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2010-06-01T05:19:55Z

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в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== A single checksum calculation for multiple files ==



<source lang="java">
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.zip.Adler32;
import java.util.zip.CheckedInputStream;
import java.util.zip.Checksum;
/**
* Perform a single checksum calculation for multiple files
*
* @author
* @version $Id$
*/
public class MultiFileChecksumHelper
{
public static long getChecksum(File[] files)
{
CheckedInputStream cis = null;
FileInputStream is = null;
Checksum checksum = new Adler32();
byte[] tempBuf = new byte[128];

for ( int i = 0; i < files.length && files[i] != null && files[i].exists() && files[i].isFile(); i++ )
{
try
{
is = new FileInputStream(files[i]);
cis = new CheckedInputStream(is, checksum);
while (cis.read(tempBuf) >= 0) {}
}
catch (Exception e)
{
throw new RuntimeException(e);
}
finally
{
if (cis != null)
{
try
{
cis.close();
}
catch (IOException ioe) {}
cis = null;
}
if (is != null)
{
try
{
is.close();
}
catch (IOException ioe) {}
is = null;
}
}
}
return checksum.getValue();
}
}</source>



== Calculating the Checksum of a Byte Array (Compute Adler-32 checksum) ==



<source lang="java">
import java.util.zip.Adler32;
import java.util.zip.Checksum;
public class Main {
public static void main(String[] argv) throws Exception {
byte[] bytes = "some data".getBytes();

Checksum checksumEngine = new Adler32();
checksumEngine.update(bytes, 0, bytes.length);
long checksum = checksumEngine.getValue();
}
}</source>



== Calculating the Checksum of a File ==



<source lang="java">
import java.io.FileInputStream;
import java.util.zip.Adler32;
import java.util.zip.CheckedInputStream;
public class Main {
public static void main(String[] argv) throws Exception {
CheckedInputStream cis = new CheckedInputStream(new FileInputStream("filename"), new Adler32());
byte[] tempBuf = new byte[128];
while (cis.read(tempBuf) >= 0) {
}
long checksum = cis.getChecksum().getValue();
}
}</source>



== Check sum for an InputStream ==



<source lang="java">
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.Adler32;
import java.util.zip.CheckedInputStream;

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/**
* implements checksum related utilities
*
* @author
* @version $Id: ChecksumHelper.java 516448 2007-03-09 16:25:47Z ate $
*/
final class ChecksumHelper
{
public static long getChecksum(InputStream is)
{
CheckedInputStream cis = null;
long checksum = 0;
try
{
cis = new CheckedInputStream(is, new Adler32());
byte[] tempBuf = new byte[128];
while (cis.read(tempBuf) >= 0)
{
}
checksum = cis.getChecksum().getValue();
}
catch (IOException e)
{
checksum = 0;
}
finally
{
if (cis != null)
{
try
{
cis.close();
}
catch (IOException ioe)
{
}
}
}
return checksum;
}
}</source>



== Compressing Streams: File Summer ==



<source lang="java">
import java.io.FileInputStream;
import java.io.IOException;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
public class Main {
public static void main(String[] args) throws IOException {
FileInputStream fin = new FileInputStream("a.zip");
Checksum cs = new CRC32();
for (int b = fin.read(); b != -1; b = fin.read()) {
cs.update(b);
}
System.out.println(cs.getValue());
fin.close();
}
}</source>



== Compressing Streams: Parity Checksum ==



<source lang="java">
import java.util.zip.Checksum;
public class ParityChecksum implements Checksum {
long checksum = 0;
public void update(int b) {
int numOneBits = 0;
for (int i = 1; i < 256; i *= 2) {
if ((b & i) != 0)
numOneBits++;
}
checksum = (checksum + numOneBits) % 2;
}
public void update(byte data[], int offset, int length) {
for (int i = offset; i < offset + length; i++) {
this.update(data[i]);
}
}
public long getValue() {
return checksum;
}
public void reset() {
checksum = 0;
}
}</source>



== Compute CRC-32 checksum ==



<source lang="java">
import java.util.zip.CRC32;
import java.util.zip.Checksum;
public class Main {
public static void main(String[] argv) throws Exception {
byte[] bytes = "some data".getBytes();
// Compute Adler-32 checksum
Checksum checksumEngine = new CRC32();
checksumEngine.update(bytes, 0, bytes.length);
long checksum = checksumEngine.getValue();
checksumEngine.reset();
}
}</source>



== The java.util.zip package can be used to create a checksum. ==



<source lang="java">
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.util.Arrays;
import java.util.zip.CRC32;
public class Main {
public static void main(String[] args) throws Exception{
BufferedInputStream is = new BufferedInputStream(new FileInputStream("a.exe"));
byte[] bytes = new byte[1024];
int len = 0;
while ((len = is.read(bytes)) >= 0) {
new CRC32().update(bytes, 0, len);
}
is.close();
System.out.println(Arrays.toString(bytes));
}
}</source>

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Java Tutorial/File/Checksum - История изменений

Admin: 1 версия

в 17:44, 31 мая 2010