Struts(二十六)：文件上传

• 表单的准备

想要使用html表单上传一个或多个文件
1、须把html表单的enctype属性设置为multipart/form-data
2、须把html表单的method属性设置为post
3、须添加<input type="file">字段

• Struts2的进行单文件上传需要操作步骤：

1、需要引入struts2需要的包，struts2上传是需要使用fileUpload拦截器实现的，而实际上上传文件是使用Commons FileUpload组建，所以需要导入commons-fileupload-1.3.2.jar、commons-io-2.2.jar包。

2、定制表单index.jsp

　　<s:form action="testUpload" method="post" enctype="multipart/form-data"
        theme="simple">
    File:<s:file name="myFile"></s:file>
    File Description:<s:textfield name="desc"></s:textfield>
        <s:submit value="Submit"></s:submit>
    </s:form>

3、基本的文件上传设置：直接在action类中定义如下三个属性，并实现getter和setter

private File myFile;
    private String myFileContentType;
    private String myFileFileName;

    public File getMyFile() {
        return myFile;
    }

    public void setMyFile(File myFile) {
        this.myFile = myFile;
    }

    public String getMyFileContentType() {
        return myFileContentType;
    }

    public void setMyFileContentType(String myFileContentType) {
        this.myFileContentType = myFileContentType;
    }

    public String getMyFileFileName() {
        return myFileFileName;
    }

    public void setMyFileFileName(String myFileFileName) {
        this.myFileFileName = myFileFileName;
    }

备注：当查看fileUpload拦截器源码

 /*
  * $Id$
  *
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you under the Apache License, Version 2.0 (the
  * "License"); you may not use this file except in compliance
  * with the License.  You may obtain a copy of the License at
  *
  *  http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing,
  * software distributed under the License is distributed on an
  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  * KIND, either express or implied.  See the License for the
  * specific language governing permissions and limitations
  * under the License.
  */

 package org.apache.struts2.interceptor;

 import com.opensymphony.xwork2.ActionContext;
 import com.opensymphony.xwork2.ActionInvocation;
 import com.opensymphony.xwork2.ActionProxy;
 import com.opensymphony.xwork2.LocaleProvider;
 import com.opensymphony.xwork2.TextProvider;
 import com.opensymphony.xwork2.TextProviderFactory;
 import com.opensymphony.xwork2.ValidationAware;
 import com.opensymphony.xwork2.inject.Container;
 import com.opensymphony.xwork2.inject.Inject;
 import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
 import com.opensymphony.xwork2.util.TextParseUtil;
 import com.opensymphony.xwork2.util.logging.Logger;
 import com.opensymphony.xwork2.util.logging.LoggerFactory;
 import org.apache.struts2.ServletActionContext;
 import org.apache.struts2.dispatcher.multipart.MultiPartRequestWrapper;
 import org.apache.struts2.util.ContentTypeMatcher;

 import javax.servlet.http.HttpServletRequest;
 import java.io.File;
 import java.text.NumberFormat;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 /**
  * <!-- START SNIPPET: description -->
  * <p/>
  * Interceptor that is based off of {@link MultiPartRequestWrapper}, which is automatically applied for any request that
  * includes a file. It adds the following parameters, where [File Name] is the name given to the file uploaded by the
  * HTML form:
  * <p/>
  * <ul>
  * <p/>
  * <li>[File Name] : File - the actual File</li>
  * <p/>
  * <li>[File Name]ContentType : String - the content type of the file</li>
  * <p/>
  * <li>[File Name]FileName : String - the actual name of the file uploaded (not the HTML name)</li>
  * <p/>
  * </ul>
  * <p/>
  * <p/> You can get access to these files by merely providing setters in your action that correspond to any of the three
  * patterns above, such as setDocument(File document), setDocumentContentType(String contentType), etc.
  * <br/>See the example code section.
  * <p/>
  * <p/> This interceptor will add several field errors, assuming that the action implements {@link ValidationAware}.
  * These error messages are based on several i18n values stored in struts-messages.properties, a default i18n file
  * processed for all i18n requests. You can override the text of these messages by providing text for the following
  * keys:
  * <p/>
  * <ul>
  * <p/>
  * <li>struts.messages.error.uploading - a general error that occurs when the file could not be uploaded</li>
  * <p/>
  * <li>struts.messages.error.file.too.large - occurs when the uploaded file is too large</li>
  * <p/>
  * <li>struts.messages.error.content.type.not.allowed - occurs when the uploaded file does not match the expected
  * content types specified</li>
  * <p/>
  * <li>struts.messages.error.file.extension.not.allowed - occurs when the uploaded file does not match the expected
  * file extensions specified</li>
  * <p/>
  * </ul>
  * <p/>
  * <!-- END SNIPPET: description -->
  * <p/>
  * <p/> <u>Interceptor parameters:</u>
  * <p/>
  * <!-- START SNIPPET: parameters -->
  * <p/>
  * <ul>
  * <p/>
  * <li>maximumSize (optional) - the maximum size (in bytes) that the interceptor will allow a file reference to be set
  * on the action. Note, this is <b>not</b> related to the various properties found in struts.properties.
  * Default to approximately 2MB.</li>
  * <p/>
  * <li>allowedTypes (optional) - a comma separated list of content types (ie: text/html) that the interceptor will allow
  * a file reference to be set on the action. If none is specified allow all types to be uploaded.</li>
  * <p/>
  * <li>allowedExtensions (optional) - a comma separated list of file extensions (ie: .html) that the interceptor will allow
  * a file reference to be set on the action. If none is specified allow all extensions to be uploaded.</li>
  * </ul>
  * <p/>
  * <p/>
  * <!-- END SNIPPET: parameters -->
  * <p/>
  * <p/> <u>Extending the interceptor:</u>
  * <p/>
  * <p/>
  * <p/>
  * <!-- START SNIPPET: extending -->
  * <p/>
  * You can extend this interceptor and override the acceptFile method to provide more control over which files
  * are supported and which are not.
  * <p/>
  * <!-- END SNIPPET: extending -->
  * <p/>
  * <p/> <u>Example code:</u>
  * <p/>
  * <pre>
  * <!-- START SNIPPET: example-configuration -->
  * &lt;action name="doUpload" class="com.example.UploadAction"&gt;
  *     &lt;interceptor-ref name="fileUpload"/&gt;
  *     &lt;interceptor-ref name="basicStack"/&gt;
  *     &lt;result name="success"&gt;good_result.jsp&lt;/result&gt;
  * &lt;/action&gt;
  * <!-- END SNIPPET: example-configuration -->
  * </pre>
  * <p/>
  * <!-- START SNIPPET: multipart-note -->
  * <p/>
  * You must set the encoding to <code>multipart/form-data</code> in the form where the user selects the file to upload.
  * <p/>
  * <!-- END SNIPPET: multipart-note -->
  * <p/>
  * <pre>
  * <!-- START SNIPPET: example-form -->
  *   &lt;s:form action="doUpload" method="post" enctype="multipart/form-data"&gt;
  *       &lt;s:file name="upload" label="File"/&gt;
  *       &lt;s:submit/&gt;
  *   &lt;/s:form&gt;
  * <!-- END SNIPPET: example-form -->
  * </pre>
  * <p/>
  * And then in your action code you'll have access to the File object if you provide setters according to the
  * naming convention documented in the start.
  * <p/>
  * <pre>
  * <!-- START SNIPPET: example-action -->
  *    package com.example;
  *
  *    import java.io.File;
  *    import com.opensymphony.xwork2.ActionSupport;
  *
  *    public UploadAction extends ActionSupport {
  *       private File file;
  *       private String contentType;
  *       private String filename;
  *
  *       public void setUpload(File file) {
  *          this.file = file;
  *       }
  *
  *       public void setUploadContentType(String contentType) {
  *          this.contentType = contentType;
  *       }
  *
  *       public void setUploadFileName(String filename) {
  *          this.filename = filename;
  *       }
  *
  *       public String execute() {
  *          //...
  *          return SUCCESS;
  *       }
  *  }
  * <!-- END SNIPPET: example-action -->
  * </pre>
  */
 public class FileUploadInterceptor extends AbstractInterceptor {

     private static final long serialVersionUID = -4764627478894962478L;

     protected static final Logger LOG = LoggerFactory.getLogger(FileUploadInterceptor.class);

     protected Long maximumSize;
     protected Set<String> allowedTypesSet = Collections.emptySet();
     protected Set<String> allowedExtensionsSet = Collections.emptySet();

     private ContentTypeMatcher matcher;
     private Container container;

     @Inject
     public void setMatcher(ContentTypeMatcher matcher) {
         this.matcher = matcher;
     }

     @Inject
     public void setContainer(Container container) {
         this.container = container;
     }

     /**
      * Sets the allowed extensions
      *
      * @param allowedExtensions A comma-delimited list of extensions
      */
     public void setAllowedExtensions(String allowedExtensions) {
         allowedExtensionsSet = TextParseUtil.commaDelimitedStringToSet(allowedExtensions);
     }

     /**
      * Sets the allowed mimetypes
      *
      * @param allowedTypes A comma-delimited list of types
      */
     public void setAllowedTypes(String allowedTypes) {
         allowedTypesSet = TextParseUtil.commaDelimitedStringToSet(allowedTypes);
     }

     /**
      * Sets the maximum size of an uploaded file
      *
      * @param maximumSize The maximum size in bytes
      */
     public void setMaximumSize(Long maximumSize) {
         this.maximumSize = maximumSize;
     }

     /* (non-Javadoc)
      * @see com.opensymphony.xwork2.interceptor.Interceptor#intercept(com.opensymphony.xwork2.ActionInvocation)
      */

     public String intercept(ActionInvocation invocation) throws Exception {
         ActionContext ac = invocation.getInvocationContext();

         HttpServletRequest request = (HttpServletRequest) ac.get(ServletActionContext.HTTP_REQUEST);

         if (!(request instanceof MultiPartRequestWrapper)) {
             if (LOG.isDebugEnabled()) {
                 ActionProxy proxy = invocation.getProxy();
                 LOG.debug(getTextMessage("struts.messages.bypass.request", new String[]{proxy.getNamespace(), proxy.getActionName()}));
             }

             return invocation.invoke();
         }

         ValidationAware validation = null;

         Object action = invocation.getAction();

         if (action instanceof ValidationAware) {
             validation = (ValidationAware) action;
         }

         MultiPartRequestWrapper multiWrapper = (MultiPartRequestWrapper) request;

         if (multiWrapper.hasErrors()) {
             for (String error : multiWrapper.getErrors()) {
                 if (validation != null) {
                     validation.addActionError(error);
                 }
             }
         }

         // bind allowed Files
         Enumeration fileParameterNames = multiWrapper.getFileParameterNames();
         while (fileParameterNames != null && fileParameterNames.hasMoreElements()) {
             // get the value of this input tag
             String inputName = (String) fileParameterNames.nextElement();

             // get the content type
             String[] contentType = multiWrapper.getContentTypes(inputName);

             if (isNonEmpty(contentType)) {
                 // get the name of the file from the input tag
                 String[] fileName = multiWrapper.getFileNames(inputName);

                 if (isNonEmpty(fileName)) {
                     // get a File object for the uploaded File
                     File[] files = multiWrapper.getFiles(inputName);
                     if (files != null && files.length > 0) {
                         List<File> acceptedFiles = new ArrayList<File>(files.length);
                         List<String> acceptedContentTypes = new ArrayList<String>(files.length);
                         List<String> acceptedFileNames = new ArrayList<String>(files.length);
                         String contentTypeName = inputName + "ContentType";
                         String fileNameName = inputName + "FileName";

                         for (int index = 0; index < files.length; index++) {
                             if (acceptFile(action, files[index], fileName[index], contentType[index], inputName, validation)) {
                                 acceptedFiles.add(files[index]);
                                 acceptedContentTypes.add(contentType[index]);
                                 acceptedFileNames.add(fileName[index]);
                             }
                         }

                         if (!acceptedFiles.isEmpty()) {
                             Map<String, Object> params = ac.getParameters();

                             params.put(inputName, acceptedFiles.toArray(new File[acceptedFiles.size()]));
                             params.put(contentTypeName, acceptedContentTypes.toArray(new String[acceptedContentTypes.size()]));
                             params.put(fileNameName, acceptedFileNames.toArray(new String[acceptedFileNames.size()]));
                         }
                     }
                 } else {
                     if (LOG.isWarnEnabled()) {
                         LOG.warn(getTextMessage(action, "struts.messages.invalid.file", new String[]{inputName}));
                     }
                 }
             } else {
                 if (LOG.isWarnEnabled()) {
                     LOG.warn(getTextMessage(action, "struts.messages.invalid.content.type", new String[]{inputName}));
                 }
             }
         }

         // invoke action
         return invocation.invoke();
     }

     /**
      * Override for added functionality. Checks if the proposed file is acceptable based on contentType and size.
      *
      * @param action      - uploading action for message retrieval.
      * @param file        - proposed upload file.
      * @param contentType - contentType of the file.
      * @param inputName   - inputName of the file.
      * @param validation  - Non-null ValidationAware if the action implements ValidationAware, allowing for better
      *                    logging.
      * @return true if the proposed file is acceptable by contentType and size.
      */
     protected boolean acceptFile(Object action, File file, String filename, String contentType, String inputName, ValidationAware validation) {
         boolean fileIsAcceptable = false;

         // If it's null the upload failed
         if (file == null) {
             String errMsg = getTextMessage(action, "struts.messages.error.uploading", new String[]{inputName});
             if (validation != null) {
                 validation.addFieldError(inputName, errMsg);
             }

             if (LOG.isWarnEnabled()) {
                 LOG.warn(errMsg);
             }
         } else if (maximumSize != null && maximumSize < file.length()) {
             String errMsg = getTextMessage(action, "struts.messages.error.file.too.large", new String[]{inputName, filename, file.getName(), "" + file.length(), getMaximumSizeStr(action)});
             if (validation != null) {
                 validation.addFieldError(inputName, errMsg);
             }

             if (LOG.isWarnEnabled()) {
                 LOG.warn(errMsg);
             }
         } else if ((!allowedTypesSet.isEmpty()) && (!containsItem(allowedTypesSet, contentType))) {
             String errMsg = getTextMessage(action, "struts.messages.error.content.type.not.allowed", new String[]{inputName, filename, file.getName(), contentType});
             if (validation != null) {
                 validation.addFieldError(inputName, errMsg);
             }

             if (LOG.isWarnEnabled()) {
                 LOG.warn(errMsg);
             }
         } else if ((!allowedExtensionsSet.isEmpty()) && (!hasAllowedExtension(allowedExtensionsSet, filename))) {
             String errMsg = getTextMessage(action, "struts.messages.error.file.extension.not.allowed", new String[]{inputName, filename, file.getName(), contentType});
             if (validation != null) {
                 validation.addFieldError(inputName, errMsg);
             }

             if (LOG.isWarnEnabled()) {
                 LOG.warn(errMsg);
             }
         } else {
             fileIsAcceptable = true;
         }

         return fileIsAcceptable;
     }

     private String getMaximumSizeStr(Object action) {
         return NumberFormat.getNumberInstance(getLocaleProvider(action).getLocale()).format(maximumSize);
     }

     /**
      * @param extensionCollection - Collection of extensions (all lowercase).
      * @param filename            - filename to check.
      * @return true if the filename has an allowed extension, false otherwise.
      */
     private boolean hasAllowedExtension(Collection<String> extensionCollection, String filename) {
         if (filename == null) {
             return false;
         }

         String lowercaseFilename = filename.toLowerCase();
         for (String extension : extensionCollection) {
             if (lowercaseFilename.endsWith(extension)) {
                 return true;
             }
         }

         return false;
     }

     /**
      * @param itemCollection - Collection of string items (all lowercase).
      * @param item           - Item to search for.
      * @return true if itemCollection contains the item, false otherwise.
      */
     private boolean containsItem(Collection<String> itemCollection, String item) {
         for (String pattern : itemCollection)
             if (matchesWildcard(pattern, item))
                 return true;
         return false;
     }

     private boolean matchesWildcard(String pattern, String text) {
         Object o = matcher.compilePattern(pattern);
         return matcher.match(new HashMap<String, String>(), text, o);
     }

     private boolean isNonEmpty(Object[] objArray) {
         boolean result = false;
         for (int index = 0; index < objArray.length && !result; index++) {
             if (objArray[index] != null) {
                 result = true;
             }
         }
         return result;
     }

     protected String getTextMessage(String messageKey, String[] args) {
         return getTextMessage(this, messageKey, args);
     }

     protected String getTextMessage(Object action, String messageKey, String[] args) {
         if (action instanceof TextProvider) {
             return ((TextProvider) action).getText(messageKey, args);
         }
         return getTextProvider(action).getText(messageKey, args);
     }

     private TextProvider getTextProvider(Object action) {
         TextProviderFactory tpf = new TextProviderFactory();
         if (container != null) {
             container.inject(tpf);
         }
         LocaleProvider localeProvider = getLocaleProvider(action);
         return tpf.createInstance(action.getClass(), localeProvider);
     }

     private LocaleProvider getLocaleProvider(Object action) {
         LocaleProvider localeProvider;
         if (action instanceof LocaleProvider) {
             localeProvider = (LocaleProvider) action;
         } else {
             localeProvider = container.getInstance(LocaleProvider.class);
         }
         return localeProvider;
     }

 }

时，发现doc文件中备注信息：

　　org.apache.struts2.interceptor.FileUploadInterceptor
    Interceptor that is based off of MultiPartRequestWrapper, which is automatically applied for any request that includes a file. 
It adds the following parameters, where [File Name] is the name given to the file uploaded by the HTML form:
    •[File Name] : File - the actual File
    •[File Name]ContentType : String - the content type of the file
    •[File Name]FileName : String - the actual name of the file uploaded (not the HTML name)
    

4、使用io进行文件上传，需要在struts.xml定义action，并在对应的action中实现io上传

        <action name="testUpload" class="com.dx.struts2.actions.UploadAction">
            <result>/success.jsp</result>
            <result name="input">/index.jsp</result>
        </action>

UploadAction.java(需要在WebContent下创建文件夹files)

package com.dx.struts2.actions;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import javax.servlet.ServletContext;

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionSupport;

public class UploadAction extends ActionSupport {
    private static final long serialVersionUID = 1L;

    private File myFile;
    private String myFileContentType;
    private String myFileFileName;

    public File getMyFile() {
        return myFile;
    }

    public void setMyFile(File myFile) {
        this.myFile = myFile;
    }

    public String getMyFileContentType() {
        return myFileContentType;
    }

    public void setMyFileContentType(String myFileContentType) {
        this.myFileContentType = myFileContentType;
    }

    public String getMyFileFileName() {
        return myFileFileName;
    }

    public void setMyFileFileName(String myFileFileName) {
        this.myFileFileName = myFileFileName;
    }

    @Override
    public String execute() throws Exception {
        System.out.println(myFile);
        System.out.println(myFileContentType);
        System.out.println(myFileFileName);
        System.out.println("execute...");

        ServletContext servletContext = ServletActionContext.getServletContext();
        String savePath = servletContext.getRealPath("/files/" + myFileFileName);
        System.out.println(savePath);

        FileOutputStream out = new FileOutputStream(savePath);
        FileInputStream in = new FileInputStream(myFile);

        byte[] bytes = new byte[1024];
        int length = 0;

        while ((length = in.read(bytes)) != -1) {
            out.write(bytes, 0, length);
        }

        out.close();
        in.close();

        return super.execute();
    }
}

• Struts2的进行多文件上传需要操作步骤：

1、form表单修改：（需要注意的是页面其他属性File Description name需要有下标，否则无法回填）

    <s:debug></s:debug>
    <s:form action="testUpload" method="post" enctype="multipart/form-data"
        theme="simple">
    File:<s:file name="myFile"></s:file>
    File Description:<s:textfield name="desc[0]"></s:textfield>
    <br><br>
    File:<s:file name="myFile"></s:file>
    File Description:<s:textfield name="desc[1]"></s:textfield>
        <s:submit value="Submit"></s:submit>
    </s:form>

2、上传文件属性文件修改为List

package com.dx.struts2.actions;

import java.io.File;
import java.util.List;

import com.opensymphony.xwork2.ActionSupport;

public class UploadAction extends ActionSupport {
    private static final long serialVersionUID = 1L;

    private List<File> myFile;
    private List<String> myFileContentType;
    private List<String> myFileFileName;

    private List<String> desc;

    public List<File> getMyFile() {
        return myFile;
    }
    public void setMyFile(List<File> myFile) {
        this.myFile = myFile;
    }
    public List<String> getMyFileContentType() {
        return myFileContentType;
    }
    public void setMyFileContentType(List<String> myFileContentType) {
        this.myFileContentType = myFileContentType;
    }
    public List<String> getMyFileFileName() {
        return myFileFileName;
    }
    public void setMyFileFileName(List<String> myFileFileName) {
        this.myFileFileName = myFileFileName;
    }
    public List<String> getDesc() {
        return desc;
    }
    public void setDesc(List<String> desc) {
        this.desc = desc;
    }

    @Override
    public String execute() throws Exception {
        System.out.println(myFile);
        System.out.println(myFileContentType);
        System.out.println(myFileFileName);
        System.out.println(desc);

        System.out.println("execute...");

        return super.execute();
    }
}

3、提交页面后，后台打印信息：

[D:\Work\Java\apache-tomcat-7.0.-windows-x64\apache-tomcat-7.0.\work\Catalina\localhost\Struts_07FileUpload\upload_c2e431f2_8b1a_4aa7_a1d6_ae448d1dddb1_00000004.tmp, 
D:\Work\Java\apache-tomcat-7.0.-windows-x64\apache-tomcat-7.0.\work\Catalina\localhost\Struts_07FileUpload\upload_c2e431f2_8b1a_4aa7_a1d6_ae448d1dddb1_00000006.tmp]
[image/jpeg, image/jpeg]
[.jpg, .jpg]
[a, b]
execute...

• 如何对上传文件的错误信息进行国际化

当我们查看fileUpload拦截器源代码时，会发现其doc文件中写着以下信息：

　　This interceptor will add several field errors, assuming that the action implements ValidationAware. 
　　These error messages are based on several i18n values stored in struts-messages.properties, a default i18n file processed for all i18n requests. 
　　You can override the text of these messages by providing text for the following keys: 

    •struts.messages.error.uploading - a general error that occurs when the file could not be uploaded
    •struts.messages.error.file.too.large - occurs when the uploaded file is too large
    •struts.messages.error.content.type.not.allowed - occurs when the uploaded file does not match the expected content types specified
    •struts.messages.error.file.extension.not.allowed - occurs when the uploaded file does not match the expected file extensions specified

因此，可以在src下创建i18n.properties文件，并在文件内容定义：

struts.messages.error.uploading=""
struts.messages.error.file.too.large=""
struts.messages.error.content.type.not.allowed=""
struts.messages.error.file.extension.not.allowed=""    

在struts.xml中定义国际化设置

<constant name="struts.custom.i18n.resources" value="i18n"></constant>

还可以参考struts-core.jar下的org.apache.struts2包下的struts-messages.properties文件中的message信息：

struts.messages.error.uploading=Error uploading: {0}
struts.messages.error.file.too.large=File {0} is too large to be uploaded. Maximum allowed size is {4} bytes!
struts.messages.error.content.type.not.allowed=Content-Type not allowed: {0} "{1}" "{2}" {3}
struts.messages.error.file.extension.not.allowed=File extension not allowed: {0} "{1}" "{2}" {3}

• 如何对上传文件限定,大小、文件内容类型、扩展名以及总文件大小显示修改

当我们查看fileUpload拦截器源代码时，会发现其doc文件中写着以下信息：

　　Interceptor parameters:
    •maximumSize (optional) - the maximum size (in bytes) that the interceptor will allow a file reference to be set on the action. Note, this is not related to the various properties found in struts.properties. Default to approximately 2MB.
    •allowedTypes (optional) - a comma separated list of content types (ie: text/html) that the interceptor will allow a file reference to be set on the action. If none is specified allow all types to be uploaded.
    •allowedExtensions (optional) - a comma separated list of file extensions (ie: .html) that the interceptor will allow a file reference to be set on the action. If none is specified allow all extensions to be uploaded.

    Extending the interceptor:
    You can extend this interceptor and override the acceptFile method to provide more control over which files are supported and which are not. 

    Example code:
     <action name="doUpload" class="com.example.UploadAction">
         <interceptor-ref name="fileUpload"/>
         <interceptor-ref name="basicStack"/>
         <result name="success">good_result.jsp</result>
     </action>        

我们可以通过重写fileUpload拦截器的maximumSize 、allowedTypes 、allowedExtensions 三个字段来设置参数，具体操作修改struts.xml

　　　　 <interceptors>
            <interceptor-stack name="myInterceptorStack">
                <interceptor-ref name="defaultStack">
                    <param name="fileUpload.maximumSize">2000</param>
                    <param name="fileUpload.allowedTypes">text/html,text/xml</param>
                    <param name="fileUpload.allowedExtensions">html,dtd,xml</param>
                </interceptor-ref>
            </interceptor-stack>
        </interceptors>

        <default-interceptor-ref name="myInterceptorStack"></default-interceptor-ref>
        

重写总文件大小限定，总文件大小设置在struts-core.jar下的org.apache.struts2包下的default.properties文件中：

struts.multipart.maxSize=2097152

可以通过在struts.xml中定义常量来覆盖：

<constant name="struts.multipart.maxSize" value="20971520"></constant>