如何在Android中为文件生成MD5校验和？

Question

在我的应用程序中,我需要为文件生成MD5校验和.你能告诉我是否有办法实现这一目标？

谢谢.

Answer 1

此代码来自CMupdater,来自CyanogenMod 10.2 android ROM.它将下载的ROM测试到更新程序App中.

代码:https://github.com/CyanogenMod/android_packages_apps_CMUpdater/blob/cm-10.2/src/com/cyanogenmod/updater/utils/MD5.java

它就像一个魅力:

/*
 * Copyright (C) 2012 The CyanogenMod Project
 *
 * * Licensed under the GNU GPLv2 license
 *
 * The text of the license can be found in the LICENSE file
 * or at https://www.gnu.org/licenses/gpl-2.0.txt
 */

package com.cyanogenmod.updater.utils;

import android.text.TextUtils;
import android.util.Log;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5 {
    private static final String TAG = "MD5";

    public static boolean checkMD5(String md5, File updateFile) {
        if (TextUtils.isEmpty(md5) || updateFile == null) {
            Log.e(TAG, "MD5 string empty or updateFile null");
            return false;
        }

        String calculatedDigest = calculateMD5(updateFile);
        if (calculatedDigest == null) {
            Log.e(TAG, "calculatedDigest null");
            return false;
        }

        Log.v(TAG, "Calculated digest: " + calculatedDigest);
        Log.v(TAG, "Provided digest: " + md5);

        return calculatedDigest.equalsIgnoreCase(md5);
    }

    public static String calculateMD5(File updateFile) {
        MessageDigest digest;
        try {
            digest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            Log.e(TAG, "Exception while getting digest", e);
            return null;
        }

        InputStream is;
        try {
            is = new FileInputStream(updateFile);
        } catch (FileNotFoundException e) {
            Log.e(TAG, "Exception while getting FileInputStream", e);
            return null;
        }

        byte[] buffer = new byte[8192];
        int read;
        try {
            while ((read = is.read(buffer)) > 0) {
                digest.update(buffer, 0, read);
            }
            byte[] md5sum = digest.digest();
            BigInteger bigInt = new BigInteger(1, md5sum);
            String output = bigInt.toString(16);
            // Fill to 32 chars
            output = String.format("%32s", output).replace(' ', '0');
            return output;
        } catch (IOException e) {
            throw new RuntimeException("Unable to process file for MD5", e);
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                Log.e(TAG, "Exception on closing MD5 input stream", e);
            }
        }
    }
}

Answer 2

将文件内容转换为字符串并使用以下方法:

public static String getMD5EncryptedString(String encTarget){
        MessageDigest mdEnc = null;
        try {
            mdEnc = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            System.out.println("Exception while encrypting to md5");
            e.printStackTrace();
        } // Encryption algorithm
        mdEnc.update(encTarget.getBytes(), 0, encTarget.length());
        String md5 = new BigInteger(1, mdEnc.digest()).toString(16);
        while ( md5.length() < 32 ) {
            md5 = "0"+md5;
        }
        return md5;
    }

请注意,这种简单的方法适用于较小的字符串,但对大文件效率不高.对于后者,请参阅dentex的答案.

Answer 3

这是干净的小 kotlin 扩展函数。也适用于大文件。

fun File.md5(): String {
    val md = MessageDigest.getInstance("MD5")
    return this.inputStream().use { fis ->
        val buffer = ByteArray(8192)
        generateSequence {
            when (val bytesRead = fis.read(buffer)) {
                -1 -> null
                else -> bytesRead
            }
        }.forEach { bytesRead -> md.update(buffer, 0, bytesRead) }
        md.digest().joinToString("") { "%02x".format(it) }
    }
}

以及与之配套的单元测试：

@Test
fun `computes md5 checksum correctly`() {
    val file = File.createTempFile("test-", ".tmp")
    // did md5 on unix machine to comfirm -- put a literal LF at end to compare
    val content = "This is the content of a file." + 0x0a.toChar()
    file.writer().use { w -> w.write(content) }
    assertEquals("a149f5161e873921d84636b2a1b3aad2", file.md5())
}

Answer 4

我有相同的任务,这个代码非常好:

public static String fileToMD5(String filePath) {
    InputStream inputStream = null;
    try {
        inputStream = new FileInputStream(filePath);
        byte[] buffer = new byte[1024];
        MessageDigest digest = MessageDigest.getInstance("MD5");
        int numRead = 0;
        while (numRead != -1) {
            numRead = inputStream.read(buffer);
            if (numRead > 0)
                digest.update(buffer, 0, numRead);
        }
        byte [] md5Bytes = digest.digest();
        return convertHashToString(md5Bytes);
    } catch (Exception e) {
        return null;
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (Exception e) { }
        }
    }
}

private static String convertHashToString(byte[] md5Bytes) {
    String returnVal = "";
    for (int i = 0; i < md5Bytes.length; i++) {
        returnVal += Integer.toString(( md5Bytes[i] & 0xff ) + 0x100, 16).substring(1);
    }
    return returnVal.toUpperCase();
}

Answer 5

如果您正在使用 Okio（如今大多数应用程序直接或间接使用 OkHttp 或 Retrofit），您还可以执行以下操作：

return File(path).source().buffer().use { source ->
   HashingSink.md5(blackholeSink()).use { sink ->
     source.readAll(sink)
     sink.hash.hex()
   }
}

这不必在内存中缓冲整个文件（HashingSink每次write调用都会更新 md5sum，然后向下调用 to blackholeSink()，这对字节没有任何作用）。您也可以使用HashingSource代替来做类似的事情。

Answer 6

public static String getMd5OfFile(String filePath)
{
    String returnVal = "";
    try 
    {
        InputStream   input   = new FileInputStream(filePath); 
        byte[]        buffer  = new byte[1024];
        MessageDigest md5Hash = MessageDigest.getInstance("MD5");
        int           numRead = 0;
        while (numRead != -1)
        {
            numRead = input.read(buffer);
            if (numRead > 0)
            {
                md5Hash.update(buffer, 0, numRead);
            }
        }
        input.close();

        byte [] md5Bytes = md5Hash.digest();
        for (int i=0; i < md5Bytes.length; i++)
        {
            returnVal += Integer.toString( ( md5Bytes[i] & 0xff ) + 0x100, 16).substring( 1 );
        }
    } 
    catch(Throwable t) {t.printStackTrace();}
    return returnVal.toUpperCase();
}

Answer 7

如果你需要计算大文件的MD5，你可能会喜欢使用这个：

进口：

import java.security.MessageDigest;

方法：

 private byte[] calculateMD5ofFile(String location) throws IOException, NoSuchAlgorithmException {
        FileInputStream fs= new FileInputStream(location);
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] buffer=new byte[bufferSize];
        int bytes=0;
        do{
            bytes=fs.read(buffer,0,bufferSize);
            if(bytes>0)
                md.update(buffer,0,bytes);

        }while(bytes>0);
        byte[] Md5Sum = md.digest();
        return Md5Sum;
    }

参考： https://docs.oracle.com/javase/7/docs/api/java/security/MessageDigest.html

将字节数组转换为十六进制。用这个

public static String ByteArraytoHexString(byte[] bytes) {
    StringBuilder hexString = new StringBuilder();
    for (int i = 0; i < bytes.length; i++) {
        String hex = Integer.toHexString(bytes[i] & 0xFF);
        if (hex.length() == 1) {
            hexString.append('0');
        }
        hexString.append(hex);
    }
    return hexString.toString();
}

参考在 Java 中，如何将字节数组转换为十六进制数字字符串，同时保留前导零？