Java 正则表达式不匹配

Question

我正在尝试编写一个程序，该程序将返回 \begin{theorem} 和 \end{theorem} 之间以及 \begin 之间的所有文本{proof} 和 \end{proof}。

使用正则表达式似乎很自然，但由于存在很多潜在的元字符，因此需要对它们进行转义。

这是我编写的代码:

import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class LatexTheoremProofExtractor {

    // This is the LaTeX source that will be processed
    private String source = null;

    // These are the list of theorems and proofs that are extracted, respectively 
    private ArrayList<String> theorems = null;
    private ArrayList<String> proofs = null;

    // These are the patterns to match theorems and proofs, respectively 
    private static final Pattern THEOREM_REGEX = Pattern.compile("\\begin\\{theorem\\}(.+?)\\end\\{theorem\\}");
    private static final Pattern PROOF_REGEX = Pattern.compile("\\begin\\{proof\\}(.+?)\\end\\{proof\\}");

    LatexTheoremProofExtractor(String source) {
        this.source = source;
    }

    public void parse() {
        extractEntity("theorem");
        extractEntity("proof");
    }

    private void extractTheorems() {
        if(theorems != null) {
            return;
        }

        theorems = new ArrayList<String>();

        final Matcher matcher = THEOREM_REGEX.matcher(source);
        while (matcher.find()) {
            theorems.add(new String(matcher.group(1)));
        }   
    }

    private void extractProofs() {
        if(proofs != null) {
            return;
        }

        proofs = new ArrayList<String>();

        final Matcher matcher = PROOF_REGEX.matcher(source);
        while (matcher.find()) {
            proofs.add(new String(matcher.group(1)));
        }       
    }

    private void extractEntity(final String entity) {   
        if(entity.equals("theorem")) {
            extractTheorems();
        } else if(entity.equals("proof")) {
            extractProofs();
        } else {
            // TODO: Throw an exception or something
        }       
    }

    public ArrayList<String> getTheorems() {
        return theorems;
    }

}

下面是我失败的测试

@Test 
public void testTheoremExtractor() {
    String source = "\\begin\\{theorem\\} Hello, World! \\end\\{theorem\\}";
    LatexTheoremProofExtractor extractor = new LatexTheoremProofExtractor(source);
    extractor.parse();
    ArrayList<String> theorems = extractor.getTheorems();
    assertEquals(theorems.get(0).trim(), "Hello, World!");
}

显然我的测试表明我希望此测试中只有一场比赛，并且应该是“Hello, World!” (修剪后)。

当前theorems是一个空的、非null数组。因此我的 Matcher 与模式不匹配。谁能帮我理解为什么？

谢谢，埃里普

Answer 1

这是您需要对代码进行的更新 - 提取器方法中的 2 个正则表达式应更改为

private static final Pattern THEOREM_REGEX = Pattern.compile(Pattern.quote("\\begin\\{theorem\\}") + "(.+?)" + Pattern.quote("\\end\\{theorem\\}"));
private static final Pattern PROOF_REGEX = Pattern.compile(Pattern.quote("\\begin\\{proof\\}") + "(.+?)" + Pattern.quote("\\end\\{proof\\}"));

结果将是“Hello, World!”。 See IDEONE demo .

您拥有的字符串实际上是 \begin\{theorem\} Hello, World!\end\{定理\}。 Java 字符串中的文字反斜杠是双倍的，当您需要将 Java 中的文字反斜杠与正则表达式匹配时，需要使用 \\\\。避免backslash hell , Pattern.quote 可以提供帮助，告诉正则表达式将其中的所有子模式视为文字。

有关Pattern.quote的更多详细信息可以在 documentation 中找到。 :

Returns a literal pattern String for the specified String.
This method produces a String that can be used to create a Pattern that would match the string s as if it were a literal pattern.

Metacharacters or escape sequences in the input sequence will be given no special meaning.