=================

Apache^® DataSketches™ Core Java Library Component

This is the core Java component of the DataSketches library. It contains all of the sketching algorithms and can be accessed directly from user applications.

This component is also a dependency of other components of the library that create adaptors for target systems, such as the Apache Pig adaptor and the Apache Hive adaptor.

Note that we have a parallel core components for C++ and Python implementations of the same sketch algorithms.

Please visit the main DataSketches website for more information.

If you are interested in making contributions to this site please see our Community page for how to contact us.

Maven Build Instructions

NOTE: This component accesses resource files for testing. As a result, the directory elements of the full absolute path of the target installation directory must qualify as Java identifiers. In other words, the directory elements must not have any space characters (or non-Java identifier characters) in any of the path elements. This is required by the Oracle Java Specification in order to ensure location-independent access to resources: See Oracle Location-Independent Access to Resources

A JDK8 with Hotspot or JDK11 with Hotspot is required to compile

This component depends on the datasketches-memory component, and, as a result, must be compiled with one of the above JDKs. If your application only relies on the APIs of this component no special JVM arguments are required. However, if your application also directly relies on the APIs of the datasketches-memory component, you may need additional JVM arguments. Please refer to the datasketches-memory README for details.

If your application uses Maven, you can also use the pom.xml of this component as an example of how to automatically configure the JVM arguments for compilation and testing based on the version of the JDK.

Recommended Build Tool

This DataSketches component is structured as a Maven project and Maven is the recommended Build Tool.

To run normal unit tests:

$ mvn clean test

To install jars built from the downloaded source:

$ mvn clean install -DskipTests=true

This will create the following jars:

• datasketches-java-X.Y.Z.jar The compiled main class files.
• datasketches-java-X.Y.Z-tests.jar The compiled test class files.
• datasketches-java-X.Y.Z-sources.jar The main source files.
• datasketches-java-X.Y.Z-test-sources.jar The test source files
• datasketches-java-X.Y.Z-javadoc.jar The compressed Javadocs.

Dependencies

Run-time

There is one run-time dependency:

• org.apache.datasketches : datasketches-memory

Testing

See the pom.xml file for test dependencies.

Special Build / Test Instructions for Eclipse

Building and running tests using JDK 8 should not be a problem.

However, with JDK 9+, and Eclipse versions up to and including 4.22.0 (2021-12), Eclipse fails to translate the required JPMS JVM arguments specified in the POM compiler or surefire plugins into the .classpath file, causing illegal reflection access errors eclipse-m2e/m2e-core Bug 543631.

There are two ways to fix this:

Method 1: Manually update .classpath file:

Open the .classpath file in a text editor and find the following classpathentry element (this assumes JDK11, change to suit):

    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">
        <attributes>
            <attribute name="module" value="true"/>
            <attribute name="maven.pomderived" value="true"/>
        </attributes>
    </classpathentry>

Then edit it as follows:

    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11">
        <attributes>
            <attribute name="module" value="true"/>
            <attribute name="add-exports" value="java.base/jdk.internal.misc=ALL-UNNAMED:java.base/jdk.internal.ref=ALL-UNNAMED"/>
            <attribute name="add-opens" value="java.base/java.nio=ALL-UNNAMED:java.base/sun.nio.ch=ALL-UNNAMED"/>
            <attribute name="maven.pomderived" value="true"/>
        </attributes>
    </classpathentry>

Finally, refresh.

Method 2: Manually update Module Dependencies

In Eclipse, open the project Properties / Java Build Path / Module Dependencies ...

• Select java.base
• Select Configured details
• Select Expose Package...
  • Enter Package = java.nio
  • Enter Target module = ALL-UNNAMED
  • Select button: opens
  • Hit OK
• Select Expose Package...
  • Enter Package = jdk.internal.misc
  • Enter Target module = ALL-UNNAMED
  • Select button: exports
  • Hit OK
• Select Expose Package...
  • Enter Package = jdk.internal.ref
  • Enter Target module = ALL-UNNAMED
  • Select button: exports
  • Hit OK
• Select Expose Package...
  • Enter Package = sun.nio.ch
  • Enter Target module = ALL-UNNAMED
  • Select button: opens
  • Hit OK

NOTE: If you execute Maven/Update Project... from Eclipse with the option Update project configuration from pom.xml checked, all of the above will be erased, and you will have to redo it.

Known Issues

SpotBugs

• Make sure you configure SpotBugs with the /tools/FindBugsExcludeFilter.xml file. Otherwise, you may get a lot of false positive or low risk issues that we have examined and eliminated with this exclusion file.