Java - Base64字符串输入和输出文本

Question

我需要将包含base64编码文本的字符串写入文本文件，然后将该字符串从文本文件读回字符串变量。

我该怎么做才能避免因编码问题而导致数据丢失？

Answer 1

Base64 仅为A＆＃8211; Z，a＆＃8211; z，0＆＃8211 ; 9，+和/。所以应该没有编码问题。只要你能够正确编码Ascii。发明Base64是为了表示 7位字符中的字节。

要进行编码和解码，您可以使用 commons编解码器Base64 。

Answer 2

Base64编码器：

// Sample program to encode a binary file into a Base64 text file.
// Author: Christian d'Heureuse (www.source-code.biz)

import java.io.BufferedInputStream;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.IOException;

public class Base64FileEncoder {

    public static void main (String args[]) throws IOException {
        if (args.length != 2) {
            System.out.println ("Command line parameters: inputFileName outputFileName");
            System.exit (9); 
        }

        encodeFile (args[0], args[1]); 
    }

    private static void encodeFile (String inputFileName, String outputFileName) throws IOException {
        BufferedInputStream in = null;
        BufferedWriter out = null;
        try {
            in = new BufferedInputStream(new FileInputStream(inputFileName));
            out = new BufferedWriter(new FileWriter(outputFileName));
            encodeStream (in, out);
            out.flush(); 
        } finally {
            if (in != null) in.close();
            if (out != null) out.close(); 
        }
    }

    private static void encodeStream (InputStream in, BufferedWriter out) throws IOException {
        int lineLength = 72;
        byte[] buf = new byte[lineLength/4*3];
        while (true) {
            int len = in.read(buf);
            if (len <= 0) break;
            out.write (Base64Coder.encode(buf, len));
            out.newLine(); 
        }
    }

} // end class Base64FileEncoder

Base64解码器：

// Sample program to decode a Base64 text file into a binary file.
// Author: Christian d'Heureuse (www.source-code.biz)

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStream;

public class Base64FileDecoder {

    public static void main (String args[]) throws IOException {
        if (args.length != 2) {
            System.out.println ("Command line parameters: inputFileName outputFileName");
            System.exit (9); 
        }

        decodeFile (args[0], args[1]); 
    }

    private static void decodeFile (String inputFileName, String outputFileName) throws IOException {
        BufferedReader in = null;
        BufferedOutputStream out = null;
        try {
            in = new BufferedReader(new FileReader(inputFileName));
            out = new BufferedOutputStream(new FileOutputStream(outputFileName));
            decodeStream (in, out);
            out.flush(); 
        } finally {
            if (in != null) in.close();
            if (out != null) out.close(); 
        }
    }

    private static void decodeStream (BufferedReader in, OutputStream out) throws IOException {
        while (true) {
            String s = in.readLine();
            if (s == null) break;
            byte[] buf = Base64Coder.decode(s);
            out.write (buf); 
        }
    }

} // end class Base64FileDecoder

测试Base64编码器：

// Test program for the Base64Coder class.

public class TestBase64Coder {

    public static void main (String args[]) throws Exception {
        System.out.println ("TestBase64Coder started");
        test1();
        test2();
        System.out.println ("TestBase64Coder completed"); 
    }

    // Test Base64Coder with constant strings.
    private static void test1() {
        System.out.println ("test1 started");
        check ("Aladdin:open sesame", "QWxhZGRpbjpvcGVuIHNlc2FtZQ==");  // example from RFC 2617
        check ("", "");
        check ("1", "MQ==");
        check ("22", "MjI=");
        check ("333", "MzMz");
        check ("4444", "NDQ0NA==");
        check ("55555", "NTU1NTU=");
        check ("abc:def", "YWJjOmRlZg==");
        System.out.println ("test1 completed"); 
    }

    private static void check (String plainText, String base64Text) {
        String s1 = Base64Coder.encodeString(plainText);
        String s2 = Base64Coder.decodeString(base64Text);
        if (!s1.equals(base64Text) || !s2.equals(plainText))
            System.out.println ("check failed for \""+plainText+"\" / \""+base64Text+"\"."); 
    }

    // Test Base64Coder against sun.misc.BASE64Encoder/Decoder with
    // random strings.
    private static void test2() throws Exception {
        System.out.println ("test2 started");
        sun.misc.BASE64Encoder enc = new sun.misc.BASE64Encoder();
        sun.misc.BASE64Decoder dec = new sun.misc.BASE64Decoder();
        java.util.Random rnd = new java.util.Random(0x538afb92);

        for (int i = 0; i < 50000; i++) {
            int len = rnd.nextInt(55);
            byte[] b0 = new byte[len];
            rnd.nextBytes(b0);
            String e1 = new String(Base64Coder.encode(b0));
            String e2 = enc.encode(b0);
            if (!e1.equals(e2)) 
                System.out.println ("Error\ne1=" + e1 + " len=" + e1.length() + "\ne2=" + e2 + " len=" + e2.length());

            byte[] b1 = Base64Coder.decode(e1);
            byte[] b2 = dec.decodeBuffer(e2);
            if (!compareByteArrays(b1, b0) || !compareByteArrays(b2, b0))
                System.out.println ("Decoded data not equal. len1=" + b1.length + " len2=" + b2.length); 
        }

        System.out.println ("test2 completed"); 
    }

    // Compares two byte arrays.
    private static boolean compareByteArrays (byte[] a1, byte[] a2) {
        if (a1.length != a2.length) return false;
        for (int p = 0; p < a1.length; p++)
            if (a1[p] != a2[p]) return false;

        return true; 
    }

} // end class TestBase64Coder

Answer 3

这是一个将编码和解码的简单代码：

编码步骤

1. 编码字节
2. 将编码字节转换为十六进制字符串

解码步骤

1. 将十六进制字符串转换为编码字节
2. 解码字节
3. 将解码的字节转换为十六进制字符串

4. 将十六进制字符串转换为ASCII字符串（普通字符串）

   // Encoding Bytes
   byte[] b64ENC = Base64.encode("Hello World".getBytes("UTF-8"));
   String ENCStr = getHexString(b64ENC,b64ENC.length);
   T1.setText(ENCStr);  //-- for output
   
   // Decoding Bytes
   byte[] DECBarray = hexStringToByteArray(ENCStr);
   byte[] b64DEC = Base64.decode(DECBarray);
   
   // Displaying Decoded Byte Array by Converting it To String
   try {
       String ResDec = new String(b64DEC,"UTF-8");
       T2.setText(ResDec);   //This Displays Hello World :)
   
   } catch (UnsupportedEncodingException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
   }
   
   // Following are the functions that I used above !
   public String getHexString(byte[] b, int length) {
       // TODO Auto-generated method stub
       String result = "";
   
       for (int i = 0; i < length; i++) {
           result += Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring(1);
       }
       return result;
   }
   
   public static String bytesToHex(byte[] data) {
       StringBuffer buf = new StringBuffer();
       for (int i = 0; i < data.length; i++) {
           buf.append(byteToHex(data[i]));
           buf.append(" ");
       }
       return (buf.toString());
   }
   
   public static String byteToHex(byte data) {
       StringBuffer buf = new StringBuffer();
       buf.append(toHexChar((data >>> 4) & 0x0F));
       buf.append(toHexChar(data & 0x0F));
       return buf.toString();
   }
   
   public static char toHexChar(int i) {
       if ((0 <= i) && (i <= 9)) {
           return (char) ('0' + i);
       } else {
           return (char) ('a' + (i - 10));
       }
   }
   
   public static byte[] hexStringToByteArray(String s) {
       int len = s.length();
       byte[] data = new byte[len / 2];
       for (int i = 0; i < len; i += 2) {
           data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                   + Character.digit(s.charAt(i+1), 16));
       }
   
       return data;
   }
   

Answer 4

有一个sun类可以为你做（虽然它会生成编译器警告：

import sun.misc.BASE64Encoder;

BASE64Encoder encoder = new BASE64Encoder();

String toEncode = "encodeMe";

String encoded = encodeBuffer(toEncode.getBytes());

从内存中，还有一个BASE64Decoder，但我没有使用它，我只采用一种方式来比较用户名的线上。