*) if ps.last endsWith "ILoggerFactory.class" => MergeStrategy.first
    case x => old(x)
  }
}

解决方法：将org, slf4j 这个下的所有类和文件，都做合并。採用的策略是：在classpath里。2选1，选的是classpath顺序里第一个self4j。

这里支持多种格式。比如ps.lat endsWith "axiom.xml" 。是以axiom.xml为结尾的文件，都採用filterDistinctLines策略，即合并两个文件，舍去反复的部分。

通过以上改动，最终攻克了slf4j冲突的问题，即deduplicate: different file contents found in the following问题。

再次sbt assembly:

[warn] Merging 'META-INF\INDEX.LIST' with strategy 'discard'
[warn] Merging 'META-INF\MANIFEST.MF' with strategy 'discard'
[warn] Merging 'META-INF\maven\log4j\log4j\pom.properties' with strategy 'first'
[warn] Merging 'META-INF\maven\log4j\log4j\pom.xml' with strategy 'first'
[warn] Merging 'META-INF\maven\org.slf4j\slf4j-api\pom.properties' with strategy 'first'
[warn] Merging 'META-INF\maven\org.slf4j\slf4j-api\pom.xml' with strategy 'first'
[warn] Merging 'META-INF\maven\org.slf4j\slf4j-log4j12\pom.properties' with strategy 'first'
[warn] Merging 'META-INF\maven\org.slf4j\slf4j-log4j12\pom.xml' with strategy 'first'
[warn] Merging 'com\esotericsoftware\minlog\Log$Logger.class' with strategy 'first'
[warn] Merging 'com\esotericsoftware\minlog\Log.class' with strategy 'first'
[warn] Merging 'org\apache\log4j\helpers\LogLog.class' with strategy 'first'
[warn] Merging 'org\slf4j\ILoggerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\IMarkerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\Logger.class' with strategy 'first'
[warn] Merging 'org\slf4j\LoggerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\MDC.class' with strategy 'first'
[warn] Merging 'org\slf4j\Marker.class' with strategy 'first'
[warn] Merging 'org\slf4j\MarkerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\BasicMDCAdapter.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\BasicMarker.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\BasicMarkerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\FormattingTuple.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\MarkerIgnoringBase.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\MessageFormatter.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\NOPLogger.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\NOPLoggerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\NOPMDCAdapter.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\NamedLoggerBase.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\SubstituteLoggerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\helpers\Util.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\Log4jLoggerAdapter.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\Log4jLoggerFactory.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\Log4jMDCAdapter.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\StaticLoggerBinder.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\StaticMDCBinder.class' with strategy 'first'
[warn] Merging 'org\slf4j\impl\StaticMarkerBinder.class' with strategy 'first'
[warn] Merging 'org\slf4j\spi\LocationAwareLogger.class' with strategy 'first'
[warn] Merging 'org\slf4j\spi\LoggerFactoryBinder.class' with strategy 'first'
[warn] Merging 'org\slf4j\spi\MDCAdapter.class' with strategy 'first'
[warn] Merging 'org\slf4j\spi\MarkerFactoryBinder.class' with strategy 'first'
[warn] Merging 'rootdoc.txt' with strategy 'concat'
[warn] Strategy 'concat' was applied to a file
[info] Strategy 'deduplicate' was applied to 373 files (Run the task at debug level to see details)
[warn] Strategy 'discard' was applied to 2 files
[warn] Strategy 'first' was applied to 38 files

[info] Done packaging.
[success] Total time: 84 s, completed 2014-11-20 19:04:52

合并策略有非常多种：

能够參考官方sbt assembly文档：https://github.com/sbt/sbt-assembly

http://stackoverflow.com/questions/19606243/resolving-dependencies-in-creating-jar-through-sbt-assembly

MergeStrategy.deduplicate is the default described above
MergeStrategy.first picks the first of the matching files in classpath order
MergeStrategy.last picks the last one
MergeStrategy.singleOrError bails out with an error message on conflict
MergeStrategy.concat simply concatenates all matching files and includes the result
MergeStrategy.filterDistinctLines also concatenates, but leaves out duplicates along the way
MergeStrategy.rename renames the files originating from jar files
MergeStrategy.discard simply discards matching files

很多其它的写法，example：

assemblyMergeStrategy in assembly := {
  case PathList("javax", "servlet", xs @ _*)         => MergeStrategy.first
  case PathList(ps @ _*) if ps.last endsWith ".html" => MergeStrategy.first
  case "application.conf"                            => MergeStrategy.concat
  case "unwanted.txt"                                => MergeStrategy.discard
  case x =>
    val oldStrategy = (assemblyMergeStrategy in assembly).value
    oldStrategy(x)
}

Final Qucik Hack：

假设以上写法都不奏效。还有最好一种，强制默认所有合并，不到万不得已，不要用。。

mergeStrategy in assembly <<= (mergeStrategy in assembly) { mergeStrategy => {
 case entry => {
   val strategy = mergeStrategy(entry)
   if (strategy == MergeStrategy.deduplicate) MergeStrategy.first
   else strategy
 }
}}

三、总结

碰到相似的问题不要慌张。细致看log描写叙述的是什么意思。

异常报出内容冗余的冲突。在看路径，发如今classpath内有全然同样的2个类，这是导致问题的根本原因。

找出原因。解决方发。消除冲突两种方法。一直是去除法，另一种是合并法。

相对于maven和gradle。sbt的冲突解决方法还是比較接近底层。假设没记错的话，maven和gradle都能自己主动解决冲突。

本文仅针对该问题提出解决方式和思路。详细的各个配置还须要继续研究。

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原创文章，转载请注明所：http://blog.csdn.net/oopsoom/article/details/41318599