java - 如何找到源代码中的所有注释？

Question

注释有两种风格，C风格和C++风格，如何识别？

/* comments */

// comments

我可以随意使用任何方法和第三库。

Answer 1

为了可靠地找到 Java 源文件中的所有注释，我不会使用正则表达式，而是使用真正的词法分析器(也称为分词器)。

Java 的两个流行选择是:

• JFlex:http://jflex.de
• ANTLR:http://www.antlr.org

与流行的看法相反，ANTLR 还可以用于创建仅 没有解析器的词法分析器。

这是一个快速的 ANTLR 演示。您需要在同一目录中包含以下文件:

• > antlr-3.2.jar
• JavaCommentLexer.g(语法)
• 主程序.java
• Test.java(一个有效的(!)java 源文件，带有异国情调的注释)

JavaCommentLexer.g

lexer grammar JavaCommentLexer;

options {
  filter=true;
}

SingleLineComment
  :  FSlash FSlash ~('\r' | '\n')*
  ;

MultiLineComment
  :  FSlash Star .* Star FSlash
  ;

StringLiteral
  :  DQuote
     ( (EscapedDQuote)=> EscapedDQuote
     | (EscapedBSlash)=> EscapedBSlash
     | Octal
     | Unicode
     | ~('\\' | '"' | '\r' | '\n')
     )*
     DQuote {skip();}
  ;

CharLiteral
  :  SQuote
     ( (EscapedSQuote)=> EscapedSQuote
     | (EscapedBSlash)=> EscapedBSlash
     | Octal
     | Unicode
     | ~('\\' | '\'' | '\r' | '\n')
     )
     SQuote {skip();}
  ;

fragment EscapedDQuote
  :  BSlash DQuote
  ;

fragment EscapedSQuote
  :  BSlash SQuote
  ;

fragment EscapedBSlash
  :  BSlash BSlash
  ;

fragment FSlash
  :  '/' | '\\' ('u002f' | 'u002F')
  ;

fragment Star
  :  '*' | '\\' ('u002a' | 'u002A')
  ;

fragment BSlash
  :  '\\' ('u005c' | 'u005C')?
  ;

fragment DQuote
  :  '"' 
  |  '\\u0022'
  ;

fragment SQuote
  :  '\'' 
  |  '\\u0027'
  ;

fragment Unicode
  :  '\\u' Hex Hex Hex Hex
  ;

fragment Octal
  :  '\\' ('0'..'3' Oct Oct | Oct Oct | Oct)
  ;

fragment Hex
  :  '0'..'9' | 'a'..'f' | 'A'..'F'
  ;

fragment Oct
  :  '0'..'7'
  ;

主程序.java

import org.antlr.runtime.*;

public class Main {
  public static void main(String[] args) throws Exception {
    JavaCommentLexer lexer = new JavaCommentLexer(new ANTLRFileStream("Test.java"));
    CommonTokenStream tokens = new CommonTokenStream(lexer);
      for(Object o : tokens.getTokens()) {
      CommonToken t = (CommonToken)o;
      if(t.getType() == JavaCommentLexer.SingleLineComment) {
        System.out.println("SingleLineComment :: " + t.getText().replace("\n", "\\n"));
      }
      if(t.getType() == JavaCommentLexer.MultiLineComment) {
        System.out.println("MultiLineComment  :: " + t.getText().replace("\n", "\\n"));
      }
    }
  }
}

测试.java

\u002f\u002a <- multi line comment start
multi
line
comment // not a single line comment
\u002A/
public class Test {

  // single line "not a string"

  String s = "\u005C" \242 not // a comment \\\" \u002f \u005C\u005C \u0022;
  /*
  regular multi line comment
  */
  char c = \u0027"'; // the " is not the start of a string

  char q1 = '\u005c'';                  // == '\''
  char q2 = '\u005c\u0027';             // == '\''
  char q3 = \u0027\u005c\u0027\u0027;   // == '\''
  char c4 = '\047';

  String t = "/*";
  \u002f\u002f another single line comment
  String u = "*/";
}

现在，要运行演示，请执行以下操作:

bart@hades:~/Programming/ANTLR/Demos/JavaComment$ java -cp antlr-3.2.jar org.antlr.Tool JavaCommentLexer.g
bart@hades:~/Programming/ANTLR/Demos/JavaComment$ javac -cp antlr-3.2.jar *.java
bart@hades:~/Programming/ANTLR/Demos/JavaComment$ java -cp .:antlr-3.2.jar Main

你会看到控制台打印了以下内容:

MultiLineComment  :: \u002f\u002a <- multi line comment start\nmulti\nline\ncomment // not a single line comment\n\u002A/
SingleLineComment :: // single line "not a string"
SingleLineComment :: // a comment \\\" \u002f \u005C\u005C \u0022;
MultiLineComment  :: /*\n  regular multi line comment\n  */
SingleLineComment :: // the " is not the start of a string
SingleLineComment :: // == '\''
SingleLineComment :: // == '\''
SingleLineComment :: // == '\''
SingleLineComment :: \u002f\u002f another single line comment

编辑

当然，您可以自己用正则表达式创建一种词法分析器。但是，以下演示不处理源文件中的 Unicode 文字:

测试2.java

/* <- multi line comment start
multi
line
comment // not a single line comment
*/
public class Test2 {

  // single line "not a string"

  String s = "\" \242 not // a comment \\\" ";
  /*
  regular multi line comment
  */
  char c = '"'; // the " is not the start of a string

  char q1 = '\'';                  // == '\''
  char c4 = '\047';

  String t = "/*";
  // another single line comment
  String u = "*/";
}

主2.java

import java.util.*;
import java.io.*;
import java.util.regex.*;

public class Main2 {

  private static String read(File file) throws IOException {
    StringBuilder b = new StringBuilder();
    Scanner scan = new Scanner(file);
    while(scan.hasNextLine()) {
      String line = scan.nextLine();
      b.append(line).append('\n');
    }
    return b.toString();
  }

  public static void main(String[] args) throws Exception {
    String contents = read(new File("Test2.java"));

    String slComment = "//[^\r\n]*";
    String mlComment = "/\\*[\\s\\S]*?\\*/";
    String strLit = "\"(?:\\\\.|[^\\\\\"\r\n])*\"";
    String chLit = "'(?:\\\\.|[^\\\\'\r\n])+'";
    String any = "[\\s\\S]";

    Pattern p = Pattern.compile(
        String.format("(%s)|(%s)|%s|%s|%s", slComment, mlComment, strLit, chLit, any)
    );

    Matcher m = p.matcher(contents);

    while(m.find()) {
      String hit = m.group();
      if(m.group(1) != null) {
        System.out.println("SingleLine :: " + hit.replace("\n", "\\n"));
      }
      if(m.group(2) != null) {
        System.out.println("MultiLine  :: " + hit.replace("\n", "\\n"));
      }
    }
  }
}

如果您运行 Main2，控制台将打印以下内容:

MultiLine  :: /* <- multi line comment start\nmulti\nline\ncomment // not a single line comment\n*/
SingleLine :: // single line "not a string"
MultiLine  :: /*\n  regular multi line comment\n  */
SingleLine :: // the " is not the start of a string
SingleLine :: // == '\''
SingleLine :: // another single line comment