在Struts 2中实现文件上传

实现原理
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。

具体实现
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 > 

清单2 FileUpload.jsp
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;
    } 
    
} 

清单3 tutorial/FileUploadAction.java
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 >

清单4 ShowUpload.jsp
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 > 

清单5 struts.xml
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 > 

清单6 WEB-INF/web.xml
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FileUpload页面

选择图片文件，填写Caption并按下Submit按钮提交，出现上传成功页面

更多配置
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 getSaveDir
INFO: Unable to find 'struts.multipart.saveDir' property setting. Defaulting to javax.servlet.context.tempdir
Mar 20 , 2007 4 : 08 : 43 PM org.apache.struts2.interceptor.FileUploadInterceptor intercept
INFO: Removing file myFile C:\Program Files\Tomcat 5.5 \work\Catalina\localhost\Struts2_Fileupload\upload_251447c2_1116e355841__7ff7_00000006.tmp 清单9 服务器控制台输出
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 清单10 struts配置
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。

错误处理
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 >

清单11 修改后的配置文件
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，页面出错提示页面

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自定义出错提示页面

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。

多文件上传
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 > 

清单14 多文件上传JSP代码片段
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; }

清单15 多文件上传数组绑定Action代码片段
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;
    } 

清单16 多文件上传列表绑定Action代码片段
总结
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。