The following guides explain the fundamental data structures used in the Java implementation of Apache Arrow.
Generated javadoc documentation is available here.
git submodule update --init --recursive # Needed for flight cd java mvn install
Arrow Cpp must be built before this step. The cpp build directory must be provided as the value for argument arrow.cpp.build.dir. eg.
cd java mvn install -P arrow-jni -am -Darrow.cpp.build.dir=../../release
The gandiva library is still in Alpha stages, and subject to API changes without deprecation warnings.
Arrow uses Google's Flatbuffers to transport metadata. The java version of the library requires the generated flatbuffer classes can only be used with the same version that generated them. Arrow packages a version of the arrow-vector module that shades flatbuffers and arrow-format into a single JAR. Using the classifier “shade-format-flatbuffers” in your pom.xml will make use of this JAR, you can then exclude/resolve the original dependency to a version of your choosing.
There are several system/environmental variables that users can configure. These trade off safety (they turn off checking) for speed. Typically they are only used in production settings after the code has been thoroughly tested without using them.
Bounds Checking for memory accesses: Bounds checking is on by default. You can disable it by setting either the system property(“arrow.enable_unsafe_memory_access”) or the environmental variable (“ARROW_ENABLE_UNSAFE_MEMORY_ACCESS”) to “true”. When both the system property and the environmental variable are set, the system property takes precedence.
null checking for gets: ValueVector get methods (not getObject) methods by default verify the slot is not null. You can disable it by setting either the system property(“arrow.enable_null_check_for_get”) or the environmental variable (“ARROW_ENABLE_NULL_CHECK_FOR_GET”) to “false”. When both the system property and the environmental variable are set, the system property takes precedence.
java.lang.UnsupportedOperationException: sun.misc.Unsafe or java.nio.DirectByteBuffer.(long, int) not available. thrown by netty.
StructVectorenable “-Darrow.struct.conflict.policy=CONFLICT_APPEND”. Duplicate fields are ignored (
CONFLICT_REPLACE) by default and overwritten. To support different policies for conflicting or duplicate fields set this JVM flag or use the correct static constructor methods for
Arrow Java follows the Google style guide here with the following differences:
VariableDeclarationUsageDistancedue to the existing code base. These rules should be followed when possible.
Refer to `java/dev/checkstyle/checkstyle.xml for rule specifics.
When running tests, Arrow Java uses the Logback logger with SLF4J. By default, it uses the logback.xml present in the corresponding module's src/test/resources directory, which has the default log level set to INFO. Arrow Java can be built with an alternate logback configuration file using the following command run in the project root directory:
See Logback Configuration for more details.
Integration tests which require more time or more memory can be run by activating the
integration-tests profile. This activates the maven failsafe plugin and any class prefixed with
IT will be run during the testing phase. The integration tests currently require a larger amount of memory (>4GB) and time to complete. To activate the profile:
mvn -Pintegration-tests <rest of mvn arguments>