一、Struts2檔案上傳
Struts2的檔案上傳實現非常簡單，只需要簡單幾步就可完成；
注意：
(1)檔案上傳的struts2標籤為：<s:file name="" label="上傳"/>
(2)檔案上傳的前提是表單屬性method="post" enctype="multipart/form-data";
(3)web應用中必須包含common-fileupload.jar和common-io.jar，因為struts2預設上傳解析器使用的是jakarta；
(4)可以在struts.xml中配置最大允許上傳的檔案大小：<constant name="struts.multipart.maxSize" value="....."/>,預設為2M；
1.普通檔案上傳
實現規則：
(1)在JSP中設定表單控制項<s:file name="upload" label="上傳"/>
(2)在Action中定義屬性：
private File upload; //包含檔案內容
private String uploadFileName; //上傳檔案的名稱；
private String uploadContentType; //上傳檔案的MIME類型；
這些屬性都會隨著檔案的上傳自動賦值；
(3)在execute()中完成寫入磁碟功能；
程式碼範例：
Upload01Action.java
package org.upload.action;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionSupport;public class Upload01Action extends ActionSupport {private File upload;private String uploadFileName;private String uploadContentType;private String name;public String execute()throws Exception{String path = ServletActionContext.getServletContext().getRealPath("/WEB-INF/upload");String filename = path+File.separator+name;FileInputStream in = new FileInputStream(upload);FileOutputStream out = new FileOutputStream(filename);byte[]b = new byte[1024];int len = 0;while((len=in.read(b))>0){out.write(b,0,len);}out.close();return SUCCESS;}public File getUpload() {return upload;}public void setUpload(File upload) {this.upload = upload;}public String getUploadFileName() {return uploadFileName;}public void setUploadFileName(String uploadFileName) {this.uploadFileName = uploadFileName;}public String getUploadContentType() {return uploadContentType;}public void setUploadContentType(String uploadContentType) {this.uploadContentType = uploadContentType;}public String getName() {return name;}public void setName(String name) {this.name = name;}}
struts.xml
<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"><struts><constant name="struts.devMode" value="true" /><constant name="struts.custom.i18n.resources" value="message"></constant><package name="default" namespace="/" extends="struts-default"><action name="upload0*" class="org.upload.action.Upload0{1}Action"><param name="name">1.jpg</param><result>/{1}.jsp</result></action></package></struts>
1.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@taglib prefix="s" uri="/struts-tags" %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>My JSP '1.jsp' starting page</title> </head> <body> <s:form action="upload01" method="post" enctype="multipart/form-data"> <s:file name="upload" label="上傳"></s:file> <s:submit value="上傳"></s:submit> </s:form> </body></html>
2.利用攔截器進行過濾
手動實現過濾的方式非常簡單，就是利用輸入校正的方式進行過濾，即在validate()中進行過濾；
而這裡要講的攔截器方式是很好的方式，只需要在設定檔中配置，靈活性很好，能夠限制檔案的類型、檔案的大小；如果上傳的檔案不符合要求，則返回input邏輯視圖；
配置攔截器步驟：
(1)檔案上傳的攔截器為fileUpload；
(2)需要給定參數allowedTypes、maximumSize;
(3)在fileUpload攔截器後，需要添加<interceptor-ref name="defaultStack"/>
程式碼範例：
由於通過攔截器進行過濾只需要配置struts.xml，因此這裡只給出struts.xml的配置
<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" "http://struts.apache.org/dtds/struts-2.0.dtd"><struts><constant name="struts.devMode" value="true" /><constant name="struts.custom.i18n.resources" value="message"></constant><package name="default" namespace="/" extends="struts-default"><action name="upload0*" class="org.upload.action.Upload0{1}Action"><interceptor-ref name="fileUpload"><param name="allowedTypes">image/jpeg,image/gif</param><param name="maximumSize">1024*1024</param></interceptor-ref><interceptor-ref name="defaultStack"></interceptor-ref><param name="name">1.jpg</param><result>/{1}.jsp</result><result name="input">/{1}.jsp</result></action></package></struts>
我們還需要設定檔上傳失敗後的錯誤提示資訊，我們需要在全域國際化資源檔案中配置：
struts.messages.error.content.type.not.allowed=檔案類型不匹配struts.messages.error.file.too.large=檔案太大
二、Struts2檔案下載
我們在學習Servlet和HTTP協議時已經可以實現檔案下載，即寫content-disposition頭即可，struts2的實現原理也是這個，但是提供了更好的封裝性；
struts2的stream結果類型專門用於實現檔案下載；
(1)struts.xml中配置stream結果類型，並配置contentType、contentDisposition、bufferSize參數即可，模板：
<action name="download" class=""><result type="stream" name="success"><param name="contentType"></param><param name="contentDisposition">attachment;filename=""</param><param name="bufferSize">4096</param></result></action>
(2)在Action中建立public InputStream getInputStream()throws Exception;方法，此方法用於獲得下載檔案的輸入資料流；
DownloadAction.java
package org.download.action;import java.io.InputStream;import org.apache.struts2.ServletActionContext;import com.opensymphony.xwork2.ActionSupport;public class DownloadAction extends ActionSupport {public InputStream getInputStream()throws Exception{return ServletActionContext.getServletContext().getResourceAsStream("/WEB-INF/upload/1.jpg");}public String execute()throws Exception{return SUCCESS;}}
struts.xml
<action name="download" class="org.download.action.DownloadAction"><result type="stream" name="success"><param name="contentType">image/jpeg</param><param name="contentDisposition">attachment;filename="1.jpg"</param><param name="bufferSize">4096</param></result></action>
就可以完成下載；
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