Avoid create 0byte files

example/config_avoid_create_0byte_file.yml

@@ -0,0 +1,55 @@
+hdfs_example: &hdfs_example
+  config_files:
+    - /etc/hadoop/conf/core-site.xml
+    - /etc/hadoop/conf/hdfs-site.xml
+  config:
+    fs.defaultFS: 'hdfs://hadoop-nn1:8020'
+    fs.hdfs.impl: 'org.apache.hadoop.hdfs.DistributedFileSystem'
+    fs.file.impl: 'org.apache.hadoop.fs.LocalFileSystem'
+
+local_fs_example: &local_fs_example
+  config:
+    fs.defaultFS: 'file:///'
+    fs.hdfs.impl: 'org.apache.hadoop.fs.RawLocalFileSystem'
+    fs.file.impl: 'org.apache.hadoop.fs.RawLocalFileSystem'
+    io.compression.codecs: 'org.apache.hadoop.io.compress.GzipCodec,org.apache.hadoop.io.compress.DefaultCodec,org.apache.hadoop.io.compress.BZip2Codec'
+
+exec:
+  min_output_tasks: 10
+
+in:
+  type: file
+  path_prefix: example/data
+  parser:
+    charset: UTF-8
+    newline: CRLF
+    type: csv
+    delimiter: ','
+    quote: '"'
+    header_line: true
+    stop_on_invalid_record: true
+    columns:
+    - {name: id, type: long}
+    - {name: account, type: long}
+    - {name: time, type: timestamp, format: '%Y-%m-%d %H:%M:%S'}
+    - {name: purchase, type: timestamp, format: '%Y%m%d'}
+    - {name: comment, type: string}
+
+
+out:
+  type: hdfs
+  <<: *local_fs_example
+  path_prefix: /tmp/embulk-output-hdfs_example/file_
+  file_ext: csv
+  delete_in_advance: FILE_ONLY
+  formatter:
+    type: csv
+    newline: CRLF
+    newline_in_field: LF
+    header_line: false
+    charset: UTF-8
+    quote_policy: NONE
+    quote: '"'
+    escape: '\'
+    null_string: ''
+    default_timezone: UTC

src/main/java/org/embulk/output/hdfs/HdfsFileOutputPlugin.java

@@ -122,30 +122,28 @@ public TransactionalFileOutput open(TaskSource taskSource, final int taskIndex)
         {
             private final List<String> hdfsFileNames = new ArrayList<>();
             private int fileIndex = 0;
+            private Path currentPath = null;
             private OutputStream output = null;
 
             @Override
             public void nextFile()
             {
                 closeCurrentStream();
-                Path path = new Path(pathPrefix + String.format(sequenceFormat, taskIndex, fileIndex) + pathSuffix);
-                try {
-                    FileSystem fs = getFs(task);
-                    output = fs.create(path, task.getOverwrite());
-                    logger.info("Uploading '{}'", path);
-                }
-                catch (IOException e) {
-                    logger.error(e.getMessage());
-                    throw new RuntimeException(e);
-                }
-                hdfsFileNames.add(path.toString());
+                currentPath = new Path(pathPrefix + String.format(sequenceFormat, taskIndex, fileIndex) + pathSuffix);
                 fileIndex++;
             }
 
             @Override
             public void add(Buffer buffer)
             {
                 try {
+                    // this implementation is for creating file when there is data.
+                    if (output == null) {
+                        FileSystem fs = getFs(task);
+                        output = fs.create(currentPath, task.getOverwrite());
+                        logger.info("Uploading '{}'", currentPath);
+                        hdfsFileNames.add(currentPath.toString());
+                    }
                     output.write(buffer.array(), buffer.offset(), buffer.limit());
                 }
                 catch (IOException e) {