七、Struts2之檔案上傳與下載
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中設定表單控制元件<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型別；
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；
程式碼示例：
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，就是利用輸入校驗的方式進行過濾，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，只需要在配置檔案中配置，靈活性很好，能夠限制檔案的型別、檔案的大小；如果上傳的檔案不符合要求，則返回input邏輯檢視；
配置攔截器步驟：
(1)檔案上傳的攔截器為fileUpload；
(2)需要給定引數allowedTypes、maximumSize;
(3)在fileUpload攔截器後，需要新增<interceptor-ref name="defaultStack"/>
程式碼示例：
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>
我們還需要配置檔案上傳失敗後的錯誤提示資訊，我們需要在全域性國際化資源檔案中配置：
struts.messages.error.content.type.not.allowed=檔案型別不匹配
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結果型別專門用於實現檔案下載；
(1)struts.xml中配置stream結果型別，並配置contentType、contentDisposition、bufferSize引數即可，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；