Struts2入門（下）

前一陣子有些朋友在電子郵件中問關於Struts 2實現檔案上傳的問題， 所以今天我們就來討論一下這個問題。

實現原理
Struts 2是通過Commons FileUpload檔案上傳。Commons FileUpload通過將HTTP的資料儲存到臨時檔案夾，然後Struts使用fileUpload攔截器將檔案綁定到Action的執行個體中。從而我們就能夠以本地檔案方式的操作瀏覽器上傳的檔案。

具體實現
前段時間Apache發布了Struts 2.0.6 GA，所以本文的實現是以該版本的Struts作為架構的。以下是例子所依賴類包的列表：

 
清單1 依賴類包的列表

首先，建立檔案上傳頁面FileUpload.jsp，內容如下：

<% @ 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 > 清單2 FileUpload.jsp
在FileUpload.jsp中，先將表單的提交方式設為POST，然後將enctype設為multipart/form-data，這並沒有什麼特別之處。接下來，<s:file/>標誌將檔案上傳控制項綁定到Action的myFile屬性。

其次是FileUploadAction.java代碼：

 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;
    }
   
} 清單3 tutorial/FileUploadAction.java
在FileUploadAction中我分別寫了setMyFileContentType、setMyFileFileName、setMyFile和setCaption四個Setter方法，後兩者很容易明白，分別對應FileUpload.jsp中的<s:file/>和<s:textfield/>標誌。但是前兩者並沒有顯式地與任何的頁面標誌綁定，那麼它們的值又是從何而來的呢？其實，<s:file/>標誌不僅僅是綁定到myFile，還有myFileContentType（上傳檔案的MIME類型）和myFileFileName（上傳檔案的檔案名稱，該檔案名稱不包括檔案的路徑）。因此，<s:file name="xxx" />對應Action類裡面的xxx、xxxContentType和xxxFileName三個屬性。

FileUploadAction作用是將瀏覽器上傳的檔案拷貝到WEB應用程式的UploadImages檔案夾下，新檔案的名稱是由系統時間與上傳檔案的尾碼組成，該名稱將被賦給imageFileName屬性，以便上傳成功的跳轉頁面使用。

下面我們就來看看上傳成功的頁面：

<% @ 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 > 清單4 ShowUpload.jsp
ShowUpload.jsp獲得imageFileName，將其UploadImages組成URL，從而將上傳的映像顯示出來。

然後是Action的設定檔：

<? 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 > 清單5 struts.xml
fileUpload Action顯式地應用fileUploadStack的攔截器。

最後是web.xml設定檔：

<? 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 >