security
Calculate the CRC Sum of a file
With this example we are going to demonstrate how to calculate the CRC Sum of a file. The Cyclic Redundancy Check is a good way to detect errors and changes to data. In short, in order to calculate the CRC-32 Sum of a file we implemented four different methods :
- The
checksumInputStream(String filepath)
method creates a FileInputStream by opening a connection to the file. - The
checksumBufferedInputStream(String filepath)
method creates a BufferedInputStream to save the input stream. - The
checksumRandomAccessFile(String filepath)
method creates a RandomAccessFile to read from the file. The mode argument is set for reading only. - The
checksumMappedFile(String filepath)
method uses a MappedByteBuffer to map the file directly into memory in a Read-only mode, through its FileChannel. - In all methods a new CRC32 Object is created. The CRC32 Object is updated for every byte read from each file. The methods are invoked in a main() method and return the CRC32 value of the same file.
Note that for each method implementation time is also calculated, as shown in the output.
Let’s take a look at the code snippets and the result output that follow:
001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 | package com.javacodegeeks.snippets.core; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; import java.util.zip.CRC32; public class Main { public static long checksumInputStream(String filepath) throws IOException { InputStream inputStreamn = new FileInputStream(filepath); CRC32 crc = new CRC32(); int cnt; while ((cnt = inputStreamn.read()) != - 1 ) { crc.update(cnt); } return crc.getValue(); } public static long checksumBufferedInputStream(String filepath) throws IOException { InputStream inputStream = new BufferedInputStream( new FileInputStream(filepath)); CRC32 crc = new CRC32(); int cnt; while ((cnt = inputStream.read()) != - 1 ) { crc.update(cnt); } return crc.getValue(); } public static long checksumRandomAccessFile(String filepath) throws IOException { RandomAccessFile randAccfile = new RandomAccessFile(filepath, "r" ); long length = randAccfile.length(); CRC32 crc = new CRC32(); for ( long i = 0 ; i < length; i++) { randAccfile.seek(i); int cnt = randAccfile.readByte(); crc.update(cnt); } return crc.getValue(); } public static long checksumMappedFile(String filepath) throws IOException { FileInputStream inputStream = new FileInputStream(filepath); FileChannel fileChannel = inputStream.getChannel(); int len = ( int ) fileChannel.size(); MappedByteBuffer buffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0 , len); CRC32 crc = new CRC32(); for ( int cnt = 0 ; cnt < len; cnt++) { int i = buffer.get(cnt); crc.update(i); } return crc.getValue(); } public static void main(String[] args) throws IOException { String filepath = "C:/Users/nikos7/Desktop/output.txt" ; System.out.println( "Input Strea method:" ); long start_timer = System.currentTimeMillis(); long crc = checksumInputStream(filepath); long end_timer = System.currentTimeMillis(); System.out.println(Long.toHexString(crc)); System.out.println((end_timer - start_timer) + " ms" ); System.out.println( "///////////////////////////////////////////////////////////" ); System.out.println( "Buffered Input Stream method:" ); start_timer = System.currentTimeMillis(); crc = checksumBufferedInputStream(filepath); end_timer = System.currentTimeMillis(); System.out.println(Long.toHexString(crc)); System.out.println((end_timer - start_timer) + " ms" ); System.out.println( "///////////////////////////////////////////////////////////" ); System.out.println( "Random Access File method:" ); start_timer = System.currentTimeMillis(); crc = checksumRandomAccessFile(filepath); end_timer = System.currentTimeMillis(); System.out.println(Long.toHexString(crc)); System.out.println((end_timer - start_timer) + " ms" ); System.out.println( "///////////////////////////////////////////////////////////" ); System.out.println( "Mapped File method:" ); start_timer = System.currentTimeMillis(); crc = checksumMappedFile(filepath); end_timer = System.currentTimeMillis(); System.out.println(Long.toHexString(crc)); System.out.println((end_timer - start_timer) + " ms" ); } } |
Output:
Input Strea method:
94ccd63e
75 ms
///////////////////////////////////////////////////////////
Buffered Input Stream method:
94ccd63e
5 ms
///////////////////////////////////////////////////////////
Random Access File method:
94ccd63e
99 ms
///////////////////////////////////////////////////////////
Mapped File method:
94ccd63e
8 ms
This was an example of calculating the CRC Sum of a file in Java.
on big files like 1GB mapped is the fasted way
thank you for post
///////////////////////////////////////////////////////////
Buffered Input Stream method:
3ef92509
29903 ms
///////////////////////////////////////////////////////////
Mapped File method:
3ef92509
2949 ms