📄 在jsf中实现分页（二）.htm
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<DIV style="PADDING-TOP: 4px">发表于 2006-1-29 18:36 <A
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name=pid2262></A><SPAN class=bold>在JSF中实现分页（二）</SPAN><BR><BR>
<DIV style="FONT-SIZE: 12px">
<P>
前面一篇直接使用了Myfaces中的两个Component完成了一个简单的分页，这里将会介绍一种On-demand
loading的方法来进行分页，仅仅在需要数据的时候加载。</P>
<P>
先来说一些题外话，为了实现这种方式的分页，公司里大约5-6个人做了半个多月的工作，扩展了dataTable，修改了dataScrollor，以及各种其他的方法，但是都不是很优雅。在上个月底的时候，在Myfaces的Mail
List中也针对这个问题展开了一系列的讨论，最后有人总结了讨论中提出的比较好的方法，提出了以下的分页方法，也是目前实现的最为优雅的方法，也就是不对dataTable和dataScrollor做任何修改，仅仅通过扩展DataModel来实现分页。</P>
<P>
DataModel是一个抽象类，用于封装各种类型的数据源和数据对象的访问，JSF中dataTable中绑定的数据实际上被包装成了一个DataModel，以消除各种不同数据源和数据类型的复杂性，在前面一篇中我们访问数据库并拿到了一个List，交给dataTable，这时候，JSF会将这个List包装成ListDataModel，dataTable访问数据都是通过这个DataModel进行的，而不是直接使用List。</P>
<P>
接下来我们要将需要的页的数据封装到一个DataPage中去，这个类表示了我们需要的一页的数据，里面包含有三个元素：datasetSize，startRow，和一个用于表示具体数据的List。datasetSize表示了这个记录集的总条数，查询数据的时候，使用同样的条件取count即可，startRow表示该页的起始行在数据库中所有记录集中的位置。<BR><BR><SPAN
lang=EN-US><o:p></P>
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style="COLOR: #008000">/**</SPAN><SPAN
style="COLOR: #008000"><BR><IMG src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * A simple class that represents a "page" of data out of a longer set, ie a<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * list of objects together with info to indicate the starting row and the full<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * size of the dataset. EJBs can return instances of this type when returning<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * subsets of available data.<BR><IMG
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align=top> </SPAN><SPAN
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align=top></SPAN><SPAN style="COLOR: #0000ff">public</SPAN><SPAN
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style="COLOR: #0000ff">class</SPAN><SPAN
style="COLOR: #000000"> DataPage<BR><IMG
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style="COLOR: #000000">{<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">private</SPAN><SPAN
style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">int</SPAN><SPAN
style="COLOR: #000000"> datasetSize;<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">private</SPAN><SPAN
style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">int</SPAN><SPAN
style="COLOR: #000000"> startRow;<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">private</SPAN><SPAN
style="COLOR: #000000"> List data;<BR><IMG
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style="BORDER-RIGHT: #808080 1px solid; BORDER-TOP: #808080 1px solid; DISPLAY: none; BORDER-LEFT: #808080 1px solid; BORDER-BOTTOM: #808080 1px solid; BACKGROUND-COLOR: #ffffff">/** */</SPAN><SPAN
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style="COLOR: #008000">/**</SPAN><SPAN
style="COLOR: #008000"><BR><IMG src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * Create an object representing a sublist of a dataset.<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * <BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * </SPAN><SPAN
style="COLOR: #808080">@param</SPAN><SPAN
style="COLOR: #008000"> datasetSize<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * is the total number of matching rows available.<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * <BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * </SPAN><SPAN
style="COLOR: #808080">@param</SPAN><SPAN
style="COLOR: #008000"> startRow<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * is the index within the complete dataset of the first element<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * in the data list.<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * <BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * </SPAN><SPAN
style="COLOR: #808080">@param</SPAN><SPAN
style="COLOR: #008000"> data<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> * is a list of consecutive objects from the dataset.<BR><IMG
src="在JSF中实现分页（二）.files/ExpandedSubBlockEnd.gif"
align=top> </SPAN><SPAN
style="COLOR: #008000">*/</SPAN></SPAN><SPAN
style="COLOR: #000000"><BR><IMG src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">public</SPAN><SPAN
style="COLOR: #000000"> DataPage(</SPAN><SPAN
style="COLOR: #0000ff">int</SPAN><SPAN
style="COLOR: #000000"> datasetSize, </SPAN><SPAN
style="COLOR: #0000ff">int</SPAN><SPAN
style="COLOR: #000000"> startRow, List data)<BR><IMG
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align=top> </SPAN><SPAN
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style="COLOR: #000000">.datasetSize </SPAN><SPAN
style="COLOR: #000000">=</SPAN><SPAN
style="COLOR: #000000"> datasetSize;<BR><IMG
src="在JSF中实现分页（二）.files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">this</SPAN><SPAN
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