[GitHub] [arrow-cookbook] amol- commented on a change in pull request #136: [Java]: Java cookbook for create arrow read/write IPC format

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amol- commented on a change in pull request #136:
URL: https://github.com/apache/arrow-cookbook/pull/136#discussion_r809885738



##########
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:
       This makes the recipe just more confusing. If we have 3 rows why writing 10? It just confusing.
   Also the for should probably get the length from the `vectorSchemaRoot` as in the standard case you want to write the content of a table, not a random number of rows




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