Java正则表达式: finding match errors

Question

我想知道正则表达式匹配失败时错误的确切位置。但我在 Matcher 和 Pattern 中都找不到任何可以做到这一点的类或方法。有什么帮助吗？

Pattern regExpPattern = Pattern.compile("My regular expression");
Matcher matcher = regExpPattern.matcher("Input string");
if (!matcher.matches()) {
    // Better error handling here
    throw new Exception("Invalid expression");
}

编辑:以下是工作代码摘录:

public class FOPRequestParser {

private static Pattern regExpPattern;
private static String requestRegexp;
private static String regexpSeparators;

private static String[] INPUT_FORMATS = new String[] {"FO", "IFP"};
private static String[] OUTPUT_FORMATS = new String[] {"PDF", "PS", "AFP", "IFP"};

static {
    regexpSeparators = new String("(\\Q|@|\\E|=)");

    requestRegexp = new String("run" + regexpSeparators + "[a-zA-Z]+.*"
            + regexpSeparators + "inputFormat=(");
    for (int i = 0; i < INPUT_FORMATS.length; ++i) {
        requestRegexp += INPUT_FORMATS[i];
        if (i != INPUT_FORMATS.length - 1) {
            requestRegexp += "|";
        }
    }
    requestRegexp += ")" + regexpSeparators + "[a-zA-Z]+.*"
            + regexpSeparators + "outputFormat=(";
    for (int i = 0; i < OUTPUT_FORMATS.length; ++i) {
        requestRegexp += OUTPUT_FORMATS[i];
        if (i != OUTPUT_FORMATS.length - 1) {
            requestRegexp += "|";
        }
    }
    requestRegexp += ")";
}


public FOPRequestParser() {
    regExpPattern = Pattern.compile(requestRegexp);
}

public void processRequest(String request) throws Exception {
    Matcher matcher = regExpPattern.matcher(request);
    if (!matcher.matches()) {
        throw new Exception("Invalid expression");
    }
}

public static void main(String[] args) {

    FOPRequestParser conversion = new FOPRequestParser();
    try {
        String exp1 = new String("run|@|" +
                "c:\\input_file.fo|@|" +
                "inputFormat=FO|@|" +
                "c:\\output_file.pdf|@|" +
                "outputFormat=PDF");
        conversion.processRequest(exp1);
        System.out.println("Valid expression");
    } catch (Exception e) {
        e.printStackTrace();
    }
}

}

Answer 1

没有 API 方法可以告诉您为什么不匹配。

如果您将其用于任何类型的(输入)验证，您必须抛出一个通用异常，例如“提供的值与预期模式不匹配 ”。