如何在Java中使用哈希sha256生成哈希代码？

Question

I would like to know the code to do this in java please?

This is what i have so far but it does not work?

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import static jdk.nashorn.tools.ShellFunctions.input;

public class Sha256hash 
{

    public static String main(String[] args) throws NoSuchAlgorithmException 
    {
        MessageDigest md = MessageDigest.getInstance("SHA1");
            md.reset();
            byte[] buffer = input.getBytes("UTF-8");
            md.update(buffer);
            byte[] digest = md.digest();

            String hexStr = "";
            for (int i = 0; i < digest.length; i++) {
                hexStr +=  Integer.toString( ( digest[i] & 0xff ) + 0x100, 16).substring( 1 );
            }
            return hexStr;
    }

}

Answer 1

I'm still unclear whether you want SHA-1 or SHA-256, so let's abstract the problem; firstly, an encode method to take a byte[] and return the hex (don't worry, you already wrote it; but I would prefer a StringBuilder over String concatenation. Java String is immutable , so you're creating garbage for later garbage collection with + ) -

private static String encodeHex(byte[] digest) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < digest.length; i++) {
        sb.append(Integer.toString((digest[i] & 0xff) + 0x100, 16).substring(1));
    }
    return sb.toString();
}

Next, we can create a method that takes the algorithm name and the String to digest and returns that digest. Like

public static String digest(String alg, String input) {
    try {
        MessageDigest md = MessageDigest.getInstance(alg);
        byte[] buffer = input.getBytes("UTF-8");
        md.update(buffer);
        byte[] digest = md.digest();
        return encodeHex(digest);
    } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
        e.printStackTrace();
        return e.getMessage();
    }
}

Then we can get a SHA-1 or a SHA-256 hash like

public static void main(String[] args) {
    System.out.println(digest("SHA1", ""));
    System.out.println(digest("SHA-256", ""));
}

Which outputs (as expected)

da39a3ee5e6b4b0d3255bfef95601890afd80709
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Answer 2

The main entry point can not return String. Furthermore, input is not declared. You maybe want to change the name of your function to generate with input as a parameter.

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import static jdk.nashorn.tools.ShellFunctions.input;

public class Sha256hash 
{

    public static String generate(String input) throws NoSuchAlgorithmException 
    {
        MessageDigest md = MessageDigest.getInstance("SHA1");
            md.reset();
            byte[] buffer = input.getBytes("UTF-8");
            md.update(buffer);
            byte[] digest = md.digest();

            String hexStr = "";
            for (int i = 0; i < digest.length; i++) {
                hexStr +=  Integer.toString( ( digest[i] & 0xff ) + 0x100, 16).substring( 1 );
            }
            return hexStr;
    }

}

This example works for me returning c3499c2729730a7f807efb8676a92dcb6f8a3f8f as result of processing the string example :

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Sha256hash 
{

    public static String generate(String input) throws NoSuchAlgorithmException, UnsupportedEncodingException 
    {
        MessageDigest md = MessageDigest.getInstance("SHA1");
            md.reset();
            byte[] buffer = input.getBytes("UTF-8");
            md.update(buffer);
            byte[] digest = md.digest();

            String hexStr = "";
            for (int i = 0; i < digest.length; i++) {
                hexStr +=  Integer.toString( ( digest[i] & 0xff ) + 0x100, 16).substring( 1 );
            }
            return hexStr;
    }

}

Main:

import java.io.UnsupportedEncodingException;
import java.security.NoSuchAlgorithmException;

public class Tester {
    public static void main(String[] args) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        String someText = "example";
        System.out.println(Sha256hash.generate(someText));
    }
}

Finally, as Elliott has pointed out If you want to use SHA-256 you should change MessageDigest.getInstance("SHA1"); to MessageDigest.getInstance("SHA256") ; Right now you are using SHA-1. Also pointed by Elliot you should use StringBuilder in the loop for improved efficiency.