<dependency>    <groupId>org.apache.velocity</groupId>    <artifactId>velocity</artifactId>    <version>1.7</version></dependency>

package com.qunar.piao.data.integration.common;import java.io.ByteArrayInputStream;import java.io.CharArrayWriter;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.InputStream;import java.io.Reader;import java.io.Writer;import java.util.HashMap;import java.util.Map;import org.apache.velocity.VelocityContext;import org.apache.velocity.app.Velocity;import org.apache.velocity.context.Context;/** * Velocity引擎帮助类 *  */public class VelocityHelper {    /** 单态实例 */    private static final VelocityHelper instance = new VelocityHelper();    /** 私有构造函数 */    private VelocityHelper() {        // 初始化velocity的信息 主要设置一些Velocity的默认属性        // 初始化        try {            Velocity.init();        } catch (Exception e) {            e.printStackTrace();        }    }    /**     * <pre>     * 取得实例     * </pre>     */    public static VelocityHelper getInstance() {        return instance;    }    /**     * <pre>     * 渲染：从reader到writer     * </pre>     *      * @param context     * @param writer     * @param reader     * @return     */    public boolean evaluate(Context context, Writer writer, Reader reader) {        try {            return Velocity.evaluate(context, writer, "", reader);        } catch (Exception e) {            throw new RuntimeException("velocity evaluate error! detail [" + e.getMessage() + "]");        }    }    /**     * <pre>     * 通过Map过滤一个输入流     * </pre>     *      * @param map     * @param reader     * @return     */    @SuppressWarnings("unchecked")    public InputStream evaluate(Map map, Reader reader) {        try {            // 把产生的输出流(字符流)，转换成输入流(字节流)            byte[] dataBytes = this.evaluateToWriter(map, reader).toString().getBytes();            return new ByteArrayInputStream(dataBytes);        } catch (Exception e) {            throw new RuntimeException("velocity evaluate error! detial [" + e.getMessage() + "]");        }    }    /**     * <pre>     * 通过Map过滤一个输入流     * </pre>     *      * @param map     * @param reader     * @return     */    @SuppressWarnings("unchecked")    public Writer evaluateToWriter(Map map, Reader reader) {        try {            VelocityContext context = convertVelocityContext(map);            CharArrayWriter writer = new CharArrayWriter();            // 开始评估            this.evaluate(context, writer, reader);            return writer;        } catch (Exception e) {            throw new RuntimeException("velocity evaluate error! detail [" + e.getMessage() + "]");        }    }    /**     * <pre>     * 取得Velocity系统属性     * </pre>     *      * @param key     * @return     */    public Object getProperty(String key) {        return Velocity.getProperty(key);    }    /**     * <pre>     * 把Map转换成Context     * </pre>     */    private VelocityContext convertVelocityContext(Map<String, Object> map) {        VelocityContext context = new VelocityContext();        if (map == null) {            return context;        }        for (Map.Entry<String, Object> entry : map.entrySet()) {            context.put(entry.getKey(), entry.getValue());        }        return context;    }    /**     * @param args     * @throws FileNotFoundException     */    public static void main(String[] args) throws FileNotFoundException {        Map<String, Object> map = new HashMap<String, Object>();        map.put("date", "2011-11-21");        map.put("weather", "晴朗 李秋");        Reader reader = new FileReader("D:\\index.vm");        Writer writer = VelocityHelper.getInstance().evaluateToWriter(map, reader);        // 今天是：2011-11-21，天气：晴朗 李秋！        System.out.println(writer.toString());    }}

今天是：${date}，天气：${weather}！

今天是：2011-11-21，天气：晴朗 李秋！

#set( $test = $test2 + 3)#set( $test.a = "abc")#set( $test.b = 1)

#foreach($conversionRate in $conversionRateList)    $velocityCount //第几个，从1开始    #foreach($member in $conversionRate.entrySet())         $velocityCount //第几个，从1开始
         $member.value //值    #end#end

#if ($foo < 10)    Go North#elseif ($foo== 10)    Go East#else    Go West#end  

$member.value.substring(0,1)

$!{str.length()}