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Action File Upload Interceptor

Available since Struts 6.4.0 as replacement for File Upload Interceptor

See this page for more examples and advanced configuration.

Interceptor that is based off of MultiPartRequestWrapper, which is automatically applied for any request that includes a file. If an action implements org.apache.struts2.action.UploadedFilesAware interface, the interceptor will pass information and content of uploaded files using the callback method withUploadedFiles(List<UploadedFile>).

See the example code section.

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:

Parameters

Dynamic Parameter Evaluation

Since Struts 7.2.0

The allowedTypes, allowedExtensions, and maximumSize parameters support ${...} expression evaluation, enabling per-request dynamic validation. This is available when used with WithLazyParams.

<interceptor-ref name="actionFileUpload">
  <param name="allowedTypes">${allowedContentTypes}</param>
  <param name="maximumSize">${maxFileSize}</param>
</interceptor-ref>

The expressions are evaluated against the ValueStack at the time of the upload, allowing your action to provide dynamic values based on the current request context.

Since Struts 7.3.0 the resolved values are held in a per-invocation org.apache.struts2.interceptor.UploadPolicy instead of being written onto the shared interceptor instance, so two concurrent requests can no longer be validated against each other’s policy — see WW-5659.

Also since Struts 7.3.0, an expression that cannot be resolved makes the policy unusable and the upload is rejected with the struts.messages.error.upload.policy.unresolved message, rather than silently validated against a partially-resolved policy. A typo in a ${...} parameter, or a parameter name with no matching property, now fails closed instead of relaxing validation. The disabled parameter is exempt: unresolved it is simply false, which leaves the interceptor running with the rest of the policy intact.

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.

Since Struts 7.3.0 acceptFile takes the per-invocation policy as its first argument:

protected boolean acceptFile(UploadPolicy policy, Object action, UploadedFile file,
                             String originalFilename, String contentType, String inputName)

Read policy.getMaximumSize(), policy.getAllowedTypes() and policy.getAllowedExtensions() instead of the former interceptor fields, which are configuration-time state only. Subclasses overriding the old five-argument signature must be updated — the old method is gone, so the compiler will point them out.

The same release changed the org.apache.struts2.interceptor.WithLazyParams interface, which is now generic over an org.apache.struts2.interceptor.InterceptorParams holder:

public interface WithLazyParams<P extends InterceptorParams> {
    P newLazyParams();
    String intercept(ActionInvocation invocation, P lazyParams) throws Exception;
}

Third-party interceptors implementing WithLazyParams must supply a holder class (extend org.apache.struts2.interceptor.DisableParams if the interceptor supports the disabled parameter) and move the resolved values off the singleton into it.

Examples

See this page for more examples and advanced configuration.

Example action mapping:

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

Notice the interceptor configuration in the preceding example.

Example JSP form tags:

   <s:form action="doUpload" method="post" enctype="multipart/form-data">
       <s:file name="upload" label="File"/>
       <s:submit/>
   </s:form>

You must set the encoding to multipart/form-data in the form where the user selects the file to upload.

Example Action class:

public class UploadAction extends ActionSupport implements UploadedFilesAware {
   private UploadedFile uploadedFile;
   private String contentType;
   private String fileName;
   private String originalName;

   @Override
   public void withUploadedFiles(List<UploadedFile> uploadedFiles) {
      if (!uploadedFiles.isEmpty()) {
         this.uploadedFile = uploadedFiles.get(0);
         this.fileName = uploadedFile.getName();
         this.contentType = uploadedFile.getContentType();
         this.originalName = uploadedFile.getOriginalName();
      }
   }

   public String execute() {
      //do something with the file
      return SUCCESS;
   }
}

Setting parameters example:

<interceptor-ref name="actionFileUpload">
  <param name="allowedTypes">
     image/png,image/gif,image/jpeg
  </param>
</interceptor-ref>

This part is optional and would be done in place of the <interceptor-ref name="actionFileUpload"/> line in the action mapping example above.

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