Velocity使用总结

<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()}