File upload is a common functionality which is used in most of the web application. Initially, people depend on third-party library Apacheโs common-fileupload and common-io to implement file upload operation. 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
Letโs have a look to annotation, class and method which is used in this article to implement file upload.
@MultipartConfig Annotation
The MultipartConfig annotation is responsible for handle 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. 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 saving 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 a eclipse maven application. In this application the following files are required to create:
- 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 operation in java.
