Jsoup中select方法详解
采用CSS或类似jquery 选择器（selector）语法来处理HTML文档中的数据。
利用方法：Element.select(String selector)和Elements.select(String selector)。
File input = new File("/tmp/input.html");
Document doc = Jsoup.parse(input, "UTF-8", "http://example.com/");
Elements links = doc.select("a[href]"); // a with href
Elements pngs = doc.select("img[src$=.png]"); // img with src ending .png
Element masthead = doc.select("div.masthead").first(); // div with class=masthead
Elements resultLinks = doc.select("h3.r > a"); // direct a after h3
Document doc = Jsoup.parse(pageString);
Document doc = Jsoup.connect(url).get();描述
Jsoup的元素支持类似CSS或（jquery）的选择器语法的查找匹配的元素，可实现功能强大且鲁棒性好的查询。
jsoup elements support a CSS(or jquery) like selector syntax to find matching elements, that allows very powerful and robust queries.
Select方法可作用于Document、Element或Elements，且是上下文相关的，因此可实现指定元素的过滤，或者链式选择访问。
The selectmethod is available in a Document, Element, or in Elements. It is contextual, so you can filter by selecting from a specific element, or by chaining select calls.
选择（操作）返回元素列表（Elements），并提供一组方法来提取或处理结果。
Select returns a list of Elements (as Elements), which provides a range of methods to extract and manipulate the results.
选择器概要（Selector overview）
tagname: find elements by tag, e.g. a
ns|tag: find elements by tag in a namespace, e.g. fb|name finds
#id: find elements by ID, e.g. #logo
.class: find elements by class name, e.g. .masthead
[attribute]: elements with attribute, e.g. [href]
[^attr]: elements with an attribute name prefix, e.g. [^data-] finds elements with HTML5 dataset attributes
[attr=value]: elements with attribute value, e.g. [width=500]
[attr^=value], [attr$=value], [attr*=value]: elements with attributes that start with, end with, or contain the value, e.g. [href*=/path/]
[attr=~regex]: elements that have the attribute key, that its value matches the supplied regular expression; e.g. img[src~=(?i)\.(png|jpe?g)]
*: all elements, e.g. *
ns|tag：通过标签在命名空间查找元素，例如：fb|name查找
#id：通过ID查找元素，例如#logo
.class：通过类型名称查找元素，例如.masthead
[attribute]：带有属性的元素，例如[href]
[^attr]：带有名称前缀的元素，例如[^data-]查找HTML5带有数据集（dataset）属性的元素
[attr=value]：带有属性值的元素，例如[width=500]
[attr^=value]，[attr$=value]，[attr*=value]：包含属性且其值以value开头、结尾或包含value的元素，例如[href*=/path/]
[attr~=regex]：属性值满足正则表达式的元素，例如img[src~=(?i)\.(png|jpe?g)]
*：所有元素，例如*
el#id: elements with ID, e.g. div#logo
el.class: elements with class, e.g. div.masthead
el[attr]: elements with attribute, e.g. a[href]
Any combination, e.g. a[href].highlight
ancestor child: child elements that descend from ancestor, e.g. .body p finds p elements anywhere under a block with class "body"
parent > child: child elements that descend directly from parent, e.g. div.content > p finds p elements; and body > * finds the direct children of the body tag
siblingA + siblingB: finds sibling B element immediately preceded by sibling A, e.g. div.head + div
siblingA ~ siblingX: finds sibling X element preceded by sibling A, e.g. h1 ~ p
el, el, el: group multiple selectors, find unique elements that match any of the selectors; e.g. div.masthead, div.logo
el#id:：带有ID的元素ID，例如div#logo
el.class：带类型的元素，例如. div.mastheadel[attr]：包含属性的元素，例如a[href]
任意组合：例如a[href].highlight
ancestor child：继承自某祖（父）元素的子元素，例如.body p查找“body”块下的p元素
parent > child：直接为父元素后代的子元素，例如: div.content > pf查找p元素，body > * 查找body元素的直系子元素
siblingA + siblingB：查找由同级元素A前导的同级元素，例如div.head + div
siblingA ~ siblingX：查找同级元素A前导的同级元素X例如h1 ~ p
el, el, el：多个选择器组合，查找匹配任一选择器的唯一元素，例如div.masthead, div.logo
el:lt(n): find elements whose sibling index (i.e. its position in the DOM tree relative to its parent) is less than n; e.g. td:lt(3)
el:gt(n): find elements whose sibling index is greater than n; e.g. div p:gt(2)
el:eq(n): find elements whose sibling index is equal to n; e.g. form input:eq(1)
el:has(seletor): find elements that contain elements matching the selector; e.g. div:has(p)
el:contains(text): find elements that contain the given text. The search is case-insensitive; e.g. p:contains(jsoup)
el:matches(regex): find elements whose text matches the specified regular expression; e.g. div:matches((?i)login).
Note that all of the above indexed pseudo-selectors are 0-based, that is, the first element is at index 0, the second at 1, etc.
:lt(n)：查找索引值（即DOM树中相对于其父元素的位置）小于n的同级元素，例如td:lt(3)
:gt(n)：查找查找索引值大于n的同级元素，例如div p:gt(2):eq(n) ：查找索引值等于n的同级元素，例如form input:eq(1)
:has(seletor)：查找匹配选择器包含元素的元素，例如div:has(p)
:not(selector)：查找不匹配选择器的元素，例如div:not(.logo)
:contains(text)：查找包含给定文本的元素，大小写铭感，例如p:contains(jsoup)
:containsOwn(text)：查找直接包含给定文本的元素
:matches(regex)：查找其文本匹配指定的正则表达式的元素，例如div:matches((?i)login)
:matchesOwn(regex)：查找其自身文本匹配指定的正则表达式的元素
注意：上述伪选择器是0-基数的，亦即第一个元素索引值为0，第二个元素index为1等
详见SelectorAPI 参考资料所列全部信息和细节。
【原文】http://jsoup.org/cookbook/extracting-data/selector-syntax
相关资料：http://www.ibm.com/developerworks/cn/java/j-lo-jsouphtml/