File Upload in Java Servlet Example

File upload is standard functionality that is used in most web applications. Initially, people depend on third-party library Apache’s common-fileupload and common-io to implement file upload operations. In this article, we will use the built-in library from Servlet3.0 API to develop the file uploading example in java. Here we will be able to upload a single file as well as multiple file uploads at a time.

Table of Contents

Servlet3.0 API For File Upload

Let’s have a look at the annotation, class, and method which is used in this article to implement file upload.

@MultipartConfig Annotation

The MultipartConfig annotation is responsible for handling the multipart/form-data requests as in file upload definitely requests should be in multipart/form-data. This annotation is used on top of the Servlet. The followings are the possible options to configure:

fileSizeThreshold: size(in bytes) of the file that is greater than this threshold will be directly written to disk, instead of saved in memory.
location: directory location where the file will be stored by method Part.write().
maxFileSize: maximum allowed size(in bytes) for a single file.
maxRequestSize: maximum allowed size(in bytes) for a request.

The Part Interface

The class of this interface represents a part as uploaded to the server as part of a multipart/form-data request body. The part may represent either an uploaded file or form data. The Part retrieve multipart/form-data request by a Servlet annotated with MultipartConfig by calling getPart(java.lang.String) or getParts() of HttpServletRequest.

Sample Java File Upload Example

We are going to create an eclipse maven application. In this application the following files are required to develop:

FileUploadServlet.java
fileupload.html
success.html
error.html
pom.xml

Eclipse Project Structure

FileUploadServlet.java

package com.javacodepoint.fileupload;

import java.io.File;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
/**
 * 
 * @author javacodepoint
 *
 */
@WebServlet("/UploadServlet")
@MultipartConfig(fileSizeThreshold = 1024 * 1024 * 2, // 2MB
		maxFileSize = 1024 * 1024 * 5, // 5MB
		maxRequestSize = 1024 * 1024 * 100) // 100MB
public class FileUploadServlet extends HttpServlet {
	
	/**
     * Location to save uploaded files on server
     */
	private static final String UPLOAD_PATH = "D:/uploads";
	
	/**
     * Method to get file name from HTTP header content-disposition
     */
	private String getFileName(Part part) {
		String contentDisp = part.getHeader("content-disposition");
		String[] items = contentDisp.split(";");
		for (String s : items) {
			if (s.trim().startsWith("filename")) {
				return s.substring(s.indexOf("=") + 2, s.length() - 1);
			}
		}
		return null;
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String resultPage="/success.html";
		try {
			File uploadsPath = new File(UPLOAD_PATH);
			if (!uploadsPath.exists()) {
				//create upload folder if not exist.
				uploadsPath.mkdir();
			}
			for (Part part : request.getParts()) {
				String fileName = getFileName(part);
				if(fileName!=null) {
					part.write(UPLOAD_PATH + File.separator + fileName);
				}
			}
			System.out.println("File uploaded successfully!");
		} catch (Exception e) {
			System.err.println("Error while uploading files!");
			e.printStackTrace();
			resultPage="/error.html";
		}
		getServletContext().getRequestDispatcher(resultPage).forward(request, response);
	}
}

fileupload.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>File Upload</title>
</head>
<body>
<center>
    <h1>File Upload</h1>
    <form method="post" action="UploadServlet"
        enctype="multipart/form-data">
        Select file to upload: <input type="file" name="file" size="60" multiple="true" /><br />
        <br /> <input type="submit" value="Upload" />
    </form>
</center>
</body>
</html>

success.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Success | File Upload</title>
</head>
<body>
<center>
    <h1 style="color:green">File Upload Successfully!</h1>
    <a href="./fileupload.html">Upload again</a>
</center>
</body>
</html>

error.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
    "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Error | File Upload</title>
</head>
<body>
<center>
    <h1 style="color:red">Something went wrong!</h1>
    <p>Please check your configurations</p>
    <a href="./fileupload.html">Try again</a>
</center>
</body>
</html>

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.javacodepoint</groupId>
	<artifactId>JavaFileUpload</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>
	<dependencies>
		<dependency>
			<groupId>javax.servlet</groupId>
			<artifactId>javax.servlet-api</artifactId>
			<version>3.0.1</version>
			<scope>provided</scope>
		</dependency>
	</dependencies>
	<build>
		<sourceDirectory>src</sourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.1</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
				</configuration>
			</plugin>
			<plugin>
				<artifactId>maven-war-plugin</artifactId>
				<version>3.2.3</version>
				<configuration>
					<warSourceDirectory>WebContent</warSourceDirectory>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

Conclusion

With the built-in API of Servlet3.0, without depending on any third-party library we will be able to do a single as well as Multiple file upload in java. Now it is very easy to use @MultipartConfig, Part Interface methods, and some newly added methods of HttpServletRequest to implement file upload operations in java.

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