Develop custom taglib using Freemarker in Spring Boot

From: Polin Wei
在 Spring Boot 使用 Freemarker 模板來快速建立客製化的標籤 (taglib) 是非常簡單的事. 作下列幾個步驟即可.

 
public class FtlTemplateTag extends TagSupport {
 
 private static final long serialVersionUID = 1L;
 
 private String fileName = null;
    private String paramsStr = null;
    private String columnsStr = null;
    private ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
    
 public void setFileName(String fileName) {
  this.fileName = fileName;
 }    
 public void setParamsStr(String paramsStr) {
  this.paramsStr = paramsStr;
 }
 public void setColumnsStr(String columnsStr) {
  this.columnsStr = columnsStr;
 }
 /**
  * JSON 字串轉換成 MAP
  * @return
  */
 private Map setParams() {
  Gson gson = new Gson();
  return gson.fromJson(paramsStr, new TypeToken
  }.getType());
 }
 
 private Map setColumns(){
  Locale locale = LocaleContextHolder.getLocale();
  
  messageSource.setBasenames("i18n/messages");
  
  Gson gson = new Gson();
  Map columns = gson.fromJson(columnsStr, new TypeToken
  
  //轉換多語系
  Map dataModel = new LinkedHashMap();
  columns.forEach( (k,v)-> dataModel.put(k, messageSource.getMessage(v, null, v, locale)) );
   
  return dataModel;
 }
 
 
 @Override
 public int doStartTag() throws JspException {
  JspWriter out = pageContext.getOut();
  
  Configuration conf = new Configuration();
  conf.setClassForTemplateLoading(this.getClass(), "/templates/");
  conf.setDefaultEncoding("UTF-8");
  
  try {
   Template  tl = conf.getTemplate(fileName);
   Map dataModel = new HashMap();
   dataModel.putAll(this.setParams());
   dataModel.put("columns", this.setColumns());
   
 
   tl.process(dataModel, out);
   
  } catch (Exception e) {
   e.printStackTrace();
  }  
  return Tag.SKIP_BODY;
 }
}

 
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
        version="2.0">
    <description>Polin WEI Tag Library</description>
 
    <tlib-version>1.0</tlib-version>
    <short-name>pw</short-name>
    <uri>/polinwei/tags</uri>
 
    <tag>
        <description>Get the file name of freemarker template</description>
        <name>FtlSampleTemplate</name>
        <tag-class>com.spring.jwt.tablibs.FtlTemplateTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <description> Freemarker Template 的檔案</description>
            <name>fileName</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>parmsStr</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>columnsStr</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

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