找出解决方案。除了application.properties配置之外，我还必须创建一个配置类，当提供适当的凭证时，该类将使我能够访问AmazonS3Client对象。我在GitHub上遵循了以下示例：

https://github.com/brant-hwang/spring-cloud-aws-
example/blob/master/src/main/java/com/axisj/spring/cloud/aws/AWSConfiguration.java

AWSConfiguration.java：

import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.regions.Region;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.s3.AmazonS3Client;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AWSConfiguration {

    @Value("${cloud.aws.credentials.accessKey}")
    private String accessKey;

    @Value("${cloud.aws.credentials.secretKey}")
    private String secretKey;

    @Value("${cloud.aws.region}")
    private String region;

    @Bean
    public BasicAWSCredentials basicAWSCredentials() {
        return new BasicAWSCredentials(accessKey, secretKey);
    }

    @Bean
    public AmazonS3Client amazonS3Client(AWSCredentials awsCredentials) {
        AmazonS3Client amazonS3Client = new AmazonS3Client(awsCredentials);
        amazonS3Client.setRegion(Region.getRegion(Regions.fromName(region)));
        return amazonS3Client;
    }
}

配置完成后，您可以在其他类中创建AmazonS3Client对象（自动装配），并使用客户端向您的S3云发出请求。该示例将包装器类用作服务，以简化其他控制器类的实现。

S3Wrapper.java：

import com.amazonaws.services.s3.AmazonS3Client;
import com.amazonaws.services.s3.model.*;
import org.apache.commons.io.IOUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;
import org.springframework.web.multipart.MultipartFile;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

@Service
public class S3Wrapper {

    @Autowired
    private AmazonS3Client amazonS3Client;

    @Value("${cloud.aws.s3.bucket}")
    private String bucket;

    private PutObjectResult upload(String filePath, String uploadKey) throws FileNotFoundException {
        return upload(new FileInputStream(filePath), uploadKey);
    }

    private PutObjectResult upload(InputStream inputStream, String uploadKey) {
        PutObjectRequest putObjectRequest = new PutObjectRequest(bucket, uploadKey, inputStream, new ObjectMetadata());

        putObjectRequest.setCannedAcl(CannedAccessControlList.PublicRead);

        PutObjectResult putObjectResult = amazonS3Client.putObject(putObjectRequest);

        IOUtils.closeQuietly(inputStream);

        return putObjectResult;
    }

    public List<PutObjectResult> upload(MultipartFile[] multipartFiles) {
        List<PutObjectResult> putObjectResults = new ArrayList<>();

        Arrays.stream(multipartFiles)
                .filter(multipartFile -> !StringUtils.isEmpty(multipartFile.getOriginalFilename()))
                .forEach(multipartFile -> {
                    try {
                        putObjectResults.add(upload(multipartFile.getInputStream(), multipartFile.getOriginalFilename()));
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                });

        return putObjectResults;
    }

    public ResponseEntity<byte[]> download(String key) throws IOException {
        GetObjectRequest getObjectRequest = new GetObjectRequest(bucket, key);

        S3Object s3Object = amazonS3Client.getObject(getObjectRequest);

        S3ObjectInputStream objectInputStream = s3Object.getObjectContent();

        byte[] bytes = IOUtils.toByteArray(objectInputStream);

        String fileName = URLEncoder.encode(key, "UTF-8").replaceAll("\\+", "%20");

        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        httpHeaders.setContentLength(bytes.length);
        httpHeaders.setContentDispositionFormData("attachment", fileName);

        return new ResponseEntity<>(bytes, httpHeaders, HttpStatus.OK);
    }

    public List<S3ObjectSummary> list() {
        ObjectListing objectListing = amazonS3Client.listObjects(new ListObjectsRequest().withBucketName(bucket));

        List<S3ObjectSummary> s3ObjectSummaries = objectListing.getObjectSummaries();

        return s3ObjectSummaries;
    }
}

注意：为了使用Apache Commons IO库，需要将以下依赖项添加到pom.xml中。

pom.xml：

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-io</artifactId>
    <version>1.3.2</version>
</dependency>