经常会遇到这样的情况，需要判断一个字符串是否是一个合法的数，包括整数，小数或者实数。
网上查到很多文章大多是判断这个字符串是否全为数字，比如下面这段来自StringUtils的代码，可以看到，13.2这样的数字实际上会返回false，可是，他的确是一个数字。
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; }
当然，网上还能查到很多其他方式，诸如用正则表达式判断是否0-9，用字符ascii码判断是否是数字以及用Double.parseDouble()是否抛出异常来判断是否为数字。
事实上，除了最后一种方式能达到我们的要求，其他的都很难真正做到类似的判断。但是最后一种方式也很难区别出到底是正整数，负整数，正小数还是负小数，而且，捕获异常的方式实在是有些难看。
基于此原因，我自己写了一个工具类，专门用作数的检测，目前能够检测正整数，负整数，整数，正小数，负小数，小数以及实数，采用的仍然是正则表达式的方式，当然，如果有遗漏或者错误，欢迎联系我以便更正，同时也欢迎修改或使用这些代码以便符合你的应用场景。
可以简单讲下正则的思想以便修改，
1. 对于正整数而言，可以带+号，第一个数字不能为0
2. 对于负整数而言，必须带负号，第一个数字也不能为0
3. 对于整数而言，实际是由0，正整数和负整数组成的，所以偷个懒用前两个方法一起判断
4. 对于正小数而言，可以考带+号，并考虑两种情况，第一个数字为0和第一个数字不为0，第一个数字为0时，则小数点后面应该不为0，第一个数字不为0时，小数点后可以为任意数字
5. 对于负小数而言，必须带负号，其余都同上
6. 对于小数，可以带正负号，并且带小数点就行了，但是至少保证小数点有一边不为空，所以这里还是分左边不为空和右边不为空的情况
7. 实数比较简单，，要么是整数，要么是小数
package com.sap.cesp.creditinsight.web.app.util; import java.util.regex.Matcher; import java.util.regex.Pattern; public class NumberValidationUtils { private static boolean isMatch(String regex, String orginal){ if (orginal == null || orginal.trim().equals("")) { return false; } Pattern pattern = Pattern.compile(regex); Matcher isNum = pattern.matcher(orginal); return isNum.matches(); } public static boolean isPositiveInteger(String orginal) { return isMatch("^\\+{0,1}[1-9]\\d*", orginal); } public static boolean isNegativeInteger(String orginal) { return isMatch("^-[1-9]\\d*", orginal); } public static boolean isWholeNumber(String orginal) { return isMatch("[+-]{0,1}0", orginal) || isPositiveInteger(orginal) || isNegativeInteger(orginal); } public static boolean isPositiveDecimal(String orginal){ return isMatch("\\+{0,1}[0]\\.[1-9]*|\\+{0,1}[1-9]\\d*\\.\\d*", orginal); } public static boolean isNegativeDecimal(String orginal){ return isMatch("^-[0]\\.[1-9]*|^-[1-9]\\d*\\.\\d*", orginal); } public static boolean isDecimal(String orginal){ return isMatch("[-+]{0,1}\\d+\\.\\d*|[-+]{0,1}\\d*\\.\\d+", orginal); } public static boolean isRealNumber(String orginal){ return isWholeNumber(orginal) || isDecimal(orginal); } }
测试用例如下：
package com.sap.cesp.creditinsight.web.app.util; import junit.framework.Assert; import org.junit.Test; public class NumberValidationUtilsTest { /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isPositiveInteger(java.lang.String)} */ //correct test case: 1, 87653521123567 //wrong test case: 0.1, 0, 0123, -1, -0.1, ab @Test public void testIsPositiveInteger() { Assert.assertTrue(NumberValidationUtils.isPositiveInteger("1")); Assert.assertTrue(NumberValidationUtils.isPositiveInteger("+12")); Assert.assertTrue(NumberValidationUtils.isPositiveInteger("87653521123567")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0.1")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0123")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("-1")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("-0.1")); Assert.assertFalse(NumberValidationUtils.isPositiveInteger("ab")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isNegativeInteger(java.lang.String)} */ //correct test case: -1, -87653521123567 //wrong test case: 0.1, 0, 0123, 1, -0.1, -ab @Test public void testIsNegativeInteger() { Assert.assertTrue(NumberValidationUtils.isNegativeInteger("-1")); Assert.assertTrue(NumberValidationUtils.isNegativeInteger("-87653521123567")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0.1")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0123")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("1")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("-0.1")); Assert.assertFalse(NumberValidationUtils.isNegativeInteger("ab")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isWholeNumber(java.lang.String)}. */ //correct test case: -1, 0, 1, 8673434231, -282464334 //wrong test case: 0.1, 0123, -0.1, ab @Test public void testIsWholeNumber() { Assert.assertTrue(NumberValidationUtils.isWholeNumber("-1")); Assert.assertTrue(NumberValidationUtils.isWholeNumber("0")); Assert.assertTrue(NumberValidationUtils.isWholeNumber("1")); Assert.assertTrue(NumberValidationUtils.isWholeNumber("+12")); Assert.assertTrue(NumberValidationUtils.isWholeNumber("8673434231")); Assert.assertTrue(NumberValidationUtils.isWholeNumber("-282464334")); Assert.assertFalse(NumberValidationUtils.isWholeNumber("0123")); Assert.assertFalse(NumberValidationUtils.isWholeNumber("0.1")); Assert.assertFalse(NumberValidationUtils.isWholeNumber("-0.1")); Assert.assertFalse(NumberValidationUtils.isWholeNumber("ab")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isPositiveDecimal(java.lang.String)} */ //correct test case: 0.1, 0.132213, 1.0 //wrong test case: 1, 0.0, 0123, -1, -0.1 @Test public void testIsPositiveDecimal() { Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("0.1")); Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("0.132213")); Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("30.00")); Assert.assertTrue(NumberValidationUtils.isDecimal("0.")); Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("+12.0")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("0123")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("1")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("0.0")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("ab")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("-1")); Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("-0.1")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isNegativeDecimal(java.lang.String)} */ //correct test case: -0.132213, -1.0 //wrong test case: 1, 0, 0123, -1, 0.1 @Test public void testIsNegativeDecimal() { Assert.assertTrue(NumberValidationUtils.isNegativeDecimal("-0.132213")); Assert.assertTrue(NumberValidationUtils.isNegativeDecimal("-1.0")); Assert.assertTrue(NumberValidationUtils.isDecimal("-0.")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("1")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0123")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0.0")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("ab")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("-1")); Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0.1")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isDecimal(java.lang.String)}. */ //correct test case: 0.1, 0.00, -0.132213 //wrong test case: 1, 0, 0123, -1, 0., ba @Test public void testIsDecimal() { Assert.assertTrue(NumberValidationUtils.isDecimal("0.1")); Assert.assertTrue(NumberValidationUtils.isDecimal("0.00")); Assert.assertTrue(NumberValidationUtils.isDecimal("+0.0")); Assert.assertTrue(NumberValidationUtils.isDecimal("-0.132213")); Assert.assertTrue(NumberValidationUtils.isDecimal("0.")); Assert.assertFalse(NumberValidationUtils.isDecimal("1")); Assert.assertFalse(NumberValidationUtils.isDecimal("0123")); Assert.assertFalse(NumberValidationUtils.isDecimal("0")); Assert.assertFalse(NumberValidationUtils.isDecimal("ab")); Assert.assertFalse(NumberValidationUtils.isDecimal("-1")); } /** * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isRealNumber(java.lang.String)}. */ //correct test case: 0.032213, -0.234, 0.0, 1, -1, 0 //wrong test case: 00.13, ab, +0.14 @Test public void testIsRealNumber() { Assert.assertTrue(NumberValidationUtils.isRealNumber("0.032213")); Assert.assertTrue(NumberValidationUtils.isRealNumber("-0.234")); Assert.assertTrue(NumberValidationUtils.isRealNumber("0.0")); Assert.assertTrue(NumberValidationUtils.isRealNumber("1")); Assert.assertTrue(NumberValidationUtils.isRealNumber("+0.14")); Assert.assertTrue(NumberValidationUtils.isRealNumber("-1")); Assert.assertTrue(NumberValidationUtils.isRealNumber("0.0")); Assert.assertFalse(NumberValidationUtils.isRealNumber("00.13")); Assert.assertFalse(NumberValidationUtils.isRealNumber("ab")); } }