public static boolean isNumeric(String str) {
        if (null == str) {
            return false;
        }

        int length = str.length();

        for (int i = 0; i < length; i++) {
            if (!Character.isDigit(str.charAt(i))) {
                return false;
            }
        }

        return true;
    }

public boolean isNumeric(String str){ 
   Pattern pattern = Pattern.compile("[0-9]*"); 
   Matcher isNum = pattern.matcher(str);
   if( !isNum.matches() ){
       return false; 
   } 
   return true; 
}

使用org.apache.commons.lang
org.apache.commons.lang.StringUtils;
boolean isNunicodeDigits=StringUtils.isNumeric("aaa123456789");
http://jakarta.apache.org/commons/lang/api-release/index.html下面的解释:
isNumeric
public static boolean isNumeric(String str)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

Among the above three methods, the second method is more flexible.

The first and third methods can only verify numbers without the negative sign "-", that is, if you enter a negative number -199, the output result will be false;

The second method can be used to verify negative numbers by modifying the regular expression. Just change the regular expression to "^-?[0-9]+" and change it to "-?[0-9]+.? [0-9]+" will match all numbers.