For S3 Java 1, refer to this example:

https://github.com/awsdocs/aws-doc-sdk-examples/blob/master/java/example_code/s3/src/main/java/GetObject.java

If you are using V2, see this client method. You can get a byte[] and then use that to meet your requirements:

https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/S3Client.html#getObjectAsBytes-software.amazon.awssdk.services.s3.model.GetObjectRequest-

Use the AWS SDK for Java and Apache Commons IO as such:

//import org.apache.commons.io.IOUtils

AmazonS3 s3  = new AmazonS3Client(credentials);  // anonymous credentials are possible if this isn't your bucket
S3Object object = s3.getObject("bucket", "key"); 
byte[] byteArray = IOUtils.toByteArray(object.getObjectContent());

Not sure what you mean by "get it removed", but IOUtils will close the object's input stream when it's done converting it to a byte array. If you mean you want to delete the object from s3, that's as easy as:

s3.deleteObject("bucket", "key"); 

Since Java 7 (published back in July 2011), there’s a better way: Files.copy() utility from java.util.nio.file.

Copies all bytes from an input stream to a file.

So you need neither an external library nor rolling your own byte array loops. Two examples below, both of which use the input stream from S3Object.getObjectContent().

InputStream in = s3Client.getObject("bucketName", "key").getObjectContent();

1) Write to a new file at specified path:

Files.copy(in, Paths.get("/my/path/file.jpg"));

2) Write to a temp file in system's default tmp location:

File tmp = File.createTempFile("s3test", "");
Files.copy(in, tmp.toPath(), StandardCopyOption.REPLACE_EXISTING);

(Without specifying the option to replace existing file, you'll get a FileAlreadyExistsException.)

Also note that getObjectContent() Javadocs urge you to close the input stream:

If you retrieve an S3Object, you should close this input stream as soon as possible, because the object contents aren't buffered in memory and stream directly from Amazon S3. Further, failure to close this stream can cause the request pool to become blocked.

So it should be safest to wrap everything in try-catch-finally, and do in.close(); in the finally block.

The above assumes that you use the official SDK from Amazon (aws-java-sdk-s3).

Below code would get you the InputStream.

ResponseInputStream responseInputStream = s3AsyncClient.getObject(GetObjectRequest.builder()
        .bucket(bucket)
        .key(key)
        .build(),
        AsyncResponseTransformer.toBlockingInputStream())

Because the original question was never answered, and I had to run into this same problem, the solution for the MD5 problem is that S3 doesn't want the Hex encoded MD5 string we normally think about.

Instead, I had to do this.

// content is a passed in InputStream
byte[] resultByte = DigestUtils.md5(content);
String streamMD5 = new String(Base64.encodeBase64(resultByte));
metaData.setContentMD5(streamMD5);

Essentially what they want for the MD5 value is the Base64 encoded raw MD5 byte-array, not the Hex string. When I switched to this it started working great for me.