Java操作FreeMarker模板引擎的基本用法示例小结

FreeMarker 是一个采用 Java 开发的模版引擎，是一个基于模版生成文本的通用工具。它被设计用来生成 HTML Web 页面，特别是基于 MVC 模式的应用程序。虽然使用FreeMarker需要具有一些编程的能力，但通常由 Java 程序准备要显示的数据，由 FreeMarker 生成页面，并通过模板显示准备的数据。
http://freemarker.org/

public void process(String template,Map<String,?> data) throws Exception { 
  Configuration cfg = new Configuration(); 
  cfg.setDirectoryForTemplateLoading(new File("ftl")); 
  cfg.setObjectWrapper(new DefaultObjectWrapper()); 
   
  //设置字符集 
  cfg.setDefaultEncoding("UTF-8"); 
   
  //设置尖括号语法和方括号语法,默认是自动检测语法 
  // 自动 AUTO_DETECT_TAG_SYNTAX 
  // 尖括号 ANGLE_BRACKET_TAG_SYNTAX 
  // 方括号 SQUARE_BRACKET_TAG_SYNTAX 
  cfg.setTagSyntax(Configuration.AUTO_DETECT_TAG_SYNTAX); 
 
  Writer out = new OutputStreamWriter(new FileOutputStream(FILE_DIR + template + ".txt"),"UTF-8"); 
  Template temp = cfg.getTemplate(template); 
  temp.process(data,out); 
  out.flush(); 
}

0、使用freemarker制作HelloWord web页面
新建一个WEB工程，并导入freemarker.jar，在WEB-INF下新建文件夹templates用于存放模版文件，在templates下新建test.ftl，这是示例模版文件。内容就是HTML内容，里面带有一个标记符，用于将来进行变量替换，内容如下：

<html> 
 <head> 
    <title>freemarker测试</title> 
  </head> 
  <body> 
    <h1>${message},${name}</h1> 
  </body> 
</html>

新建一个Servlet，用于请求设置变量，并处理模版的输出：

package com.test.servlet; 
import java.io.IOException; 
import java.io.Writer; 
import java.util.HashMap; 
import java.util.Map; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import freemarker.template.Configuration; 
import freemarker.template.Template; 
import freemarker.template.TemplateException; 
@SuppressWarnings("serial") 
public class HelloFreeMarkerServlet extends HttpServlet { 
  // 负责管理FreeMarker模板的Configuration实例 
  private Configuration cfg = null; 
  public void init() throws ServletException { 
    // 创建一个FreeMarker实例 
    cfg = new Configuration(); 
    // 指定FreeMarker模板文件的位置 
    cfg.setServletContextForTemplateLoading(getServletContext(),"/WEB-INF/templates"); 
  } 
  @SuppressWarnings("unchecked") 
  public void doPost(HttpServletRequest request,HttpServletResponse response) 
      throws ServletException,IOException { 
    // 建立数据模型 
    Map root = new HashMap(); 
    root.put("message","hello world"); 
    root.put("name","java小强"); 
    // 获取模板文件 
    Template t = cfg.getTemplate("test.ftl"); 
    // 使用模板文件的Charset作为本页面的charset 
    // 使用text/html MIME-type 
    response.setContentType("text/html; charset=" + t.getEncoding()); 
    Writer out = response.getWriter(); 
    // 合并数据模型和模板，并将结果输出到out中 
    try { 
      t.process(root,out); // 往模板里写数据 
    } catch (TemplateException e) { 
      e.printStackTrace(); 
    } 
  } 
  public void doGet(HttpServletRequest request,IOException { 
    doPost(request,response); 
  } 
  public void destroy() { 
    super.destroy(); 
  } 
}

注意要在你的web.xml中配置该Servlet：

<?xml version="1.0" encoding="UTF-8"?> 
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  
  http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 
  <servlet> 
    <servlet-name>hello</servlet-name> 
    <servlet-class> 
      com.test.servlet.HelloFreeMarkerServlet 
    </servlet-class> 
  </servlet> 
  <servlet-mapping> 
    <servlet-name>hello</servlet-name> 
    <url-pattern>/hello</url-pattern> 
  </servlet-mapping> 
  <welcome-file-list> 
    <welcome-file>index.jsp</welcome-file> 
  </welcome-file-list> 
</web-app>

为了方便测试，访问工程直接跳转到Servlet，对主页index.jsp做一个简单修改：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 
<% 
String path = request.getContextPath(); 
String basePath = request.getScheme()+"://"+request.getServerName() 
+":"+request.getServerPort()+path+"/"; 
%> 
<html> 
 <body> 
  <% 
  String mypath = "hello"; 
  response.sendRedirect(basePath + mypath); 
  %> 
 </body> 
</html>

部署工程到Tomcat，启动并访问http://localhost:8080/f ，这里我建立的工程名称就是 f 。

1、计算式

<#-- 1、算术运算 -->[BR] 
${3 + 4} 

<#-- 2、内建函数 -->[BR] 
${"rensanning"?upper_case}

2、输出一个值

HashMap t2root = new HashMap<String,String>(); 
t2root.put("user","RenSanNing"); 

${user},Welcome!

3、输出一个列表

Map<String,Object> t3root = new HashMap<String,Object>(); 
List<Food> menu = new ArrayList<Food>(); 
menu.add(new Food("iText in Action",98)); 
menu.add(new Food("iBATIS in Action",118)); 
menu.add(new Food("Lucene in Action",69)); 
t3root.put("menu",menu); 

<#list menu as food> 
${food.name} ${food.price?string.currency} 
</#list>

4、逻辑判断（IF,SWITCH)

Map<String,Object> t4root = new HashMap<String,Object>(); 
t4root.put("x",2); 
t4root.put("y","medium");

<1>if,else,elseif: 
<#if x == 1> 
 x is 1 
<#elseif x == 2> 
 x is 2 
<#elseif x == 3> 
 x is 3 
<#elseif x == 4> 
 x is 4 
<#else> 
 x is not 1 nor 2 nor 3 nor 4 
</#if> 

<2>switch,case,default,break: 
<#switch y> 
 <#case "small"> 
   This will be processed if it is small 
   <#break> 
 <#case "medium"> 
   This will be processed if it is medium 
   <#break> 
 <#case "large"> 
   This will be processed if it is large 
   <#break> 
 <#default> 
   This will be processed if it is neither 
</#switch> 

<3>list,break: 
<#assign seq = ["winter","spring","summer","autumn"]> 
<#list seq as x> 
 ${x_index + 1}. ${x}<#if x_has_next>,</#if> 
</#list>

5、自定义函数

<#function fact n> 
 <#if n == 0> 
  <#return 1 /> 
 <#else> 
  <#return fact(n - 1) * n /> 
 </#if> 
</#function> 

<#list 0..10 as i> 
 ${i}! => ${fact(i)} 
</#list>

6、定义变量

<#-- 1、本地变量 -->[BR] 
<#function partg n lst> 
 <#local ans = []> 
 <#list lst as x> 
  <#if (x >= n)> 
   <#local ans = ans + [x]> 
  </#if> 
 </#list> 
 <#return ans> 
</#function> 

<#assign ls = [10,2,4,5,8,1,3]> 
<#list partg(4,ls) as x>${x} </#list> 

<#-- 2、变量域测试 -->[BR] 
<#macro test> 
  03. ${x} 
  <#global x = "global2"> 
  04. ${x} 
  <#assign x = "assign2"> 
  05. ${x} 
  <#local x = "local1"> 
  06. ${x} 
  <#list ["循环1"] as x> 
    07. ${x} 
    <#local x = "local2"> 
    08. ${x} 
    <#assign x = "assign3"> 
    09. ${x} 
  </#list> 
  10. ${x} 
</#macro> 

<#global x = "global1" /> 
01. ${x} 
<#assign x = "assign1" /> 
02. ${x} 
<@test /> 
11. ${x}

7、定义宏macro

<#-- 1、无参数 -->[BR] 
<#macro greet> 
Welcome! 
</#macro> 

<@greet /> 

<#-- 2、有参数 -->[BR] 
<#macro greet user> 
${user},Welcome! 
</#macro> 

<@greet user="RenSanNing"/> 

<#-- 3、有多个参数 -->[BR] 
<#macro table cols rows> 
 <table> 
  <#list 1..rows as row> 
   <tr> 
    <#list 1..cols as col> 
     <td>${row},${col}</td> 
    </#list> 
   </tr> 
  </#list> 
 </table> 
</#macro> 

<@table cols=3 rows=2 /> 

<#-- 4、中间跳出 -->[BR] 
<#macro out> 
 显示文字 
 <#return> 
 不显示文字 
</#macro> 

<@out /> 

<#-- 5、嵌套 -->[BR] 
<#macro lprint lst> 
 <#list lst as item> 
 ・${item}<#nested item /> 
 </#list> 
</#macro> 

<@lprint 1..3; x>^2 = ${x * x}</@lprint> 
<@lprint 1..3; x>^3 = ${x * x * x}</@lprint> 
<@lprint ["Let's go","to the","land of Medetai"] />

8、include

<#include "T108include.ftl"> 
${url} 
<@greet name="rensanning" />

T108include.ftl

<#macro greet name> 
${name},Welcome! 
</#macro> 

<#assign url="http://www.baidu.com/">

9、名字空间

<#import "T109include.ftl" as my> 
<#assign url="http://www.google.com/"> 

${my.url} 
<@my.greet name="rensanning" /> 

${url}

T109include.ftl

<#macro greet name> 
${name},Welcome! 
</#macro> 

<#assign url="http://www.baidu.com/">

10、自定义指令Directive

public class SystemDateDirective implements TemplateDirectiveModel { 
   
  public void execute(Environment env,Map params,TemplateModel[] loopVars,TemplateDirectiveBody body) throws TemplateException,IOException { 
    Calendar cal = Calendar.getInstance(); 
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss"); 
    env.getOut().append(sdf.format(cal.getTime())); 
  } 
 
} 


public class TextCutDirective implements TemplateDirectiveModel { 
  public static final String PARAM_S = "s"; 
  public static final String PARAM_LEN = "len"; 
  public static final String PARAM_APPEND = "append"; 
 
  @SuppressWarnings("unchecked") 
  public void execute(Environment env,IOException { 
    String s = getString(PARAM_S,params); 
    Integer len = getInt(PARAM_LEN,params); 
    String append = getString(PARAM_APPEND,params); 
    if (s != null) { 
      Writer out = env.getOut(); 
      if (len != null) { 
        out.append(textCut(s,len,append)); 
      } else { 
        out.append(s); 
      } 
    } 
  }

....

Map<String,Object> t10root = new HashMap<String,Object>(); 
t10root.put("systemdate",new SystemDateDirective()); 
t10root.put("text_cut",new TextCutDirective());

Java操作FreeMarker模板引擎的基本用法示例小结

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