Sometimes, some jars include 3rd party dependencies embedded, or the same jar can be found under different organizations.
If there are 2 different implementations of the same class in the same JVM, it is random which one will be used, and this can produce nasty bugs like it works in my computer but not in yours.
Use the checkDuplicatedDependencies task for detecting it.
It will fail and provide a list of all incompatibilities, in case it finds the same class in 2 different jars.
If the same class is duplicated, but it's the same implementation, it won't complain.
This is detected by computing a MD5 hash of the contents of the file.
If you consider the found conflicts are inoffensive, in order to ignore them in a future run, use the checkDuplicateExclude setting. The value of this setting is automatically given.
Here is an example of report:
> checkDuplicatedDependencies
Conflict between org.slf4j:jcl-over-slf4j:1.7.10 and commons-logging:commons-logging:1.1.3:
org/apache/commons/logging/impl/NoOpLog
org/apache/commons/logging/impl/SimpleLog$1
org/apache/commons/logging/impl/SimpleLog
org/apache/commons/logging/Log
Conflict between commons-collections:commons-collections:3.2.1 and commons-beanutils:commons-beanutils-core:1.7.0:
org/apache/commons/collections/ArrayStack
org/apache/commons/collections/BufferUnderflowException
org/apache/commons/collections/FastHashMap$1
Conflict between org.eclipse.birt.runtime:org.eclipse.birt.runtime:4.3.1 and commons-codec:commons-codec:1.6:
org/apache/commons/codec/binary/Base32
org/apache/commons/codec/binary/Base32InputStream
org/apache/commons/codec/binary/Base32OutputStream
org/apache/commons/codec/binary/Base64
org/apache/commons/codec/binary/Base64InputStream
org/apache/commons/codec/binary/Base64OutputStream
org/apache/commons/codec/binary/BaseNCodec
Conflict between xerces:xercesImpl:2.9.1 and org.python:jython-standalone:2.5.2:
org/w3c/dom/html/HTMLDOMImplementation
Conflict between commons-collections:commons-collections:3.2.1 and commons-beanutils:commons-beanutils:1.8.3:
org/apache/commons/collections/ArrayStack
org/apache/commons/collections/Buffer
org/apache/commons/collections/BufferUnderflowException
org/apache/commons/collections/FastHashMap$1
org/apache/commons/collections/FastHashMap$CollectionView$CollectionViewIterator
Conflict between org.python:jython-standalone:2.5.2 and com.google.guava:guava:15.0:
com/google/common/base/package-info
com/google/common/collect/package-info
com/google/common/io/package-info
com/google/common/net/package-info
com/google/common/primitives/package-info
com/google/common/util/concurrent/package-info
Conflict between org.eclipse.birt.runtime:org.eclipse.osgi:3.9.1.v20130814-1242 and org.eclipse.birt.runtime:org.eclipse.osgi.services:3.3.100.v20130513-1956:
org/osgi/service/log/LogService
org/osgi/service/log/LogListener
org/osgi/service/log/LogEntry
org/osgi/service/log/LogReaderService
Conflict between commons-beanutils:commons-beanutils:1.8.3 and commons-beanutils:commons-beanutils-core:1.7.0:
org/apache/commons/beanutils/BasicDynaBean
org/apache/commons/beanutils/BasicDynaClass
org/apache/commons/beanutils/BeanAccessLanguageException
Conflict between javax.mail:mail:1.4.1 and com.sun.mail:javax.mail:1.5.1:
com/sun/mail/handlers/image_gif
com/sun/mail/handlers/image_jpeg
com/sun/mail/handlers/message_rfc822
javax/mail/Address
javax/mail/AuthenticationFailedException
javax/mail/Authenticator
javax/mail/BodyPart
...
If you consider these conflicts are inoffensive, in order to ignore them, use:
set checkDuplicatedExclude := Seq(
"org.slf4j" % "jcl-over-slf4j" % "1.7.10" -> "commons-logging" % "commons-logging" % "1.1.3",
"commons-collections" % "commons-collections" % "3.2.1" -> "commons-beanutils" % "commons-beanutils-core" % "1.7.0",
"org.eclipse.birt.runtime" % "org.eclipse.birt.runtime" % "4.3.1" -> "commons-codec" % "commons-codec" % "1.6",
"xerces" % "xercesImpl" % "2.9.1" -> "org.python" % "jython-standalone" % "2.5.2",
"commons-collections" % "commons-collections" % "3.2.1" -> "commons-beanutils" % "commons-beanutils" % "1.8.3",
"org.python" % "jython-standalone" % "2.5.2" -> "com.google.guava" % "guava" % "15.0",
"org.eclipse.birt.runtime" % "org.eclipse.osgi" % "3.9.1.v20130814-1242" -> "org.eclipse.birt.runtime" % "org.eclipse.osgi.services" % "3.3.100.v20130513-1956",
"commons-beanutils" % "commons-beanutils" % "1.8.3" -> "commons-beanutils" % "commons-beanutils-core" % "1.7.0",
"javax.mail" % "mail" % "1.4.1" -> "com.sun.mail" % "javax.mail" % "1.5.1"
)
[error] (checkDuplicatedDependencies) Detected 424 conflict(s)
As suggested, the checkDuplicatedExclude setting can be used to ignore them.
###Implementation notes
Internally, it uses parallelism.
It has been measured in a 4-core system and with a SSD disk, an improvement in time in a large app with 300 dependencies, from 229 seconds to 91 seconds.
###Credits