freemarker编写自定义标签

freemarker提供了TemplateDirectiveModel接口，我们可以利用它来实现自定义标签的编写。

例子来源于freemarker中文参考手册

如有:repeatDirective.rj

<#assign x = 1><@repeat count=4>Test ${x}<#assign x = x + 1></@repeat><@repeat count=3 hr=true>Test</@repeat><@repeat count=3; cnt>${cnt}. Test</@repeat>

其中repeat指重复输出，count指次数，cnt指变量，输出最终结果是:

Test 1Test 2Test 3Test 4Test<hr> Test<hr> Test1. Test2. Test3. Test

定义一个RepeatDirective类，是实现TemplateDirectiveModel接口，重写其中的execute方法。

public void execute(Environment env, Map params, TemplateModel[] loopVars, TemplateDirectiveBody body) throws TemplateException,IOException

其中params是指参数，是以Map<String,TemplateModel>结构存储的，如上面中的<@repeat count=3; cnt>其中count=3就以键值对的形式存在map中，只是3不是java类型，而是TemplateModel类型(整数:TemplateNumberModel,字符串:TemplateScalarModel等)，所以利用map.getValue(......)返回的是一个TemplateModel类型的数据，需转换成int类型数据。

loopVars:变量，如cnt，loopVars是一个TemplateModel类型的数组，我们可以在程序中给它赋值。

具体操作如下:

RepeatDirective

package com.xuzengqiang.freemarker.customDirective;import java.io.IOException;import java.io.Writer;import java.util.Iterator;import java.util.Map;import freemarker.core.Environment;import freemarker.template.SimpleNumber;import freemarker.template.TemplateBooleanModel;import freemarker.template.TemplateDirectiveBody;import freemarker.template.TemplateDirectiveModel;import freemarker.template.TemplateException;import freemarker.template.TemplateModel;import freemarker.template.TemplateModelException;import freemarker.template.TemplateNumberModel;import freemarker.template.TemplateScalarModel;/* * <@repeat> * ... * <@repeat> */@SuppressWarnings("all")public class RepeatDirective implements TemplateDirectiveModel{private static final String COUNT="count";private static final String HR="hr";@Overridepublic void execute(Environment env, Map params, TemplateModel[] loopVars, TemplateDirectiveBody body) throws TemplateException, IOException{if(body==null){throw new TemplateModelException("null body");}else {int count=0;boolean hr=false;Iterator iterator=params.entrySet().iterator();while(iterator.hasNext()){Map.Entry<String,TemplateModel> param=(Map.Entry<String, TemplateModel>)iterator.next();String paramName=param.getKey();TemplateModel paramValue=param.getValue();if(paramName.equals(COUNT)){count=getInt(paramName,paramValue);if(count<0){throw new TemplateModelException("次数不能小于0");}}if(paramName.equals(HR)){hr=getBoolean(paramName,paramValue);}}Writer out=env.getOut();for(int i=0;i<count;i++){if(hr && i!=0){out.write("<hr>");}//设置了循环变量if(loopVars.length>0){loopVars[0]=new SimpleNumber(i+1);}body.render(out);                       }}}public static int getInt(String paramName,TemplateModel paramValue) throws TemplateModelException{if(paramValue==null){return 0;}else {if(paramValue instanceof TemplateScalarModel)  //是字符串{String value=((TemplateScalarModel)paramValue).getAsString();return Integer.valueOf(value);}else if(paramValue instanceof TemplateNumberModel)  //数字 {return ((TemplateNumberModel)paramValue).getAsNumber().intValue();}else {throw new TemplateModelException("int转换异常!");}}}public static boolean getBoolean(String paramName,TemplateModel paramValue) throws TemplateModelException{if(paramValue==null){return false;}else {if(paramValue instanceof TemplateScalarModel)  //是字符串{String value=((TemplateScalarModel)paramValue).getAsString();return Boolean.valueOf(value);}else if(paramValue instanceof TemplateBooleanModel)  //boolean {return ((TemplateBooleanModel)paramValue).getAsBoolean();}else {throw new TemplateModelException("boolean转换异常!");}}}}

主类:

package com.xuzengqiang.freemarker;import java.io.File;import java.io.OutputStreamWriter;import java.io.Writer;import java.util.HashMap;import java.util.Map;import com.xuzengqiang.freemarker.customDirective.RepeatDirective;import com.xuzengqiang.freemarker.framework.RepeatMethod;import freemarker.template.Configuration;import freemarker.template.DefaultObjectWrapper;import freemarker.template.Template;@SuppressWarnings("all")public class RepeatMethodTest{public static void initData(){try{Configuration cfg = new Configuration();cfg.clearTemplateCache();  //手动清除缓存//加载模板cfg.setDirectoryForTemplateLoading(new File("template"));cfg.setObjectWrapper(new DefaultObjectWrapper());Template temp=cfg.getTemplate("repeatDirective.rj");Map root=new HashMap();root.put("repeat", new RepeatDirective());Writer writer=new OutputStreamWriter(System.out); //直接在控制台输出temp.process(root, writer);writer.flush();} catch(Exception e){e.printStackTrace();}}public static void main(String[] args){initData();}}