详解Java判断是否是整数，小数或实数的正则表达式

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")); 
     
  } 
 
} 

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