Java 预先计算文件流校验和
我正在努力确保输出文件的完整性,以防磁盘空间不足、网络问题或流式传输到文件过程中可能发生的任何异常。 是否有方法在写入磁盘之前预先计算FileStream校验和,然后检查文件是否正确写入。 对我来说,这听起来有点荒谬,一个系统通过校验和来验证自己导出的XML的完整性,通常情况下,另一端的工作是验证使用的文件是否与另一个系统生成的文件相符 但这是我必须执行的一项要求 她是我作为文件编写的流:Java 预先计算文件流校验和,java,java-io,java.nio.file,Java,Java Io,Java.nio.file,我正在努力确保输出文件的完整性,以防磁盘空间不足、网络问题或流式传输到文件过程中可能发生的任何异常。 是否有方法在写入磁盘之前预先计算FileStream校验和,然后检查文件是否正确写入。 对我来说,这听起来有点荒谬,一个系统通过校验和来验证自己导出的XML的完整性,通常情况下,另一端的工作是验证使用的文件是否与另一个系统生成的文件相符 但这是我必须执行的一项要求 她是我作为文件编写的流: String xmlTransfer =""; File testFile = new Fil
String xmlTransfer ="";
File testFile = new File("testFile.xml");
InputStream in = new ByteArrayInputStream(xmlTransfer.getBytes("utf-8"));
FileOutputStream out = new FileOutputStream(testFile)
byte[] buffer = new byte[2048];
int bytesRead;
while ((bytesRead = in.read(buffer)) != -1) {
out.write(buffer, 0, bytesRead);
}
out.close();
in.close();
不,您无法预先计算有多少数据将来自流。这根本不是流的工作方式
如果编写代码的两端,您可以做的是首先计算发送端的文件大小,然后在发送文件内容之前发送该大小。最好的方法是捕获异常。如果出现问题,将启动异常,在这种情况下,您可以删除部分写入的文件 第二种方法是在写入文件系统之前先有一个内存流,但它会消耗内存 第三种方法是确保目标磁盘容量(新文件(path).getFreeSpace()
关于这个问题,MD5检查对我来说太慢了。您应该按MD5检查,而不是按文件大小检查 您可以在读取流时计算MD5 看 然后,保存文件后,可以再次生成md5并进行比较 更新-以下是我对此的更详细想法。我假设您只想计算MD5,而不必将整个字节[]放入内存。在这种情况下,我认为你有两个选择
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.commons.io.IOUtils;
import org.apache.commons.io.output.NullOutputStream;
public class MD5OnTheFly {
/**
* @param args
* @throws NoSuchAlgorithmException
* @throws IOException
*/
public static void main(String[] args) throws NoSuchAlgorithmException, IOException {
long ini = System.currentTimeMillis();
File file = new File("/home/leoks/Downloads/VirtualBox-4.3.0.tar");
System.out.println("size:"+file.length());
InputStream is = new FileInputStream(file);
MessageDigest md = MessageDigest.getInstance("MD5");
DigestInputStream dis = new DigestInputStream(is, md);
IOUtils.copy(dis, new NullOutputStream());
byte[] digest = md.digest();
StringBuffer hexString = new StringBuffer();
for (int i = 0; i < digest.length; i++) {
String hex = Integer.toHexString(0xff & digest[i]);
if (hex.length() == 1)
hexString.append('0');
hexString.append(hex);
}
System.out.println(hexString);
long end = System.currentTimeMillis();
System.out.println(end-ini+" millis");
}
}
然后
[leoks@home ~]$ md5sum /home/leoks/Downloads/VirtualBox-4.3.0.tar
dda81aea75a83b1489662c6bcd0677e4 /home/leoks/Downloads/VirtualBox-4.3.0.tar
[leoks@home ~]$
试试这个:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.security.MessageDigest;
public class CheckSumFileTest
{
private File buildChecksumFile(File fileToCheck, String filePrefix, String checksumAlgorithm) throws Exception
{
String checksum = null;
File checksumFile = null;
String tempDir = System.getProperty("java.io.tmpdir");
try {
checksumFile = new File(tempDir, filePrefix+"."+ checksumAlgorithm.toLowerCase());
checksumFile.createNewFile();
checksumFile.deleteOnExit();
} catch (Exception e1) {
e1.printStackTrace();
throw e1;
}
FileWriter fw = null;
try {
checksum = checkSum(fileToCheck,checksumAlgorithm);
fw = new FileWriter(checksumFile);
fw.write(checksum);
} catch (Exception e) {
e.printStackTrace();
throw e;
}
finally
{
if(fw !=null)
fw.close();
}
return checksumFile;
}
private static String checkSum(File file, String checksumAlgorithm) throws Exception
{
MessageDigest digest = MessageDigest.getInstance(checksumAlgorithm);
InputStream input = null;
StringBuffer sb = new StringBuffer();
try{
input = new FileInputStream(file);
byte[] buffer = new byte[8192];
do {
int read = input.read(buffer);
if(read <= 0)
break;
digest.update(buffer, 0, read);
} while(true);
byte[] sum = digest.digest();
for (int i = 0; i < sum.length; i++) {
sb.append(Integer.toString((sum[i] & 0xff) + 0x100, 16).substring(1));
}
}catch(IOException io)
{
}finally{
if(input != null)
input.close();
}
return sb.toString();
}
private static String checkSumInStream(InputStream stream, String checksumAlgorithm) throws Exception
{
MessageDigest digest = MessageDigest.getInstance(checksumAlgorithm);
InputStream input = null;
StringBuffer sb = new StringBuffer();
try{
input = stream;
byte[] buffer = new byte[8192];
do {
int read = input.read(buffer);
if(read <= 0)
break;
digest.update(buffer, 0, read);
} while(true);
byte[] sum = digest.digest();
for (int i = 0; i < sum.length; i++) {
sb.append(Integer.toString((sum[i] & 0xff) + 0x100, 16).substring(1));
}
}catch(IOException io)
{
}finally{
if(input != null)
input.close();
}
return sb.toString();
}
private boolean checkIntegrity(String targetFileName, String checksumFileName, String checksumAlgorithm) throws Exception
{
FileInputStream stream = null;
BufferedReader br = null;
InputStreamReader ipsr = null;
File checksumFile = null;
String checksumString="";
File targetFile = new File(targetFileName);
try{
checksumFile = new File(checksumFileName);
stream = new FileInputStream(checksumFile);
ipsr = new InputStreamReader(stream);
br = new BufferedReader(ipsr);
//In checksum file : only one line to read
checksumString = br.readLine();
}finally
{
if(br != null)
br.close();
if(ipsr != null)
ipsr.close();
if(stream != null)
stream.close();
}
if(checksumString.equals(checkSum(targetFile,checksumAlgorithm)))
{
return true;
}
else
{
return false;
}
}
/**
* @param args
*/
public static void main(String[] args)
{
String str = "Amine";
InputStream stream = new ByteArrayInputStream(str.getBytes());
//step1
try {
System.out.println(checkSumInStream(stream,"MD5"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//step2
File file = new File("c:/test.txt");
// if file doesnt exists, then create it
if (!file.exists()) {
try {
file.createNewFile();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
FileWriter fw;
BufferedWriter bw;
try {
fw = new FileWriter(file.getAbsoluteFile());
bw = new BufferedWriter(fw);
bw.write(str);
bw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
System.out.println(checkSum(file, "MD5"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Done");
}
}
导入java.io.BufferedReader;
导入java.io.BufferedWriter;
导入java.io.ByteArrayInputStream;
导入java.io.File;
导入java.io.FileInputStream;
导入java.io.FileNotFoundException;
导入java.io.FileOutputStream;
导入java.io.FileWriter;
导入java.io.IOException;
导入java.io.InputStream;
导入java.io.InputStreamReader;
导入java.io.OutputStream;
导入java.security.MessageDigest;
公共类CheckSumFileTest
{
私有文件buildChecksumFile(文件fileToCheck、字符串filePrefix、字符串checksumAlgorithm)引发异常
{
字符串校验和=null;
文件checksumFile=null;
字符串tempDir=System.getProperty(“java.io.tmpdir”);
试一试{
checksumFile=新文件(tempDir,filePrefix+“+”+checksumfalgorithm.toLowerCase());
checksumFile.createNewFile();
checksumFile.deleteOnExit();
}捕获(异常e1){
e1.printStackTrace();
抛出e1;
}
FileWriter fw=null;
试一试{
校验和=校验和(fileToCheck,checksum算法);
fw=新文件写入程序(checksumFile);
fw.写入(校验和);
}捕获(例外e){
e、 printStackTrace();
投掷e;
}
最后
{
如果(fw!=null)
fw.close();
}
返回检查文件;
}
私有静态字符串校验和(文件文件、字符串校验和算法)引发异常
{
MessageDigest=MessageDigest.getInstance(checksumAlgorithm);
InputStream输入=null;
StringBuffer sb=新的StringBuffer();
试一试{
输入=新文件输入流(文件);
字节[]缓冲区=新字节[8192];
做{
int read=输入.读取(缓冲区);
if(读取如何在读取文件流时计算MD5,保存后再次检查?如果在计算MD5时出现问题,我将无法知道写入磁盘的结果文件是否有效。如果我在计算MD5时遇到任何问题,我将假定我必须再次写入该文件。。。(别忘了添加max retries)thx对于提示答案,异常解决方案的问题是,由于文件被另一个进程使用,我无法删除该文件,这是一个奇怪的问题,即使我确保每个流都已正确关闭。
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.security.MessageDigest;
public class CheckSumFileTest
{
private File buildChecksumFile(File fileToCheck, String filePrefix, String checksumAlgorithm) throws Exception
{
String checksum = null;
File checksumFile = null;
String tempDir = System.getProperty("java.io.tmpdir");
try {
checksumFile = new File(tempDir, filePrefix+"."+ checksumAlgorithm.toLowerCase());
checksumFile.createNewFile();
checksumFile.deleteOnExit();
} catch (Exception e1) {
e1.printStackTrace();
throw e1;
}
FileWriter fw = null;
try {
checksum = checkSum(fileToCheck,checksumAlgorithm);
fw = new FileWriter(checksumFile);
fw.write(checksum);
} catch (Exception e) {
e.printStackTrace();
throw e;
}
finally
{
if(fw !=null)
fw.close();
}
return checksumFile;
}
private static String checkSum(File file, String checksumAlgorithm) throws Exception
{
MessageDigest digest = MessageDigest.getInstance(checksumAlgorithm);
InputStream input = null;
StringBuffer sb = new StringBuffer();
try{
input = new FileInputStream(file);
byte[] buffer = new byte[8192];
do {
int read = input.read(buffer);
if(read <= 0)
break;
digest.update(buffer, 0, read);
} while(true);
byte[] sum = digest.digest();
for (int i = 0; i < sum.length; i++) {
sb.append(Integer.toString((sum[i] & 0xff) + 0x100, 16).substring(1));
}
}catch(IOException io)
{
}finally{
if(input != null)
input.close();
}
return sb.toString();
}
private static String checkSumInStream(InputStream stream, String checksumAlgorithm) throws Exception
{
MessageDigest digest = MessageDigest.getInstance(checksumAlgorithm);
InputStream input = null;
StringBuffer sb = new StringBuffer();
try{
input = stream;
byte[] buffer = new byte[8192];
do {
int read = input.read(buffer);
if(read <= 0)
break;
digest.update(buffer, 0, read);
} while(true);
byte[] sum = digest.digest();
for (int i = 0; i < sum.length; i++) {
sb.append(Integer.toString((sum[i] & 0xff) + 0x100, 16).substring(1));
}
}catch(IOException io)
{
}finally{
if(input != null)
input.close();
}
return sb.toString();
}
private boolean checkIntegrity(String targetFileName, String checksumFileName, String checksumAlgorithm) throws Exception
{
FileInputStream stream = null;
BufferedReader br = null;
InputStreamReader ipsr = null;
File checksumFile = null;
String checksumString="";
File targetFile = new File(targetFileName);
try{
checksumFile = new File(checksumFileName);
stream = new FileInputStream(checksumFile);
ipsr = new InputStreamReader(stream);
br = new BufferedReader(ipsr);
//In checksum file : only one line to read
checksumString = br.readLine();
}finally
{
if(br != null)
br.close();
if(ipsr != null)
ipsr.close();
if(stream != null)
stream.close();
}
if(checksumString.equals(checkSum(targetFile,checksumAlgorithm)))
{
return true;
}
else
{
return false;
}
}
/**
* @param args
*/
public static void main(String[] args)
{
String str = "Amine";
InputStream stream = new ByteArrayInputStream(str.getBytes());
//step1
try {
System.out.println(checkSumInStream(stream,"MD5"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//step2
File file = new File("c:/test.txt");
// if file doesnt exists, then create it
if (!file.exists()) {
try {
file.createNewFile();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
FileWriter fw;
BufferedWriter bw;
try {
fw = new FileWriter(file.getAbsoluteFile());
bw = new BufferedWriter(fw);
bw.write(str);
bw.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
System.out.println(checkSum(file, "MD5"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Done");
}
}