为什么SBT程序集发现冲突时Maven程序集可以工作 [英] Why Maven assembly works when SBT assembly find conflicts

问题描述

标题也可以是:
Maven和SBT程序集插件之间有什么区别.

The title could also be:
What are the differences between Maven and SBT assembly plugins.

在将项目从Maven迁移到SBT时，我发现这是一个问题.

I have found this to be an issue, while migrating a project from Maven to SBT.

为了描述这个问题，我创建了一个示例项目，该项目依赖于构建工具，而我发现它们的行为有所不同.

To describe the problem I have created an example project with dependencies that I found to behave differently, depending on the build tool.

https://github.com/atais/mvn-sbt-assembly

唯一的依赖项是(sbt样式)

The only dependencies are (sbt style)

"com.netflix.astyanax" % "astyanax-cassandra" % "3.9.0",
"org.apache.cassandra" % "cassandra-all" % "3.4",

我不理解的是，为什么mvn package成功创建胖子罐，而sbt assembly却产生冲突:

and what I do not understand is, why mvn package creates the fat jar successfully, while sbt assembly gives conflicts:

[error] 39 errors were encountered during merge
[error] java.lang.RuntimeException: deduplicate: different file contents found in the following:
[error] /home/siatkowskim/.ivy2/cache/org.slf4j/jcl-over-slf4j/jars/jcl-over-slf4j-1.7.7.jar:org/apache/commons/logging/<some classes>
[error] /home/siatkowskim/.ivy2/cache/commons-logging/commons-logging/jars/commons-logging-1.1.1.jar:org/apache/commons/logging/<some classes>
...
[error] /home/siatkowskim/.ivy2/cache/com.github.stephenc.high-scale-lib/high-scale-lib/jars/high-scale-lib-1.1.2.jar:org/cliffc/high_scale_lib/<some classes>
[error] /home/siatkowskim/.ivy2/cache/com.boundary/high-scale-lib/jars/high-scale-lib-1.0.6.jar:org/cliffc/high_scale_lib/<some classes>
...

推荐答案

扩展为 Alexey Romanov答案.

我还用详细说明更新了我的项目，所以您可能想要看看.

Extension to Alexey Romanov answer.

I have also updated my project with detailed explanation, so you might want to check it out.

遵循建议

对于这种情况，您可以通过解压缩Maven生成的jar和SBT错误消息中的依赖jar，然后检查Maven使用了哪个.class文件来对此进行验证.

You can verify it for this case by unpacking the jar Maven produces and the dependency jars in SBT error message, then checking which .class file Maven used.

我比较了maven和sbt产生的fat-jars与

• MergeStrategy.first，其中显示了一些额外的文件
• MergeStrategy.last，显示二进制差异&多余的文件

• MergeStrategy.first, that showed some extra files
• MergeStrategy.last, that showed binary differences & extra files

我已经进行了下一步，并针对sbt发现冲突的依赖项检查了fat-jars，具体来说:

I have taken the next step and checked the fat-jars against the dependencies sbt found conflicts at, specifically:

• 常见问题-logging-1.1.1.jar

• jcl-over-slf4j-1.7.7.jar
• commons-logging-1.1.1.jar

maven-assembly-plugin解决了jar级别的冲突. 当发现任何冲突时，它将选择第一个jar，而忽略其他所有内容.

maven-assembly-plugin resolves conflicts on jar level. When it finds any conflict, it picks the first jar and simply ignores all the content from the other.

sbt-assembly则混合所有class文件，以逐个文件的方式在本地解决冲突.

Whereas sbt-assembly mixes all the class files, resolving conflicts locally, file by file.

我的理论将是，如果您用maven-assembly-plugin制作的fat-jar可行，则您可以 对于sbt中的所有冲突，请指定MergeStrategy.first. 它们唯一的区别是，用sbt生成的jar会更大，包含被maven忽略的额外类.

My theory would be, that if your fat-jar made with maven-assembly-plugin works, you can specify MergeStrategy.first for all the conflicts in sbt. They only difference would be, that the jar produced with sbt will be even bigger, containing extra classes that were ignored by maven.

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