public static String sha256(String s) {
    try {
        return DatatypeConverter.printHexBinary(MessageDigest.getInstance("SHA-256").digest(s.getBytes(StandardCharsets.UTF_8))).toLowerCase();
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }
    return null;
}

在Java 8中

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Scanner;
import javax.xml.bind.DatatypeConverter;


Scanner scanner = new Scanner(System.in);
String password = scanner.nextLine();
scanner.close();

MessageDigest digest = null;
try {
    digest = MessageDigest.getInstance("SHA-256");
} catch (NoSuchAlgorithmException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
byte[] hash = digest.digest(password.getBytes(StandardCharsets.UTF_8));
String encoded = DatatypeConverter.printHexBinary(hash);        
System.out.println(encoded.toLowerCase());

String hashWith256(String textToHash) {
    MessageDigest digest = MessageDigest.getInstance("SHA-256");
    byte[] byteOfTextToHash = textToHash.getBytes(StandardCharsets.UTF_8);
    byte[] hashedByetArray = digest.digest(byteOfTextToHash);
    String encoded = Base64.getEncoder().encodeToString(hashedByetArray);
    return encoded;
}

如果你使用的是Java 8，你可以这样编码字节[]

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(text.getBytes(StandardCharsets.UTF_8));
String encoded = Base64.getEncoder().encodeToString(hash);

完整的例子哈希字符串作为另一个字符串。

public static String sha256(final String base) {
    try{
        final MessageDigest digest = MessageDigest.getInstance("SHA-256");
        final byte[] hash = digest.digest(base.getBytes("UTF-8"));
        final StringBuilder hexString = new StringBuilder();
        for (int i = 0; i < hash.length; i++) {
            final String hex = Integer.toHexString(0xff & hash[i]);
            if(hex.length() == 1) 
              hexString.append('0');
            hexString.append(hex);
        }
        return hexString.toString();
    } catch(Exception ex){
       throw new RuntimeException(ex);
    }
}

SHA-256不是“编码”——它是单向哈希。

你基本上可以将字符串转换为字节(例如使用text.getBytes(StandardCharsets.UTF_8))，然后哈希字节。注意，哈希的结果也可能是任意二进制数据，如果你想在字符串中表示它，你应该使用base64或十六进制…不要尝试使用String(byte[]， String)构造函数。

e.g.

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] hash = digest.digest(text.getBytes(StandardCharsets.UTF_8));