Findjars: a gradle plugin to debug classpath issues

Findjars is a gradle plugin that helped Criteo debugging classpath issues when migrating from maven to gradle.

It permits to find:

• which jars contain a file identified by its path,
• conflicts among the jars selected above, a conflict being a file with the same path present in two different jars with a different digest.

More precisely, let's take as example the following build.gradle that uses the plugin.

$ cat build.gradle
plugins {
  id 'com.criteo.gradle.findjars' version '0.1'
}

apply plugin: 'java-library'

repositories {
  mavenCentral()
}

dependencies {
  compile group: 'com.google.protobuf', name: 'protobuf-java', version: '3.6.1'
  compile group: 'org.apache.hive', name: 'hive-exec', version: '3.1.1'
}

We first install gradlew

$ gradle wrapper

We can find the jars that contain protobuf classes with

$ ./gradlew findJars --contains "com/google/protobuf/.*class" --configuration compile
...
> Task :findJars
- /<pathToCache>/org.apache.hive/hive-exec/3.1.1/<digest>/hive-exec-3.1.1.jar
- /<pathToCache>/com.google.protobuf/protobuf-java/3.6.1/<digest>/protobuf-java-3.6.1.jar

We can check whether there are conflicts with

$ ./gradlew findJars --find-conflicts --configuration compile --contains "com/google/protobuf/.*.class"
...
> Task :findJars
Jars:
- /<pathToCache>/com.google.protobuf/protobuf-java/3.6.1/<digest>/protobuf-java-3.6.1.jar
- /<pathToCache>/org.apache.hive/hive-exec/3.1.1/<digest>/hive-exec-3.1.1.jar
conflict on:
 - com/google/protobuf/AbstractMessage$Builder.class
 - com/google/protobuf/AbstractMessage.class
 - com/google/protobuf/AbstractMessageLite$Builder$LimitedInputStream.class
 - com/google/protobuf/AbstractMessageLite$Builder.class
 - com/google/protobuf/AbstractMessageLite.class
 - ... (233 more)

All the conflicts can be found with:

$ ./gradlew findJars --find-conflicts --configuration compile
...
> Task :findJars
Jars:
- /<pathToCache>/org.apache.hive/hive-common/3.1.1/<digest>/hive-common-3.1.1.jar
- /<pathToCache>/org.apache.hive/hive-exec/3.1.1/<digest>/hive-exec-3.1.1.jar
conflict on:
 - org/apache/hadoop/hive/ant/GenHiveTemplate.class
 - org/apache/hadoop/hive/common/BlobStorageUtils.class
 - org/apache/hadoop/hive/common/CompressionUtils.class
 - org/apache/hadoop/hive/common/CopyOnFirstWriteProperties.class
 - org/apache/hadoop/hive/common/FileUtils$1.class
 - ... (186 more)
Jars:
- /<pathToCache>/org.apache.hive/hive-exec/3.1.1/<digest>/hive-exec-3.1.1.jar
- /<pathToCache>/org.apache.hive/hive-storage-api/2.7.0/<digest>/hive-storage-api-2.7.0.jar
conflict on:
 - org/apache/hadoop/hive/common/DiskRangeInfo.class
 - org/apache/hadoop/hive/common/Pool$PoolObjectHelper.class
 - org/apache/hadoop/hive/common/Pool.class
 - org/apache/hadoop/hive/common/ValidCompactorWriteIdList.class
 - org/apache/hadoop/hive/common/ValidReadTxnList.class
 - ... (99 more)
Jars:
- /<pathToCache>/org.apache.hive/hive-exec/3.1.1/<digest>/hive-exec-3.1.1.jar
- /<pathToCache>/org.apache.orc/orc-core/1.5.1/<digest>/orc-core-1.5.1.jar
conflict on:
 - org/apache/orc/BinaryColumnStatistics.class
 - org/apache/orc/BooleanColumnStatistics.class
 - org/apache/orc/ColumnStatistics.class
 - org/apache/orc/CompressionCodec$Modifier.class
 - org/apache/orc/CompressionCodec.class
 - ... (380 more)
...

The available options can be listed with:

./gradlew help --task findJars