Java 8 file read method

I have a method which extracts filedata and converts it into a String array:

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import org.apache.james.mime4j.message.BodyPart;
import org.apache.james.mime4j.message.Message;
import org.apache.james.mime4j.message.Multipart;
import org.apache.james.mime4j.message.TextBody;

protected String[] extractLedesText(byte[] fileData) {
    // Remove the BOM if present
    byte[] array = { (byte) 0xEF, (byte) 0xBB, (byte) 0xBF };
    byte[] data =  { fileData[0], fileData[1], fileData[2] };
    if (fileData.length > 3 && Arrays.equals(data, array)) {
        fileData = ArrayUtils.subarray(fileData, 3, fileData.length-1);            
    }

    String ledes = new String(fileData);
    if (ledes.startsWith("MIME")) {

        try {
            ledes = null;
            Message signed = new Message(new ByteArrayInputStream(fileData));
            for (BodyPart part : ((Multipart) signed.getBody()).getBodyParts()) {
                if (part.getMimeType().equalsIgnoreCase("text/plain")) {
                    TextBody tb = (TextBody) part.getBody();
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    tb.writeTo(baos);
                    return extractLedesText(baos.toByteArray());
                }
            }
            throw new BaseApplicationException(
                    "No MIME part found with MIME type of 'text/plain' while parsing submitted invoice file.");
        } catch (IOException ioe) {
            throw new BaseApplicationException(ioe);
        }
    } else {
        return ledes.split("\\[]");
    }

}

For example, below is the leads file:

LEDES98BI V2[]
INVOICE_DATE|INVOICE_NUMBER|CLIENT_ID|LAW_FIRM_MATTER_ID|INVOICE_TOTAL[]
20150301|INV-Error_Test1|160|LF_MAT_1221|22[]
20150301|INV-Error_Test1|160|LF_MAT_1221|22[]
20150301|INV-Error_Test1|160|LF_MAT_1221|22[]


It looks like extractLedesText() is trying to do three things:

• Strip away any BOM from fileData.

• If this is a MIME message, extract only the TextBody part and pass that recursively into this method again.

• Else just do a split("\\[]") to get our desired String[] array.

So...

Data massaging

You can use a helper method to achieve this:

private static byte[] filterBOM(byte[] fileData) {
    if (fileData.length  3 && Arrays.equals(data, array) ? 
        Arrays.copyRangeOf(fileData, 3, fileData.length) : fileData;
}

I think it may be better to do a fileData.length < 3 check before you construct your data array. Also, I am using the Arrays utility class instead of ArrayUtils to copy part of the array.

Extracting the TextBody from a MIME message

You can make use of try-with-resources for both your ByteArrayInputStream and ByteArrayOutputStream instances, and I suppose this is where we can employ a bit of Stream trickery...

private static byte[] getTextBody(final String ledes) {
    final TextBody tb;
    try (final InputStream input = new ByteArrayInputStream(ledes.getBytes(StandardCharsets.UTF_8))) {
        tb = ((Multipart) new Message(input).getBody()).getBodyParts().stream()
                .filter(part -> part.getMimeType().equalsIgnoreCase("text/plain"))
                .findFirst().orElseThrow(() -> new BaseApplicationException(
                    "No MIME part found with MIME type of 'text/plain' while parsing submitted invoice file."))
                .getBody();
    } catch (IOException e) {
        throw new BaseApplicationException(e);
    }
    try (final ByteArrayOutputStream output = new ByteArrayOutputStream()) {
        tb.writeTo(output);
        return output.toByteArray();
    } catch (IOException e) {
        throw new BaseApplicationException(e);
    }
}

We stream on the List from getBodyParts(), filtering those where their MIME type is "text/plain" and then look for the first matching BodyPart. If there isn't any, we call orElseThrow() with a new BaseApplicationException(...), otherwise we will getBody() and writeTo() your ByteArrayOutputStream. The output of this method is a byte[] array if there are no thrown Exceptions.

Putting it all together

protected String[] extractLedesText(byte[] fileData) {
    final String ledes = new String(filterBOM(fileData));
    return ledes.startsWith("MIME") ? extractLedesText(getTextBody(ledes)) : ledes.split("\\[]");
}

StackExchange Code Review Q#85009, answer score: 3