根据文件内容前几个字节，判断文件类型<知识点>
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package com.lr.downlaod;import java.io.FileInputStream;public class TestDownload {public static String bytesToHexString(byte[] src) {StringBuilder stringBuilder = new StringBuilder();if (src == null || src.length <= 0) {return null;}for (int i = 0; i < src.length; i++) {int v = src[i] & 0xFF;String hv = Integer.toHexString(v);if (hv.length() < 2) {stringBuilder.append(0);}stringBuilder.append(hv);}return stringBuilder.toString();}public static void main(String[] args) throws Exception {FileInputStream is = new FileInputStream("G://lr//005.jpg");byte[] b = new byte[3];is.read(b, 0, b.length);System.out.println(bytesToHexString(b));}}?
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