📁 Struts 2 File Upload Guide

Struts 2 provides robust support for handling file uploads in web applications. Below is a concise overview of the key concepts and implementation steps:

🔧 Core Concepts

<s:file> Tag: Used to create an HTML file input element in forms.
Action Class: Requires implementation of Action interface and validate() method for file processing.
interceptor: The fileUpload interceptor is essential for parsing uploaded data.

✅ Implementation Steps

Configure struts.xml
Add the fileUpload interceptor to the stack:

<interceptors>
    <interceptor-stack name="fileUploadStack">
        <interceptor-ref name="fileUpload"/>
        <interceptor-ref name="defaultStack"/>
    </interceptor-stack>
</interceptors>

Create Upload Form
Use <s:file> in JSP:

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

Handle File in Action Class
Example code snippet:

public class UploadAction extends ActionSupport {
    private File myFile;
    private String myFileContentType;
    private String myFileFileName;

    // Getters and setters for these fields
    public String execute() {
        // File processing logic here
        return SUCCESS;
    }
}

Validate File Size/Type
Configure validation in struts.xml:

<action name="upload" class="UploadAction">
    <interceptor-ref name="fileUploadStack"/>
    <param name="maxFileSize">1024000</param> <!-- 1MB -->
    <param name="maxSwallowSize">102400</param>
    <result name="success">uploadSuccess.jsp</result>
</action>

⚠️ Common Issues

enctype="multipart/form-data": Must be set in the form tag.
File Path: Use <s:property value="myFileFileName"/> to retrieve the uploaded file name.
Security: Always sanitize file names to avoid path traversal vulnerabilities.

📚 Related Resources

For deeper exploration: