I'm on the process of designing a web application based on Google App Engine (Java) platform. I'm basically from relational database world and I'm trying to understand how to use the persistence that GAE provides.
So my questions is, in RDBMS, I can easily access my data without going through my application. i.e, I can use an SQL client to connect to my data and manipulate it. Is the same thing possible with GAE?
Both yes and no. You can open https://appengine.google.com/ and go to "Datastore Viewer". Here is a possibility to write a GQL query. But you will not be able to operate data sets with more than 500 records and with offset >1000. Good luck!
Install AppWrench Tools plugin for eclipse. I use it. It allows you to create/edit/delete/browse your local and production datastore entities from within eclipse.
Related
I am making an inventory management program which has a Swing GUI as front end, with multiple users on LAN sharing a database.
I have successfully made my GUI components and a local DB and run the program as per my requirements on a standalone pc(without networking).
Now, I need some insight as to how to scale my application to a network environment. I have already tried the following and it fails:
Having MSACCESS on one of the computers, I make a connection to the db with DriverManager.getConnection("jdbc:ucanaccess:////COMPUTER-PC/admin/DB.accdb");
All works well, however when 2 users are simultaneously connecting to the database, after certain update queries from both users, the data does not remain consistent. I am stuck here. How to manage the data and maintain consistency.
You're describing a 2-tier architecture (client-db).
In most cases you want to have the business logic, consistency check etc. on the backend and thus a 3-tier architecture (client-backend-db).
You can e.g. use Spring Boot to create a simple backend.
Spring Initializr can get you started e.g. with Spring Web (MVC), Spring Data JPA and H2 Database (if you don't need to use MS Access) module selected.
The downsides are:
you need a server to run the Spring Boot JAR. But you can also run it on the machine currently running MS Access.
you need to think about client-backend communication, e.g. using REST. But there are many samples on the Internet, e.g. using Spring RestTemplate or Spring WebClient.
Your question seems little basic to me .
This book by Martin Fowler is little old but It will give you a solid foundation .
Patterns of Enterprise Application Architecture Hardcover
by Martin Fowler
I am creating a java based application and i want to use google app engine for its deployment. But i want this application to be movable to other servers like tomcat etc on my local or other machines. So i though want to use google app engine. But want to keep my application independent of any Google specific things. Can somebody summarize the points i must take care of. I want to keep it independent both from application and database layer perspective.
Though I am not master in google app engine however the thumb rule to make your webapp portable is to use standard specification APIs instead of vendor specific APIs. For example if your app is using google app engine UserServive (com.google.appengine.api.users.UserService) or data store com.google.appengine.api.datastore.DatastoreService , if is tightly bound with Google app engine and can not be migrated to standalone tomcat engine.
To loose couple your database for further migration you should consider using MySQl schema in google app engine. Because in future you can host your database anywhere by just taking a dump. Also, you should use JDBC apis/JPA for database operations from your application using MySQL JDBC JAR
To summarize, you should avoid any API call which has com.google.appengine* import in your source. Also, you should have your own mysql schema running in google app engine cloud.
I think you can and it's only a matter of design.
Just an example: if your application need user authentication, you can create an interface AuthenticationService and two implementations:
GAEAuthenticationService for the Google App Engine
FakeAuthenticationService for local tests running with jetty (for example)
DataSourceAuthenticationService for authentication based on a DataSource
You can do the same think with persistence, scheduler, etc... the only thing to do is:
define the objects you need and use interfaces when you need different implementations that depends on platforms
I am studying Information Technology at a local college. I am currently doing a Java project for one of my Modules. We are expected to make a Java application that communicates with a Microsoft Access database. I am working in a group, and all of us are assigned to code separate functions of the software. However, we need to share one database. We are currently using ODBC on our individual computers and are using JDBC to connect to the database on the local machine. What we have thought is to just work on separate Microsoft Access databases and then just combine them later on. But I think that's not the best way. Is there a way that will allow me and my group members to have a centralized database, to which all of us can connect and make our queries? Is this possible by hosting the Microsoft Access database somewhere online, and then connecting to it from inside the Java software. Please help me out, as I have no idea how to get a centralized Microsoft Access database.
If you want to get rid of this by using Microsoft Access is because that's the easiest way out for you and your group to solve this kind of problem but I'd rather suggest you to use the database using a database provided by Java Derby database, it's quite help you to short your code within the server. Maybe I will suggest you to use Netbeans as a GUI and the Derby to control the database.
So what's your core problem is that a programming side or configuration and control within the hosting ? Thanks
I have written a relatively simple Java App Engine application which I would like to be able to port to another cloud provider.
I am using the JDO datastore API so I think my data handling should be portable to other backends as listed here: http://www.datanucleus.org/products/accessplatform/index.html
I would ideally like to deploy my application onto EC2 with minimal code changes. What is my best approach?
Note: I am aware of the http://code.google.com/p/appscale/ project but I want to avoid using this as it doesn't look like they are updating very often.
AppScale remains your best option to avoid rewriting any code. They do keep up to date with official App Engine - for instance, they just released preliminary support for Go. Even if they weren't so assiduous at keeping up to date, though, this would only be relevant if some feature you required wasn't yet supported - and it sounds like your needs are fairly basic.
JDO should be trivial, there might be some Google specific configuration here and there but generally it should be easy. The storage model Google promotes is not bad for RDBMS either, but you might need to fine tune your model depending on the backend you end up with.
If you're not using the low-level Google APIs, you should be pretty much there.
I managed to get my application working on EC2 using the following components.
Tomcat 7
Datanucelus
HBase
I had to manually create a table in HBase for each of my data classes but was able to configure Datanucleus to auto create the columns.
I also had to change my primary key value generation strategy from identity to increment as per this table of supported features.
http://www.datanucleus.org/products/accessplatform_3_0/datastore_features.html
I've been reading a little about Google's AppEngine that provides application hosting. I've been trying it out as I think it looks quite interesting but I'm a bit concerned about the database part.
Say I'm developing my Java app locally. I don't want to deploy to Google every time I make change to the code, so I setup a nice little Servlet container on my development machine to test things easily. With AppEngine you store things using their datastore API, which basically lets you model your data using Java objects - which is nice.
However, it seems like this data is embedded in the application code itself (inside the .war that is deployed to Google). Can I simply use their datastore api locally? How will it be stored on my local machine? Is this all handled by them so that I just have to worry about using the datastore API and when I deploy it to Google the data will just be stored in a different way than how it's stored on my local machine?
I'm just a little confused because I'm used to having the data part layered out of my application code.
I hope I'm clear enough. Thanks.
Development datastore and Production datastore are two different and separated things:
Development datastore is tipically a file based datastore named local_db.bin that it's just useful to store your data in your testing environment; the data is not replicated to the production environment when you deploy your application.
This kind of datastore is meant to be used with a fairly small number of entities and its performance has nothing to do with the powerful Production datastore beast based on Big Table.
All you need to do is to use the Datastore API that creates a level of abstraction between your code and the underlying datastore; in testing your data will be stored in the local datastore file, in production the created data will be saved to the Google App Engine datastore with all the features and limitations that this implies.