将字符串修剪为忽略 HTML 的长度
https://stackoverflow.com/questions/736155
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Russian题
这个问题是一个具有挑战性的问题。我们的应用程序允许用户在主页上发布新闻。该新闻是通过允许 HTML 的富文本编辑器输入的。在主页上，我们只想显示新闻项目的截断摘要。
例如，这是我们显示的全文，包括 HTML
为了在办公室和厨房腾出更多空间，我随机拿出了所有杯子并将它们放在午餐室的桌子上。 除非您对 1992 年的 Cheyenne Courier 马克杯或 1997 年的 BC Tel Advanced Communications 马克杯的所有权有强烈的感觉，否则它们将被放入盒子中并捐赠给比我们更需要马克杯的办公室。
我们希望将新闻项目修剪为 250 个字符，但排除 HTML。
目前我们使用的修剪方法包括 HTML，这会导致一些 HTML 较多的新闻帖子被大幅截断。
例如，如果上面的示例包含大量 HTML，它可能如下所示：
为了在办公室、厨房腾出更多空间，我拉了……
这不是我们想要的。
有没有人有办法标记 HTML 标签，以保持字符串中的位置，对字符串执行长度检查和/或修剪，并将字符串内的 HTML 恢复到其旧位置？
解决方案
开始在后的第一个字符，跨过每个字符。每次你跨过一个字符时，计数器递增。当你发现一个“<”字符，停止增加计数器，直到你打一个“>”字符。当计数器到达250您现在的位置是你真正想要切断。
注意到，这会对你必须处理的HTML标签被打开，但截止前未关闭时与另一个问题。
其他提示
继2个状态的有限机的建议，我刚刚研制出一种简单的HTML解析器为此，在Java中：
和这里测试用例：
和这里的Java代码：
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
public class HtmlShortener {
private static final String TAGS_TO_SKIP = "br,hr,img,link";
private static final String[] tagsToSkip = TAGS_TO_SKIP.split(",");
private static final int STATUS_READY = 0;
private int cutPoint = -1;
private String htmlString = "";
final List<String> tags = new LinkedList<String>();
StringBuilder sb = new StringBuilder("");
StringBuilder tagSb = new StringBuilder("");
int charCount = 0;
int status = STATUS_READY;
public HtmlShortener(String htmlString, int cutPoint){
this.cutPoint = cutPoint;
this.htmlString = htmlString;
}
public String cut(){
// reset
tags.clear();
sb = new StringBuilder("");
tagSb = new StringBuilder("");
charCount = 0;
status = STATUS_READY;
String tag = "";
if (cutPoint < 0){
return htmlString;
}
if (null != htmlString){
if (cutPoint == 0){
return "";
}
for (int i = 0; i < htmlString.length(); i++){
String strC = htmlString.substring(i, i+1);
if (strC.equals("<")){
// new tag or tag closure
// previous tag reset
tagSb = new StringBuilder("");
tag = "";
// find tag type and name
for (int k = i; k < htmlString.length(); k++){
String tagC = htmlString.substring(k, k+1);
tagSb.append(tagC);
if (tagC.equals(">")){
tag = getTag(tagSb.toString());
if (tag.startsWith("/")){
// closure
if (!isToSkip(tag)){
sb.append("</").append(tags.get(tags.size() - 1)).append(">");
tags.remove((tags.size() - 1));
}
} else {
// new tag
sb.append(tagSb.toString());
if (!isToSkip(tag)){
tags.add(tag);
}
}
i = k;
break;
}
}
} else {
sb.append(strC);
charCount++;
}
// cut check
if (charCount >= cutPoint){
// close previously open tags
Collections.reverse(tags);
for (String t : tags){
sb.append("</").append(t).append(">");
}
break;
}
}
return sb.toString();
} else {
return null;
}
}
private boolean isToSkip(String tag) {
if (tag.startsWith("/")){
tag = tag.substring(1, tag.length());
}
for (String tagToSkip : tagsToSkip){
if (tagToSkip.equals(tag)){
return true;
}
}
return false;
}
private String getTag(String tagString) {
if (tagString.contains(" ")){
// tag with attributes
return tagString.substring(tagString.indexOf("<") + 1, tagString.indexOf(" "));
} else {
// simple tag
return tagString.substring(tagString.indexOf("<") + 1, tagString.indexOf(">"));
}
}
}
如果我正确理解问题，您希望保留 HTML 格式，但不希望将其计入您保留的字符串长度的一部分。
您可以使用实现简单的代码来完成此任务 有限状态机.
2 个状态：标签内、标签外
标签内：
- 转到 OutOfTag 如果>遇到字符
- 遇到任何其他字符则返回自身
标签外：
- 转到 InTag 如果<遇到字符
- 遇到任何其他字符则返回自身
您的起始状态将为 OutOfTag。
您可以通过一次处理 1 个字符来实现有限状态机。每个角色的处理都会带你进入一个新的状态。
当您通过有限状态机运行文本时，您还希望保留输出缓冲区和到目前为止遇到的变量的长度（以便您知道何时停止）。
- 每次处于 OutOfTag 状态并处理另一个字符时，递增 Length 变量。如果有空格字符，您可以选择不增加此变量。
- 当没有更多字符或达到 #1 中提到的所需长度时，算法结束。
- 在输出缓冲区中，包含您遇到的字符，直到 #1 中提到的长度为止。
- 保留一堆未关闭的标签。当达到长度时，为堆栈中的每个元素添加一个结束标记。当您运行算法时，您可以通过保留 current_tag 变量来知道何时遇到标签。current_tag 变量在进入 InTag 状态时开始，在进入 OutOfTag 状态时结束（或者在 InTag 状态中遇到空格字符时）。如果您有开始标记，请将其放入堆栈中。如果有结束标记，则将其从堆栈中弹出。
下面就是我想出了，在C＃中实现：
public static string TrimToLength(string input, int length)
{
if (string.IsNullOrEmpty(input))
return string.Empty;
if (input.Length <= length)
return input;
bool inTag = false;
int targetLength = 0;
for (int i = 0; i < input.Length; i++)
{
char c = input[i];
if (c == '>')
{
inTag = false;
continue;
}
if (c == '<')
{
inTag = true;
continue;
}
if (inTag || char.IsWhiteSpace(c))
{
continue;
}
targetLength++;
if (targetLength == length)
{
return ConvertToXhtml(input.Substring(0, i + 1));
}
}
return input;
}
和几个单元测试我通过TDD使用：
[Test]
public void Html_TrimReturnsEmptyStringWhenNullPassed()
{
Assert.That(Html.TrimToLength(null, 1000), Is.Empty);
}
[Test]
public void Html_TrimReturnsEmptyStringWhenEmptyPassed()
{
Assert.That(Html.TrimToLength(string.Empty, 1000), Is.Empty);
}
[Test]
public void Html_TrimReturnsUnmodifiedStringWhenSameAsLength()
{
string source = "<div lang=\"en\" class=\"textBody localizable\" id=\"pageBody_en\">" +
"<img photoid=\"4041\" src=\"http://xxxxxxxx/imagethumb/562103830000/4041/300x300/False/mugs.jpg\" style=\"float: right;\" class=\"photoRight\" alt=\"\"/>" +
"<br/>" +
"In an attempt to make a bit more space in the office, kitchen, I";
Assert.That(Html.TrimToLength(source, 250), Is.EqualTo(source));
}
[Test]
public void Html_TrimWellFormedHtml()
{
string source = "<div lang=\"en\" class=\"textBody localizable\" id=\"pageBody_en\">" +
"<img photoid=\"4041\" src=\"http://xxxxxxxx/imagethumb/562103830000/4041/300x300/False/mugs.jpg\" style=\"float: right;\" class=\"photoRight\" alt=\"\"/>" +
"<br/>" +
"In an attempt to make a bit more space in the office, kitchen, I've pulled out all of the random mugs and put them onto the lunch room table. Unless you feel strongly about the ownership of that Cheyenne Courier mug from 1992 or perhaps that BC Tel Advanced Communications mug from 1997, they will be put in a box and donated to an office in more need of mugs than us. <br/><br/>" +
"In the meantime we have a nice selection of white Ikea mugs, some random Starbucks mugs, and others that have made their way into the office over the years. Hopefully that will suffice. <br/><br/>" +
"</div>";
string expected = "<div lang=\"en\" class=\"textBody localizable\" id=\"pageBody_en\">" +
"<img photoid=\"4041\" src=\"http://xxxxxxxx/imagethumb/562103830000/4041/300x300/False/mugs.jpg\" style=\"float: right;\" class=\"photoRight\" alt=\"\"/>" +
"<br/>" +
"In an attempt to make a bit more space in the office, kitchen, I've pulled out all of the random mugs and put them onto the lunch room table. Unless you feel strongly about the ownership of that Cheyenne Courier mug from 1992 or perhaps that BC Tel Advanced Communications mug from 1997, they will be put in";
Assert.That(Html.TrimToLength(source, 250), Is.EqualTo(expected));
}
[Test]
public void Html_TrimMalformedHtml()
{
string malformedHtml = "<div lang=\"en\" class=\"textBody localizable\" id=\"pageBody_en\">" +
"<img photoid=\"4041\" src=\"http://xxxxxxxx/imagethumb/562103830000/4041/300x300/False/mugs.jpg\" style=\"float: right;\" class=\"photoRight\" alt=\"\"/>" +
"<br/>" +
"In an attempt to make a bit more space in the office, kitchen, I've pulled out all of the random mugs and put them onto the lunch room table. Unless you feel strongly about the ownership of that Cheyenne Courier mug from 1992 or perhaps that BC Tel Advanced Communications mug from 1997, they will be put in a box and donated to an office in more need of mugs than us. <br/><br/>" +
"In the meantime we have a nice selection of white Ikea mugs, some random Starbucks mugs, and others that have made their way into the office over the years. Hopefully that will suffice. <br/><br/>";
string expected = "<div lang=\"en\" class=\"textBody localizable\" id=\"pageBody_en\">" +
"<img photoid=\"4041\" src=\"http://xxxxxxxx/imagethumb/562103830000/4041/300x300/False/mugs.jpg\" style=\"float: right;\" class=\"photoRight\" alt=\"\"/>" +
"<br/>" +
"In an attempt to make a bit more space in the office, kitchen, I've pulled out all of the random mugs and put them onto the lunch room table. Unless you feel strongly about the ownership of that Cheyenne Courier mug from 1992 or perhaps that BC Tel Advanced Communications mug from 1997, they will be put in";
Assert.That(Html.TrimToLength(malformedHtml, 250), Is.EqualTo(expected));
}
我知道这是发布日期之后不少，但我有一个类似的问题，这是我的最终解决它。我的关心将是正则表达式的速度与通过阵列作用中。
此外，如果你有一个HTML标签之前的空间，并在此之后不能修复
private string HtmlTrimmer(string input, int len)
{
if (string.IsNullOrEmpty(input))
return string.Empty;
if (input.Length <= len)
return input;
// this is necissary because regex "^" applies to the start of the string, not where you tell it to start from
string inputCopy;
string tag;
string result = "";
int strLen = 0;
int strMarker = 0;
int inputLength = input.Length;
Stack stack = new Stack(10);
Regex text = new Regex("^[^<&]+");
Regex singleUseTag = new Regex("^<[^>]*?/>");
Regex specChar = new Regex("^&[^;]*?;");
Regex htmlTag = new Regex("^<.*?>");
while (strLen < len)
{
inputCopy = input.Substring(strMarker);
//If the marker is at the end of the string OR
//the sum of the remaining characters and those analyzed is less then the maxlength
if (strMarker >= inputLength || (inputLength - strMarker) + strLen < len)
break;
//Match regular text
result += text.Match(inputCopy,0,len-strLen);
strLen += result.Length - strMarker;
strMarker = result.Length;
inputCopy = input.Substring(strMarker);
if (singleUseTag.IsMatch(inputCopy))
result += singleUseTag.Match(inputCopy);
else if (specChar.IsMatch(inputCopy))
{
//think of as 1 character instead of 5
result += specChar.Match(inputCopy);
++strLen;
}
else if (htmlTag.IsMatch(inputCopy))
{
tag = htmlTag.Match(inputCopy).ToString();
//This only works if this is valid Markup...
if(tag[1]=='/') //Closing tag
stack.Pop();
else //not a closing tag
stack.Push(tag);
result += tag;
}
else //Bad syntax
result += input[strMarker];
strMarker = result.Length;
}
while (stack.Count > 0)
{
tag = stack.Pop().ToString();
result += tag.Insert(1, "/");
}
if (strLen == len)
result += "...";
return result;
}
难道最快的方法是使用jQuery的text()方法？
例如：
<ul>
<li>One</li>
<li>Two</li>
<li>Three</li>
</ul>
var text = $('ul').text();
会得到在text变量中的值OneTwoThree。这将让你得到该文本的实际长度，而不包括HTML。
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