分割字符串到数组/替换字符串/返回指定字节长度的字符串/判断是否为浮点数，包括double和float/email判断/是否纯汉字判断/空白判断

package 字符串类;
import java.util.*;
import java.util.regex.Pattern;

public class 某人编写的字符串工具类 {

/**
* 分割字符串到数组
*
* @param str String 原始字符串
* @param splitsign String 分隔符
* @return String[] 分割后的字符串数组
*/
@SuppressWarnings("unchecked")
public static String[] split(String str, String splitsign) {
int index;
if (str == null || splitsign == null)
return null;
ArrayList al = new ArrayList();
while ((index = str.indexOf(splitsign)) != -1) {
al.add(str.substring(0, index));
str = str.substring(index + splitsign.length());
}
al.add(str);
return (String[]) al.toArray(new String[0]);
}

/**
* 替换字符串
*
* @param from String 原始字符串
* @param to String 目标字符串
* @param source String 母字符串
* @return String 替换后的字符串
*/
public static String replace(String from, String to, String source) {
if (source == null || from == null || to == null)
return null;
StringBuffer bf = new StringBuffer("");
int index = -1;
while ((index = source.indexOf(from)) != -1) {
bf.append(source.substring(0, index) + to);
source = source.substring(index + from.length());
index = source.indexOf(from);
}
bf.append(source);
return bf.toString();
}

/**
* 替换字符串，能能够在HTML页面上直接显示(替换双引号和小于号)
*
* @param str String 原始字符串
* @return String 替换后的字符串
*/
public static String htmlencode(String str) {
if (str == null) {
return null;
}

return replace("\"", """, replace("<", "<", str));
}

/**
* 替换字符串，将被编码的转换成原始码（替换成双引号和小于号）
*
* @param str String
* @return String
*/
public static String htmldecode(String str) {
if (str == null) {
return null;
}

return replace(""", "\"", replace("<", "<", str));
}

private static final String _BR = "<br/>";

/**
* 在页面上直接显示文本内容，替换小于号，空格，回车，TAB
*
* @param str String 原始字符串
* @return String 替换后的字符串
*/
public static String htmlshow(String str) {
if (str == null) {
return null;
}

str = replace("<", "<", str);
str = replace(" ", " ", str);
str = replace("\r\n", _BR, str);
str = replace("\n", _BR, str);
str = replace("\t", "    ", str);
return str;
}

/**
* 返回指定字节长度的字符串
*
* @param str String 字符串
* @param length int 指定长度
* @return String 返回的字符串
*/
public static String toLength(String str, int length) {
if (str == null) {
return null;
}
if (length <= 0) {
return "";
}
try {
if (str.getBytes("GBK").length <= length) {
return str;
}
} catch (Exception ex) {
}
StringBuffer buff = new StringBuffer();

int index = 0;
char c;
length -= 3;
while (length > 0) {
c = str.charAt(index);
if (c < 128) {
length--;
} else {
length--;
length--;
}
buff.append(c);
index++;
}
buff.append("...");
return buff.toString();
}

/**
* 判断是否为整数
*
* @param str 传入的字符串
* @return 是整数返回true,否则返回false
*/
public static boolean isInteger(String str) {
Pattern pattern = Pattern.compile("^[-\\+]?[\\d]*$");
return pattern.matcher(str).matches();
}

/**
* 判断是否为浮点数，包括double和float
*
* @param str 传入的字符串
* @return 是浮点数返回true,否则返回false
*/
public static boolean isDouble(String str) {
Pattern pattern = Pattern.compile("^[-\\+]?[.\\d]*$");
return pattern.matcher(str).matches();
}

/**
* 判断输入的字符串是否符合Email样式.
*
* @param str 传入的字符串
* @return 是Email样式返回true,否则返回false
*/
public static boolean isEmail(String str) {
Pattern pattern = Pattern.compile("^\\w+([-+.]\\w+)*@\\w+([-.]\\w+)*\\.\\w+([-.]\\w+)*$");
return pattern.matcher(str).matches();
}

/**
* 判断输入的字符串是否为纯汉字
*
* @param str 传入的字符窜
* @return 如果是纯汉字返回true,否则返回false
*/
public static boolean isChinese(String str) {
Pattern pattern = Pattern.compile("[\u0391-\uFFE5]+$");
return pattern.matcher(str).matches();
}

/**
* 是否为空白,包括null和""
*
* @param str
* @return
*/
public static boolean isBlank(String str) {
return str == null || str.trim().length() == 0;
}

/**
* 判断是否为质数
*
* @param x
* @return
*/
public static boolean isPrime(int x) {
if (x <= 7) {
if (x == 2 || x == 3 || x == 5 || x == 7)
return true;
}
int c = 7;
if (x % 2 == 0)
return false;
if (x % 3 == 0)
return false;
if (x % 5 == 0)
return false;
int end = (int) Math.sqrt(x);
while (c <= end) {
if (x % c == 0) {
return false;
}
c += 4;
if (x % c == 0) {
return false;
}
c += 2;
if (x % c == 0) {
return false;
}
c += 4;
if (x % c == 0) {
return false;
}
c += 2;
if (x % c == 0) {
return false;
}
c += 4;
if (x % c == 0) {
return false;
}
c += 6;
if (x % c == 0) {
return false;
}
c += 2;
if (x % c == 0) {
return false;
}
c += 6;
}
return true;
}

public static void main(String[] args) {
String[] numbers = { "12345", "-12345", "123.45", "-123.45", ".12345", "-.12345", "a12345", "12345a", "123.a45" };
for (String str : numbers) {
System.out.println(str + "=" + isInteger(str) + " " + isDouble(str));
}

String[] emails = { "1@2.com", "1.2@3.com", "1@3.4.5.com" };
for (String str : emails) {
System.out.println(str + "=" + isEmail(str));
}
String[] chineses = { "中国", "1中国", "中国1", "1中国2", "中1国" };
for (String str : chineses) {
System.out.println(str + "=" + isChinese(str));
}
}
}