转：在Struts 2中实现文件上传

（本文转自：http://www.blogjava.net/max/archive/2007/03/21/105124.html）

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

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。