属性模式匹配需要很长时间

I have a regex to get the src and the remaining attributes for all the images present in the content.

我有一个正则表达式来获取内容中存在的所有图像的src和剩余属性。

<img *((.|\s)*?) *src *= *['"]([^'"]*)['"] *((.|\s)*?) */*>

If the content I am matching against is like

如果我匹配的内容是这样的

<img src=src1"/> <img src=src2"/>

the find(index) hangs and I see the following in the thread dump

find(索引)挂起,我在线程转储中看到以下内容

at java.util.regex.Pattern$LazyLoop.match(Pattern.java:4357)
    at java.util.regex.Pattern$GroupTail.match(Pattern.java:4227)
    at java.util.regex.Pattern$BranchConn.match(Pattern.java:4078)
    at java.util.regex.Pattern$CharProperty.match(Pattern.java:3345)
    at java.util.regex.Pattern$Branch.match(Pattern.java:4114)
    at java.util.regex.Pattern$GroupHead.match(Pattern.java:4168)
    at java.util.regex.Pattern$LazyLoop.match(Pattern.java:4357)
    at java.util.regex.Pattern$GroupTail.match(Pattern.java:4227)
    at java.util.regex.Pattern$BranchConn.match(Pattern.java:4078)
    at java.util.regex.Pattern$CharProperty.match(Pattern.java:3345)
    at java.util.regex.Pattern$Branch.match(Pattern.java:4114)
    at java.util.regex.Pattern$GroupHead.match(Pattern.java:4168)
    at java.util.regex.Pattern$LazyLoop.match(Pattern.java:4357)
    at java.util.regex.Pattern$GroupTail.match(Pattern.java:4227)
    at java.util.regex.Pattern$BranchConn.match(Pattern.java:4078)
    at java.util.regex.Pattern$CharProperty.match(Pattern.java:3345)
    at java.util.regex.Pattern$Branch.match(Pattern.java:4114)
    at java.util.regex.Pattern$GroupHead.match(Pattern.java:4168)
    at java.util.regex.Pattern$LazyLoop.match(Pattern.java:4357)
    at java.util.regex.Pattern$GroupTail.match(Pattern.java:4227)
    at java.util.regex.Pattern$BranchConn.match(Pattern.java:4078)
    at java.util.regex.Pattern$CharProperty.match(Pattern.java:3345)

Is there a solution or a workaround for solving this issue?

是否有解决此问题的解决方案或解决方法?

2 个解决方案

#1

A workaround is to use a HTML parser such as JSoup, for example

解决方法是使用HTML解析器,例如JSoup

Document doc = 
      Jsoup.parse("<html><img src=\"src1\"/> <img src=\"src2\"/></html>");
Elements elements = doc.select("img[src]");
for (Element element: elements) {
    System.out.println(element.attr("src"));
    System.out.println(element.attr("alt"));
    System.out.println(element.attr("height"));
    System.out.println(element.attr("width"));
}

#2

It looks like what you've got is an "evil regex", which is not uncommon when you try to construct a complicated regex to match one thing (src) within another thing (img). In particular, evil regexs usually happen when you try to apply repetition to a complex subexpression, which you are doing with (.|\s)*?.

看起来你所拥有的是一个“邪恶的正则表达式”,当你试图构造一个复杂的正则表达式以匹配另一个东西(img)中的一个东西(src)时,这并不罕见。特别是,当您尝试将重复应用于复杂的子表达式时,通常会发生邪恶的正则表达式,您正在使用(。| \ s)* ?.

A better approach would be to use two regexes; one to match all <img> tags, and then another to match the src attribute within it.

更好的方法是使用两个正则表达式;一个匹配所有属性模式匹配需要很长时间标签,然后另一个匹配其中的src属性。

My Java's rusty, so I'll just give you the pseudocode solution:

我的Java生锈了,所以我只给你一个伪代码解决方案:

foreach( imgTag in input.match( /<img .*?>/ig ) ) {
    src = imgTag.match( /\bsrc *= *(['\"])(.*?)\1/i );
    // if you want to get other attributes, you can do that the same way:
    alt = imgTag.match( /\balt *= *(['\"])(.*?)\1/i );
    // even better, you can get all the attributes in one go:
    attrs = imgTag.match( /\b(\w+) *= *(['\"])(.*?)\2/g );
    // attrs is now an array where the first group is the attr name
    // (alt, height, width, src, etc.) and the second group is the
    // attr value
}

Note the use of a backreference to match the appropriate type of closing quote (i.e., this will match src='abc' and src="abc". Also note that the quantifiers are lazy here (*? instead of just *); this is necessary to prevent too much from being consumed.

注意使用反向引用来匹配相应类型的结束引用(即,这将匹配src ='abc'和src =“abc”。还要注意量词在这里是惰性的(*?而不仅仅是*);这有必要防止被消耗太多。

EDIT: even though my Java's rusty, I was able to crank out an example. Here's the solution in Java:

编辑:即使我的Java生锈了,我还是能够做出一个例子。这是Java中的解决方案:

import java.util.regex.*;

public class Regex {

    public static void main( String[] args ) {
        String input = "<img alt=\"altText\" src=\"src\" height=\"50\" width=\"50\"/> <img alt='another image' src=\"foo.jpg\" />";
        Pattern attrPat = Pattern.compile( "\\b(\\w+) *= *(['\"])(.*?)\\2" );
        Matcher imgMatcher = Pattern.compile( "<img .*?>" ).matcher( input );
        while( imgMatcher.find() ) {
            String imgTag = imgMatcher.group();
            System.out.println( imgTag );
            Matcher attrMatcher = attrPat.matcher( imgTag );
            while( attrMatcher.find() ) {
                String attr = attrMatcher.group(1);
                System.out.format( "\tattr: %s, value: %s\n", attrMatcher.group(1), attrMatcher.group(3) );
            }
        }
    }
}

#1