在Struts 2中實現文件上傳

時間 2019-11-24

原文原文鏈接

前一陣子有些朋友在電子郵件中問關於Struts 2實現文件上傳的問題，因此今天咱們就來討論一下這個問題。

實現原理

Struts 2是經過Commons FileUpload文件上傳。Commons FileUpload經過將HTTP的數據保存到臨時文件夾，而後Struts使用fileUpload攔截器將文件綁定到Action的實例中。從而咱們就可以以本地文件方式的操做瀏覽器上傳的文件。

具體實現

前段時間Apache發佈了Struts 2.0.6 GA，因此本文的實現是以該版本的Struts做爲框架的。如下是例子所依賴類包的列表：

清單1 依賴類包的列表

首先，建立文件上傳頁面FileUpload.jsp，內容以下：

<% @ 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爲POST，而後將enctype設爲multipart/form-data，這並無什麼特別之處。接下來，<s:file/>標誌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 p_w_picpathFileName;

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 p_w_picpathFileName;

}

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() {

p_w_picpathFileName = new Date().getTime() + getExtention(fileName);

File p_w_picpathFile = new File(ServletActionContext.getServletContext().getRealPath( " /UploadImages " ) + " / " + p_w_picpathFileName);

copy(myFile, p_w_picpathFile);

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，後二者很容易明白，分別對應FileUpload.jsp中的<s:file/>和<s:textfield/>標誌。可是前二者並無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/>標誌不只僅是綁定到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）。所以，<s:file name="xxx" />對應Action類裏面的xxx、xxxContentType和xxxFileName三個屬性。

FileUploadAction做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後綴組成，該名稱將被賦給p_w_picpathFileName屬性，以便上傳成功的跳轉頁面使用。

下面咱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 ="p_w_picpathFileName" /> ' />
< br />
< s:property value ="caption" />
</ div >
</ body >
</ html >

清單4 ShowUpload.jsp

ShowUpload.jsp得到p_w_picpathFileName，將其UploadImages組成URL，從而將上傳的圖像顯示出來。

而後是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。

最後是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 [url]http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd[/url]" >

< 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 >

清單6 WEB-INF/web.xml

發佈運行應用程序，在瀏覽器地址欄中鍵入： [url]http://localhost:8080/Struts2_Fileupload/FileUpload.jsp[/url]，出現圖示頁面：

清單7 FileUpload頁面

選擇圖片文件，填寫Caption並按下Submit按鈕提交，出現圖示頁面：

清單8 上傳成功頁面

錯誤處理

上述例子實現的圖片上傳的功能，因此應該阻止用戶上傳非圖片類型的文件。在Struts 2中如何實現這點呢？其實這也很簡單，對上述例子做以下修改便可。

首先修改FileUpload.jsp，在<body>與<s:form>之間加入「<s:fielderror />」，用於在頁面上輸出錯誤信息。

而後修改struts.xml文件，將Action fileUpload的定義改成以下所示：

< action name ="fileUpload" class ="tutorial.FileUploadAction" >
< interceptor-ref name ="fileUpload" >
< param name ="allowedTypes" >
p_w_picpath/bmp,p_w_picpath/png,p_w_picpath/gif,p_w_picpath/jpeg
</ param >
</ interceptor-ref >
< interceptor-ref name ="defaultStack" />
< result name ="input" > /FileUpload.jsp </ result >
< result name ="success" > /ShowUpload.jsp </ result >
</ action >

清單11 修改後的配置文件

顯而易見，起做用就是fileUpload攔截器的allowTypes參數。另外，配置還引入defaultStack它會幫咱們添加驗證等功能，因此在出錯以後會跳轉到名稱爲「input」的結果，也便是FileUpload.jsp。

發佈運行應用程序，出錯時，頁面以下圖所示：

清單12 出錯提示頁面

上面的出錯提示是Struts 2默認的，大多數狀況下，咱們都須要自定義和國際化這些信息。經過在全局的國際資源文件中加入「struts.messages.error.content.type.not.allowed=The file you uploaded is not a p_w_picpath」，能夠實現以上說起的需求。對此有疑問的朋友能夠參考我以前的文章《在Struts 2.0中國際化(i18n)您的應用程序》。

實現以後的出錯頁面以下圖所示：

清單13 自定義出錯提示頁面

一樣的作法，你可使用參數「maximumSize」來限制上傳文件的大小，它對應的字符資源名爲：「struts.messages.error.file.too.large」。

字符資源「struts.messages.error.uploading」用提示通常的上傳出錯信息。

多文件上傳

與單文件上傳類似，Struts 2實現多文件上傳也很簡單。你能夠將多個<s:file />綁定Action的數組或列表。以下例所示。

< 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 >

清單14 多文件上傳JSP代碼片斷

若是你但願綁定到數組，Action的代碼應相似：

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; }

清單15 多文件上傳數組綁定Action代碼片斷

若是你想綁定到列表，則應相似：

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;

}

清單16 多文件上傳列表綁定Action代碼片斷

總結

在Struts 2中實現文件上傳的確是垂手可得，您要作的只是使用<s:file />與Action的屬性綁定。這又一次有力地證實了Struts 2的簡單易用。

[例二]

Struts2使用開源項目Apache Jakarta Commons FileUpload和內建的FileUploadInterceptor攔截器實現文件上傳，所需的jar包以下：

commons-logging-1.1.jar
freemarker-2.3.8.jar
ognl-2.6.11.jar
struts2-core-2.0.6.jar
xwork-2.0.1.jar
commons-io-1.3.1.jar
commons-fileupload-1.2.jar

★ 文件上傳頁面 fileupload.jsp

<%@ page language="java" contentType="text/html; charset=GBK"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
<head>
<body>
<s:form action="fileUpload" method="post" enctype="multipart/form-data">
<s:file name="doc" label="File"/>
<s:submit/>
<s:form>
<body>
<html>

這裏須要注意的是，form的enctype屬性必須設置爲multipart/form-data。

★ 處理文件上傳 FileUploadAction.java

package fileupload;
import java.io.File;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;
import javax.servlet.ServletContext;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.util.ServletContextAware;
import com.opensymphony.xwork2.ActionSupport;
public class FileUploadAction extends ActionSupport implements ServletContextAware {
private static final long serialVersionUID = -5016873153441103539L;
private File doc;
private String fileName;
private String contentType;
private ServletContext context;
public void setDoc(File file) {
this.doc = file;
}
public void setDocFileName(String fileName) {
this.fileName = fileName;
}
public void setDocContentType(String contentType) {
this.contentType = contentType;
}
public void setServletContext(ServletContext context) {
this.context = context;
}
public String execute() throws Exception {
String targetDirectory = context.getRealPath("/upload");
String targetFileName = generateFileName(fileName);
File target = new File(targetDirectory, targetFileName);
FileUtils.copyFile(doc, target);
return SUCCESS;
}
private String generateFileName(String fileName) {
DateFormat format = new SimpleDateFormat("yyMMddHHmmss");
String formatDate = format.format(new Date());
int random = new Random().nextInt(10000);
int position = fileName.lastIndexOf(".");
String extension = fileName.substring(position);
return formatDate + random + extension;
}
}

在fileupload.jsp中，只有doc一個字段，而FileUploadAction.java中，卻有三個字段，Struts2怎麼經過頁面的一個字段設置Action裏的三個字段呢？沒錯，這就是FileUploadInterceptor的功勞了！你所要作的只是按照必定的樣式命名這三個字段的set方法，而字段名能夠任意命名。第一個File類型的字段的set方法仍是以常規的方式命名，另兩個String類型的字段的set方法必須分別以「File字段的set方法名+FileName」和「File字段的set方法名+ContentType」來命名。

★ 配置文件 struts.xml