場景

在做一個CMS網站時，要列出網站欄目，比如有新聞，科技，體育，財經等欄目。欄目內容存放在資料庫中。

呼叫語法

                //沒有迴圈變數
        <@user_def_dir_exp param1=val1 param2=val2 ... paramN=valN/>

                //有迴圈變數
        <@user_def_dir_exp param1=val1 param2=val2 ... paramN=valN ;lv1, lv2, ..., lvN/>

自定義指令使用

cms_chanel_list指令的作用是按傳入的引數count找出指定數量的欄目，並且過濾掉名字為“體育”的欄目。

    <@cms_chanel_list count=5 exclude="體育">
        <#list chllist as c>
        <dt>
        <a href="#" target="_self"><span>${c.name}</span></a>
        </dt>
        </#list>
    </@cms_chanel_list> 

自定定義指令

首先要實現TemplateDirectiveModel介面。

public class ChanelListDirective implements TemplateDirectiveModel {
    @Inject
    private ChanelDao chanelDao;
    /*
     * @param 傳入的引數，params型別為Map<String,
     * TemplateModel>,由於歷史原因沒用泛型。比如傳入引數“count=5”，String為count，TemplateModel為5
     * 
     * @loopVars 迴圈變數
     * 
     * @see freemarker.template.TemplateDirectiveModel#execute(freemarker.core.
     * Environment, java.util.Map, freemarker.template.TemplateModel[],
     * freemarker.template.TemplateDirectiveBody)
     */
 

    public void execute(Environment env, @SuppressWarnings("rawtypes") Map params, TemplateModel[] loopVars,
            TemplateDirectiveBody body) throws TemplateException, IOException {
        // TODO Auto-generated method stub
        if (params == null || params.size() == 0) {
            throw new TemplateException("params can not be empty", env);
        }
        int count = 0;
        String excludeStr = null;
        // 處理傳入的引數
        for (Object key : params.keySet()) {
            String name = (String) key;
            if (name.equalsIgnoreCase("count")) {
                if (params.get(key) instanceof TemplateNumberModel)
                    count = ((TemplateNumberModel) params.get(key)).getAsNumber().intValue();
                else
                    throw new TemplateException("count param must be number", env);
            }
            if (name.equalsIgnoreCase("exclude")) {
                if (params.get(key) instanceof TemplateScalarModel)
                    excludeStr = ((TemplateScalarModel) params.get(key)).getAsString();
                else
                    throw new TemplateException("execlude param must be string", env);
            }
        }
        List<Chanel> chanleList = chanelDao.loadAll();
        List<Chanel> list = new ArrayList<>();
        for (int i = 0; i < count && i < chanleList.size(); i++) {
            if (chanleList.get(i).getName().equals(excludeStr))
                continue;
            list.add(chanleList.get(i));
        }
        env.setVariable("chllist", ObjectWrapper.DEFAULT_WRAPPER.wrap(list));
        if (body != null) {
            body.render(env.getOut());
        }
    }
}

在freemarker中配置

需要繫結該指令為cms_chanel_list

    ...
    <bean id="chanelListDirective" class="com.ydoing.web.directives.ChanelListDirective"/>
    <!-- 配置freeMarker的模板路徑 -->
    <bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
        <property name="templateLoaderPath" value="/WEB-INF/t/cms/www/default/" />
        <property name="defaultEncoding" value="UTF-8" />
        <property name="freemarkerVariables">
            <map>
                <entry key="cms_chanel_list" value-ref="chanelListDirective"/>
            </map>
        </property> 
    ...