Freemarker自定义指令

场景

在做一个CMS网站时，要列出网站栏目，比如有新闻，科技，体育，财经等栏目。栏目内容存放在数据库中。

调用语法

                //没有循环变量        <@user_def_dir_exp param1=val1 param2=val2 ... paramN=valN/>                //有循环变量        <@user_def_dir_exp param1=val1 param2=val2 ... paramN=valN ;lv1, lv2, ..., lvN/>
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自定义指令使用

cms_chanel_list指令的作用是按传入的参数count找出指定数量的栏目，并且过滤掉名字为“体育”的栏目。

    <@cms_chanel_list count=5 exclude="体育">        <#list chllist as c>        <dt>        <a href="#" target="_self"><span>${c.name}</span></a>        </dt>        </#list>    </@cms_chanel_list> 
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自定定义指令

首先要实现TemplateDirectiveModel接口。

public class ChanelListDirective implements TemplateDirectiveModel {    @Inject    private ChanelDao chanelDao;    /*     * @param 传入的参数，params类型为Map<String,     * TemplateModel>,由于历史原因没用泛型。比如传入参数“count=5”，String为count，TemplateModel为5     *      * @loopVars 循环变量     *      * @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;        // 处理传入的参数        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());        }    }}
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在freemarker中配置

需要绑定该指令为cms_chanel_list

    ...    <bean id="chanelListDirective" class="com.ydoing.web.directives.ChanelListDirective"/>    <!-- 配置freeMarker的模板路径 -->    <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>     ...