java判断文件是否相同的方法:

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1、计算MD5或SHA-1然后对比判断

 // 计算文件的 MD5 值 根据MD5值 判断文件是否是同一个文件
public static String getFileMD5(File file) {
        if (!file.isFile()) {
            return null;
        }
        MessageDigest digest = null;
        FileInputStream in = null;
        byte buffer[] = new byte[8192];
        int len;
        try {
            digest =MessageDigest.getInstance("MD5");
            in = new FileInputStream(file);
            while ((len = in.read(buffer)) != -1) {
                digest.update(buffer, 0, len);
            }
            BigInteger bigInt = new BigInteger(1, digest.digest());
            return bigInt.toString(16);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        } finally {
            try {
                in.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

// 计算文件的 SHA-1 值 根据SHA-1值 判断文件是否是同一个文件
    public static String getFileSha1(File file) {
        if (!file.isFile()) {
            return null;
        }
        MessageDigest digest = null;
        FileInputStream in = null;
        byte buffer[] = new byte[8192];
        int len;
        try {
            digest =MessageDigest.getInstance("SHA-1");
            in = new FileInputStream(file);
            while ((len = in.read(buffer)) != -1) {
                digest.update(buffer, 0, len);
            }
            BigInteger bigInt = new BigInteger(1, digest.digest());
            return bigInt.toString(16);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        } finally {
            try {
                in.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

2、直接判断内容是否相同

 public class  IOOperation  
{  
    public static void main(String[] args)   
    {  
        FileInputStream File1 = null;  
        FileInputStream File2 = null;  
        BufferedReader in = null;  
        String sFile;  

        if(args.length != 2)  
        {  
            System.out.println("The command line should be: java IOOperation testX.txt testX.txt");  
            System.out.println("X should be one of the array: 1, 2, 3");  
            System.exit(0);  
        }  

        try  
        {  
            File1 = new FileInputStream(args[0]);  
            File2 = new FileInputStream(args[1]);  

            try  
            {  

                if(File1.available() != File2.available())  
                {  
                   //长度不同内容肯定不同  
                    System.out.println(args[0] + " is not equal to " + args[1]);  
                }  
                else  
                {  
                    boolean tag = true;  

                    while( File1.read() != -1 && File2.read() != -1)  
                    {  
                        if(File1.read() != File2.read())  
                        {  
                            tag = false;  
                            break;  
                        }  
                    }  

                    if(tag == true)  
                        System.out.println(args[0] + " equals to " + args[1]);  
                    else  
                        System.out.println(args[0] + " is not equal to " + args[1]);  
                }  
            }  
            catch(IOException e)  
            {  
                System.out.println(e);  
            }  
        }  
        catch (FileNotFoundException e)  
        {  
            System.out.println("File can't find..");  
        }  
        finally  
        {  

            try  
            {  
                if(File1 != null)  
                    File1.close();  
                if(File2 != null)  
                    File2.close();  
            }  
            catch (IOException e)  
            {  
                System.out.println(e);  
            }  
        }  
    }

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