[I] [java] Is there a way to get the length of the data from bytes at a small system cost? [arrow-java]

["zzzzming95 (via GitHub)" <gi...@apache.org>]

zzzzming95 opened a new issue, #138:
URL: https://github.com/apache/arrow-java/issues/138

   ### Describe the usage question you have. Please include as many useful details as  possible.
   
   
   [java] Is there a way to get the length of the data from bytes at a small system cost?
   
   Like the arrow doc example, https://arrow.apache.org/docs/java/ipc.html#writing-and-reading-streaming-format
   
   We generate the arrow data to bytes[] and transfer it.
   
   ```
     ByteArrayOutputStream out = new ByteArrayOutputStream();
   
     // create VectorSchemaRoot
     List<Field> fields = Arrays.asList(encodedVector.getField());
     List<FieldVector> vectors = Arrays.asList(encodedVector);
     try (VectorSchemaRoot root = new VectorSchemaRoot(fields, vectors)) {
   
         // write data
         ArrowStreamWriter writer = new ArrowStreamWriter(root, provider, Channels.newChannel(out));
         writer.start();
         writer.writeBatch();
         writer.end();
     }
   
     // gen arrow data as bytep[]
     out.toByteArray()
   ```
   
   I want to get the data length with a small system load(cpu mem).
   
   Now i using this way to get data lengeh:
   
   ```
               ByteArrayInputStream input = new ByteArrayInputStream(out.toByteArray());
               ReadChannel readChannel = new ReadChannel(Channels.newChannel(input));
               MessageMetadataResult messageMeta = MessageSerializer.readMessage(readChannel);
               RecordBatch recordBatch =
                       (RecordBatch) messageMeta.getMessage().header(new RecordBatch());
               input.close();
               readChannel.close();
   
               // get data length
               recordBatch.length()
   ```
   
   
   Is there documentation to guide me on what to do? thanks~
   
   
   
   ### Component(s)
   
   Java


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