在做性能测试的时候，发现一个MD5的工具类有问题，在大压力的情况下，会出现计算出错的问题，分析了一下代码，找到了原因所在。
这是原来的代码：
public class MD5 {
// ------------------------------------------------------------ Private data
private static SecureRandom random = null;
private static MessageDigest md = null;
// ------------------------------------------------------------ Constructors
/** Creates a new instance of MD5 */
protected MD5() {
}
// ---------------------------------------------------------- Public methods
/**
* Returns a new nonce to be used for MD5 authentication. The nonce bytes
* are guaranteed to be in the printable range from ascii 32 to 128.
*
* @return a new 16 bytes long nonce
*/
public static byte[] getNextNonce() {
byte[] nextNonce = new byte[16];
random.nextBytes(nextNonce);
int i;
for (int j=0; j i = nextNonce[j] & 0x000000ff; if ((i<32) || (i>128)) { nextNonce[j] = (byte)(32 + (i % 64)); } } return nextNonce; } /** * MD5ies the given content * * @param data the data to be digested * */ public static byte[] digest(byte[] data) { md.reset(); return md.digest(data); } // --------------------------------------------------------- Private methods /** * Creates and initialize the random generator. Called ad class loading * time. */ private static void randomGeneratorInit() throws java.security.NoSuchAlgorithmException { random = SecureRandom.getInstance("SHA1PRNG"); } // ------------------------------------------------------------- Static code static { try { randomGeneratorInit(); md = MessageDigest.getInstance("MD5"); } catch(Exception e) { e.printStackTrace(); } } } 这是我修改后的代码： public class MD5 { // ------------------------------------------------------------ Private data private static SecureRandom random = null; private static MessageDigest md = null; // ------------------------------------------------------------ Constructors /** Creates a new instance of MD5 */ protected MD5() { } // ---------------------------------------------------------- Public methods /** * Returns a new nonce to be used for MD5 authentication. The nonce bytes * are guaranteed to be in the printable range from ascii 32 to 128. * * @return a new 16 bytes long nonce */ public static byte[] getNextNonce() { byte[] nextNonce = new byte[16]; random.nextBytes(nextNonce); int i; for (int j=0; j i = nextNonce[j] & 0x000000ff; if ((i<32) || (i>128)) { nextNonce[j] = (byte)(32 + (i % 64)); } } return nextNonce; } /** * MD5ies the given content * * @param data the data to be digested * */ public static byte[] digest(byte[] data) { synchronized (md) { md.reset(); return md.digest(data); } } // --------------------------------------------------------- Private methods /** * Creates and initialize the random generator. Called ad class loading * t