前一陣子有些朋友在電子郵件中問關于Struts 2實現文件上傳的問題， 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文件上傳。Commons FileUpload通過將HTTP的數據保存到臨時文件夾，然后Struts使用fileUpload攔截器將文件綁定到Action的實例中。從而我們就能夠以本地文件方式的操作瀏覽器上傳的文件。
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作為框架的。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，創建文件上傳頁面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，然后將enctype設為multipart/form-data，這并沒有什么特別之處。接下來，<s:file/>標志將文件上傳控件綁定到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，后兩者很容易明白，分別對應FileUpload.jsp中的<s:file/>和<s:textfield/>標志。但是前兩者并沒有顯式地與任何的頁面標志綁定，那么它們的值又是從何而來的呢？其實，<s:file/>標志不僅僅是綁定到myFile，還有myFileContentType（上傳文件的MIME類型）和myFileFileName（上傳文件的文件名，該文件名不包括文件的路徑）。因此，<s:file name="xxx" />對應Action類里面的xxx、xxxContentType和xxxFileName三個屬性。
FileUploadAction作用是將瀏覽器上傳的文件拷貝到WEB應用程序的UploadImages文件夾下，新文件的名稱是由系統時間與上傳文件的后綴組成，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，從而將上傳的圖像顯示出來。
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 > 清單5 struts.xml
fileUpload Action顯式地應用fileUploadStack的攔截器。
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 >