Blob streaming (example)

This application demonstrates how to stream possibly huge blobs from the database via a rest service. The streaming is done complety without copying the data to the applications memory. So this approach should be suitable for very large blobs without using to much memory.

The example is implemented with devon4j using a Oracle RDBMS.

Setup Oracle

To start the provided sample application you need an Oracle RDBMS. The easiest way to setup such a database is to use the Oracle container provided by Oracle.

The container is available only after (free) registration in docker hub.

To start the database run the following commands

docker login -u <username>
docker pull store/oracle/database-enterprise:12.2.0.1
docker run -d -it --name orablobdb -p 1521:1521 store/oracle/database-enterprise:12.2.0.1

Afterwards you need to create a user for the database:

docker exec -it orablobdb /bin/bash
[oracle@bd1c54148ee4 /]$ sqlplus sys as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Mon Feb 10 09:38:43 2020

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Enter password: <just hit enter>

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> CREATE USER c##blobapp IDENTIFIED BY blobapp;
GRANT CREATE SESSION TO c##blobapp;
GRANT CREATE TABLE TO c##blobapp;
GRANT CREATE SEQUENCE TO c##blobapp;
GRANT UNLIMITED TABLESPACE TO c##blobapp;
User created.

...

SQL> exit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

Tip	The default password for SYS und SYSTEM is Oradoc_db1.

The example application

The example application is a Spring Boot app. The main class is SpringBootApp.java.

Download

BinaryRestService.java defines the rest service via JAX-RS. getBinaryObjectMultiPart defines the operation to actual stream the data from the DB:

link:api/src/main/java/com/devonfw/example/blobapp/binary/service/api/rest/BinaryRestService.java[role=include]

Important is the content type defintion @Produces("multipart/mixed")`

The implementation is as follows:

link:core/src/main/java/com/devonfw/example/blobapp/binary/service/impl/rest/BinaryRestServiceImpl.java[role=include]

The multipart result contains two parts. The root part contains a JSON-encoded BinaryObjectEto. The actual data is provided as an InputStream in the data part. The InputStream is provided by the BinaryObjectEntity.java. The data is mapped as java.sql.Blob.

Upload

In BinaryRestService.java saveBinaryObject defines the operation to upload a new blob to the DB:

link:api/src/main/java/com/devonfw/example/blobapp/binary/service/api/rest/BinaryRestService.java[role=include]

As you can see to allow streaming a multipart is used. It contains two parts. The root part contains a JSON-encoded BinaryObjectEto. The actual data is provided as an InputStream in the data part.

To save the stream to the database we implemented a custom Spring Data repository

link:core/src/main/java/com/devonfw/example/blobapp/binary/dataaccess/impl/CustomBinaryObjectRepositoryImpl.java[role=include]

Consuming the REST services

BinaryServiceTest.java implementes some simple tests using Apache CXF WebClient which demonstrate how to consume the rest services of the example.

If you like to experiment a bit you may use DbTest.java to e.g. load a huge blob into your DB.