Java Regex模式，由多个字符串包围

Question

This is a continuation of a question I asked earlier. I need to extract a date pattern, which is surrounded by the strings String1, String2, String3 String4. What I did was

Pattern pattern = Pattern.compile("(?<=String1\sString2\s(?:0?[1-9]|[12][0-9]|3[01])([- /.])(?:0?[1-9]|1[012])\\1(?:19|20)?\\d\\d?=\sString3\sString4)");

my date pattern is

(0?[1-9]|[12][0-9]|3[01])([- /.])(0?[1-9]|1[012])\\2(19|20)\\d\\d

which works fine but when trying to surround it with strings, I am facing trouble.

The date is in between String2 and String3. I am quite sure there is something wrong, as there is an error on my program saying invalid escape sequence but I can't figure it out. Any help is appreciated. Thanks in advance.

Answer 1

Here you have an invalid escape sequence:

"...(?<=String1\sString..."
               ^^

You have to escape the backslash literal in a java String to pass it into a regular expression pattern:

"...(?<=String1\\sString..."
               ^^^

You already had it right with the \\\\d for digits, but not with the \\\\s for whitespace.

Answer 2

Your regex is ending with:

\\d?=\sString3\sString4)

There it looks like you missed an opening square bracket to make it positive lookahead and of course \\s should be \\\\s . Change that part to:

\\d(?=\\sString3\\sString4)

Answer 3

I know that many people are not aware of the features of the wonderful class MessageFormat , so here a quick reminder:

MessageFormat format = new MessageFormat("String1 String2 {0,date} String3 String4");
try {
    Object[] parse = format.parse("String1 String2 31.8.2000 String3 String4");
    Date date = (Date) parse[0];
    System.out.println(date);
} catch (ParseException e) {
    e.printStackTrace();
}