davisusanibar commented on code in PR #13788:
URL: https://github.com/apache/arrow/pull/13788#discussion_r937770470
##########
docs/source/java/cdata.rst:
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@@ -220,4 +221,252 @@ Let's create a Java class to test our bridge:
C++-allocated array: [1, 2, 3, null, 5, 6, 7, 8, 9, 10]
+Share an Int32 array from Java to C++
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+**Java Side**
+
+For this example, we will build a JAR with all dependencies bundled.
+
+.. 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>cpptojava</artifactId>
+ <version>1.0-SNAPSHOT</version>
+ <properties>
+ <maven.compiler.source>11</maven.compiler.source>
+ <maven.compiler.target>11</maven.compiler.target>
+ <arrow.version>8.0.0</arrow.version>
+ </properties>
+ <repositories>
+ <repository>
+ <id>arrow-nightly</id>
+ <url>https://nightlies.apache.org/arrow/java</url>
+ </repository>
+ </repositories>
+ <dependencies>
+ <dependency>
+ <groupId>org.apache.arrow</groupId>
+ <artifactId>arrow-c-data</artifactId>
+ <version>${arrow.version}</version>
+ </dependency>
+ <dependency>
+ <groupId>org.apache.arrow</groupId>
+ <artifactId>arrow-memory-netty</artifactId>
+ <version>${arrow.version}</version>
+ </dependency>
+ </dependencies>
+ <build>
+ <plugins>
+ <plugin>
+ <groupId>org.apache.maven.plugins</groupId>
+ <artifactId>maven-assembly-plugin</artifactId>
+ <executions>
+ <execution>
+ <phase>package</phase>
+ <goals>
+ <goal>single</goal>
+ </goals>
+ <configuration>
+ <archive>
+ <manifest>
+ <mainClass>
+ ToBeCalledByCpp
+ </mainClass>
+ </manifest>
+ </archive>
+ <descriptorRefs>
+
<descriptorRef>jar-with-dependencies</descriptorRef>
+ </descriptorRefs>
+ </configuration>
+ </execution>
+ </executions>
+ </plugin>
+ </plugins>
+ </build>
+ </project>
+
+.. code-block:: java
+
+ import org.apache.arrow.c.ArrowArray;
+ import org.apache.arrow.c.ArrowSchema;
+ import org.apache.arrow.c.Data;
+ import org.apache.arrow.memory.BufferAllocator;
+ import org.apache.arrow.memory.RootAllocator;
+ import org.apache.arrow.vector.FieldVector;
+ import org.apache.arrow.vector.IntVector;
+ import org.apache.arrow.vector.VectorSchemaRoot;
+
+ import java.util.Arrays;
+
+ public class ToBeCalledByCpp {
+ final static BufferAllocator allocator = new RootAllocator();
+
+ public static void fillVector(long schemaAddress, long arrayAddress){
+ try (ArrowArray arrow_array = ArrowArray.wrap(arrayAddress);
+ ArrowSchema arrow_schema = ArrowSchema.wrap(schemaAddress) ) {
+ Data.exportVector(allocator, populateFieldVectorToExport(),
null, arrow_array, arrow_schema);
+ }
+ }
+
+ public static FieldVector populateFieldVectorToExport(){
+ IntVector intVector = new IntVector("int-to-export", allocator);
+ intVector.allocateNew(3);
+ intVector.setSafe(0, 1);
+ intVector.setSafe(1, 2);
+ intVector.setSafe(2, 3);
+ intVector.setValueCount(3);
+ System.out.println("[Java] FieldVector: \n" + intVector);
+ return intVector;
+ }
+
+ public static void fillVectorSchemaRoot(long schemaAddress, long
arrayAddress){
+ try (ArrowArray arrow_array = ArrowArray.wrap(arrayAddress);
+ ArrowSchema arrow_schema = ArrowSchema.wrap(schemaAddress) ) {
+ Data.exportVectorSchemaRoot(allocator,
populateVectorSchemaRootToExport(), null, arrow_array, arrow_schema);
+ }
+ }
+
+ public static VectorSchemaRoot populateVectorSchemaRootToExport(){
+ IntVector intVector = new IntVector("age-to-export", allocator);
+ intVector.setSafe(0, 10);
+ intVector.setSafe(1, 20);
+ intVector.setSafe(2, 30);
+ VectorSchemaRoot root = new
VectorSchemaRoot(Arrays.asList(intVector));
+ root.setRowCount(3);
+ System.out.println("[Java] VectorSchemaRoot: \n" +
root.contentToTSVString());
+ return root;
+ }
+ }
+
+
+Build the JAR and copy it to the C++ project.
+
+.. code-block:: shell
+
+ $ mvn clean install
+ $ cp target/cpptojava-1.0-SNAPSHOT-jar-with-dependencies.jar <c++ project
path>/cpptojava.jar
+
+**C++ Side**
+
+This application uses JNI to call Java code, but transfers data (zero-copy)
via the C Data Interface instead.
+
+.. code-block:: cpp
+
+ #include <iostream>
+ #include <arrow/api.h>
+ #include <arrow/c/bridge.h>
+ #include <jni.h>
+
+ JNIEnv *CreateVM(JavaVM **jvm) {
+ JNIEnv *env;
+ JavaVMInitArgs vm_args;
+ JavaVMOption options[2];
+ options[0].optionString = "-Djava.class.path=cpptojava.jar"; // java
jar name
+ options[1].optionString = "-DXcheck:jni:pedantic";
+ vm_args.version = JNI_VERSION_1_8;
+ vm_args.nOptions = 2;
+ vm_args.options = options;
+ int status = JNI_CreateJavaVM(jvm, (void **) &env, &vm_args);
+ if (status < 0) {
+ std::cout << "\n<<<<< Unable to Launch JVM >>>>>\n" << std::endl;
+ std::abort();
+ }
+ return env;
+ }
+
+ int main() {
+ JNIEnv *env;
+ JavaVM *jvm;
+ env = CreateVM(&jvm);
+ if (env == nullptr) return 1;
+ jclass javaClassToBeCalledByCpp = NULL;
+ javaClassToBeCalledByCpp = env->FindClass("ToBeCalledByCpp");
+ if (javaClassToBeCalledByCpp != NULL) {
+ jmethodID fillVector = NULL;
Review Comment:
Updated
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