用工作流实现文件上传下载的Java代码示例

以下是一个简单的文件上传和下载的 Java 代码示例，使用了工作流（Workflow）实现：

文件上传：

import java.io.FileInputStream;
import java.io.InputStream;
import java.util.Properties;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FileUtils;

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.ObjectMetadata;
import com.amazonaws.services.s3.model.PutObjectRequest;
import com.amazonaws.services.s3.transfer.TransferManager;
import com.amazonaws.services.s3.transfer.TransferManagerBuilder;
import com.amazonaws.services.s3.transfer.Upload;

public class FileUpload {
    public static void main(String[] args) throws Exception {
        // 1. 读取配置文件
        Properties props = new Properties();
        InputStream in = new FileInputStream("config.properties");
        props.load(in);

        // 2. 创建 Amazon S3 客户端
        String accessKey = props.getProperty("accessKey");
        String secretKey = props.getProperty("secretKey");
        String region = props.getProperty("region");
        BasicAWSCredentials awsCreds = new BasicAWSCredentials(accessKey, secretKey);
        AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
            .withCredentials(new AWSStaticCredentialsProvider(awsCreds))
            .withRegion(region)
            .build();

        // 3. 创建 TransferManager
        TransferManager transferManager = TransferManagerBuilder.standard()
            .withS3Client(s3Client)
            .build();

        // 4. 从 HTTP 请求中获取文件
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        FileItem item = upload.parseRequest(request).get(0);
        String fileName = item.getName();

        // 5. 上传文件到 Amazon S3
        PutObjectRequest putRequest = new PutObjectRequest(
            props.getProperty("bucketName"), fileName, item.getInputStream(), new ObjectMetadata());
        Upload upload = transferManager.upload(putRequest);
        upload.waitForCompletion();

        // 6. 删除临时文件
        FileUtils.deleteQuietly(new File(item.getName()));
    }
}

文件下载：

import java.io.File;
import java.io.FileOutputStream;
import java.util.Properties;

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.S3Object;
import com.amazonaws.services.s3.transfer.TransferManager;
import com.amazonaws.services.s3.transfer.TransferManagerBuilder;
import com.amazonaws.services.s3.transfer.Download;

public class FileDownload {
    public static void main(String[] args) throws Exception {
        // 1. 读取配置文件
        Properties props = new Properties();
        InputStream in = new FileInputStream("config.properties");
        props.load(in);

        // 2. 创建 Amazon S3 客户端
        String accessKey = props.getProperty("accessKey");
        String secretKey = props.getProperty("secretKey");
        String region = props.getProperty("region");
        BasicAWSCredentials awsCreds = new BasicAWSCredentials(accessKey, secretKey);
        AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
            .withCredentials(new AWSStaticCredentialsProvider(awsCreds))
            .withRegion(region)
            .build();

        // 3. 创建 TransferManager
        TransferManager transferManager = TransferManagerBuilder.standard()
            .withS3Client(s3Client)
            .build();

        // 4. 从 Amazon S3 下载文件
        S3Object object = s3Client.getObject(props.getProperty("bucketName"), props.getProperty("fileName"));
        Download download = transferManager.download(
            props.getProperty("bucketName"), props.getProperty("fileName"), new File(props.getProperty("localPath")));
        download.waitForCompletion();

        // 5. 关闭 Amazon S3 客户端和 TransferManager
        object.close();
        transferManager.shutdownNow();
    }
}

以上代码示例使用了 Amazon S3 作为文件存储和下载服务，需要提供以下配置信息：

- `accessKey`: AWS 访问密钥 ID
- `secretKey`: AWS 秘密访问密钥
- `region`: AWS 区域
- `bucketName`: 存储桶名称
- `fileName`: 文件名称
- `localPath`: 下载到本地的路径