Java determine whether two files are identical

    How to use Java to determine whether two files are identical it? My approach is

(1) first compares the content length of the two documents;

(2) In the case of the same length, the MD5 value and then compare two files.

     Jar package need to be introduced:

        <dependency>
            <groupId>commons-codec</groupId>
            <artifactId>commons-codec</artifactId>
            <version>1.11</version>
        </dependency>

     Provides a function to verify whether two files are the same byte stream:

 / ** 
     * verify whether the stream is equal to two bytes of the file 
     * @return Boolean equal to true 
     * @throws IOException
      * / 
    Private  static  Boolean isSameFiles ( byte [] fileByte1, byte [] fileByte2) { 
        String firstFileMd5 = DigestUtils.md5Hex (fileByte1) ; 
        String secondFileMd5 = DigestUtils.md5Hex (fileByte2);
         IF (firstFileMd5.equals (secondFileMd5)) { 
            System.out.println ( "---- ------ MD5 the equals" + firstFileMd5);
             return  to true ; 
        }else {
            System.out.println(firstFileMd5 + " is firstFileMd5 ++ unequal ++ secondFileMd5 = " + secondFileMd5);
            return false;
        }
    }

Check whether a base64 string of bits equal to the file

      Transferred directly to the string into a byte array, and then calls the function isSameFiles.

public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        String img = "iVBORw0KGgoAAAANSUhEUgAAApsAAAEPCAYAAAANjQ + sAAAOqUlEQVR4Xu3WMREAAAgDMerfNCp CwI65Bh + + + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt 5wgQIECAAAECBAhEAot2zRIgQIAAAQIECBA4sekJCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + + + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQ gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJtIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + + + gAABAgQIECBAIBMQmxmt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + + + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt +gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + + + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGx gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJtmdEaJkCAAAECBAgQEJt + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAABsekHCBAgQIAAAQIEMgGxmdEaJkCAAAECBAgQEJt + + + gAABAgQIECBAIBMQmxmtYQIECBAgQIAAAbHpBwgQIECAAAECBDIBsZnRGiZAgAABAgQIEBCbfoAAAQIECBAgQCATEJsZrWECBAgQIECAAAGx6QcIECBAgAABAgQyAbGZ0RomQIAAAQIECBAQm36AAAECBAgQIEAgExCbGa1hAgQIECBAgAAB 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";

        String imgReal = "iVBOI=";

        BASE64Decoder decoder = new BASE64Decoder();
        if (isBase64(img)) {
            System.out.println("img is base 64");
        }
        if (isBase64(imgReal)) {
            System.out.println("imgReal is base 64");
        }
        byte[] imageByteArray = null;
        try {
            imageByteArray = decoder.decodeBuffer(img);
            System.out.println(isSameFiles(imageByteArray, decoder.decodeBuffer(imgReal)));
        } catch (IOException e) {
            e.printStackTrace();
        }

        System.out.println(chechFile());
    }

Checking whether two documents are equal 2

     After reading the file, converts it into a byte stream:

    /**
     * 检查两个文件是否相等，假设 C:\Users\Pictures目录下有两个图片文件
     * @return boolean true 相等
     * @throws IOException
     */
    private static boolean chechFile() throws IOException {
        File file1 = new File("C:\\Users\\Pictures\\test1.jpg");
        File file2 = new File("C:\\Users\\Pictures\\test2.jpg");
        if (file1.length() != file2.length()) {
            System.out.println("+++++++++ unequal +++++++++++++");
            return false;
        }
        InputStream fileStream1 = new FileInputStream(file1);
        InputStream fileStream2 = new FileInputStream(file2);
//        InputStream 转 byte[]
        byte[] imageByteArray = new byte[fileStream1.available()];
        System.out.println(isSameFiles(imageByteArray, new byte[fileStream2.available()]));
        return true;
    }

 

     以上方法验证小文件妥妥的，大文件请移步：《JAVA MD5 验证大文件(改)》

Reference

https://blog.csdn.net/wxz980927155/article/details/82257225

https://www.cnblogs.com/DylanZ/p/6269042.html