NoClassDefFoundError: org/apache/commons/lang3/StringUtils

If you're using Maven, put this inside your pom.xml file:

Maven Central Repository for Commons Lang:

<dependency>
    <groupId>commons-lang</groupId>
    <artifactId>commons-lang</artifactId>
    <version>2.6</version>
</dependency>

Maven Central Repository for Apache Commons Lang:

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.11</version>
</dependency>

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Don't forget: Update Maven Project

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Apache Commons Lang ™ Dependency Information

Last Published: 30 August 2020 | Version: 3.11

Apache Maven

<dependency>
  <groupId>org.apache.commons</groupId>
  <artifactId>commons-lang3</artifactId>
  <version>3.11</version>
</dependency>

Apache Buildr

'org.apache.commons:commons-lang3:jar:3.11'

Apache Ivy

<dependency org="org.apache.commons" name="commons-lang3" rev="3.11">
  <artifact name="commons-lang3" type="jar" />
</dependency>

Groovy Grape

@Grapes(
@Grab(group='org.apache.commons', module='commons-lang3', version='3.11')
)

Gradle/Grails

compile 'org.apache.commons:commons-lang3:3.11'

Scala SBT

libraryDependencies += "org.apache.commons" % "commons-lang3" % "3.11"

Leiningen

[org.apache.commons/commons-lang3 "3.11"]

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Reference:

• https://commons.apache.org/proper/commons-lang/dependency-info.html

I have added commons-lang-2.6.jar & commons-lang3-3.1-sources.jar...

Here's your problem: commons-lang-2.6.jar doesn't contain the org.apache.commons.lang3 package, since that's part of version 3, and commons-lang3-3.1-sources.jar contains the source code, not the byte code.

You need to include commons-lang3-3.1.jar instead.