"Go" Java compute hash value of the file

Original address: http://blog.csdn.net/qq_25646191/article/details/78863110

How do I know if a file has changed? Of course, with the method of comparing file hash value, file hash is called file signature, even if a bit in the file is changed, the file hash will be different.

The more commonly used file hash algorithms are MD5 and SHA-1.
I am using the MD5 algorithm, in Java, the calculation MD5 can be used messagedigest this class.

Here's the code:

[Java]View plain copy

Package com.test;
Import Java.io.FileInputStream;
Import java.io.FileNotFoundException;
Import Java.io.InputStream;
Import Java.math.BigInteger;
Import Java.security.MessageDigest;
Public class Md5util {
public static void Main (string[] args) {
try {
//Here I'm testing the MD5 value of my native JDK source file
String FilePath = "C:\\Program Files\\java\\jdk1.7.0_45\\src.zip";
String Md5hashcode = Md5hashcode (FilePath);
String md5hashcode32 = md5hashcode32 (FilePath);
System.out.println (Md5hashcode + ": MD5 value of the file");
System.out.println (md5hashcode32+": MD5 value of the file 32 bits");
//system.out.println ( -100 & 0xff);
} catch (FileNotFoundException e) {
E.printstacktrace ();
}
}
/** 
* Get the MD5 value of the file, it may not be 32-bit
* @param filePath file path
* @return
* @throws FileNotFoundException
*/
public static string Md5hashcode (String FilePath) throws filenotfoundexception{
FileInputStream FIS = new FileInputStream (FilePath);
return Md5hashcode (FIS);
}
/** 
* Ensure that the MD5 value of the file is 32 bits
* @param filePath file path
* @return
* @throws FileNotFoundException
*/
public static string Md5hashcode32 (String FilePath) throws filenotfoundexception{
FileInputStream FIS = new FileInputStream (FilePath);
return md5hashcode32 (FIS);
}
/** 
* Java gets the MD5 value of the file
* @param FIS Input stream
* @return
*/
public static String Md5hashcode (InputStream fis) {
try {
//Get a MD5 converter, if you want to use SHA-1 or SHA-256, pass in sha-1,sha-256
MessageDigest MD = messagedigest.getinstance ("MD5");
//several times to read a file in, for large files, it is recommended this way, less memory consumption.
byte[] buffer = new byte[1024];
int length =-1;
While (length = fis.read (buffer, 0, 1024x768))! =-1) {
Md.update (buffer, 0, length);
}
Fis.close ();
//Convert and return a byte array containing 16 elements, returning a numeric range of 128 to 127
byte[] md5bytes = Md.digest ();
BigInteger bigInt = new BigInteger (1, md5bytes); 1 stands for absolute value
return bigint.tostring (+); Convert to 16 binary
} catch (Exception e) {
E.printstacktrace ();
return "";
}
}
/** 
* Java Compute file 32-bit MD5 value
* @param FIS Input stream
* @return
*/
public static String md5hashcode32 (InputStream fis) {
try {
//Get a MD5 converter, if you want to use SHA-1 or SHA-256, pass in sha-1,sha-256
MessageDigest MD = messagedigest.getinstance ("MD5");
//several times to read a file in, for large files, it is recommended this way, less memory consumption.
byte[] buffer = new byte[1024];
int length =-1;
While (length = fis.read (buffer, 0, 1024x768))! =-1) {
Md.update (buffer, 0, length);
}
Fis.close ();
//Convert and return a byte array containing 16 elements, returning a numeric range of 128 to 127
byte[] md5bytes = Md.digest ();
StringBuffer hexvalue = new StringBuffer ();
For (int i = 0; i < md5bytes.length; i++) {
int val = ((int) md5bytes[i]) & 0xFF; Explanation See the bottom
if (Val < ) {
/** 
* If less than 16, then the 16 binary form of the Val value must be a bit,
* Because the decimal 0,1...9,10,11,12,13,14,15 corresponds to the 16 binary for the 0,1...9,a,b,c,d,e,f;
* The high point is 0.
*/
Hexvalue.append ("0");
}
//Here is the use of the integer class method to achieve the conversion of 16 binary
Hexvalue.append (Integer.tohexstring (Val));
}
return hexvalue.tostring ();
} catch (Exception e) {
E.printstacktrace ();
return "";
}
}
/** 
* Method Md5hashcode32 ((int) md5bytes[i]) & 0xFF operation Explanation:
* Some operations that involve byte array data in the Java language, often see Byte[i] & 0xFF, here is a summary of what is included here:
* 1, 0xFF is 16 binary (decimal is 255), it is shaped by default, bits is 32 bits, the lowest eight bits is "1111 1111", the remaining 24 bits are 0.
* 2, & arithmetic: If 2 bit is 1, then 1, otherwise 0;
* 3, Byte[i] & 0xFF: First, this operation is generally in the process of transferring the byte data into int or other shaping data, and using this operation, the final shaping data is only 8 bits with data and the other bits are 0.
* 4, the operation of the resulting shaping data is greater than or equal to 0 and less than or equal to 255
*/
}

Running results such as:

PS: In fact, there is one more important point, is how to know that their generated MD5 value is correct?

A lot of methods, in fact, there is a very simple method, do not need to install what software.

Use the command that comes with Windows: Certutil-hashfile [File path] MD5,

Examples are as follows:

"Go" Java compute hash value of the file