信息摘要，通俗来说，就是信息的指纹。就像人类的指纹是不会重复的一样，使用信息摘要算法计算任何两个不同信息，得出的摘要（指纹）也是不一样的。
这通常用在校验文件是否被修改过，在Web项目中MD5也用在密码加密上。
下面的信息摘要工具类MsgDigest，可以计算文件的MD5、CRC32、SHA1摘要，字符串的MD5、SHA1摘要。
MsgDigest类：
1 package com.dong.framework.tool;
2
3 import java.io.BufferedInputStream;
4 import java.io.File;
5 import java.io.FileInputStream;
6 import java.io.FileNotFoundException;
7 import java.io.IOException;
8 import java.io.InputStream;
9 import java.security.MessageDigest;
10 import java.security.NoSuchAlgorithmException;
11 import java.util.zip.CRC32;
12
13
14 /**
15 * 信息摘要，可以获得CRC32、MD5、SHA-1值
16 * @version 1.0
17 * @author dongliyang
18 */
19 public class MsgDigest {
20
21 /**
22 * 计算文件的32位循环冗余校验和CRC32
23 * @param filepath 文件名
24 * @return String
25 * @throws IOException IOException异常
26 */
27 public static String crc32Digest(String filepath) {
28
29 try {
30
31 InputStream in = new BufferedInputStream(new FileInputStream(filepath));
32 CRC32 crc = new CRC32();
33
34 int c;
35 while((c = in.read()) != -1){
36 crc.update(c);
37 }
38 in.close();
39 return Long.toHexString(crc.getValue());
40 } catch (FileNotFoundException e) {
41 System.out.println("文件未找到异常!");
42 throw new RuntimeException(e.getMessage());
43 } catch (IOException e) {
44 System.out.println("IO异常!");
45 throw new RuntimeException(e.getMessage());
46 }
47
48 }
49
50 /**
51 * 计算文件的32位循环冗余校验和CRC32
52 * @param file 文件
53 * @return String
54 * @throws IOException IOException异常
55 */
56 public static String crc32Digest(File file){
57
58 try {
59
60 InputStream in = new BufferedInputStream(new FileInputStream(file));
61 CRC32 crc = new CRC32();
62
63 int c;
64 while((c = in.read()) != -1){
65 crc.update(c);
66 }
67 in.close();
68 return Long.toHexString(crc.getValue());
69 } catch (FileNotFoundException e) {
70 System.out.println("文件未找到异常!");
71 throw new RuntimeException(e.getMessage());
72 } catch (IOException e) {
73 System.out.println("IO异常!");
74 throw new RuntimeException(e.getMessage());
75 }
76
77
78 }
79
80 /**
81 * 计算字符串的MD5值
82 * @param input 字符串
83 * @return String
84 */
85 public static String md5Digest(String input){
86
87 byte[] data = input.getBytes();
88 try {
89 MessageDigest messageDigest = getMD5();
90 messageDigest.update(data);
91 return toHexString(messageDigest.digest());
92 } catch (NoSuchAlgorithmException e) {
93 System.out.println("MD5算法初始化失败!");
94 throw new RuntimeException(e.getMessage());
95 }
96
97 }
98
99 /**
100 * 计算文件的MD5值
101 * @param filename 文件名
102 * @return String
103 */
104 public static String md5FileDigest(String filepath){
105 String md5 = "";
106 File file = new File(filepath);
107 if(file.exists()){
108 try {
109 MessageDigest messageDigest = getMD5();
110 InputStream in = new BufferedInputStream(new FileInputStream(file));
111 byte[] cache = new byte[CACHE_SIZE];
112 int len;
113 while((len = in.read(cache)) != -1){
114 messageDigest.update(cache, 0, len);
115 }
116 in.close();
117 byte[] data = messageDigest.digest();
118 md5 = toHexString(data);
119 } catch (NoSuchAlgorithmException e) {
120 System.out.println("MD5算法初始化失败!");
121 throw new RuntimeException(e.getMessage());
122 } catch (FileNotFoundException e) {
123 System.out.println("文件未找到异常!");
124 throw new RuntimeException(e.getMessage());
125 } catch (IOException e) {
126 System.out.println("IO异常!");
127 throw new RuntimeException(e.getMessage());
128 }
129 }
130 return md5;
131 }
132
133 /**
134 * 计算文件的MD5值
135 * @param file 文件
136 * @return String
137 */
138 public static String md5FileDigest(File file){
139
140 String md5 = "";
141 if(file.exists()){
142 try {
143 MessageDigest messageDigest = getMD5();
144 InputStream in = new BufferedInputStream(new FileInputStream(file));
145 byte[] cache = new byte[CACHE_SIZE];
146 int len;
147 while((len = in.read(cache)) != -1){
148 messageDigest.update(cache, 0, len);
149 }
150 in.close();
151 byte[] data = messageDigest.digest();
152 md5 = toHexString(data);
153 } catch (NoSuchAlgorithmException e) {
154 System.out.println("MD5算法初始化失败!");
155 throw new RuntimeException(e.getMessage());
156 } catch (FileNotFoundException e) {
157 System.out.println("文件未找到异常!");
158 throw new RuntimeException(e.getMessage());
159 } catch (IOException e) {
160 System.out.println("IO异常!");
161 throw new RuntimeException(e.getMessage());
162 }
163 }
164 return md5;
165 }
166
167 /**
168 * 计算字符串的SHA-1值
169 * @param input 字符串
170 * @return String
171 */
172 public static String sha1Digest(String input){
173
174 byte[] data = input.getBytes();
175 try {
176 MessageDigest messageDigest = getSHA1();
177 messageDigest.update(data);
178 return toHexString(messageDigest.digest());
179 } catch (NoSuchAlgorithmException e) {
180 System.out.println("MD5算法初始化失败!");
181 throw new RuntimeException(e.getMessage());
182 }
183 }
184
185 /**
186 * 计算文件的SHA-1值
187 * @param filepath 文件名
188 * @return String
189 */
190 public static String sha1FileDigest(String filepath){
191
192 String sha1 = "";
193 File file = new File(filepath);
194 if(file.exists()){
195 try {
196 MessageDigest messageDigest = getSHA1();
197 InputStream in = new BufferedInputStream(new FileInputStream(file));
198 byte[] cache = new byte[CACHE_SIZE];
199 int len;
200 while((len = in.read(cache)) != -1){
201 messageDigest.update(cache, 0, len);
202 }
203 in.close();
204 byte[] data = messageDigest.digest();
205 sha1 = toHexString(data);
206 } catch (NoSuchAlgorithmException e) {
207 System.out.println("MD5算法初始化失败!");
208 throw new RuntimeException(e.getMessage());
209 } catch (FileNotFoundException e) {
210 System.out.println("文件未找到异常!");
211 throw new RuntimeException(e.getMessage());
212 } catch (IOException e) {
213 System.out.println("IO异常!");
214 throw new RuntimeException(e.getMessage());
215 }
216 }
217 return sha1;
218 }
219
220 /**
221 * 计算文件的SHA-1值
222 * @param file 文件
223 * @return String
224 */
225 public static String sha1FileDigest(File file){
226
227 String sha1 = "";
228 if(file.exists()){
229 try {
230 MessageDigest messageDigest = getSHA1();
231 InputStream in = new BufferedInputStream(new FileInputStream(file));
232 byte[] cache = new byte[CACHE_SIZE];
233 int len;
234 while((len = in.read(cache)) != -1){
235 messageDigest.update(cache, 0, len);
236 }
237 in.close();
238 byte[] data = messageDigest.digest();
239 sha1 = toHexString(data);
240 } catch (NoSuchAlgorithmException e) {
241 System.out.println("MD5算法初始化失败!");
242 throw new RuntimeException(e.getMessage());
243 } catch (FileNotFoundException e) {
244 System.out.println("文件未找到异常!");
245 throw new RuntimeException(e.getMessage());
246 } catch (IOException e) {
247 System.out.println("IO异常!");
248 throw new RuntimeException(e.getMessage());
249 }
250 }
251 return sha1;
252
253 }
254 /**
255 * 字节数组转换为16进制字符串
256 * @param data 字节数组
257 * @return String
258 */
259 private static String toHexString(byte[] data){
260 StringBuilder digestStr = new StringBuilder();
261 String stmp = "";
262 for(int i = 0;i < data.length; i++){
263 stmp = Integer.toHexString(data[i] & 0XFF);
264 if(stmp.length() == 1){
265 digestStr.append("0" + stmp);
266 }else {
267 digestStr.append(stmp);
268 }
269 }
270 return digestStr.toString();
271 }
272
273 /**
274 * 获取MD5实例
275 * @return MessageDigest
276 * @throws NoSuchAlgorithmException 异常
277 */
278 private static MessageDigest getMD5() throws NoSuchAlgorithmException{
279 return MessageDigest.getInstance(ALGORIGTHM_MD5);
280 }
281
282 private static MessageDigest getSHA1() throws NoSuchAlgorithmException {
283 return MessageDigest.getInstance(ALGORIGTHM_SHA1);
284 }
285
286 /** MD5算法名称 */
287 private static final String ALGORIGTHM_MD5 = "MD5";
288 /** SHA-1算法名称 */
289 private static final String ALGORIGTHM_SHA1 ="SHA-1";
290 /** 字节数组缓存大小 */
291 private static final int CACHE_SIZE = 2048;
292 }
