工具类：获得随机字母和数字的组合（字母+数字组合，字母组合，数字组合）

package util;

import java.util.Random;
/**
 * 
 * @author jkfeng
 * 获得随机字母和数字的组合（字母+数字组合，字母组合，数字组合）
 *
 */
public class RandomCharOrNumUtil {
	public static void main(String[] args) {
		System.out.println(getCharAndNum(6));
		System.out.println(getChar(6));
		System.out.println(getNum(6));
	}
	/**
	 * 获得随机子母和数字的组合
	 * @param length
	 * @return 随机字母和数字的组合
	 */
	public static String getCharAndNum(int length) {
		String val = "";
		Random random = new Random();
		String charOrNum = "";
		for (int i = 0; i < length; i++) {
			if (i == 0) {
				charOrNum = "char";
			}else if (i == (length-1)) {
				charOrNum = "num";
			}else {
				charOrNum = (random.nextInt(2)%2 == 0) ? "char":"num";
			}
			if ("num".equalsIgnoreCase(charOrNum)) {//如何获得 0-9之间的数字
				int num = random.nextInt(10);
				if (num == 0) {
					num = 2;
				}
				if (num == 1) {
					num = 5;
				}
				val += String.valueOf(num);
			}else {//如何获得随机的字符				//97 - 122   0-25
				char char1  = (char)(97+random.nextInt(26));
				if (char1 == 'o') {
					char1 = 'm';
				}
				val += String.valueOf(char1);
			}
		}
		val = val.toUpperCase();
		return val;
		
 	}
	
	/**
	 * 获得随机字母组合
	 * @param length
	 * @return 随机字母组合
	 */
	public static String getChar(int length) {
		String val = "";
		Random random = new Random();
		for (int i = 0; i < length; i++) {
			//如何获得随机的字符				//97 - 122   0-25
			char char1  = (char)(97+random.nextInt(26));
			val += String.valueOf(char1);
		}
		val = val.toUpperCase();
		return val;
 	}
	
	/**
	 * 获得随机数字组合
	 * @param length
	 * @return 随机数字组合
	 */
	public static String getNum(int length) {
		String val = "";
		Random random = new Random();
		for (int i = 0; i < length; i++) {//如何获得 0-9之间的数字
			int num  = random.nextInt(10);
			val += String.valueOf(num);
		}
		val = val.toUpperCase();
		return val;
 	}
}