Why Does My Java BufferedWriter Result in Incomplete Writes to a File?

BufferedWriter Incomplete Write Issue

In the provided Java program, the code encounters an issue where the BufferedWriter out fails to completely write all the intended text to the output file nyccrash.sql. This results in incomplete SQL statements and missing data in the output.

The cause of the incomplete write is due to the default buffer size of BufferedWriter, which is set to 8192 characters. This means that the write operations to the BufferedWriter will not be immediately flushed to the underlying file until the buffer reaches its capacity.

In the given scenario, the program processes over 10,000 lines of input data, generating a large amount of SQL strings that exceed the buffer size. Consequently, the buffer becomes full and holds several hundred lines of unwritten data.

To address this issue, it is crucial to manually flush the buffer by calling the close() method on the BufferedWriter after the write operations are complete. This action ensures that all remaining data in the buffer is written to the file before it is closed, resolving the incomplete write problem.

The corrected code below includes the close() call:

...
            while ((line = in.readLine()) != null) {
                String[] esa = line.split(",");
                sqlstr = "insert into nyccrash values (" + esa[0] + ", " + esa[1] + ", " + esa[2] + ", " + esa[3] + ", " + esa[4] + ", " + esa[5] + ", " + esa[6] + ");\n";
                out.write(sqlstr);
            }
            out.close();
        }
...

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