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java.security.MessageDigest

MessageDigest的含义

message含义是:消息,信息

digest的含义是

digest
必应词典
n.摘要；文摘；概要；汇编
v.消化；领会；领悟；理解
海词
n. 摘要
vt. 消化；理解
vi. 消化
金山词霸
v.
消化; 理解
n.
摘要; 文摘
有道
v.
理解，领悟；消化
n.
文摘，摘要；分解物，提炼物

所以 MessageDigest 可以理解为 消息消化

额,不是.

应该是 信息摘要 或 数据摘要

它能将很大的信息(数据)(文件)通过某种算法(algorithm),简化为简短的内容, 用于判断大数据是否相同.

动态获取 MessageDigest 所支持的算法名称

java.security.Security.getAlgorithms("MessageDigest"); 可获得算法名称的Set<String>集合 , 参数为"MessageDigest",不区分大小写

java.util.Set<String> messageDigest_AlgorithmNames_Set = java.security.Security.getAlgorithms("MessageDigest"); //不区分大小写

java.util.Set<String> messageDigest_AlgorithmNames_Set = java.security.Security.getAlgorithms("messagedigest"); //不区分大小写

示例

public class Try动态获取MessageDigest支持的算法名称列表 {static Integer numA = 1;static public void main(String...arguments)throws Exception{java.util.Set<String> messageDigest_AlgorithmNames_Set = java.security.Security.getAlgorithms("messagedigest");
//		java.util.Set<String> messageDigest_AlgorithmNames_Set = java.security.Security.getAlgorithms("MessageDigest");System.out.println("MessageDigest的算法种类个数为: "+messageDigest_AlgorithmNames_Set.size() + " , 分别为👇");messageDigest_AlgorithmNames_Set.forEach(算法名称->{System.out.println(numA+++".\t\t"+算法名称);});		}
}

控制台输出👇 (JDK17)

MessageDigest的算法种类个数为: 13 , 分别为👇
1.		SHA3-512
2.		SHA-1
3.		SHA-384
4.		SHA3-384
5.		SHA-224
6.		SHA-512/256
7.		SHA-256
8.		MD2
9.		SHA-512/224
10.		SHA3-256
11.		SHA-512
12.		MD5
13.		SHA3-224

获取 MessageDigest 的实例

MessageDigest 的实例由 MessageDigest.getInstance(x) 方法获得;
一个MessageDigest实例只能指定一种算法;

MessageDigest md_SHA3512   = MessageDigest.getInstance("SHA3-512");
MessageDigest md_SHA1      = MessageDigest.getInstance("SHA-1");
MessageDigest md_SHA384    = MessageDigest.getInstance("SHA-384");
MessageDigest md_SHA3384   = MessageDigest.getInstance("SHA3-384");
MessageDigest md_SHA224    = MessageDigest.getInstance("SHA-224");
MessageDigest md_SHA512256 = MessageDigest.getInstance("SHA-512/256");
MessageDigest md_SHA256    = MessageDigest.getInstance("SHA-256");
MessageDigest md_MD2       = MessageDigest.getInstance("MD2");
MessageDigest md_SHA512224 = MessageDigest.getInstance("SHA-512/224");
MessageDigest md_SHA3256   = MessageDigest.getInstance("SHA3-256");
MessageDigest md_SHA512    = MessageDigest.getInstance("SHA-512");
MessageDigest md_MD5       = MessageDigest.getInstance("MD5");
MessageDigest md_SHA3224   = MessageDigest.getInstance("SHA3-224");

将byte数组计算为Hash

MessageDigest 通过 update 和 digest 方法, 将一个或多个byte[]数组计算为Hash摘要

digest(byte[] input) 是一步到位的方法, 直接计算出input数组的Hash, 但是有一个问题, 数组索引是int, int<=Integer.MAX; 大概2G多, 所以对很大的文件无能为力.

digest(byte[] input) 的源码👇

public byte[] digest(byte[] input) {update(input);return digest();}

可看出也是分为两步, 第一步是update(input), 将数组放入MessageDigest,
让后再digest()计算.
实际上update方法可以多次调用,
所以可以将大文件用缓存数组buffer拆分成多段用update放入
而且update有个现成的重载:update(byte[] input, int offset, int len)

示例

				FileInputStream is = new FileInputStream(pathStr);MessageDigest digest = MessageDigest.getInstance("SHA-256");byte[] bf = new byte[10240];int numRead;do {numRead = is.read(bf);if (numRead > 0) {digest.update(bf, 0, numRead);}} while (numRead != -1);is.close();byte[] resultByteArray = digest.digest();

得到的结果还是byte数组, 可将其转为16进制

将digest的结果数组转为16进制

假设已得到结果: resultByteArray

将其转为16进制的办法

    public static String bytesToHex(byte[] bytes) {StringBuilder sb = new StringBuilder();for (int i = 0; i < bytes.length; i++) {sb.append(String.format("%02x", bytes[i]));}return sb.toString();}String resultHex = bytesToHex(resultByteArray)

小写

public static String hexLowerCaseFromByteArray(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)>>>4)).append(simple.charAt(b<<28>>>28));}return sb.toString();}String resultHex = bytesToHex(resultByteArray)

大写

	public static String hexUpperCaseFromByteArray(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)>>>4)).append(simple.charAt(b<<28>>>28));}return sb.toString();}String resultHex = bytesToHex(resultByteArray)

	public static String hexLowerCaseFromByteArray2(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)/16)).append(simple.charAt((b&0xff)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray2(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)/16)).append(simple.charAt((b&0xff)%16));}return sb.toString();}

	public static String hexLowerCaseFromByteArray3(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&255)/16)).append(simple.charAt((b&255)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray3(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&255)/16)).append(simple.charAt((b&255)%16));}return sb.toString();}

	public static String hexLowerCaseFromByteArray4(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {int i=b>=0?b:b+256;sb.append(simple.charAt(i/16)).append(simple.charAt(i%16));}return sb.toString();}public static String hexUpperCaseFromByteArray4(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {int i=b>=0?b:b+256;sb.append(simple.charAt(i/16)).append(simple.charAt(i%16));}return sb.toString();}

	public static String hexLowerCaseFromByteArray5(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt(Byte.toUnsignedInt(b)/16)).append(simple.charAt(Byte.toUnsignedInt(b)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray5(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt(Byte.toUnsignedInt(b)/16)).append(simple.charAt(Byte.toUnsignedInt(b)%16));}return sb.toString();}

测试

package 将byte数组转为16进制字符串的方法;import java.awt.FileDialog;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.FileInputStream;
import java.security.MessageDigest;import javax.swing.JFrame;public class ByteArrayToHexString {public static String hexLowerCaseFromByteArray(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)>>>4)).append(simple.charAt(b<<28>>>28));}return sb.toString();}public static String hexUpperCaseFromByteArray(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)>>>4)).append(simple.charAt(b<<28>>>28));}return sb.toString();}public static String hexLowerCaseFromByteArray2(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)/16)).append(simple.charAt((b&0xff)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray2(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&0xff)/16)).append(simple.charAt((b&0xff)%16));}return sb.toString();}public static String hexLowerCaseFromByteArray3(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&255)/16)).append(simple.charAt((b&255)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray3(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt((b&255)/16)).append(simple.charAt((b&255)%16));}return sb.toString();}public static String hexLowerCaseFromByteArray4(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {int i=b>=0?b:b+256;sb.append(simple.charAt(i/16)).append(simple.charAt(i%16));}return sb.toString();}public static String hexUpperCaseFromByteArray4(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {int i=b>=0?b:b+256;sb.append(simple.charAt(i/16)).append(simple.charAt(i%16));}return sb.toString();}public static String hexLowerCaseFromByteArray5(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789abcdef";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt(Byte.toUnsignedInt(b)/16)).append(simple.charAt(Byte.toUnsignedInt(b)%16));}return sb.toString();}public static String hexUpperCaseFromByteArray5(byte[] byteArray) {if(byteArray==null)return null;String simple = "0123456789ABCDEF";StringBuilder sb = new StringBuilder(byteArray.length*2);for(byte b : byteArray) {sb.append(simple.charAt(Byte.toUnsignedInt(b)/16)).append(simple.charAt(Byte.toUnsignedInt(b)%16));}return sb.toString();}public static String hexLowerCaseFromByteArray6(byte[] byteArray) {if(byteArray==null)return null;StringBuilder sb = new StringBuilder();for (int i = 0; i < byteArray.length; i++) {sb.append(String.format("%02x", byteArray[i]));}return sb.toString();}public static void main(String...arguments)throws Exception{JFrame frame = new JFrame(Thread.currentThread().getStackTrace()[1].getClassName());frame.addWindowListener(new WindowAdapter() {@Override public void windowClosing(WindowEvent ev) {System.exit(0);}});FileDialog fDialog = new FileDialog(frame);fDialog.setVisible(true);if(fDialog.getFile()!=null) {String pathFile = fDialog.getDirectory()+fDialog.getFile();FileInputStream is = new FileInputStream(pathFile);MessageDigest digest = MessageDigest.getInstance("SHA-256");byte[] bf = new byte[10240];int numRead;do {numRead = is.read(bf);if (numRead > 0) {digest.update(bf, 0, numRead);}} while (numRead != -1);is.close();byte[] resultByteArray = digest.digest();String result;result = hexLowerCaseFromByteArray(resultByteArray); System.out.println(result);result = hexUpperCaseFromByteArray(resultByteArray); System.out.println(result);result = hexLowerCaseFromByteArray2(resultByteArray); System.out.println(result);result = hexUpperCaseFromByteArray2(resultByteArray); System.out.println(result);result = hexLowerCaseFromByteArray3(resultByteArray); System.out.println(result);result = hexUpperCaseFromByteArray3(resultByteArray); System.out.println(result);result = hexLowerCaseFromByteArray4(resultByteArray); System.out.println(result);result = hexUpperCaseFromByteArray4(resultByteArray); System.out.println(result);result = hexLowerCaseFromByteArray5(resultByteArray); System.out.println(result);result = hexUpperCaseFromByteArray5(resultByteArray); System.out.println(result);result = hexLowerCaseFromByteArray6(resultByteArray); System.out.println(result);}System.exit(0);}}

一些应用例子

例1

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.FileInputStream;
import java.security.MessageDigest;
import java.util.*;import javax.swing.*;//import javax.swing.JButton;public class SHA_MD_MessageDigest_230528 extends Frame{/*** */private static final long serialVersionUID = 5242216018207119189L;static void pln(Object o) {System.out.println(o);}public final SHA_MD_MessageDigest_230528 I;public final TextArea resultLowercaseShow = new TextArea("这里展示小写结果");public final TextArea resultUppercaseShow = new TextArea("这里展示大写结果");public final HashMap<String, MessageDigest> DigestGroup = new HashMap<>();public final LinkedHashMap<String, Panel> ButtonForComputedGroup  = new LinkedHashMap<>();{Set<String> set = java.security.Security.getAlgorithms("MessageDigest"); //获得支持的格式ArrayList<String> nmAl = new ArrayList<>(set);nmAl.sort((o1,o2)->o1.compareTo(o2));try {for(String nm : set) {DigestGroup.put(nm, MessageDigest.getInstance(nm));}nmAl.forEach(nm->{ButtonForComputedGroup.put(nm, new Btn(nm));});}catch(Exception ex) {ex.printStackTrace();}}//constructor 构造方法在此public SHA_MD_MessageDigest_230528() {I=this;setTitle("文件校验, 点击按钮选择文件 ");addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {I.dispose();System.exit(0);}});setLayout(new GridLayout(3, 0, 1, 3));Panel up = new Panel(); add(up); up.setBackground(Color.DARK_GRAY);Panel panel010 = new Panel(); add(panel010);
//		Panel panel020 = new Panel(); add(panel020);JPanel panel020 = new JPanel(); add(panel020);ButtonForComputedGroup.forEach((lb,btn)->{up.add(btn);});panel010.setLayout(new BorderLayout(200,200));  panel010.add(resultLowercaseShow);System.out.println(panel020.getLayout());panel020.setLayout(new BorderLayout());panel020.add(resultUppercaseShow);setBounds(258, 235, 1600, 666);setVisible(true);
//		show();}public static void main(String ags[]) {new SHA_MD_MessageDigest_230528();}void computed(String nm) {pln(nm);String lowercaseMapping = "0123456789abcdef" , uppercaseMapping = lowercaseMapping.toUpperCase();FileDialog fileDialog = new FileDialog(this, "选择要生成Hash的文件", FileDialog.LOAD);fileDialog.setVisible(true);String directoryStr = fileDialog.getDirectory() , fileStr = fileDialog.getFile();if(directoryStr!=null && fileStr!=null) {try {String pathStr = directoryStr+fileStr;resultLowercaseShow.setText("正在计算  "+pathStr+"   的"+nm+"值");FileInputStream is = new FileInputStream(pathStr);MessageDigest digest = DigestGroup.get(nm);byte[] bf = new byte[10240];int numRead;do {numRead = is.read(bf);if (numRead > 0) {digest.update(bf, 0, numRead);}} while (numRead != -1);is.close();bf = digest.digest();StringBuilder sb = new StringBuilder(bf.length*2);for(byte b : bf) {int idx1=(b&0xff)>>>4 , idx2=b<<28>>>28;pln("idx1="+idx1+"      idx2="+idx2);sb.append(lowercaseMapping.charAt(idx1)).append(lowercaseMapping.charAt(idx2));}String hexLower = sb.toString();resultLowercaseShow.setText(hexLower);sb = new StringBuilder(bf.length*2);for(byte b : bf) {int idx1=(b&0xff)>>>4 , idx2=b<<28>>>28;pln("idx1="+idx1+"      idx2="+idx2);sb.append(uppercaseMapping.charAt(idx1)).append(uppercaseMapping.charAt(idx2));}String hexUpper = sb.toString();resultUppercaseShow.setText(hexUpper);}catch(Throwable ex) {ex.printStackTrace(); resultLowercaseShow.setText(ex.toString()); }}}class Btn extends Panel{/*** 镶嵌在Panel中的Button*/private static final long serialVersionUID = -3494086542207800072L;public final Button btn;Btn(String label){super();this.setBackground(Color.blue);
//			setLayout(new BorderLayout());setLayout(null);setSize(210,60);btn = new Button(label);switch (label) {case"MD5","SHA-256": btn.setForeground(Color.BLUE); break;case"SHA-512": btn.setForeground(Color.WHITE);btn.setBackground(new Color(0,168,255)); break;}btn.setBounds(5, 5, 200, 50);setFont(new Font("宋体", Font.CENTER_BASELINE, 25));btn.addActionListener(ev->{computed(btn.getActionCommand());});add(btn);}}}