davisusanibar commented on a change in pull request #136: URL: https://github.com/apache/arrow-cookbook/pull/136#discussion_r809969275
########## File path: java/source/io.rst ########## @@ -0,0 +1,542 @@ +.. _arrow-io: + +======================== +Reading and writing data +======================== + +The `Arrow IPC format <https://arrow.apache.org/docs/java/ipc.html>`_ defines two types of binary formats +for serializing Arrow data: the streaming format and the file format (or random access format). Such files can +be directly memory-mapped when read. + +.. contents:: + +Writing +======= + +Both writing file and streaming formats use the same API. + +Writing Random Access Files +*************************** + +Write - Out to File +------------------- + +.. testcode:: + + import org.apache.arrow.memory.RootAllocator; + import org.apache.arrow.vector.VarCharVector; + import org.apache.arrow.vector.IntVector; + import org.apache.arrow.vector.types.pojo.Field; + import org.apache.arrow.vector.types.pojo.FieldType; + import org.apache.arrow.vector.types.pojo.ArrowType; + import org.apache.arrow.vector.types.pojo.Schema; + import org.apache.arrow.vector.VectorSchemaRoot; + import static java.util.Arrays.asList; + import org.apache.arrow.vector.ipc.ArrowFileWriter; + + import java.io.File; + import java.io.FileOutputStream; + import java.io.IOException; + + try (RootAllocator rootAllocator = new RootAllocator(Long.MAX_VALUE)) { + Field name = new Field("name", FieldType.nullable(new ArrowType.Utf8()), null); + Field age = new Field("age", FieldType.nullable(new ArrowType.Int(32, true)), null); + Schema schemaPerson = new Schema(asList(name, age)); + try(VectorSchemaRoot vectorSchemaRoot = VectorSchemaRoot.create(schemaPerson, rootAllocator)){ + VarCharVector nameVector = (VarCharVector) vectorSchemaRoot.getVector("name"); + nameVector.allocateNew(3); + nameVector.set(0, "David".getBytes()); + nameVector.set(1, "Gladis".getBytes()); + nameVector.set(2, "Juan".getBytes()); + IntVector ageVector = (IntVector) vectorSchemaRoot.getVector("age"); + ageVector.allocateNew(3); + ageVector.set(0, 10); + ageVector.set(1, 20); + ageVector.set(2, 30); + vectorSchemaRoot.setRowCount(3); + File file = new File("randon_access_to_file.arrow"); + try (FileOutputStream fileOutputStream = new FileOutputStream(file); + ArrowFileWriter writer = new ArrowFileWriter(vectorSchemaRoot, null, fileOutputStream.getChannel()) + ) { + writer.start(); + for (int i = 0; i < 10; i++) { + // All the data that is going to write comes from the root and as we were not changing root data we are writing the same data 10x times Review comment: In this case the data are containing two columns and 3 rows per columns is assigned to the root holder. In this case with writer.writeBatch() one batch were added with 3 records. We put a for to show how another 09 batch were added with the same 3 records each, it is because that root was not changed. Please let me know if after this comment is needed to delete the for.. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
