Cannot Figure Out This Syntax Error

[Natalie Kopple]

Would you please help?

I just cannot figure out the syntax error saying: "This method must return a result of type byte[]" at

private static byte[] transformDocument( byte[] data ) { ...} 

where I do have a byte[] return type specified.

The problem may be a result of some mistakes made elsewhere, therefore, I would like to show more code:

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.StringWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.net.MalformedURLException;
import java.net.URL;

public class ABC 
{
	private static URL url;
	
    public ABC() {
    }

    public static void main(String args[]) throws Exception
    {
        // create file object    
    	File file = new File(".\\src\\ConvertedFromOriginal.xml");
    	// convert the XML file to a byte array
    	byte[] data = getBytesFromFile( file );
    	url = new URL( ".\\src\\Style.xsl" );
    	// convert the XML byte array to a text array
    	byte[] text = transformDocument( data );
    	// write out the text byte array
    	writeByteArrayToFile( text );
   	}
    
    private static byte[] getBytesFromFile( File file ) throws IOException {
        FileInputStream is = new FileInputStream( file );
    
        // Get the size of the file
        long length = file.length();
    
        if (length > Integer.MAX_VALUE) {
        	System.out.println("File is to larger");
        }
    
        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];
    
        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while (offset < bytes.length
               && ( numRead = is.read( bytes, offset, bytes.length-offset ) ) >= 0 ) 
        {
            offset += numRead;
        }
    
        // Ensure all the bytes have been read in
        if ( offset < bytes.length ) {
            throw new IOException("Could not completely read file " + file.getName() );
        }
    
        // Close the input stream and return bytes
        is.close();
        return bytes;
    } 

    private static byte[] transformDocument( byte[] data ) {  // The syntax error occurred at this line
        String xml = new String( data );
        try {
            XSLTUtils util = new XSLTUtils();
            String xslt = util.transform( xml, url );
            return xslt.getBytes();
        } catch ( Exception e ) {
        	e.printStackTrace();
        }
    }
                        
    private static void writeByteArrayToFile( byte[] text ) {
    	
    	BufferedOutputStream bos = null;
    	try {
    		/*
   			 * Write byte array to a file using the
   			 * public void write(byte[] b) method of BufferedOutputStream class.
   			 */
    		bos.write( text );
		} catch(FileNotFoundException fnfe) {
			System.out.println("Specified file not found" + fnfe);
		} catch(IOException ioe) {
			System.out.println("Error while writing file" + ioe);
		}
		finally	{
			if(bos != null)
			{
				try	{
					//flush the BufferedOutputStream
					bos.flush();
					//close the BufferedOutputStream
					bos.close(); 
				}
				catch(Exception e){
					e.printStackTrace();
				}
			}
		}
	}
}

[Paul Clapham]

Natalie Kopple wrote:Would you please help?

I just cannot figure out the syntax error saying: "This method must return a result of type byte[]" at

private static byte[] transformDocument( byte[] data ) { ...} 

where I do have a byte[] return type specified.

It doesn't mean that you have to declare it to return byte[]. Clearly you already did that. It means that the code must always return a result of type byte[], and your code doesn't always do that.

[fred rosenberger]

if you look at the method:

private static byte[] transformDocument( byte[] data ) {  // The syntax error occurred at this line  
        String xml = new String( data );  
        try {  
            XSLTUtils util = new XSLTUtils();  
            String xslt = util.transform( xml, url );  
            return xslt.getBytes();  
        } catch ( Exception e ) {  
            e.printStackTrace();  
        }  
    }  

What will it return if an exception is thrown?

[Natalie Kopple]

Thanks a lot. I have figured it out.

[Paul Clapham]

Figured it out? Good! But I'm curious about what you did to fix the problem. I have a solution in mind and I'd be interested to see if it's the same as yours.

[Natalie Kopple]

Please comment:

    private static byte[] transformDocument( byte[] data ) {
        String xml = new String( data );
        String xslt = null;
        try {
            XSLTUtils util = new XSLTUtils();
            xslt = util.transform( xml, url );
        } catch ( MalformedURLException mue ) {
        	System.out.println( "Malformed URL : " + mue.getMessage());
        } catch (IOException ioe ) {
        	System.out.println( "File operation error : " + ioe.getMessage());
        } catch ( TransformerConfigurationException tce ) {
        	System.out.println( "Transformer configuration error : " + tce.getMessageAndLocation() );
        } catch ( TransformerException te ){
        	System.out.println( "Transformer error : " + te.getMessageAndLocation() );
        }
        return xslt.getBytes();        	
    }

[Matthew Brown]

OK. What's going to happen on line 16 if an exception was thrown? What will be the value of xslt at that point?

[Paul Clapham]

Or to put it another way, my solution is very different from yours. Here's mine:

private static byte[] transformDocument( byte[] data ) throws Exception {
        String xml = new String( data );  
        XSLTUtils util = new XSLTUtils();  
        String xslt = util.transform( xml, url );  
        return xslt.getBytes();  
}  

Why do you think I did it that way?

[Natalie Kopple]

Sorry, I do not know why. And I cannot answer "what to return in case that an exception is thrown?"

[Matthew Brown]

OK, going into a bit more detail - in your last example, if any exception is thrown then xslt will still be null. Which means that when you reach line 16, you're going to get a NullPointerException thrown.

The question you need to ask yourself is: what do I want the method to do in case of error? I reckon there are three plausible options.
1. Return null
2. Return an empty array
3. Throw an exception

Paul's suggestion is to go for option 3. In that case you just throw the exception up to the calling code, and let it decide what to do. This looks sensible to me because the calling code is going to have a better idea about what should be done in the event of error. This utility method doesn't really know enough about the context to know what to do next.

If you want to use 1 or 2, you can do that with a small modification to your code, but you need to allow for the problem I pointed out above.

(By the way - where is the url variable coming from? I'd suggest that should be passed into the method as an argument rather than reliying on a static variable - unless it's a constant).

[Natalie Kopple]

Thanks very much for all the feedbacks.

I have been coding but do not really understand how to deal with exceptions. Fortunately, I came to the Forum and raised a question about my code. I can see better now.

The "url" is the location of a XSL file. Is it qualified to be a constant?

[Paul Clapham]

Natalie Kopple wrote:Sorry, I do not know why. And I cannot answer "what to return in case that an exception is thrown?"

Then that's why. If you don't know what to return from a method if an exception is thrown, then that method isn't qualified to handle exceptions. So it shouldn't handle exceptions. Hence my code.

[Matthew Brown]

Natalie Kopple wrote:The "url" is the location of a XSL file. Is it qualified to be a constant?

I can't tell you. That entirely depends on the application. Is it always going to be the same XSL file? Are you happy having to recompile the application in order to use a different file location? If not, then no, it shouldn't be a constant.