code: public void writer(String bucketName, String blobName) throws IOException {
      // [START writer]
      BlobId blobId = BlobId.of(bucketName, blobName);
      byte[] content = "Hello, World!".getBytes(UTF_8);
      BlobInfo blobInfo = BlobInfo.newBuilder(blobId).setContentType("text/plain").build();
      try (WriteChannel writer = storage.writer(blobInfo)) {
        try {
          writer.write(ByteBuffer.wrap(content, 0, content.length));
        } catch (Exception ex) {
          // handle exception
        }
      }
      // [END writer]
    }
docs: [VARIABLE "my_blob_name"]