Java中常用类

import org.apache.commons.codec.digest.DigestUtils;

/**
 * MD5通用类
 */
public class MD5 {

	/**
	 * MD5方法
	 * 
	 * @param text
	 *            明文
	 * @param key
	 *            密钥
	 * @return 密文
	 * @throws Exception
	 */
	public static String md5(String text,String key) throws Exception {
		// 加密后的字符串
		String encodeStr = DigestUtils.md5Hex(text + key);
		return encodeStr;
	}

	/**
	 * MD5验证方法
	 * 
	 * @param text
	 *            明文
	 * @param key
	 *            密钥
	 * @param md5
	 *            密文
	 * @return true/false
	 * @throws Exception
	 */
	public static boolean verify(String text,String key, String md5) throws Exception {
		// 根据传入的密钥进行验证
		String md5Text = md5(text , key);
		if (md5Text.equalsIgnoreCase(md5)) {
			System.out.println("MD5验证通过");
			return true;
		}
		return false;
	}
}

import org.apache.commons.codec.binary.Base64;
import org.apache.commons.io.IOUtils;

import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

public class RSAUtils {

	public static final String CHARSET = "UTF-8";
	public static final String RSA_ALGORITHM = "RSA";

	/**
	 * 创建公钥密钥
	 * 
	 * @param keySize
	 *           密钥长度
	 * @return 公钥私钥
	 */
	public static Map<String, String> createKeys(int keySize) {
		// 为RSA算法创建一个KeyPairGenerator对象
		KeyPairGenerator kpg;
		try {
			kpg = KeyPairGenerator.getInstance(RSA_ALGORITHM);
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalArgumentException("No such algorithm-->[" + RSA_ALGORITHM + "]");
		}

		// 初始化KeyPairGenerator对象,密钥长度
		kpg.initialize(keySize);
		// 生成密匙对
		KeyPair keyPair = kpg.generateKeyPair();
		// 得到公钥
		Key publicKey = keyPair.getPublic();
		String publicKeyStr = Base64.encodeBase64URLSafeString(publicKey.getEncoded());
		// 得到私钥
		Key privateKey = keyPair.getPrivate();
		String privateKeyStr = Base64.encodeBase64URLSafeString(privateKey.getEncoded());
		Map<String, String> keyPairMap = new HashMap<String, String>();
		keyPairMap.put("publicKey", publicKeyStr);
		keyPairMap.put("privateKey", privateKeyStr);

		return keyPairMap;
	}

	/**
	 * 得到公钥
	 * 
	 * @param publicKey
	 *            密钥字符串（经过base64编码）
	 * @throws Exception
	 */
	public static RSAPublicKey getPublicKey(String publicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
		// 通过X509编码的Key指令获得公钥对象
		KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
		X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(Base64.decodeBase64(publicKey));
		RSAPublicKey key = (RSAPublicKey) keyFactory.generatePublic(x509KeySpec);
		return key;
	}

	/**
	 * 得到私钥
	 * 
	 * @param privateKey
	 *            密钥字符串（经过base64编码）
	 * @throws Exception
	 */
	public static RSAPrivateKey getPrivateKey(String privateKey)
			throws NoSuchAlgorithmException, InvalidKeySpecException {
		// 通过PKCS#8编码的Key指令获得私钥对象
		KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
		PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(Base64.decodeBase64(privateKey));
		RSAPrivateKey key = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8KeySpec);
		return key;
	}

	/**
	 * 公钥加密
	 * 
	 * @param data
	 * @param publicKey
	 * @return
	 */
	public static String publicEncrypt(String data, RSAPublicKey publicKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
			cipher.init(Cipher.ENCRYPT_MODE, publicKey);
			return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET),
					publicKey.getModulus().bitLength()));
		} catch (Exception e) {
			throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
		}
	}

	/**
	 * 私钥解密
	 * 
	 * @param data
	 * @param privateKey
	 * @return
	 */

	public static String privateDecrypt(String data, RSAPrivateKey privateKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
			cipher.init(Cipher.DECRYPT_MODE, privateKey);
			return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data),
					privateKey.getModulus().bitLength()), CHARSET);
		} catch (Exception e) {
			throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
		}
	}

	/**
	 * 私钥加密
	 * 
	 * @param data
	 * @param privateKey
	 * @return
	 */

	public static String privateEncrypt(String data, RSAPrivateKey privateKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
			cipher.init(Cipher.ENCRYPT_MODE, privateKey);
			return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET),
					privateKey.getModulus().bitLength()));
		} catch (Exception e) {
			throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
		}
	}

	/**
	 * 公钥解密
	 * 
	 * @param data
	 * @param publicKey
	 * @return
	 */

	public static String publicDecrypt(String data, RSAPublicKey publicKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
			cipher.init(Cipher.DECRYPT_MODE, publicKey);
			return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data),
					publicKey.getModulus().bitLength()), CHARSET);
		} catch (Exception e) {
			throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
		}
	}

	private static byte[] rsaSplitCodec(Cipher cipher, int opmode, byte[] datas, int keySize) {
		int maxBlock = 0;
		if (opmode == Cipher.DECRYPT_MODE) {
			maxBlock = keySize / 8;
		} else {
			maxBlock = keySize / 8 - 11;
		}
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		int offSet = 0;
		byte[] buff;
		int i = 0;
		try {
			while (datas.length > offSet) {
				if (datas.length - offSet > maxBlock) {
					buff = cipher.doFinal(datas, offSet, maxBlock);
				} else {
					buff = cipher.doFinal(datas, offSet, datas.length - offSet);
				}
				out.write(buff, 0, buff.length);
				i++;
				offSet = i * maxBlock;
			}
		} catch (Exception e) {
			throw new RuntimeException("加解密阀值为[" + maxBlock + "]的数据时发生异常", e);
		}
		byte[] resultDatas = out.toByteArray();
		IOUtils.closeQuietly(out);
		return resultDatas;
	}

}

Map<String, String> keyMap = RSAUtils.createKeys(1024);
        String  publicKey = keyMap.get("publicKey");
        String  privateKey = keyMap.get("privateKey");
        System.out.println("公钥: \n\r" + publicKey);
        System.out.println("私钥： \n\r" + privateKey);

        System.out.println("公钥加密——私钥解密");
        String str = "站在大明门前守卫的禁卫军，事先没有接到\n" +
                "有关的命令，但看到大批盛装的官员来临，也就\n" +
                "以为确系举行大典，因而未加询问。进大明门即\n" +
                "为皇城。文武百官看到端门午门之前气氛平静，\n" +
                "城楼上下也无朝会的迹象，既无几案，站队点名\n" +
                "的御史和御前侍卫“大汉将军”也不见踪影，不免\n" +
                "心中揣测，互相询问：所谓午朝是否讹传？";
        System.out.println("\r明文：\r\n" + str);
        System.out.println("\r明文大小：\r\n" + str.getBytes().length);
        String encodedData = RSAUtils.publicEncrypt(str, RSAUtils.getPublicKey(publicKey));
        System.out.println("密文：\r\n" + encodedData);
        String decodedData = RSAUtils.privateDecrypt(encodedData, RSAUtils.getPrivateKey(privateKey));
        System.out.println("解密后文字: \r\n" + decodedData);