基于Struts2的portlet開發時，實作多個portlet中的同一個js隻加載一次

使用struts2開發portlet時，需要在jsp頁面上加載現有的js庫進行互動。這個portlet可能在頁面上重複使用，這就要求確定頁面上的多個portlet中同樣的js檔案隻會加載一次。經過研究，發現可以通過擴充Jsr286Dispatcher類，然後重寫doHeaders方法實作，代碼如下：

@Override
	protected void doHeaders(RenderRequest request, RenderResponse response) {
		super.doHeaders(request, response);
		
//        if (request.getPortalContext().getProperty(PortalContext.MARKUP_HEAD_ELEMENT_SUPPORT) == null) {
//			logger.warn("The Portal Server does not support adding markup to the header. This may lead to portlets that do not work properly.");        
//		} else {            
			for (String cssFile : styles) {                    
				Element htmlHeader = response.createElement("link");                    
				htmlHeader.setAttribute("rel", "stylesheet");                    
				htmlHeader.setAttribute("type", "text/css");                    
				htmlHeader.setAttribute("href", response.encodeURL(request.getContextPath() + cssFile));  
				
				response.addProperty(MimeResponse.MARKUP_HEAD_ELEMENT, htmlHeader);                    
				logger.debug("Added {} CSS file to the portal header.", cssFile);                
			}                
				
			for (String javascriptFile : scripts) {                    
				Element htmlHeader = response.createElement("script");                    
				htmlHeader.setAttribute("src", response.encodeURL(request.getContextPath() + javascriptFile));                    
				htmlHeader.setAttribute("type", "text/javascript");   
				
				response.addProperty(MimeResponse.MARKUP_HEAD_ELEMENT, htmlHeader);
				logger.debug("Added {} Javascript file to the portal header.", javascriptFile);                
			}            
//		}    
	}
           

 運作後發現doHeaders方法不執行，然後查閱Jsr286Dispatcher類的源代碼和GenericPortlet類的源代碼，發現struts2已經修改了render方法，不再執行調用doHeaders的方法，是以我又重寫了render方法，整體代碼如下：

/**
 * 
 */
package com.lily.dap.web.portlet.dispatcher;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.portlet.MimeResponse;
//import javax.portlet.PortalContext;
import javax.portlet.PortletConfig;
import javax.portlet.PortletException;
import javax.portlet.RenderRequest;
import javax.portlet.RenderResponse;

import org.apache.struts2.portlet.dispatcher.Jsr286Dispatcher;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Element;

/**
 * 支援加載js腳本檔案、css樣式檔案
 * 
 * @author zouxuemo
 *
 */
public class Dispatcher extends Jsr286Dispatcher {
	protected final Logger logger = LoggerFactory.getLogger(getClass());
	
	private List<String> scripts = new ArrayList<String>();
	
	private List<String> styles = new ArrayList<String>();
	
	@Override
	public void init(PortletConfig cfg) throws PortletException {
		super.init(cfg);
		
		String s = cfg.getInitParameter("scripts");
		if (s != null) {
			String[] tmp = s.split(" ");
			for (String script : tmp) {
				script = script.trim();
				if (script.charAt(0) != '/')
					script = '/' + script;
				
				scripts.add(script);
			}
		}
		
		s = cfg.getInitParameter("styles");
		if (s != null) {
			String[] tmp = s.split(" ");
			for (String style : tmp) {
				style = style.trim();
				if (style.charAt(0) != '/')
					style = '/' + style;
				
				styles.add(style);
			}
		}
	}

	@Override
	public void render(RenderRequest request, RenderResponse response)
			throws PortletException, IOException {
		doHeaders(request, response);
		
		super.render(request, response);
	}

	@Override
	protected void doHeaders(RenderRequest request, RenderResponse response) {
		super.doHeaders(request, response);
		
//        if (request.getPortalContext().getProperty(PortalContext.MARKUP_HEAD_ELEMENT_SUPPORT) == null) {
//			logger.warn("The Portal Server does not support adding markup to the header. This may lead to portlets that do not work properly.");        
//		} else {            
			for (String cssFile : styles) {                    
				Element htmlHeader = response.createElement("link");                    
				htmlHeader.setAttribute("rel", "stylesheet");                    
				htmlHeader.setAttribute("type", "text/css");                    
				htmlHeader.setAttribute("href", response.encodeURL(request.getContextPath() + cssFile));  
				
				response.addProperty(MimeResponse.MARKUP_HEAD_ELEMENT, htmlHeader);                    
				logger.debug("Added {} CSS file to the portal header.", cssFile);                
			}                
				
			for (String javascriptFile : scripts) {                    
				Element htmlHeader = response.createElement("script");                    
				htmlHeader.setAttribute("src", response.encodeURL(request.getContextPath() + javascriptFile));                    
				htmlHeader.setAttribute("type", "text/javascript");   
				
				response.addProperty(MimeResponse.MARKUP_HEAD_ELEMENT, htmlHeader);
				logger.debug("Added {} Javascript file to the portal header.", javascriptFile);                
			}            
//		}    
	}
}
           

然後在portlet.xml中添加js腳本的初始參數設定，代碼如下：

<portlet id="AnalysisPresentation">
        <description xml:>分析資料展現</description>
        <portlet-name>AnalysisPresentation</portlet-name>
        <display-name xml:>分析資料展現</display-name>
        <portlet-class>com.lily.dap.web.portlet.dispatcher.Dispatcher</portlet-class>

        <init-param>
            <name>scripts</name>
            <value>/scripts/jquery-1.7.1/jquery.min.js /fc/FusionCharts.js /fc/FusionCharts.jqueryplugin.js /scripts/presentation-chart.js</value>
        </init-param>

        <init-param>
            <name>styles</name>
            <value>/styles/report.css</value>
        </init-param>

        <!-- The view mode namespace. Maps to a namespace in the Struts 2 config file. -->
        <init-param>
            <name>viewNamespace</name>
            <value>/presentation</value>
        </init-param>

        <!-- The default action to invoke in view mode. -->
        <init-param>
            <name>defaultViewAction</name>
            <value>analysis-presentation</value>
        </init-param>

        <!-- The edit mode namespace. Maps to a namespace in the Struts 2 config file. -->
        <init-param>
            <name>editNamespace</name>
            <value>/presentation</value>
        </init-param>

        <!-- The default action to invoke in edit mode. -->
        <init-param>
            <name>defaultEditAction</name>
            <value>analysis-presentation-edit</value>
        </init-param>
        ...
    </portlet>
      

至此，即實作了多個portlet中的同一個js隻加載一次的要求