base64decoder.java

论坛软件系统亦称电子公告板(BBS)系统

package cn.jsprun.utils;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;

public final class Base64Decoder extends FilterInputStream {

	private static final char[] chars = { 'A', 'B', 'C', 'D', 'E', 'F', 'G',
			'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
			'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
			'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
			'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6',
			'7', '8', '9', '+', '/' };

	private static final int[] ints = new int[128];
	static {
		for (int i = 0; i < 64; i++) {
			ints[chars[i]] = i;
		}
	}

	private int charCount;

	private int carryOver;

	public Base64Decoder(InputStream in) {
		super(in);
	}

	public int read() throws IOException {
		int x;
		do {
			x = in.read();
			if (x == -1) {
				return -1;
			}
		} while (Character.isWhitespace((char) x));
		charCount++;

		if (x == '=') {
			return -1;  
		}

		x = ints[x];

		int mode = (charCount - 1) % 4;

		if (mode == 0) {
			carryOver = x & 63;
			return read();
		}
		else if (mode == 1) {
			int decoded = ((carryOver << 2) + (x >> 4)) & 255;
			carryOver = x & 15;
			return decoded;
		}
		else if (mode == 2) {
			int decoded = ((carryOver << 4) + (x >> 2)) & 255;
			carryOver = x & 3;
			return decoded;
		}
		else if (mode == 3) {
			int decoded = ((carryOver << 6) + x) & 255;
			return decoded;
		}
		return -1;  
	}

	public int read(byte[] b, int off, int len) throws IOException {
		int i;
		for (i = 0; i < len; i++) {
			int x = read();
			if (x == -1 && i == 0) {  
				return -1;
			} else if (x == -1) {  
				break;
			}
			b[off + i] = (byte) x;
		}
		return i;
	}

	public static String decode(String encoded,String charsetName) {
		byte[] bytes = null;
		try {
			bytes = encoded.getBytes(charsetName);
		} catch (UnsupportedEncodingException ignored) {
		}

		Base64Decoder in = new Base64Decoder(new ByteArrayInputStream(bytes));

		ByteArrayOutputStream out = new ByteArrayOutputStream((int) (bytes.length * 0.67));

		try {
			byte[] buf = new byte[4 * 1024];  
			int bytesRead;
			while ((bytesRead = in.read(buf)) != -1) {
				out.write(buf, 0, bytesRead);
			}
			out.close();

			return out.toString(charsetName);
		} catch (IOException ignored) {
			return null;
		}
	}
}