Uploading multiple files does not work in spring boot controller

Question

I can upload one file to a spring boot controller like this:

@RequestMapping(value = "/projects",
    produces = { "application/json" },
    consumes = { "multipart/form-data" },
    method = RequestMethod.POST)
public ResponseEntity<Void> upload(@RequestParam(value="file", required=false) MultipartFile files)) {
    //
}

But I can not upload multiple files to the similar spring boot controllers:

@RequestMapping(value = "/projects",
    produces = { "application/json" },
    consumes = { "multipart/form-data" },
    method = RequestMethod.POST)
public ResponseEntity<Void> upload(@RequestParam(value="files", required=false) MultipartFile[] files)) {
    //
}

@RequestMapping(value = "/projects",
    produces = { "application/json" },
    consumes = { "multipart/form-data" },
    method = RequestMethod.POST)
public ResponseEntity<Void> upload(@RequestParam(value="files", required=false) List<MultipartFile> files)) {
    //
}

*The two controllers above have empty list or array when I try to upload files

Do I need some extra configuration in my spring boot to upload multiple files?

Answer 1

Here're my configs for the test project:

1. 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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.2.5.RELEASE</version>
            <relativePath/> <!-- lookup parent from repository -->
        </parent>
        <groupId>com.example</groupId>
        <artifactId>multipart-demo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <name>multipart-demo</name>
        <description>Demo project for Spring Boot</description>
   
        <properties>
            <java.version>11</java.version>
        </properties>
   
        <dependencies>
            <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>
                <exclusions>
                    <exclusion>
                        <groupId>org.junit.vintage</groupId>
                        <artifactId>junit-vintage-engine</artifactId>
                    </exclusion>
                </exclusions>
            </dependency>
        </dependencies>
   
        <build>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                </plugin>
            </plugins>
        </build>
   
        <repositories>
            <repository>
                <id>spring-milestones</id>
                <name>Spring Milestones</name>
                <url>https://repo.spring.io/milestone</url>
            </repository>
            <repository>
                <id>spring-snapshots</id>
                <name>Spring Snapshots</name>
                <url>https://repo.spring.io/snapshot</url>
                <snapshots>
                    <enabled>true</enabled>
                </snapshots>
            </repository>
        </repositories>
        <pluginRepositories>
            <pluginRepository>
                <id>spring-milestones</id>
                <name>Spring Milestones</name>
                <url>https://repo.spring.io/milestone</url>
            </pluginRepository>
            <pluginRepository>
                <id>spring-snapshots</id>
                <name>Spring Snapshots</name>
                <url>https://repo.spring.io/snapshot</url>
                <snapshots>
                    <enabled>true</enabled>
                </snapshots>
            </pluginRepository>
        </pluginRepositories>
   
    </project>
   

2. MultipartDemoApplication.java

    package com.example.multipartdemo;
   
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
   
    @SpringBootApplication
    public class MultipartDemoApplication {
   
        public static void main(String[] args) {
            SpringApplication.run(MultipartDemoApplication.class, args);
        }
    }
   

3. FileUploadController.java

    package com.example.multipartdemo;
   
    import org.springframework.http.HttpStatus;
    import org.springframework.http.ResponseEntity;
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestMethod;
    import org.springframework.web.bind.annotation.RequestParam;
    import org.springframework.web.multipart.MultipartFile;
   
    import java.util.Arrays;
    import java.util.stream.Collectors;
   
    @Controller
    public class FileUploadController {
        @RequestMapping(value = "/projects",
                produces = {"application/json"},
                consumes = {"multipart/form-data"},
                method = RequestMethod.POST)
        public ResponseEntity<String> uploadFiles(@RequestParam(value = "files", required = false) MultipartFile[] files) {
            try {
                String fileNames = Arrays.stream(files)
                        .map(MultipartFile::getOriginalFilename)
                        .collect(Collectors.joining(" : "));
                return ResponseEntity.status(HttpStatus.OK).body(fileNames);
            } catch (Exception e) {
                return ResponseEntity.status(HttpStatus.EXPECTATION_FAILED).body("Unable to download files");
            }
        }
   
        @RequestMapping(value = "/projects",
                produces = {"text/plain"},
                method = RequestMethod.GET)
        public ResponseEntity<String> uploadFiles() {
            return ResponseEntity.status(HttpStatus.EXPECTATION_FAILED).body("OK");
        }
    }
   

4. application.properties

    spring.servlet.multipart.max-file-size=100KB
    spring.servlet.multipart.max-request-size=500KB
   

After starting application it works as expected:

Only in case of body absence I got the next response, but it's another story of debugging.

So, can you please check your configs? What're the differences with mine?