java – preCalculate文件流校验和

我正在尝试确保在磁盘空间不足,网络问题或在流式传输到文件进程期间可能发生的任何异常的情况下输出文件完整性.
有没有办法在写入磁盘之前预先计算FileStream checkSum,然后检查文件是否写得正确.
对我来说这听起来有点荒谬,系统通过checkSum验证自己导出的XML的完整性,通常,另一端的工作是验证消耗的文件是否符合其他系统生成的文件.

但这是我必须实施的要求.

她是我作为文件写的流：

 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();

解决方法:

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");
    }

}

标签：java-nio-file,java,java-io
来源： https://codeday.me/bug/20190725/1531634.html