Gatling构建Fat Jar后无法生成HTML报告问题排查

运行Gatling构建的Fat Jar时，功能正常但无法生成HTML报告，报错如下：

Parsing log file(s)...
Parsing log file(s) done in 0s.
Generating reports...
Exception in thread "main" java.lang.ExceptionInInitializerError
        at io.gatling.charts.report.ReportsGenerator.generateFor(ReportsGenerator.scala:56)
        at io.gatling.app.RunResultProcessor.generateReports(RunResultProcessor.scala:61)
        at io.gatling.app.RunResultProcessor.processRunResult(RunResultProcessor.scala:35)
        at io.gatling.app.Gatling$.start(Gatling.scala:102)
        at io.gatling.app.Gatling$.fromArgs(Gatling.scala:54)
        at io.gatling.app.Gatling$.main(Gatling.scala:42)
        at io.gatling.app.Gatling.main(Gatling.scala)
Caused by: java.lang.IllegalStateException: Couldn't find a ComponentLibrary implementation
        at io.gatling.charts.component.ComponentLibrary$.<clinit>(ComponentLibrary.scala:30)
        ... 7 more

当前build.sbt配置：

import sbtassembly.AssemblyKeys.assembly

enablePlugins(GatlingPlugin)

scalaVersion := "2.13.13"

scalacOptions := Seq(
  "-encoding", "UTF-8", "-release:8", "-deprecation",
  "-feature", "-unchecked", "-language:implicitConversions", "-language:postfixOps")

// 3.10.5
val gatlingVersion = "3.10.5"
libraryDependencies += "io.gatling.highcharts" % "gatling-charts-highcharts" % gatlingVersion //% "test,it"
libraryDependencies += "io.gatling"            % "gatling-test-framework"    % gatlingVersion //% "test,it"
libraryDependencies += "io.github.gatling-cql" % "gatling-cql" % "3.9.0-1"
libraryDependencies += "com.esri.geometry" % "esri-geometry-api" % "1.2.1"
libraryDependencies += "org.apache.tinkerpop" % "gremlin-core" % "3.5.3"
libraryDependencies += "org.apache.tinkerpop" % "tinkergraph-gremlin" % "3.5.3"
libraryDependencies += "com.datastax.oss" % "java-driver-core" % "4.14.1"
libraryDependencies += "com.datastax.oss" % "java-driver-query-builder" % "4.14.1"
libraryDependencies += "com.datastax.oss" % "java-driver-mapper-runtime" % "4.14.1"

mainClass in assembly := Some("com.example.CassandraSimulation2")

assemblyMergeStrategy in assembly := {
  case  PathList("META-INF", "native", "libnetty_tcnative_linux_x86_64.so") => MergeStrategy.last
  case PathList("META-INF", _*) => MergeStrategy.discard
  case "reference.conf" => MergeStrategy.concat
  case _                        => MergeStrategy.first
}

排查情况 #

• 在sbt Shell中运行时，报告可正常生成
• Fat Jar内部已包含io.gatling.charts.highcharts.component.ComponentLibraryImpl和io.gatling.charts.component.ComponentLibrary类

问题原因 #

Gatling通过Java ServiceLoader机制加载ComponentLibrary的实现类，需要读取META-INF/services/io.gatling.charts.component.ComponentLibrary配置文件，该文件中声明了实现类的全路径。但当前的assemblyMergeStrategy直接丢弃了所有META-INF下的文件，导致这个关键配置文件缺失，ServiceLoader无法找到实现类，从而触发报错。

解决方案 #

修改assemblyMergeStrategy，保留META-INF/services目录下的服务配置文件，调整后的配置如下：

assemblyMergeStrategy in assembly := {
  case PathList("META-INF", "native", "libnetty_tcnative_linux_x86_64.so") => MergeStrategy.last
  case PathList("META-INF", "services", _*) => MergeStrategy.filterDistinctLines // 合并服务配置文件，避免重复条目
  case PathList("META-INF", _*) => MergeStrategy.discard // 其他非必要META-INF文件仍丢弃
  case "reference.conf" => MergeStrategy.concat
  case _ => MergeStrategy.first
}

重新构建Fat Jar后，运行时就能正确加载ComponentLibraryImpl，生成HTML报告。

内容的提问来源于stack exchange，提问作者Pavel Orekhov