Spring Boot File Upload with jQuery Ajax Example

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1- Objective of lesson

In this lesson, we are going to create a  Spring Boot file upload application with jQuery Ajax. Below is the preview image of the application to be performed:
Notify when an error occurs:
See more example of file Upload with the  Spring Boot not using  AJAX:
File Upload + AngularJS:

2- Create a Spring Boot project

On the  Eclipse, create the  Spring Boot project:
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<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
    http://maven.apache.org/xsd/maven-4.0.0.xsd">
    
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.o7planning</groupId>
    <artifactId>SpringBootFileUploadAjax</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>SpringBootFileUploadAjax</name>
    <description>Spring Boot + File Upload + JQuery Ajax</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>
SpringBootFileUploadAjaxApplication.java
package org.o7planning.sbfileupload;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringBootFileUploadAjaxApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootFileUploadAjaxApplication.class, args);
    }
    
}

3- Form, Controller, Exception Handler

The  UploadForm class represents the data of HTML form.
UploadForm.java
package org.o7planning.sbfileupload.form;

import org.springframework.web.multipart.MultipartFile;

public class UploadForm {

    private String description;

    private MultipartFile[] files;

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public MultipartFile[] getFiles() {
        return files;
    }

    public void setFiles(MultipartFile[] files) {
        this.files = files;
    }

}
MainController.java
package org.o7planning.sbfileupload.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class MainController {

    @GetMapping("/")
    public String index() {
        return "upload";
    }

}
The  MainRESTController class defines a  REST API to process the data of the files uploaded by users. This  REST API will be called by the  jQuery Ajax (See in  main.js).
MainRESTController.java
package org.o7planning.sbfileupload.restcontroller;

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import org.o7planning.sbfileupload.form.UploadForm;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

@RestController
public class MainRESTController {

    // Linux: /home/{user}/test
    // Windows: C:/Users/{user}/test
    private static String UPLOAD_DIR = System.getProperty("user.home") + "/test";

    @PostMapping("/rest/uploadMultiFiles")
    public ResponseEntity<?> multiUploadFileModel(@ModelAttribute UploadForm form) {

        System.out.println("Description:" + form.getDescription());

        String result = null;
        try {

            result = this.saveUploadedFiles(form.getFiles());

        }
        // Here Catch IOException only.
        // Other Exceptions catch by RestGlobalExceptionHandler class.
        catch (IOException e) {
            e.printStackTrace();
            return new ResponseEntity<>("Error: " + e.getMessage(), HttpStatus.BAD_REQUEST);
        }

        return new ResponseEntity<String>("Uploaded to: <br/>" + result, HttpStatus.OK);

    }

    // Save Files
    private String saveUploadedFiles(MultipartFile[] files) throws IOException {

        // Make sure directory exists!
        File uploadDir = new File(UPLOAD_DIR);
        uploadDir.mkdirs();

        StringBuilder sb = new StringBuilder();

        for (MultipartFile file : files) {

            if (file.isEmpty()) {
                continue;
            }
            String uploadFilePath = UPLOAD_DIR + "/" + file.getOriginalFilename();

            byte[] bytes = file.getBytes();
            Path path = Paths.get(uploadFilePath);
            Files.write(path, bytes);

            sb.append(uploadFilePath).append("<br/>");
        }
        return sb.toString();
    }
}
The default size of the file uploaded to Server shall not exceed 1MB. And if the user uploads many files at the same time, total size of the files shall not exceed 1MB. However, you can configure to change these parameters.
application.properties
spring.servlet.multipart.max-file-size=1MB
spring.servlet.multipart.max-request-size=5MB

spring.thymeleaf.cache=false
The RestGlobalExceptionHandler is a custom class, extended from the ResponseEntityExceptionHandler class. In this class, you can handle exceptions thrown from REST methods. This helps you handle centralized exceptions at a location instead of at each REST method.
RestGlobalExceptionHandler.java
package org.o7planning.sbfileupload.exceptionhandler;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

import javax.servlet.http.HttpServletRequest;

@ControllerAdvice
public class RestGlobalExceptionHandler extends ResponseEntityExceptionHandler {

    // Catch max file size Exception.
    @ExceptionHandler(MultipartException.class)
    @ResponseBody
    public ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {

        HttpStatus status = this.getStatus(request);
        return new ResponseEntity<String>("(Message in RestGlobalExceptionHandler *): " + ex.getMessage(), status);
    }

    // Cache Other Exception
    @ExceptionHandler(Exception.class)
    @ResponseBody
    public ResponseEntity<?> handleControllerRootException(HttpServletRequest request, Throwable ex) {

        HttpStatus status = this.getStatus(request);
        return new ResponseEntity<String>("(Message in RestGlobalExceptionHandler **): " + ex.getMessage(), status);
    }

    private HttpStatus getStatus(HttpServletRequest request) {
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
        if (statusCode == null) {
            return HttpStatus.INTERNAL_SERVER_ERROR;
        }
        return HttpStatus.valueOf(statusCode);
    }

}

4- Javascript, View

upload.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <title>Upload Files</title>
      <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
      <script type="text/javascript" th:src="@{/main.js}"></script>
   </head>
   <body>
      <h1>Spring Boot File Upload with jQuery Ajax</h1>
      <form method="POST" enctype="multipart/form-data" id="fileUploadForm">
         Description: <br/>
         <input type="text" name="description" style="width:350px;"/>
         <br/><br/>                 
         File to upload (1): <input type="file" name="files"/><br />      
         File to upload (2): <input type="file" name="files"/><br />    
         File to upload (3): <input type="file" name="files"/><br />    
         File to upload (4): <input type="file" name="files"/><br />    
         File to upload (5): <input type="file" name="files"/><br />    
         <input type="submit" value="Submit" id="submitButton"/>
      </form>
      <h2>Upload Results:</h2>
      <div style="border:1px solid #ccc;padding: 5px;">
         <span id="result"></span>
      </div>
      
   </body>
</html>
main.js
$(document).ready(function() {

    $("#submitButton").click(function(event) {

        // Stop default form Submit.
        event.preventDefault();

        // Call Ajax Submit.

        ajaxSubmitForm();

    });

});

function ajaxSubmitForm() {

    // Get form
    var form = $('#fileUploadForm')[0];

    var data = new FormData(form);


    $("#submitButton").prop("disabled", true);

    $.ajax({
        type: "POST",
        enctype: 'multipart/form-data',
        url: "/rest/uploadMultiFiles",
        data: data,

        // prevent jQuery from automatically transforming the data into a query string
        processData: false,
        contentType: false,
        cache: false,
        timeout: 1000000,
        success: function(data, textStatus, jqXHR) {

            $("#result").html(data);
            console.log("SUCCESS : ", data);
            $("#submitButton").prop("disabled", false);
            $('#fileUploadForm')[0].reset();
        },
        error: function(jqXHR, textStatus, errorThrown) {  

            $("#result").html(jqXHR.responseText);
            console.log("ERROR : ", jqXHR.responseText);
            $("#submitButton").prop("disabled", false);

        }
    });

}

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