ReadBinaryNIO2.java

/*
    ReadBinaryNIO2.java
    Dave Klick
    CIS 260
    2014-01-29
    
    In-class demonstration of new Java NIO features
    for reading binary data files.
*/
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class ReadBinaryNIO2 {
    public static void main(String[] args) {
        
        if (args.length == 0) {
            // No command line arguments were supplied
            System.out.println("Usage: java ReadBinaryNIO2 filelist");
        } else {
            for (String filename : args) {
                System.out.println("Specs for: " + filename);
                Path file = Paths.get(filename);
                if (!Files.exists(file)) {
                    System.err.println("File does not exist");
                    continue;  // skip rest of loop, process next argument
                }
                try {
                    // Files.readAllBytes will handle opening and closing
                    // the file - even if there are errors
                    byte[] buffer = Files.readAllBytes(file);
                    
                    // the & 0xFF eliminates the "sign" of the byte
                    if ((buffer[0x00] & 0xFF) == 0xCA) {
                        // this match indicates a Java class file
                        System.out.println("Match - Java class file");
                    } else {
                        // this indicates the file was not a Java class file
                        System.out.println("No match - not a Java class file");
                    }
                    System.out.println();
                } catch (IOException e) {
                    System.out.println("Error reading file");
                }
            }
        }
    }
}