Tapestry 最新版5.1.0.5教程（十二）：自定义前缀prefix

在教程的第四部分（http://www.blogjava.net/usherlight/archive/2009/06/20/283396.html）我们已经粗略地介绍了Tapestry的前缀，其中提及最常用的两种literal和prop。这里顺便再介绍一下其他的几个前缀.
1、context，这个经常在引用图片的时候用到。比如：<img src="${context:images/icon.png}"/> 这样就能够在页面上显示在web-inf/images/icon.png
2、message，这个是需要I18N的应用必用的前缀。${message:some-key}
3、var，用于定义生成一个临时变量。比如：<li t:type="loop" source="1..10" value="var:index">${var:index}</li>。如果没有加这个前缀var:的话，就需要在页面类中添加一个property： index以及相应的getter和setter。
我们这次介绍自定义一个cycle前缀，这个可以用于在表格中显示不同背景的行（也就是斑马条）。
比如：
<t:grid .... rowClass="cycle:line1,line2">
...
</t:grid>
或者
<t:loop ...>
<div class="${cycle:line1,line2}">aaaa</div>
</tloop>

自定义prefix一般来说是3个步骤，
1、定义一个BindingFactory，这个需要实现BindingFactory接口
2、定义一个Binding继承AbstractBinding
3、注册这个Binding

看一下具体的prefix的类：

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import java.util.ArrayList;
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import java.util.List;
3


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import org.apache.tapestry5.Binding;
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import org.apache.tapestry5.BindingConstants;
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import org.apache.tapestry5.ComponentResources;
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import org.apache.tapestry5.ioc.Location;
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import org.apache.tapestry5.services.BindingFactory;
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import org.apache.tapestry5.services.BindingSource;
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/** *//**
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* Implementation of the cycle: binding prefix -- we parse list of bindings
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* and generate delegate bindings for each element<br>
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* default binding is literal, other bindings can be used by specifying prefix.<br>
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* example: "cycle:prop:name,prop:lastName,sth,sth else"
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*/
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public class CycleBindingFactory implements BindingFactory

{
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private final BindingSource _bindingSource;
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public CycleBindingFactory(BindingSource source)

{
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this._bindingSource = source;
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}
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public Binding newBinding(String description, ComponentResources container, ComponentResources component,
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String expression, Location location)
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{
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List<Binding> delegates = new ArrayList<Binding>();
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String[] bindingNames = expression.split(",");
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for (String bindingName : bindingNames)

{
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String defaultBinding = BindingConstants.LITERAL;
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Binding binding = _bindingSource.newBinding(description, container, component, defaultBinding, bindingName, location);
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delegates.add(binding);
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}
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CycleBinding cycleBinding = new CycleBinding(delegates);
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container.addPageLifecycleListener(cycleBinding);
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return cycleBinding;
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}
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}

1

import java.util.List;
2


3

import org.apache.tapestry5.Binding;
4

import org.apache.tapestry5.internal.bindings.AbstractBinding;
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import org.apache.tapestry5.runtime.PageLifecycleListener;
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7


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public class CycleBinding extends AbstractBinding implements PageLifecycleListener

{
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private final List<Binding> delegates;
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private int index = 0;
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public CycleBinding(List<Binding> delegates)

{
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this.delegates = delegates;
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}
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public Object get()

{
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Object ret = delegates.get(index).get();
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index ++;
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if(index>=delegates.size()) index = 0;
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return ret;
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}
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@Override
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public boolean isInvariant()

{
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return false;
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}
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@Override
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public Class<Object> getBindingType()

{
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return Object.class;
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}
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public void containingPageDidDetach()

{
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index=0;
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}
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public void containingPageDidAttach()

{/**//*not interested*/}
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public void containingPageDidLoad()

{/**//*not interested*/}
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}

Binding和BindingFactory写好了，注册后就可以使用了，注册的过程是在AppModel中添加以下一段代码：

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public static void contributeBindingSource(
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MappedConfiguration<String, BindingFactory> configuration,
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BindingSource bindingSource
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)
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{
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configuration.add("cycle",new CycleBindingFactory(bindingSource));
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}