Beetl 自定义标签的使用笔记

最近写一个小博客网站用到模版引擎Beetl http://www.ibeetl.com，  Beetl对自定义标签有很友好的支持；

使用自定义标签只需3步：

1)继承Tag类(或GeneralVarTagBinding类)实现render方法;

2)注册标签：

BeetlViewFactory.groupTemplate.registerTag("page", PageTag.class);

3)使用标签:

<#page  val="${pageData.page}">
……
</#page>



Tag类的源码：

引用

public abstract class Tag
{
protected Object[] args = null;
protected GroupTemplate gt;
protected Context ctx;
protected ByteWriter bw;
protected Statement bs;

protected void doBodyRender()
{

bs.execute(ctx);

}

protected BodyContent getBodyContent()
{
ByteWriter writer = ctx.byteWriter;
ByteWriter tempWriter = ctx.byteWriter.getTempWriter();
ctx.byteWriter = tempWriter;
doBodyRender();
ctx.byteWriter = writer;
return tempWriter.getTempConent();
}

public abstract void render();

public void init(Context ctx, Object[] args, Statement st)
{
this.ctx = ctx;
this.bw = ctx.byteWriter;
this.gt = ctx.gt;
this.args = args;
this.bs = st;
}

}

其中args参数第一个是标签名，即你自定义的标签名称 第二个是个Map保存了自定义标签的属性名,如：

分页标签<#page  val="${pageData.page}">,   args={'tage', Map[val=page]}

ctx是模版上下文，可以取全局变量:ctx.getGloabl("名字");

Beetl还有一个更友好的抽象类GeneralVarTagBinding，它提供一个getAttributeValue以属性名获取标签的属性值

GeneralVarTagBinding源码:

引用

package org.beetl.core;

import java.util.Map;

/**
* 此类子类将可以作为html 标签使用，除了能实现bindVars来初始化绑定的变量外，允许render方法里通过调用
* 方法bing(name,value) 来绑定变量，如下是一个例子
* <pre>
* public class TestGeneralVarTagBinding extends GeneralVarTagBinding
{


public void render()
{
for (int i = 0; i < 5; i++)
{
this.bind("value", i);
this.doBodyRender();
}

}

}

  </pre>
  此例子会循环渲染标签体5次，并且每次循环都会设置value的值，如下是模板内容
  <pre>
<#tag ; value>
${value}
</#tag>
</pre>

*/
public abstract class GeneralVarTagBinding extends Tag implements TagVarBinding
{
private Map<String, Integer> name2Index = null;

@Override
public Object[] bindVars()
{
// TODO Auto-generated method stub
return null;
}

public void mapName2Index(Map<String, Integer> map)
{
name2Index = map;
}

public void bind(String name, Object value)
{
if (name2Index == null)
{
throw new RuntimeException();
}
Integer index = name2Index.get(name);
if (index == null)
{
throw new RuntimeException();
}
ctx.vars[index] = value;
}

public Object getAttributeValue(String attrName)
{
Map map = (Map) this.args[1];
return map.get(attrName);

}

public String getHtmlTagName()
{
return (String) this.args[0];
}

}

下面是我写的分页标签的实现：

引用

public class PageTag extends GeneralVarTagBinding {
    private  long total = 0;
    private  int perSize = 0;
    private int curNo = 0;
    private int pageNum = 0;
    private static final String SPAN = "span";
    private static final String A = "a";

    private void init(){
        Page page = (Page)getAttributeValue("val");
        total = page.getTotalNum();
        perSize = page.getPerSize();
        curNo = page.getCurNo();
        pageNum = (int)(total / perSize);
        if(pageNum * perSize < total){
            pageNum++;
        }
    }

    @Override
    public void render(){
        init();
        StringBuilder paging = new StringBuilder("");
        paging.append("<div class=\"pagination\">");
        if(curNo > 1){
            paging.append("<a class=\"firstPage\"> </a>")
                    .append("<a class=\"previousPage\"> </a>");
            if(curNo > 4){
                paging.append("<span class=\"pageBreak\">...</span>");
            }
            if(curNo - 2 > 0){
                paging.append("<a href=\"javascript:;\">").append(curNo - 2).append("</a>");
            }
            if(curNo - 1 > 0){
                paging.append("<a href=\"javascript:;\">").append(curNo - 1).append("</a>");
            }
        }else if(curNo == 1){
            paging.append("<span class=\"firstPage\"> </span>")
                    .append("<span class=\"previousPage\"> </span>");
        }
        paging.append("<span class=\"currentPage\">").append(curNo).append("</span>");
        if(curNo + 1 <= pageNum){
            paging.append("<a href=\"javascript:;\">").append(curNo + 1).append("</a>");
        }
        if(curNo + 2 <= pageNum){
            paging.append("<a href=\"javascript:;\">").append(curNo + 2).append("</a>");
        }
        if(pageNum - curNo > 2){
           paging.append("<span class=\"pageBreak\">...</span>");
        }
        if(curNo >= pageNum){
            paging.append("<span class=\"nextPage\" href=\"javascript:;\"> </span>")
                    .append("<span class=\"lastPage\" href=\"javascript:;\"> </span>");
        } else{
            paging.append("<a class=\"nextPage\" href=\"javascript:;\"> </a>")
                    .append("<a class=\"lastPage\" href=\"javascript:;\"> </a>");
        }
            paging.append("<span class=\"pageSkip\">")
                 .append("共").append(pageNum).append("页").append(total).append("条记录 到第<input id=\"pageNumber\" name=\"pageNumber\" value=\"1\" maxlength=\"9\" onpaste=\"return false;\" />")
                 .append("页<button type=\"submit\"> </button>")
                 .append("</span></div>");
        try{
            ctx.byteWriter.writeString(paging.toString());
            this.doBodyRender();
            ctx.byteWriter.writeString(paging.toString());
        }catch (IOException e){
            throw new RuntimeException(e);
        }
    }
}

doBodyRender()方法是输出标签内的HTML

最终效果



更详细的使用文档可以去Beetl在线文档上看 http://ibeetl.com/guide/#_%E8%87%AA%E5%AE%9A%E4%B9%89%E6%A0%87%E7%AD%BE