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在Struts 2中实现文件上传

2009-02-09 10:49 656 查看
在Struts
2中实现文件上传
前一阵子有些朋友在电子邮件中问关于Struts 2实现文件上传的问题, 所以今天我们就来讨论一下这个问题。

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:



清单1 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,出现图示页面:



清单7 FileUpload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:



清单8 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,页面如下图所示:



清单12 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如下图所示:



清单13 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。
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