Java – Base64字符串输入和输出文本
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。
我怎么能这样做，以免因编码问题而导致数据丢失？
Base64只有A-Z，a-z，0-9，+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位字符的字节。
要编码和解码，您可以使用commons编解码器Base64 。
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
这是一个简单的代码，它将编码和解码：
编码步骤
- 编码字节
- 将编码字节转换为hex字符串
解码步骤
- 将hex字符串转换为编码字节
- 解码字节
- 将解码的字节转换为hex字符串
-
将hex字符串转换为ASCII字符串（正常字符串）
// 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; }
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。