java的class文件的magic number, cafebabe

java的class文件的前4个字节叫做magic number,

用来识别是否为java的class文件.

package pkg;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * @author qefee.com
 *
 */
public class MagicNumber {

	public static void main(String[] args) {
		String pathname = "./bin/pkg/MagicNumber.class";
		File file = new File(pathname);

		FileInputStream fis = null;
		try {
			fis = new FileInputStream(file);

			int magicNumber = 0;

			magicNumber = fis.read();
			magicNumber = (magicNumber << 8) ^ fis.read();
			magicNumber = (magicNumber << 8) ^ fis.read();
			magicNumber = (magicNumber << 8) ^ fis.read();

			String magicNumberString = Integer.toHexString(magicNumber);

			System.out.println(magicNumber);
			System.out.println(magicNumberString);

		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fis != null) {
				try {
					fis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}
}

或者

package pkg;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * @author qefee.com
 *
 */
public class MagicNumber {

	public static void main(String[] args) {
		String pathname = "./bin/pkg/MagicNumber.class";
		File file = new File(pathname);

		FileInputStream fis = null;
		try {
			fis = new FileInputStream(file);

			System.out.print(Integer.toHexString(fis.read()));
			System.out.print(Integer.toHexString(fis.read()));
			System.out.print(Integer.toHexString(fis.read()));
			System.out.print(Integer.toHexString(fis.read()));
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (fis != null) {
				try {
					fis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

}

输出

cafebabe