問題描述
為什麼 Document.html() 這麼慢？ (Why is Document.html() so slow?)
I was under the impression that the most costly method in Jsoup's API is parse().
But I just discovered that Document.html() could be even slower.
Given that the Document is the output of parse() (i.e. this is after parsing), I find this surprising.
Why is Document.html() so slow?
參考解法
方法 1:
Answering myself. The Element.html() method is implemented as:
public String html() {
StringBuilder accum = new StringBuilder();
html(accum);
return accum.toString().trim();
}
Using StringBuilder instead of String is already a good thing, and the use of StringBuilder.toString() and String.trim() may not explain the slowness of Document.html(), even for a relatively large document.
But in the middle, our method calls an overloaded version, Element.html(StringBuilder) which loops through all child nodes in the document:
private void html(StringBuilder accum) {
for (Node node : childNodes)
node.outerHtml(accum);
}
Thus if the document contains lots of child nodes, it will be slow.
It would be interesting to see whether there could be a faster implementation of this.
For example, if Jsoup stores a cached version of the raw html that was provided to it via Jsoup.parse(). As an option of course, to maintain backward compatibility and small footprint in memory.