Question

在java语言中如何随机地生成一个字符串

在java语言中如何随机地生成一个字符串

Answer 1

可以配合UUID或者GUID来实现

GUID是一个128位长的数字，一般用16进制表示。算法的核心思想是结合机器的网卡、当地时间、一个随机数来生成GUID。从理论上讲，如果一台机器每秒产生10000000个GUID，则可以保证（概率意义上）3240年不重复。

UUID是1.5中新增的一个类，在java.util下，用它可以产生一个号称全球唯一的ID
import java.util.UUID;
public class Test {
public static void main(String[] args) {
UUID uuid = UUID.randomUUID();
System.out.println (uuid);
}
}
编译运行输出：
07ca3dec-b674-41d0-af9e-9c37583b08bb

两种方式生成guid 与uuid

需要comm log 库
/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

public class RandomGUID extends Object {
protected final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory
.getLog(getClass());

public String valueBeforeMD5 = "";
public String valueAfterMD5 = "";
private static Random myRand;
private static SecureRandom mySecureRand;

private static String s_id;
private static final int PAD_BELOW = 0x10;
private static final int TWO_BYTES = 0xFF;

/*
* Static block to take care of one time secureRandom seed.
* It takes a few seconds to initialize SecureRandom. You might
* want to consider removing this static block or replacing
* it with a "time since first loaded" seed to reduce this time.
* This block will run only once per JVM instance.
*/

static {
mySecureRand = new SecureRandom();
long secureInitializer = mySecureRand.nextLong();
myRand = new Random(secureInitializer);
try {
s_id = InetAddress.getLocalHost().toString();
} catch (UnknownHostException e) {
e.printStackTrace();
}

}

/*
* Default constructor. With no specification of security option,
* this constructor defaults to lower security, high performance.
*/
public RandomGUID() {
getRandomGUID(false);
}

/*
* Constructor with security option. Setting secure true
* enables each random number generated to be cryptographically
* strong. Secure false defaults to the standard Random function seeded
* with a single cryptographically strong random number.
*/
public RandomGUID(boolean secure) {
getRandomGUID(secure);
}

/*
* Method to generate the random GUID
*/
private void getRandomGUID(boolean secure) {
MessageDigest md5 = null;
StringBuffer sbValueBeforeMD5 = new StringBuffer(128);

try {
md5 = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
logger.error("Error: " + e);
}

try {
long time = System.currentTimeMillis();
long rand = 0;

if (secure) {
rand = mySecureRand.nextLong();
} else {
rand = myRand.nextLong();
}
sbValueBeforeMD5.append(s_id);
sbValueBeforeMD5.append(":");
sbValueBeforeMD5.append(Long.toString(time));
sbValueBeforeMD5.append(":");
sbValueBeforeMD5.append(Long.toString(rand));

valueBeforeMD5 = sbValueBeforeMD5.toString();
md5.update(valueBeforeMD5.getBytes());

byte[] array = md5.digest();
StringBuffer sb = new StringBuffer(32);
for (int j = 0; j < array.length; ++j) {
int b = array[j] & TWO_BYTES;
if (b < PAD_BELOW)
sb.append('0');
sb.append(Integer.toHexString(b));
}

valueAfterMD5 = sb.toString();

} catch (Exception e) {
logger.error("Error:" + e);
}
}

/*
* Convert to the standard format for GUID
* (Useful for SQL Server UniqueIdentifiers, etc.)
* Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
*/
public String toString() {
String raw = valueAfterMD5.toUpperCase();
StringBuffer sb = new StringBuffer(64);
sb.append(raw.substring(0, 8));
sb.append("-");
sb.append(raw.substring(8, 12));
sb.append("-");
sb.append(raw.substring(12, 16));
sb.append("-");
sb.append(raw.substring(16, 20));
sb.append("-");
sb.append(raw.substring(20));

return sb.toString();
}

// Demonstraton and self test of class
public static void main(String args[]) {
for (int i=0; i< 100; i++) {
RandomGUID myGUID = new RandomGUID();
System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
System.out.println("rawGUID=" + myGUID.valueAfterMD5);
System.out.println("RandomGUID=" + myGUID.toString());
}
}

}

Answer 2

我的想法是 先随机生成一个字符串的长度值 n
然后随机生成一些字符：
Random r = new Random();

int n = Math.abs(r.nextInt());
char s[] = new char[n];

for(int i = 0; i< n; i++)
{
s[i] = (char)r.nextInt(128);
}

String s1 = new String(s);

最后这个s1就是生成的随机字串

Answer 3

没明白..具体点呗?

Answer 4

这个是个简单的方法：
public static String getCharRandom(int length) {
int[] array=new int[length];
char[] chars = new char[length];
for(int i = 0; i < length; i ++){
while (true) {
array[i] = (int)(Math.random()*1000);
if ((array[i] > 64 && array[i] < 91) ||
(array[i] > 96 && array[i] < 123)) break;
}
chars[i] = (char) array[i];
}
return new String(chars);
}