VB.NET 正则表达式完全指南

VB.NET通过 System.Text.RegularExpressions 命名空间提供正则表达式支持。本指南将详细介绍VB.NET中正则表达式的使用方法、性能优化和最佳实践。

1. 基础知识

1.1 导入命名空间

Imports System.Text.RegularExpressions

1.2 基本使用

Public Class RegexBasicsPublic Sub BasicExamples()Dim text As String = "Hello, my phone is 123-456-7890"' 创建正则表达式对象Dim regex As New Regex("\d+")' 检查是否匹配Dim isMatch As Boolean = regex.IsMatch(text)' 查找第一个匹配Dim match As Match = regex.Match(text)If match.Success ThenConsole.WriteLine($"Found: {match.Value}")End If' 查找所有匹配Dim matches As MatchCollection = regex.Matches(text)For Each m As Match In matchesConsole.WriteLine($"Found: {m.Value}")NextEnd Sub
End Class

1.3 正则表达式选项

Public Class RegexOptionsPublic Sub OptionsExample()' 不区分大小写Dim caseInsensitive As New Regex("hello", RegexOptions.IgnoreCase)' 多行模式Dim multiline As New Regex("^start", RegexOptions.Multiline)' 忽略空白字符和注释Dim ignored As New Regex("\d+  # 匹配数字\s*  # 可选的空白字符\w+  # 匹配单词", RegexOptions.IgnorePatternWhitespace)' 编译正则表达式以提高性能Dim compiled As New Regex("\d+", RegexOptions.Compiled)End Sub
End Class

2. 正则表达式语法

2.1 字符匹配

Public Class CharacterMatchingPublic Sub MatchingExamples()Dim text As String = "VB.NET 2022 is awesome! Price: $99.99"' 匹配数字Dim digits As New Regex("\d+")For Each m As Match In digits.Matches(text)Console.WriteLine($"Number: {m.Value}")Next' 匹配单词Dim words As New Regex("\w+")Dim wordMatches = words.Matches(text).Cast(Of Match)().Select(Function(m) m.Value).ToList()' 匹配空白字符Dim parts() As String = Regex.Split(text, "\s+")' 自定义字符类Dim vowels As New Regex("[aeiou]", RegexOptions.IgnoreCase)Dim vowelMatches = vowels.Matches(text).Cast(Of Match)().Select(Function(m) m.Value).ToList()End Sub
End Class

2.2 分组和捕获

Public Class GroupingExamplePublic Sub GroupExamples()Dim text As String = "John Smith, Jane Doe, Bob Johnson"' 基本分组Dim regex As New Regex("(\w+)\s(\w+)")For Each match As Match In regex.Matches(text)Console.WriteLine($"Full name: {match.Groups(0).Value}")Console.WriteLine($"First name: {match.Groups(1).Value}")Console.WriteLine($"Last name: {match.Groups(2).Value}")Next' 命名分组Dim namedRegex As New Regex("(?<first>\w+)\s(?<last>\w+)")For Each match As Match In namedRegex.Matches(text)Console.WriteLine($"First: {match.Groups("first").Value}")Console.WriteLine($"Last: {match.Groups("last").Value}")NextEnd Sub
End Class

3. 高级特性

3.1 替换操作

Public Class ReplacementOperationsPublic Function ReplaceExample(text As String) As String' 简单替换Dim result1 As String = Regex.Replace(text, "\d+", "X")' 使用委托Dim result2 As String = Regex.Replace(text, "\d+", _Function(match As Match)Dim number As Integer = Integer.Parse(match.Value)Return (number * 2).ToString()End Function)' 使用命名组的替换Dim regex As New Regex("(?<first>\w+)\s(?<last>\w+)")Dim result3 As String = regex.Replace(text, "${last}, ${first}")Return result3End Function
End Class

3.2 前瞻和后顾

Public Class LookAroundExamplePublic Sub LookAroundDemo()Dim text As String = "Price: $100, Cost: $50"' 正向前瞻Dim positiveAhead As New Regex("\d+(?=\s*dollars)")' 负向前瞻Dim negativeAhead As New Regex("\d+(?!\s*dollars)")' 正向后顾Dim positiveBehind As New Regex("(?<=\$)\d+")' 负向后顾Dim negativeBehind As New Regex("(?<!\$)\d+")End Sub
End Class

4. 实用工具类

4.1 验证器

Public Class ValidatorPrivate Shared ReadOnly EmailRegex As New Regex("^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$",RegexOptions.Compiled)Private Shared ReadOnly PhoneRegex As New Regex("^1[3-9]\d{9}$",RegexOptions.Compiled)Private Shared ReadOnly PasswordRegex As New Regex("^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$",RegexOptions.Compiled)Public Shared Function IsValidEmail(email As String) As BooleanIf String.IsNullOrEmpty(email) Then Return FalseReturn EmailRegex.IsMatch(email)End FunctionPublic Shared Function IsValidPhone(phone As String) As BooleanIf String.IsNullOrEmpty(phone) Then Return FalseReturn PhoneRegex.IsMatch(phone)End FunctionPublic Shared Function IsValidPassword(password As String) As BooleanIf String.IsNullOrEmpty(password) Then Return FalseReturn PasswordRegex.IsMatch(password)End Function
End Class

4.2 文本处理器

Public Class TextProcessorPrivate Shared ReadOnly UrlRegex As New Regex("https?://(?:[-\w.]|(?:%[\da-fA-F]{2}))+[^\s]*",RegexOptions.Compiled)Private Shared ReadOnly HtmlTagRegex As New Regex("<[^>]+>",RegexOptions.Compiled)Public Shared Function ExtractUrls(text As String) As IEnumerable(Of String)If String.IsNullOrEmpty(text) Then Return Enumerable.Empty(Of String)Return UrlRegex.Matches(text).Cast(Of Match)().Select(Function(m) m.Value)End FunctionPublic Shared Function StripHtmlTags(html As String) As StringIf String.IsNullOrEmpty(html) Then Return String.EmptyReturn HtmlTagRegex.Replace(html, String.Empty)End FunctionPublic Shared Function CleanWhitespace(text As String) As StringIf String.IsNullOrEmpty(text) Then Return String.EmptyReturn Regex.Replace(text.Trim(), "\s+", " ")End Function
End Class

5. 性能优化

5.1 静态编译正则表达式

Public Class RegexOptimization' 使用共享字段存储编译后的正则表达式Private Shared ReadOnly CompiledRegex As New Regex("\d+",RegexOptions.Compiled)' 使用延迟初始化Private Shared ReadOnly LazyRegex As New Lazy(Of Regex)(Function() New Regex("\d+", RegexOptions.Compiled))Public Sub OptimizedExample()' 使用编译后的正则表达式Dim isMatch As Boolean = CompiledRegex.IsMatch("123")' 使用延迟初始化的正则表达式Dim lazyMatch As Boolean = LazyRegex.Value.IsMatch("123")End Sub
End Class

5.2 性能考虑

Public Class PerformanceConsiderations' 1. 使用适当的选项Private Shared ReadOnly FastRegex As New Regex("\d+",RegexOptions.Compiled Or RegexOptions.ExplicitCapture)' 2. 避免过度使用通配符Private Shared ReadOnly BetterRegex As New Regex("[^/]*foo[^/]*",  ' 比 .*foo.* 更高效RegexOptions.Compiled)' 3. 使用非捕获组Private Shared ReadOnly NonCapturingRegex As New Regex("(?:\d+)(?:[a-z]+)",  ' 使用(?:)表示非捕获组RegexOptions.Compiled)
End Class

6. 异常处理

Public Class RegexExceptionHandlingPublic Shared Function CreateSafeRegex(pattern As String) As RegexTryReturn New Regex(pattern, RegexOptions.Compiled)Catch ex As ArgumentExceptionThrow New ArgumentException($"Invalid regex pattern: {ex.Message}", ex)End TryEnd FunctionPublic Shared Function SafeIsMatch(input As String, pattern As String) As BooleanTryReturn Regex.IsMatch(input, pattern)Catch ex As RegexMatchTimeoutExceptionConsole.WriteLine($"Regex matching timed out: {ex.Message}")Return FalseCatch ex As ArgumentExceptionConsole.WriteLine($"Invalid regex pattern: {ex.Message}")Return FalseEnd TryEnd Function
End Class

7. 单元测试

<TestClass>
Public Class ValidatorTests<TestMethod>Public Sub TestEmailValidation()Assert.IsTrue(Validator.IsValidEmail("test@example.com"))Assert.IsTrue(Validator.IsValidEmail("user@domain.co.uk"))Assert.IsFalse(Validator.IsValidEmail("invalid.email"))Assert.IsFalse(Validator.IsValidEmail("@domain.com"))End Sub<TestMethod>Public Sub TestPhoneValidation()Assert.IsTrue(Validator.IsValidPhone("13812345678"))Assert.IsFalse(Validator.IsValidPhone("12345678"))Assert.IsFalse(Validator.IsValidPhone("2381234567"))End Sub<TestMethod>Public Sub TestTextProcessing()Dim html As String = "<p>Hello</p><div>World</div>"Assert.AreEqual("HelloWorld",TextProcessor.StripHtmlTags(html))Dim text As String = "  multiple   spaces   here  "Assert.AreEqual("multiple spaces here",TextProcessor.CleanWhitespace(text))End Sub
End Class