Java操作FreeMarker模板引擎的基本用法示例小结

2020-04-11 10:44:25

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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, HttpServletResponse response)       throws ServletException, 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, Map params, TemplateModel[] loopVars,       TemplateDirectiveBody body) throws TemplateException, 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());

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