在项目中遇到一处bug，调试的结果竟然是StringUtils.isNumeric(String str) 在捣鬼（采用的是org.apache.commons.lang.StringUtils），下面的代码是判断一个参数非空，且为整数：
if(StringUtils.isNumeric(str) && StringUtils.isNotBlank(str)){// do sth
} 在简单不过的代码，却隐藏着bug !
因为如果 str = "-1"; StringUtils.isNumeric(str) 返回的是 false! 真是肯爹不偿命啊。
下面是测试：
public static void main(String[] args)
{System.out.println(StringUtils.isNumeric("-1"));
} 运行结果：false
肯爹吧？用正则表达式实现不是很简单吗？怎么会这样，看了下源码：
public static boolean isNumeric(String str) {if (str == null) { return false; } int sz = str.length(); for (int i = 0; i < sz; i++) { if (Character.isDigit(str.charAt(i)) == false) { return false; } } return true; } 继续跳进去：
public static boolean isDigit(char ch) {return isDigit((int)ch); } 继续：
public static boolean isDigit(int codePoint) {boolean bDigit = false; <span style="color:#0000ff;">if (codePoint >= MIN_CODE_POINT && codePoint <=<span style="color:#000000;"> FAST_PATH_MAX) {bDigit =<span style="color:#000000;"> CharacterDataLatin1.isDigit(codePoint);} <span style="color:#0000ff;">else<span style="color:#000000;"> {<span style="color:#0000ff;">int plane =<span style="color:#000000;"> getPlane(codePoint);<span style="color:#0000ff;">switch<span style="color:#000000;">(plane) {<span style="color:#0000ff;">case(0<span style="color:#000000;">):bDigit =<span style="color:#000000;"> CharacterData00.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">case(1<span style="color:#000000;">):bDigit =<span style="color:#000000;"> CharacterData01.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">case(2<span style="color:#000000;">):bDigit =<span style="color:#000000;"> CharacterData02.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">case(3): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(4): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(5): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(6): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(7): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(8): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(9): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(10): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(11): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(12): <span style="color:#008000;">//<span style="color:#008000;"> Undefined<span style="color:#0000ff;">case(13): <span style="color:#008000;">//<span style="color:#008000;"> UndefinedbDigit =<span style="color:#000000;"> CharacterDataUndefined.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">case(14<span style="color:#000000;">):bDigit =<span style="color:#000000;"> CharacterData0E.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">case(15): <span style="color:#008000;">//<span style="color:#008000;"> Private Use<span style="color:#0000ff;">case(16): <span style="color:#008000;">//<span style="color:#008000;"> Private UsebDigit =<span style="color:#000000;"> CharacterDataPrivateUse.isDigit(codePoint);<span style="color:#0000ff;">break<span style="color:#000000;">;<span style="color:#0000ff;">default<span style="color:#000000;">:<span style="color:#008000;">//<span style="color:#008000;"> the argument's plane is invalid, and thus is an invalid codepoint<span style="color:#008000;">//<span style="color:#008000;"> bDigit remains false;<span style="color:#0000ff;">break<span style="color:#000000;">; }}<span style="color:#0000ff;">return<span style="color:#000000;"> bDigit;
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></pre>
在下面一步失败：
static boolean isDigit(int ch) {int type = getType(ch); return (type == Character.DECIMAL_DIGIT_NUMBER); }
也就是说他的实现完全没有考虑到 - + 前缀的问题，这不是傻叉吗？
下面的结果都是 false:
public static void main(String[] args)
{System.out.println(StringUtils.isNumeric("-1"));System.out.println(StringUtils.isNumeric("+1")); }
这是他的方法注释：
Checks if the String contains only unicode digits. A decimal point is not a unicode digit and returns false.
null will return false. An empty String ("") will return true.
StringUtils.isNumeric(null) = false
StringUtils.isNumeric("") = true
StringUtils.isNumeric(" ") = false
StringUtils.isNumeric(“123”) = true
StringUtils.isNumeric(“12 3”) = false
StringUtils.isNumeric(“ab2c”) = false
StringUtils.isNumeric(“12-3”) = false
StringUtils.isNumeric(“12.3”) = false
Parameters:
str the String to check, may be null
Returns:
true if only contains digits, and is non-null
只能包含 unicode 的数字， +， -， . 三者都不能算作是unicode 数字。
http://www.cnblogs.com/digdeep/p/4207097.html
