Struts 2是通过Commons FileUpload文件上传。Commons FileUpload通过将HTTP的数据保存到临时文件夹，然后Struts使用fileUpload拦截器将文件绑定到Action的实例中。从而我们就能够以本地文件方式的操作浏览器上传的文件。
前段时间Apache发布了Struts 2.0.6 GA，所以本文的实现是以该版本的Struts作为框架的。以下是例子所依赖类包的列表：
首先，创建文件上传页面FileUpload.jsp，内容如下：
<% @ page language = " java " contentType = " text/html; charset=utf-8 " pageEncoding = " utf-8 " %> <% @ taglib prefix = " s " uri = " /struts-tags " %> <! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > < html xmlns ="http://www.w3.org/1999/xhtml" > < head > < title > Struts 2 File Upload </ title > </ head > < body > < s:form action ="fileUpload" method ="POST" enctype ="multipart/form-data" > < s:file name ="myFile" label ="Image File" /> < s:textfield name ="caption" label ="Caption" /> < s:submit /> </ s:form > </ body > </ html >
在FileUpload.jsp中，先将表单的提交方式设为POST，然后将enctype设为multipart/form-data，这并没有什么特别之处。接下来，<s:file/>标志将文件上传控件绑定到Action的myFile属性。
其次是FileUploadAction.java代码：
package tutorial; import java.io.BufferedInputStream; import java.io.BufferedOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.InputStream; import java.io.OutputStream; import java.util.Date; import org.apache.struts2.ServletActionContext; import com.opensymphony.xwork2.ActionSupport; public class FileUploadAction extends ActionSupport { private static final long serialVersionUID = 572146812454l ; private static final int BUFFER_SIZE = 16 * 1024 ; private File myFile; private String contentType; private String fileName; private String imageFileName; private String caption; public void setMyFileContentType(String contentType) { this .contentType = contentType; } public void setMyFileFileName(String fileName) { this .fileName = fileName; } public void setMyFile(File myFile) { this .myFile = myFile; } public String getImageFileName() { return imageFileName; } public String getCaption() { return caption; } public void setCaption(String caption) { this .caption = caption; } private static void copy(File src, File dst) { try { InputStream in = null ; OutputStream out = null ; try { in = new BufferedInputStream( new FileInputStream(src), BUFFER_SIZE); out = new BufferedOutputStream( new FileOutputStream(dst), BUFFER_SIZE); byte [] buffer = new byte [BUFFER_SIZE]; while (in.read(buffer) > 0 ) { out.write(buffer); } } finally { if ( null != in) { in.close(); } if ( null != out) { out.close(); } } } catch (Exception e) { e.printStackTrace(); } } private static String getExtention(String fileName) { int pos = fileName.lastIndexOf( " . " ); return fileName.substring(pos); } @Override public String execute() { imageFileName = new Date().getTime() + getExtention(fileName); File imageFile = new File(ServletActionContext.getServletContext().getRealPath( " /UploadImages " ) + " / " + imageFileName); copy(myFile, imageFile); return SUCCESS; } }
在FileUploadAction中我分别写了setMyFileContentType、setMyFileFileName、setMyFile和setCaption四个Setter方法，后两者很容易明白，分别对应FileUpload.jsp中的<s:file/>和<s:textfield/>标志。但是前两者并没有显式地与任何的页面标志绑定，那么它们的值又是从何而来的呢？其实，<s:file/>标志不仅仅是绑定到myFile，还有myFileContentType（上传文件的MIME类型）和myFileFileName（上传文件的文件名，该文件名不包括文件的路径）。因此，<s:file name="xxx" />对应Action类里面的xxx、xxxContentType和xxxFileName三个属性。
FileUploadAction作用是将浏览器上传的文件拷贝到WEB应用程序的UploadImages文件夹下，新文件的名称是由系统时间与上传文件的后缀组成，该名称将被赋给imageFileName属性，以便上传成功的跳转页面使用。
下面我们就来看看上传成功的页面：
<% @ page language = " java " contentType = " text/html; charset=utf-8 " pageEncoding = " utf-8 " %> <% @ taglib prefix = " s " uri = " /struts-tags " %> <! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" > < html xmlns ="http://www.w3.org/1999/xhtml" > < head > < title > Struts 2 File Upload </ title > </ head > < body > < div style ="padding: 3px; border: solid 1px #cccccc; text-align: center" > < img src ='UploadImages/<s:property value ="imageFileName" /> ' /> < br /> < s:property value ="caption" /> </ div > </ body > </ html >
ShowUpload.jsp获得imageFileName，将其UploadImages组成URL，从而将上传的图像显示出来。
然后是Action的配置文件：
<? 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 > < package name ="fileUploadDemo" extends ="struts-default" > < action name ="fileUpload" class ="tutorial.FileUploadAction" > < interceptor-ref name ="fileUploadStack" /> < result name ="success" > /ShowUpload.jsp </ result > </ action > </ package > </ struts >
fileUpload Action显式地应用fileUploadStack的拦截器。
最后是web.xml配置文件：
<? xml version="1.0" encoding="UTF-8" ?> < web-app id ="WebApp_9" version ="2.4" 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-app_2_4.xsd" > < display-name > Struts 2 Fileupload </ display-name > < filter > < filter-name > struts-cleanup </ filter-name > < filter-class > org.apache.struts2.dispatcher.ActionContextCleanUp </ filter-class > </ filter > < filter > < filter-name > struts2 </ filter-name > < filter-class > org.apache.struts2.dispatcher.FilterDispatcher </ filter-class > </ filter > < filter-mapping > < filter-name > struts-cleanup </ filter-name > < url-pattern > /* </ url-pattern > </ filter-mapping > < filter-mapping > < filter-name > struts2 </ filter-name > < url-pattern > /* </ url-pattern > </ filter-mapping > < welcome-file-list > < welcome-file > index.html </ welcome-file > </ welcome-file-list > </ web-app >
发布运行应用程序，在浏览器地址栏中键入：http://localhost:8080/Struts2_Fileupload/FileUpload.jsp，出现图示页面：
选择图片文件，填写Caption并按下Submit按钮提交，出现图示页面：
在运行上述例子，如果您留心一点的话，应该会发现服务器控制台有如下输出：
Mar 20 , 2007 4 : 08 : 43 PM org.apache.struts2.dispatcher.Dispatcher getSaveDirINFO: Unable to find 'struts.multipart.saveDir' property setting. Defaulting to javax.servlet.context.tempdirMar 20 , 2007 4 : 08 : 43 PM org.apache.struts2.interceptor.FileUploadInterceptor interceptINFO: Removing file myFile C:/Program Files/Tomcat 5.5 /work/Catalina/localhost/Struts2_Fileupload/upload_251447c2_1116e355841__7ff7_00000006.tmp
上述信息告诉我们，struts.multipart.saveDir没有配置。struts.multipart.saveDir用于指定存放临时文件的文件夹，该配置写在struts.properties文件中。例如，如果在struts.properties文件加入如下代码：
struts.multipart.saveDir = /tmp
这样上传的文件就会临时保存到你根目录下的tmp文件夹中（一般为c:/tmp），如果此文件夹不存在，Struts 2会自动创建一个。
上述例子实现的图片上传的功能，所以应该阻止用户上传非图片类型的文件。在Struts 2中如何实现这点呢？其实这也很简单，对上述例子作如下修改即可。
首先修改FileUpload.jsp，在<body>与<s:form>之间加入“<s:fielderror />”，用于在页面上输出错误信息。
然后修改struts.xml文件，将Action fileUpload的定义改为如下所示：
< action name ="fileUpload" class ="tutorial.FileUploadAction" > < interceptor-ref name ="fileUpload" > < param name ="allowedTypes" > image/bmp,image/png,image/gif,image/jpeg </ param > </ interceptor-ref > < interceptor-ref name ="defaultStack" /> < result name ="input" > /FileUpload.jsp </ result > < result name ="success" > /ShowUpload.jsp </ result > </ action >
显而易见，起作用就是fileUpload拦截器的allowTypes参数。另外，配置还引入defaultStack它会帮我们添加验证等功能，所以在出错之后会跳转到名称为“input”的结果，也即是FileUpload.jsp。
发布运行应用程序，出错时，页面如下图所示：
上面的出错提示是Struts 2默认的，大多数情况下，我们都需要自定义和国际化这些信息。通过在全局的国际资源文件中加入“struts.messages.error.content.type.not.allowed=The file you uploaded is not a image”，可以实现以上提及的需求。对此有疑问的朋友可以参考我之前的文章《在Struts 2.0中国际化(i18n)您的应用程序》。
实现之后的出错页面如下图所示：
同样的做法，你可以使用参数“maximumSize”来限制上传文件的大小，它对应的字符资源名为：“struts.messages.error.file.too.large”。
字符资源“struts.messages.error.uploading”用提示一般的上传出错信息。
与单文件上传相似，Struts 2实现多文件上传也很简单。你可以将多个<s:file />绑定Action的数组或列表。如下例所示。
< s:form action ="doMultipleUploadUsingList" method ="POST" enctype ="multipart/form-data" > < s:file label ="File (1)" name ="upload" /> < s:file label ="File (2)" name ="upload" /> < s:file label ="FIle (3)" name ="upload" /> < s:submit /> </ s:form >
如果你希望绑定到数组，Action的代码应类似：
private File[] uploads; private String[] uploadFileNames; private String[] uploadContentTypes; public File[] getUpload() { return this .uploads; } public void setUpload(File[] upload) { this .uploads = upload; } public String[] getUploadFileName() { return this .uploadFileNames; } public void setUploadFileName(String[] uploadFileName) { this .uploadFileNames = uploadFileName; } public String[] getUploadContentType() { return this .uploadContentTypes; } public void setUploadContentType(String[] uploadContentType) { this .uploadContentTypes = uploadContentType; }
如果你想绑定到列表，则应类似：
private List < File > uploads = new ArrayList < File > (); private List < String > uploadFileNames = new ArrayList < String > (); private List < String > uploadContentTypes = new ArrayList < String > (); public List < File > getUpload() { return this .uploads; } public void setUpload(List < File > uploads) { this .uploads = uploads; } public List < String > getUploadFileName() { return this .uploadFileNames; } public void setUploadFileName(List < String > uploadFileNames) { this .uploadFileNames = uploadFileNames; } public List < String > getUploadContentType() { return this .uploadContentTypes; } public void setUploadContentType(List < String > contentTypes) { this .uploadContentTypes = contentTypes; }
在Struts 2中实现文件上传的确是轻而易举，您要做的只是使用<s:file />与Action的属性绑定。这又一次有力地证明了Struts 2的简单易用。
文章来源：http://www.blogjava.net/max/archive/2007/03/21/105124.html
