英文:
Extracting a password from a String using regular expressions
问题
我正在尝试解决一个练习，在这个练习中我需要从给定的文本中提取密码并打印出来。规则如下：
> 密码由数字和拉丁字母的大写和小写组成；
密码总是紧跟在单词“password”之后（它可以是大写或小写字母书写），但是可以用任意数量的空格和冒号:字符与之分隔。
我的问题是，我需要确保密码之前有单词“password”、随机数量的空格和一个冒号，并且我只需要打印出密码。
例如，如果输入是：
My email javacoder@gmail.com with password SECRET115. Here is my old PASSWORD: PASS111.
输出应为：
SECRET115
PASS111
我遇到了前瞻和后顾的问题，并在正则表达式中尝试了它们：
```java
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String text = scanner.nextLine();
Pattern pattern = Pattern.compile("(?<=password[\\s:]*)\\w*(?=\\W)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(text);
if (!matcher.find()) {
System.out.println("No passwords found.");
}
while (matcher.find()) {
System.out.println(matcher.group());
}
}
}
这个解决方案确实只打印了密码，但是它也不知名地打印了额外的换行。以上输入的输出看起来是这样的：
SECRET115
PASS111
另外，当我尝试将正则表达式更改为"(?<=password[\\s:]*)\\w{5,}(?=\\W)"以便只接受长度至少为5的密码时，程序只输出：
PASS111
另一个密码显然超过5个字符，为什么它被忽略了？
<details>
<summary>英文:</summary>
I am trying to solve an exercise in which I have to print the password in a given text. The rules are:
> a password consists of digits and Latin upper- and lowercase letters;
a password always follows the word "password" (it can be written in upper- or lowercase letters), but can be separated from it by any number of whitespaces and colon : characters.
My problem is that I need to make sure that the password is preceded by "password" and a random number of whitespaces and a colon, but I also must print the password only.
For example, if the input is:
My email javacoder@gmail.com with password SECRET115. Here is my old PASSWORD: PASS111.
The output should be:
SECRET115
PASS111
I stumbled upon lookaheads and lookbehinds and tried them in my regex:
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String text = scanner.nextLine();
Pattern pattern = Pattern.compile("(?<=password[\\s:]*)\\w*(?=\\W)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(text);
if (!matcher.find()) {
System.out.println("No passwords found.");
}
while (matcher.find()) {
System.out.println(matcher.group());
}
}
}
This solution does print passwords only, but it also prints extra newlines for no reason. The output for the above input looked like this:
SECRET115
PASS111
Also, when I try to change the regex to `"(?<=password[\\s:]*)\\w{5,}(?=\\W)"` so that the password accepted be at least of length 5, the program outputs just:
PASS111
The other password is clearly longer than 5 characters, why was it left out?
</details>
# 答案1
**得分**: 2
以下是翻译好的内容：
您可以使用正则表达式 `(?<=password|password:)\\s*(\\p{Alnum}+)`，这不仅易于理解，还能准确地给您提供结果。
```java
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static void main(String[] args) {
Pattern pattern = Pattern.compile("(?<=password|password:)\\s*(\\p{Alnum}+)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern
.matcher("我的电子邮件是javacoder@gmail.com，带有密码SECRET115。这是我的旧密码：PASS111。");
while (matcher.find()) {
System.out.println(matcher.group(1));
}
}
}
输出:
SECRET115
PASS111
正则表达式解释:
\p{Alnum}匹配字母数字字符。查阅此链接以了解更多信息。请注意，对于您的要求，不应该使用\w，因为它除了字母和数字之外，还会匹配下划线(_)。- 正则表达式使用正向后顾断言来断言
\\s*(\\p{Alnum}+)应该紧跟在(?<=password|password:)之后，即password或password: - 所需结果来自于指定为
(\\p{Alnum}+)的group(1)
如果您不喜欢使用 \p{Alnum}，您可以使用 [A-Za-z0-9] 来替代。
英文:
You can use the regex, (?<=password|password:)\\s*(\\p{Alnum}+) which is not only simple to understand but also gives you the result precisely.
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static void main(String[] args) {
Pattern pattern = Pattern.compile("(?<=password|password:)\\s*(\\p{Alnum}+)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern
.matcher("My email javacoder@gmail.com with password SECRET115. Here is my old PASSWORD: PASS111.");
while (matcher.find()) {
System.out.println(matcher.group(1));
}
}
}
Output:
SECRET115
PASS111
Explanation of the regex:
\p{Alnum}matches an alphanumeric character. Check this to learn more about it. Note that you should not use\wfor your requirement because it also matches underscore(_) apart from alphabets and digits.- The regex uses the positive lookbehind to assert that
\\s*(\\p{Alnum}+)should be followed by(?<=password|password:)i.e.passwordorpassword: - The desired result comes from
group(1)which is specified as(\\p{Alnum}+)
If you are not comfortable with \p{Alnum}, you can use [A-Za-z0-9] instead.
答案2
得分: 2
当您的密码正则表达式包含\w*时，正则表达式首先匹配空字符串。由于在if条件中调用了matcher.find()，此匹配不会显示出来。当您使用\w{5}时，第一个匹配是SECRET115，并且不会显示出来。
使用
\bpassword[\s:]*(\w+)
查看证明
解释
NODE EXPLANATION
--------------------------------------------------------------------------------
\b 单词字符 (\w) 与非单词字符之间的边界
--------------------------------------------------------------------------------
password 'password'
--------------------------------------------------------------------------------
[\s:]* 任意字符：空白字符 (\n、\r、\t、\f 和 ' ')，':'（出现次数为0次或多次，尽可能匹配最多的次数）
--------------------------------------------------------------------------------
( 分组并捕获到 ：
--------------------------------------------------------------------------------
\w+ 单词字符（a-z、A-Z、0-9、_）（出现次数为1次或多次，尽可能匹配最多的次数）
--------------------------------------------------------------------------------
) 结束
Scanner scanner = new Scanner(System.in);
String text = scanner.nextLine();
Pattern pattern = Pattern.compile("\\bpassword[\\s:]*(\\w+)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(text);
Boolean found = false;
while (matcher.find()) {
System.out.println(matcher.group(1));
found = true;
}
if (!found) {
System.out.println("No passwords found.");
}
输出：
SECRET115
PASS111
英文:
When your password regex contains \w* the regex matches an empty string first. This match is not shown because you call matcher.find() in the if condition. When you use \w{5}, the first match is the SECRET115, and it is not displayed.
Use
\bpassword[\s:]*(\w+)
See proof
EXPLANATION
NODE EXPLANATION
--------------------------------------------------------------------------------
\b the boundary between a word char (\w) and
something that is not a word char
--------------------------------------------------------------------------------
password 'password'
--------------------------------------------------------------------------------
[\s:]* any character of: whitespace (\n, \r, \t,
\f, and " "), ':' (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
( group and capture to :
--------------------------------------------------------------------------------
\w+ word characters (a-z, A-Z, 0-9, _) (1 or
more times (matching the most amount
possible))
--------------------------------------------------------------------------------
) end of
Scanner scanner = new Scanner(System.in);
String text = scanner.nextLine();
Pattern pattern = Pattern.compile("\\bpassword[\\s:]*(\\w+)", Pattern.CASE_INSENSITIVE);
Matcher matcher = pattern.matcher(text);
Boolean found = false;
while (matcher.find()) {
System.out.println(matcher.group(1));
found = true;
}
if (!found) {
System.out.println("No passwords found.");
}
Output:
SECRET115
PASS111
答案3
得分: 0
第一个匹配是因为在if条件中的matcher.find()调用而被吃掉的。只有从第二个匹配开始才会产生输出。
英文:
The first match is eaten because of the matcher.find() call in the if condition. Only starting from the second match you produce output.
答案4
得分: 0
尝试匹配 (?i)(password[\s:]*)(\w+) 并提取每个匹配中的第二组。在Java中，不支持可变长度的回顾后断言。
英文:
Try (?i)(password[\s:]*)(\w+)
and extract second group in every match
In java variable length lookbehind are not possible...
答案5
得分: 0
private static final Pattern PASSWORD_PATTERN =
Pattern.compile("password\\s*:?\\s*(?<password>[A-Za-z0-9]+)", Pattern.CASE_INSENSITIVE);
public static List<String> getAllPasswords(String str) {
Matcher matcher = PASSWORD_PATTERN.matcher(str);
List<String> passwords = new ArrayList<>();
while (matcher.find()) {
passwords.add(matcher.group("password"));
}
return passwords;
}
Demo you can find at regex101.com
英文:
private static final Pattern PASSWORD_PATTERN =
Pattern.compile("password\\s*:?\\s*(?<password>[A-Za-z0-9]+)", Pattern.CASE_INSENSITIVE);
public static List<String> getAllPasswords(String str) {
Matcher matcher = PASSWORD_PATTERN.matcher(str);
List<String> passwords = new ArrayList<>();
while (matcher.find()) {
passwords.add(matcher.group("password"));
}
return passwords;
}
Demo you can find at regex101.com
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