Java – SHAおよびMD5を使用してファイルチェックサムを作成する
この記事では、SHA-256およびMD5アルゴリズムを使用してファイルのチェックサムを生成する方法を示します。
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MessageDigest.getInstance(“algorithm”)
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Apache Commons Codec
1. メッセージダイジェスト
d:\server.log
hello world
1.1 Generate a file checksum with a SHA256 algorithm.
FileCheckSumSHA.java
package com.example.hashing;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
public class FileCheckSumSHA {
public static void main(String[] args) throws NoSuchAlgorithmException, IOException {
MessageDigest md = MessageDigest.getInstance("SHA-256"); //SHA, MD2, MD5, SHA-256, SHA-384...
String hex = checksum("d:\\server.log", md);
System.out.println(hex);
}
private static String checksum(String filepath, MessageDigest md) throws IOException {
// file hashing with DigestInputStream
try (DigestInputStream dis = new DigestInputStream(new FileInputStream(filepath), md)) {
while (dis.read() != -1) ; //empty loop to clear the data
md = dis.getMessageDigest();
}
// bytes to hex
StringBuilder result = new StringBuilder();
for (byte b : md.digest()) {
result.append(String.format("%02x", b));
}
return result.toString();
}
}
出力
b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9
1.2 Generate a file checksum with a MD5 algorithm.
FileCheckSumMD5.java
package com.example.hashing;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
public class FileCheckSumMD5 {
public static void main(String[] args) throws NoSuchAlgorithmException, IOException {
MessageDigest md = MessageDigest.getInstance("MD5");
String hex = checksum("d:\\server.log", md);
System.out.println(hex);
}
private static String checksum(String filepath, MessageDigest md) throws IOException {
// DigestInputStream is better, but you also can hash file like this.
try (InputStream fis = new FileInputStream(filepath)) {
byte[] buffer = new byte[1024];
int nread;
while ((nread = fis.read(buffer)) != -1) {
md.update(buffer, 0, nread);
}
}
// bytes to hex
StringBuilder result = new StringBuilder();
for (byte b : md.digest()) {
result.append(String.format("%02x", b));
}
return result.toString();
}
}
出力
5eb63bbbe01eeed093cb22bb8f5acdc3
2. Apache Commons Codec
pom.xml
commons-codec commons-codec 1.11
2.1 File checksum.
FileCheckSum.java
package com.example.hashing;
import org.apache.commons.codec.digest.DigestUtils;
import java.io.FileInputStream;
import java.io.IOException;
public class App {
public static void main(String[] args) throws IOException {
String checksumSHA256 = DigestUtils.sha256Hex(new FileInputStream("d:\\server.log"));
System.out.println("checksumSHA256 : " + checksumSHA256);
String checksumMD5 = DigestUtils.md5Hex(new FileInputStream("d:\\server.log"));
System.out.println("checksumMD5 : " + checksumMD5);
}
}
出力
checksumSHA256 : b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9 checksumMD5 : 5eb63bbbe01eeed093cb22bb8f5acdc3