图片防止篡改部分

第一步，获取图片的md5字符串，并转为字节数组

//将图片使用md5加密

private static byte[] img2Md5Bytes(File file,String salt) throws Exception{

FileInputStream inputStream=new FileInputStream(file);

StringBuilder builder=new StringBuilder();

byte[] bytes=new byte[1024];

int bytesRead;

while ((bytesRead=inputStream.read(bytes))!=-1){

builder.append(new String(bytes,0,bytesRead));

}

inputStream.close();

builder.append(salt);

String md5=md5(builder.toString());

return hexStringToBytes(md5);

}

//16进制转字节数组

private static byte[] hexStringToBytes(String hexString) {

if (hexString == null || hexString.equals("")) {

return null;

}

hexString = hexString.toUpperCase();

int length = hexString.length() / 2;

char[] hexChars = hexString.toCharArray();

byte[] d = new byte[length];

for (int i = 0; i < length; i++) {

int pos = i * 2;

d[i] = (byte) (charToByte(hexChars[pos]) << 6 | charToByte(hexChars[pos + 1]));

}

return d;

}

private static byte charToByte(char c) {

return (byte) "0123456789ABCDEF".indexOf(c);

}

//md5加密字符串

private static String md5(String str) {

try {

MessageDigest md = MessageDigest.getInstance("MD5");

md.update(str.getBytes());

return new BigInteger(1, md.digest()).toString(16);

} catch (Exception e) {

return "";

}

}

第二步，图片末尾加md5字节数组

//图片末尾加md5字节数组

private static void imgAppendMd5Bytes(File file,byte[] md5Bytes) throws Exception{

RandomAccessFile accessFile=new RandomAccessFile(file,"rw");

long length=accessFile.length();

accessFile.seek(length);

accessFile.write(md5Bytes);

accessFile.close();

}

第三步，封装一下

//防止图片被篡改

private static void preventTamper(File file,String salt) throws Exception{

byte[] md5bytes=img2Md5Bytes(file,salt);

imgAppendMd5Bytes(file,md5bytes);

}

图片验证部分

第一步，获取图片的末尾存储的md5字节数组

//获取存储在图片末尾的16个md5字节

public static byte[] popMd5Bytes(File file) throws Exception{

RandomAccessFile accessFile=new RandomAccessFile(file,"rw");

byte[] bytes=new byte[16];

long length=accessFile.length();

accessFile.seek(length-16);

for (int i=0;i<16;i++){

bytes[i]=accessFile.readByte();

}

accessFile.close();

return bytes;

}

第二步，去除图片末尾的16个md5字节后，重新计算图片的md5值

//去除图片末尾的16个md5字节

private static void imgDelEndMd5Bytes(File file) throws Exception{

RandomAccessFile accessFile=new RandomAccessFile(file,"rw");

FileChannel fc = accessFile.getChannel();

fc.truncate(accessFile.length()-16);

fc.close();

accessFile.close();

}

byte[] imgMd5=img2Md5Bytes(file,salt);

第三步，封装为方法

//验证图片是否被篡改

private static boolean notTamper(File file,String salt) throws Exception{

byte[] storageMd5=popMd5Bytes(file);//获取存储在图片末尾的16个md5字节

imgDelEndMd5Bytes(file);//删除末尾md5字节数组

byte[] imgMd5=img2Md5Bytes(file,salt);

return Arrays.equals(storageMd5,imgMd5);

}

简单实现，没有进行调优