java对称加密字符串示例

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作者：wallimn　电邮：[e-mail]　时间：2009-08-11
博客：http://wallimn.iteye.com
网络硬盘：http://wallimn.ys168.com
/***********文章发表请与本人联系，作者保留所有权利*************/
　　将字符串使用对称加密的方式加一下密，并转化成可显示字符；将加密结果还原为原来的字符串，是可能在很多场合会用到。
　　下面是一个完成上述功能的工具类，觉得有用可以拿去用。

package com.wallimn.gyz.util;

import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

/**
 * 这个类用来给一个较短的字符串加、解密<br/>
 * 编码：wallimn　时间：2009-8-12　上午07:43:29<br/>
 * 版本：V1.0<br/>
 */
public class KeyUtil {

	private static final String EncodeAlgorithm = "DES";
	private static KeyUtil instance = null;

	public static KeyUtil getInstance() {
		if (instance == null) {
			instance = new KeyUtil();
			if (!instance.init()) {
				instance = null;
			}
		}
		return instance;
	}

	private SecretKey key = null;

	private boolean init() {
		try {
			KeyGenerator keygen = KeyGenerator.getInstance(EncodeAlgorithm);
			SecureRandom random = new SecureRandom();
			keygen.init(random);
			key = keygen.generateKey();

		} catch (Exception e) {
			e.printStackTrace();
		}
		return key != null;
	}

	private Cipher getCipher(int mode) {
		try {
			Cipher cipher = Cipher.getInstance(EncodeAlgorithm);
			cipher.init(mode, key);
			return cipher;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public Cipher getEncodeCipher() {
		return this.getCipher(Cipher.ENCRYPT_MODE);
	}

	public Cipher getDecodeCipher() {
		return this.getCipher(Cipher.DECRYPT_MODE);
	}

	/**
	 * 解密，若输入为null或加/解密过程出现异常，则输出为null <br/>
	 * 作者：wallimn　时间：2009-8-12　上午08:09:44<br/>
	 * 博客：http://wallimn.iteye.com<br/>
	 * 参数：<br/>
	 * 
	 * @param str
	 * @return
	 */
	public String decode(String str) {
		if(str==null)return null;
		Cipher cipher = getDecodeCipher();
		StringBuffer sb = new StringBuffer();
		int blockSize = cipher.getBlockSize();
		int outputSize = cipher.getOutputSize(blockSize);
		byte[] src = stringToBytes(str);
		byte[] outBytes = new byte[outputSize];
		int i = 0;
		try {
			for (; i <= src.length - blockSize; i = i + blockSize) {
				int outLength = cipher.update(src, i, blockSize, outBytes);
				sb.append(new String(outBytes, 0,outLength));
			}
			if (i == src.length)
				outBytes = cipher.doFinal();
			else {
				outBytes = cipher.doFinal(src, i, src.length - i);
			}
			sb.append(new String(outBytes));
			return sb.toString();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 加密，若输入为null或加/解密过程出现异常，则输出为null <br/>
	 * 作者：wallimn　时间：2009-8-12　上午08:09:59<br/>
	 * 博客：http://wallimn.iteye.com<br/>
	 * 参数：<br/>
	 * 
	 * @param str
	 * @return
	 */
	public String encode(String str) {
		if(str==null)return null;
		Cipher cipher = getEncodeCipher();
		StringBuffer sb = new StringBuffer();
		int blockSize = cipher.getBlockSize();
		int outputSize = cipher.getOutputSize(blockSize);
		byte[] src = str.getBytes();
		byte[] outBytes = new byte[outputSize];
		int i = 0;
		try {
			for (; i <= src.length - blockSize; i = i + blockSize) {
				int outLength = cipher.update(src, i, blockSize, outBytes);
				sb.append(bytesToString(outBytes, outLength));
			}
			if (i == src.length)
				outBytes = cipher.doFinal();
			else {
				outBytes = cipher.doFinal(src, i, src.length - i);
			}
			sb.append(bytesToString(outBytes));
			return sb.toString();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	private String bytesToString(byte[] bs) {
		if (bs == null || bs.length == 0)
			return "";
		return bytesToString(bs, bs.length);
	}

	private String bytesToString(byte[] bs, int len) {
		if (bs == null || bs.length == 0)
			return "";
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < len; i++) {
			// System.out.println(bs[i]+":"+String.format("%02X", bs[i]));
			sb.append(String.format("%02X", bs[i]));
		}
		return sb.toString();
	}

	private byte[] stringToBytes(String str) {
		if (str == null || str.length() < 2 || str.length() % 2 != 0)
			return new byte[0];
		int len = str.length();
		byte[] bs = new byte[len / 2];
		for (int i = 0; i * 2 < len; i++) {
			bs[i] = (byte) (Integer.parseInt(str.substring(i * 2, i * 2 + 2),
					16) & 0xFF);
			// System.out.println(str.substring(i * 2, i * 2 + 2)+":"+bs[i]);
		}
		return bs;
	}
}

使用示例：

	public void testCrypt(){
		String str = "[e-mail],http://wallimn.iteye.com";
		String tmp = KeyUtil.getInstance().encode(str);
		System.out.println("加密结果："+ tmp);
		System.out.println("解密结果："+KeyUtil.getInstance().decode(tmp ));
	}