Display values of MS-DOS Portable Executable header

Main.java

// Needs Guava to compile:
//
// compile group: 'com.google.guava', name: 'guava', version: '23.4-jre'
//
import com.google.common.io.LittleEndianDataInputStream;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.stream.IntStream;

import static java.util.stream.Collectors.joining;

public class Main {

	// from: http://www.ntcore.com/files/inject2exe.htm#TheMSDOSdata2_1
	private final static List<HeaderField> msdosHeaderFields = Arrays.asList(
			new HeaderField("e_magic", "c2", "Magic number 'MZ'"),
			new HeaderField("e_cblp", "s", "Bytes on last page of file"),
			new HeaderField("e_cp", "s", "Pages in file"),
			new HeaderField("e_crlc", "s", "Relocations"),
			new HeaderField("e_cparhdr", "s", "Size of header in paragraphs"),
			new HeaderField("e_minalloc", "s", "Minimum extra paragraphs needed"),
			new HeaderField("e_maxalloc", "s", "Maximum extra paragraphs needed"),
			new HeaderField("e_ss", "s", "Initial (relative) SS value"),
			new HeaderField("e_sp", "s", "Initial SP value"),
			new HeaderField("e_csum", "s", "Checksum"),
			new HeaderField("e_ip", "s", "Initial IP value"),
			new HeaderField("e_cs", "s", "Initial (relative) CS value"),
			new HeaderField("e_lfarlc", "s", "File address of relocation table"),
			new HeaderField("e_ovno", "s", "Overlay number"),
			new HeaderField("e_res", "c8", "Reserved ss"),
			new HeaderField("e_oemid", "s", "OEM identifier (for e_oeminfo)"),
			new HeaderField("e_oeminfo", "s", "OEM information; e_oemid specific"),
			new HeaderField("e_res2", "c20", "Reserved ss"),
			new HeaderField("e_lfanew", "l", "File address of the new exe header")
	);

	public static void main(String[] args) throws IOException {
		if (args.length != 1) {
			System.err.println("usage: " + System.getProperty("sun.java.command") + " program.com");
			System.exit(1);
		}

		String comProgramFilename = args[0];

		// Data in COM and PE file headers is always stored using little-endian convention.
		// This means that an int whose value is 0x11223344 will
		// be represented with bytes 0x44 0x33 0x22 0x11 in exactly that order.
		// In other words little-endian conventions tell us that we should store
		// LSB first and MSB last.
		// Here we use LittleEndianDataInputStream from Guava library.
		try (LittleEndianDataInputStream dataInputStream =
					 new LittleEndianDataInputStream(new FileInputStream(comProgramFilename))) {

			for (HeaderField field : msdosHeaderFields) {
				switch (field.type) {
					case "s":
						print(field.name, String.format("0x%04x",
								Short.toUnsignedInt(dataInputStream.readShort())),
								field.comment);
						break;

					case "l":
						print(field.name,
								String.format("0x%08x", dataInputStream.readInt()),
								field.comment);
						break;

					default: // cN - format
						int numberOfBytes = Integer.parseInt(field.type.substring(1));

						String hexString = IntStream.range(0, numberOfBytes)
								.mapToObj(i -> {
									try {
										byte c = dataInputStream.readByte();
										return String.format("%02x", Byte.toUnsignedInt(c));
									} catch (IOException e) {
										throw new RuntimeException(e);
									}
								})
								.collect(joining(" "));

						print(field.name, hexString, field.comment);
						break;
				}
			}
		}
	}

	private static void print(String fieldName, String fieldValue, String comment) {
		System.out.printf("%16s: %-16s // %s%n", fieldName, fieldValue, comment);
	}

	private static class HeaderField {
		public final String name;

		/** s - short, l - long, cN - N characters */
		public final String type;
		public final String comment;

		public HeaderField(String fieldName, String fieldSize, String comment) {
			this.name = fieldName;
			this.type = fieldSize;
			this.comment = comment;
		}
	}
}