FastBufferedWriter.flush() does not flush the underlying Writer

[mreid-exiger]

Describe the bug

When using the internally buffered writer, there is no way to flush the underlying Writer. It initially appears this should work, as the when supplying your own Writer, the flushWriter flag is true, which causes the Writer.flush() to be called when a record is completed; but for FastBufferedWriter, only the internal buffer gets flushed, the underlying Writer is never actually flushed:

        @Override
        public void flush() throws IOException {
            writer.write(buf, 0, pos);
            pos = 0;
        }

Arguably you don't want to flush the underlying buffer after each record, but if that's the case, it certainly would be helpful to allow the caller to control when the writer is flushed. Presently the only way to flush the underlying Writer is to close it.

To Reproduce
JUnit test to reproduce the behavior:

@Test
void testFlush() throws Exception {
  CsvWriter csvWriter = CsvWriter.builder().build(new OutputStreamWriter(System.out, "UTF-8"));
  csvWriter.writeRecord("one", "two", "three");
  // Nothing happens until CsvWriter.close() is called
}

Additional context

I suppose its atypical to use System.out as the target of CsvWriter, but I do find that useful, particularly when utilities are being developed I prefer to look at output on the console rather than writing into a file.

[osiegmar]

I don't see where this is a bug.

If you want to use your own writer for whatever reason, just call flush() on that one if you want it to flush. The CsvWriter already sent all the data to it.

OutputStreamWriter writer = new OutputStreamWriter(System.out, "UTF-8");
CsvWriter csvWriter = CsvWriter.builder().build(writer);
csvWriter.writeRecord("one", "two", "three");
writer.flush();

[mreid-exiger]

Certainly this can be worked around with relatively little effort. I reported as a bug as it goes against the typical pattern for wrapping Writers. For example, all wrappers in standard library flush the wrapped writer/stream:

• java.io.BufferedWriter
• java.io.FilterWriter
• java.io.OutputStreamWriter (flushes StreamEncoder)
• java.io.PrinterWriter
• etc.

This remains true for any other I/O wrappers I can remember dealing with in other libraries.

The behavoiur here caught me by surprise as it goes against the rest of the Java ecosystem.

[osiegmar]

All the writer examples you mentioned inherit from java.io.Writer! They are designed to wrap other writers, maintaining the same interface while extending functionality.

In contrast, the CsvWriter is not a writer in the sense of a java.io.Writer inheritor. It does not implement methods like write(char[], int, int), append(char), or many others either. The java.io.Writer class implements the Appendable, Closeable, and Flushable interfaces, whereas I chose to implement only Closeable for the CsvWriter.

Nevertheless, thank you for the feedback. I will consider implementing Flushable in the future and will keep this issue open for now.

[osiegmar]

I've implemented multiple functionality with 0f6bf93.

Implement Flushable interface for CsvWriter to allow flushing the underlying writer

CsvWriter csv = CsvWriter.builder().build(new OutputStreamWriter(System.out, "UTF-8"));
csvWriter.writeRecord("one", "two", "three");

// This would be possible now:
csv.flush();

Implement autoFlush option for CsvWriter to automatically flush the writer after writing a record

CsvWriter csv = CsvWriter.builder()
    .autoFlush(true) // Enable autoFlush
    .build(new OutputStreamWriter(System.out, "UTF-8"));

// Since autoFlush is enabled, the following would automatically flush the writer
csv.writeRecord("one", "two", "three");

Implement toConsole method for CsvWriter to write records to the console

A more convenient way to write records to the console:

CsvWriter csv = CsvWriter.builder().toConsole();

// Since toConsole is used, the following would write the record directly to the console
csv.writeRecord("one", "two", "three");

A release will follow soon.

[mreid-exiger]

Very nice, thanks!