java生成字符

1. 在java语言中如何随机地生成一个字符串

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 rece 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());
}
}

}

2. Java怎么生成一个指定长度的字符串类似于验证码

我写了个方法，参数是你指定的长度，按照这个方法，可以随机生成字符串。但是不保证重复，可以参考一下。

publicclassRandomString{

	privatefinalstaticbyte[]seed={'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'};


	(intlength){//参数为指定的字符串长度
		Stringstr="";

		StringBufferbuffer=newStringBuffer();
		for(intj=0;j<length;j++){
			inti=(int)(Math.random()*25);
			charb=(char)seed[i];
			buffer.append(b);
		}
		str=buffer.toString();

		returnstr;
	}


	publicstaticvoidmain(String[]args){

		StringrandomStr=getRandomString(6);

		System.out.println(randomStr);
	}


}

3. Java怎么生成一个指定长度的字符串

public class GenString {x0dx0apublic static String gen(int length) {x0dx0a char[] ss = new char[length];x0dx0a int[] flag = {0,0,0}; //A-Z, a-z, 0-9x0dx0a int i=0;x0dx0awhile(flag[0]==0 || flag[1]==0 || flag[2]==0 || i

4. Java如何生成随机字符串

import java.util.Random;

public class Stat {
public static void main(String[] args) {
// Math.random() 获取0～1之间的double类型数值
int num = (int)(Math.random()*100); // 获取0～100之间的整数
System.out.println(num);
System.out.println(getRandomString(12));
}

// 获取随机字符串
public static String getRandomString(int length) { // length 字符串长度
StringBuffer buffer = new StringBuffer("");
StringBuffer sb = new StringBuffer();
Random r = new Random();
int range = buffer.length();
for (int i = 0; i < length; i ++) {
sb.append(buffer.charAt(r.nextInt(range)));
}
return sb.toString();
}
}

5. java随机生成字符串

代码如下：
import java.util.Random;

public class Demo {
public static void main(String args[]){
Demo demo = new Demo();
System.out.println(demo.getRandomString(20));
}

public static String getRandomString(int length) {
StringBuffer buffer = new StringBuffer("");
StringBuffer sb = new StringBuffer();
Random random = new Random();
int range = buffer.length();
for (int i = 0; i < length; i ++) {
sb.append(buffer.charAt(random.nextInt(range)));
}
return sb.toString();
}
}
代码解读：

调用getRandomString（）方法时的length参数为要返回的随机字符串的长度。

StringBuffer buffer = new StringBuffer("");此段字符串代表要出现的字符还可以是其他字符

如：- + = * 。.等等

6. Java随机生成字符串

代码如下，供参考：

importjava.util.Random;

publicclassMain{
publicstaticvoidmain(String[]args){
char[]chs={'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'};
Stringstr=newMain().getStr(chs);
System.out.println(str);
}

publicStringgetStr(char[]chs){
Stringstr="";
Randomrandom=newRandom();
for(inti=0;i<4;i++){
//这种写法易于扩展，chs内容改了不用修改代码
str+=chs[random.nextInt(chs.length)];
}
str+=random.nextInt(10);

returnstr;
}
}

7. java怎么随机生成一个字符串

/**
* 产生随机字符串
* */
private static Random randGen = null;
private static char[] numbersAndLetters = null;

public static final String randomString(int length) {
if (length < 1) {
return null;
}
if (randGen == null) {
randGen = new Random();
numbersAndLetters = ("" +
"").toCharArray();
//numbersAndLetters = ("").toCharArray();
}
char [] randBuffer = new char[length];
for (int i=0; i<randBuffer.length; i++) {
randBuffer[i] = numbersAndLetters[randGen.nextInt(71)];
//randBuffer[i] = numbersAndLetters[randGen.nextInt(35)];
}
return new String(randBuffer);
}

//调用此方法randomString(int),int是字符串的长度，即可产生指定长度的随机字符串。