Java正則表達式：查找匹配錯誤

Question

我想知道當正則表達式匹配失敗時錯誤的確切位置。 但是我在Matcher中找不到任何類或方法都無法在Pattern中做到這一點。 有什么幫助嗎？

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");
}

編輯：這是一個工作代碼摘錄：

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

沒有API方法可以告訴您為什么不匹配。

如果將其用於任何形式的（輸入）驗證，則必須拋出一個通用異常，其內容為“提供的值與預期的模式<put-regex-or-human-可讀模式-here>不匹配” 。

Answer 2

這個解決方案是什么。 確實不是很好，但是對於我的需求卻有效：

int index = -1;
try {
     Field declaredField = Matcher.class.getDeclaredField("last");      
     declaredField.setAccessible(true); 
     index =Integer.parseInt(declaredField.get(matcher).toString()); } catch
(Exception e) { }