(转载)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：
CycleBindingFactory.java

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

import org.apache.tapestry5.Binding;
import org.apache.tapestry5.BindingConstants;
import org.apache.tapestry5.ComponentResources;
import org.apache.tapestry5.ioc.Location;
import org.apache.tapestry5.services.BindingFactory;
import org.apache.tapestry5.services.BindingSource;

/** *//**
 * Implementation of the cycle: binding prefix -- we parse list of bindings
 * and generate delegate bindings for each element<br>
 * default binding is literal, other bindings can be used by specifying prefix.<br>
 * example: "cycle:prop:name,prop:lastName,sth,sth else"
 */
public class CycleBindingFactory implements BindingFactory {
    private final BindingSource _bindingSource;

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

        for (String bindingName : bindingNames){
            String defaultBinding = BindingConstants.LITERAL;

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

CycleBinding.java

import java.util.List;

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


public class CycleBinding extends AbstractBinding implements PageLifecycleListener {
    private final List<Binding> delegates;
    private int index = 0;

    public CycleBinding(List<Binding> delegates) {
        this.delegates = delegates;
    }

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


    public void containingPageDidDetach() {
        index=0;
    }

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

    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：

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

原文地址：http://www.blogjava.net/usherlight/archive/2010/03/06/314700.html