经常要用到java来产生随机字符串，感觉org.apache.commons.lang.RandomStringUtils还是不够用，比如不能按照指定格式来产生随机串，因此自己写了一个RandomString类，放在这里记录一下。源文件在用法简介的后面。
一、用法简介：
//产生4位的，由数字和大写字母组成的随机字符串；
String s1=RandomString.get(4);

//产生5位的，由数字组成的随机字符串；
String s2=RandomString.getNum(5);

//产生6位的，由十六进制字符组成的随机字符串；
String s3=RandomString.getHex(6);

//产生如下格式的随机字符串“{E3-K91Z}”，“?”表示一个占位符；
String s4=RandomString.get("{??-????}");

//产生如下格式的随机字符串“Are you W5B?”，可以自己指定临时占位符，这里用“#”；
String s5=RandomString.get("Are you ###?",'#');
二、源文件：
public class RandomString {
private static final String src_number = "0123456789";
private static final String src_lower = "abcdefghijklmnopqrstuvwxyz";
private static final String src_upper = src_lower.toUpperCase();
private static final String src_hex_lower = "0123456789abcdef";
private static final String src_hex_upper = src_hex_lower.toUpperCase();
private static final String esc_char = "?";

public static String get(int size) {
StringBuffer r = new StringBuffer(size);
String src = src_number + src_upper;
for (int i = 0; i < size; i++) {
r.append(getRandomChar(src));
}
return r.toString();
}

public static String get(String format) {
StringBuffer r = new StringBuffer(format.length());
String src = src_number + src_upper;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(esc_char)) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}

public static String get(String format, char esc) {
StringBuffer r = new StringBuffer(format.length());
String src = src_number + src_upper;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(String.valueOf(esc))) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}

public static String getNum(int size) {
StringBuffer r = new StringBuffer(size);
String src = src_number;
for (int i = 0; i < size; i++) {
r.append(getRandomChar(src));
}
return r.toString();
}

public static String getNum(String format) {
StringBuffer r = new StringBuffer(format.length());
String src = src_number;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(esc_char)) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}
//Java中文网:http://www.javaweb.cc
public static String getNum(String format, char esc) {
StringBuffer r = new StringBuffer(format.length());
String src = src_number;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(String.valueOf(esc))) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}

public static String getHex(int size) {
StringBuffer r = new StringBuffer(size);
String src = src_hex_upper;
for (int i = 0; i < size; i++) {
r.append(getRandomChar(src));
}
return r.toString();
}

public static String getHex(String format) {
StringBuffer r = new StringBuffer(format.length());
String src = src_hex_upper;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(esc_char)) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}

public static String getHex(String format, char esc) {
StringBuffer r = new StringBuffer(format.length());
String src = src_hex_upper;
for (int i = 0; i < format.length(); i++) {
String curr = String.valueOf(format.charAt(i));
if (curr.equalsIgnoreCase(String.valueOf(esc))) {
r.append(getRandomChar(src));
} else {
r.append(curr);
}
}
return r.toString();
}
//Java教程:http://www.javaweb.cc
private static final String getRandomChar(String src) {
if (null==src||"".equals(src)) {
return "";
}
return String.valueOf((src.charAt((int) (Math.random() * src.length()))));
}
}