docs/source/java/install.rst

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=======================
Installing Java Modules
=======================

.. contents::

System Compatibility
====================

Java modules are regularly built and tested on macOS and Linux distributions.

Java Compatibility
==================

Java modules are compatible with JDK 8 and above.
Currently, JDK 8, 11, 17, and 18 are tested in CI.

When using Java 9 or later, some JDK internals must be exposed by
adding ``--add-opens=java.base/java.nio=ALL-UNNAMED`` to the ``java`` command:

.. code-block:: shell

   # Directly on the command line
   $ java --add-opens=java.base/java.nio=ALL-UNNAMED -jar ...
   # Indirectly via environment variables
   $ env _JAVA_OPTIONS="--add-opens=java.base/java.nio=ALL-UNNAMED" java -jar ...

Otherwise, you may see errors like ``module java.base does not "opens
java.nio" to unnamed module``.

If using Maven and Surefire for unit testing, :ref:`this argument must
be added to Surefire as well <java-install-maven-testing>`.

Installing from Maven
=====================

By default, Maven will download from the central repository: https://repo.maven.apache.org/maven2/org/apache/arrow/

Configure your pom.xml with the Java modules needed, for example:
arrow-vector, and arrow-memory-netty.

.. code-block:: xml

    <?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>org.example</groupId>
        <artifactId>demo</artifactId>
        <version>1.0-SNAPSHOT</version>
        <properties>
            <arrow.version>9.0.0</arrow.version>
        </properties>
        <dependencies>
            <dependency>
                <groupId>org.apache.arrow</groupId>
                <artifactId>arrow-vector</artifactId>
                <version>${arrow.version}</version>
            </dependency>
            <dependency>
                <groupId>org.apache.arrow</groupId>
                <artifactId>arrow-memory-netty</artifactId>
                <version>${arrow.version}</version>
            </dependency>
        </dependencies>
    </project>

To use the Arrow Flight dependencies, also add the ``os-maven-plugin``
plugin. This plugin generates useful platform-dependent properties
such as ``os.detected.name`` and ``os.detected.arch`` needed to resolve
transitive dependencies of Flight.

.. code-block:: xml

    <?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>org.example</groupId>
        <artifactId>demo</artifactId>
        <version>1.0-SNAPSHOT</version>
        <properties>
            <arrow.version>9.0.0</arrow.version>
        </properties>
        <dependencies>
            <dependency>
                <groupId>org.apache.arrow</groupId>
                <artifactId>flight-core</artifactId>
                <version>${arrow.version}</version>
            </dependency>
        </dependencies>
        <build>
            <extensions>
                <extension>
                    <groupId>kr.motd.maven</groupId>
                    <artifactId>os-maven-plugin</artifactId>
                    <version>1.7.0</version>
                </extension>
            </extensions>
        </build>
    </project>

.. _java-install-maven-testing:

The ``--add-opens`` flag must be added when running unit tests through Maven:

.. code-block:: xml

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>3.0.0-M6</version>
                <configuration>
                        <argLine>--add-opens=java.base/java.nio=ALL-UNNAMED</argLine>
                </configuration>
            </plugin>
        </plugins>
    </build>

Or they can be added via environment variable, for example when executing your code:

.. code-block::

    _JAVA_OPTIONS="--add-opens=java.base/java.nio=ALL-UNNAMED" mvn exec:java -Dexec.mainClass="YourMainCode"

Installing from Source
======================

See :ref:`java-development`.

IDE Configuration
=================

Generally, no additional configuration should be needed.  However,
ensure your Maven or other build configuration has the ``--add-opens``
flag as described above, so that the IDE picks it up and runs tests
with that flag as well.