I have been fetching data from database to my JAVA program by using JDBC till now and I am doing so by creating a connection class and in that class I will use the DriverManager.getConnection() fnc, but as I am moving towards JPA I have learnt that a persistence.xml file is needed to connect to mysql. In the project where I am using JPA am i supposed to create this connection class again and should I place the connector jar file in the project where I will be using jpa.
Excuse my unawarness of the concept I am still in the learning phase.Any help is appreciated as I am new to this.
Here Need to clear for you.
JPA is a specification. Different ORM technology uses it. Like hibernate implemented JPA specification. Specification defines how it works.
Hibernate is ORM technology. It binds Your Plain Java Object (Entity) to your database tables. And table's column will be Entity's field. Like Table has Id column of number type, in entity it will be Long id; . table name will be entity name or others that is defined in hibernate docs.
3rd One is Database connector. Yes there is different types of connector for every database. like for mysql connector is using to connect your implemented code with databases. You can think Its a communication Layer for database and your code. Your code is communicating with database through this connector.
Hope now you get concept why mysql connector is needed to connect. Happy Coding :)
I have a finalized database in SQL SERVER containing 50+ tables in it and needed to connect it with Dropwizard Code.
I am new to JAVA so my conception about Migrations.xml is it is used to create the tables in database or if any change in database is needed it will be updated through migrations.xml.
So if i don't need any change in database (as told earlier it is finalized).
Can i skip this migrations.xml file?
Need some experts advice please.
If you are handling your database changes elsewhere, then you have no need for any migration xml files within your dropwizard project. It's an optional module, you don't need to use it. You don't even need to include the dropwizard-migrations dependency if you don't want to include database updates in your dropwizard project. You can still connect to your database fine within dropwizard. The docs provide examples using modules dropwizard-jdbi and dropwizard-hibernate.
To connect to your database, add the appropriate code the your java configuration file and yml config as explained in the docs.
jdbi
http://www.dropwizard.io/0.9.2/docs/manual/jdbi.html
hibernate
http://www.dropwizard.io/0.9.2/docs/manual/hibernate.html
I am building a stand alone java application using Spring JPA frame
work. I am able to access the DB in below scenario: if I give the
DB details in application.properties file as
spring.datasource.url=******** spring.datasource.username=******
spring.datasource.password=******
then it's working properly.
but I have to create two DB connections in the same application so,
I changes the names as below
spring.Datasource1.url=********* spring.Datasource1.username=******
spring.Datasource1.password
spring.Datasource2.url=************ spring.Datasource2.username=****
spring.Datasource2.password=*****
then it's not working.
Can you please provide the solution for it?
I have uploaded my code base in below location.
https://github.com/nagtej/MultipleDataSource
This might be helpful to you http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-two-datasources
Also, to connect to multiple data sources you would need to manually configure a DataSource, EntityManagerFactory and JpaTransactionManager.
For this, you can have a look at code placed at https://github.com/spring-projects/spring-data-examples/tree/master/jpa/multiple-datasources
Another good example for this is shared at http://xantorohara.blogspot.com.au/2013/11/spring-boot-jdbc-with-multiple.html
I use JDBC and created h2 database called usaDB from sql script. Then I filled all tables with jdbc.
The problem is that after I connect to usaDB at localhost:8082 I cannot see on the left tree
my tables. There is only INFORMATION_SCHEMA database and rootUser which I specified creating usaDB.
How to view the content of tables in my h2 database?
I tried query SELECT * FROM INFORMATION_SCHEMA.TABLES.
But it returned many table names except those I created. My snapshot:
I had the same issue and the answer seems to be really stupid: when you type your database name you shouldn't add ".h2.db" suffix, for example, if you have db file "D:\somebase.h2.db" your connection string should be like "jdbc:h2:file:/D:/somebase". In other way jdbc creates new empty database file named "somebase.h2.db.h2.db" and you see what you see: only system tables.
You can use the SHOW command:
Using this command, you can lists the schemas, tables, or the columns of a table. e.g.:
SHOW TABLES
This problem drove me around the twist and besides this page I read many (many!) others until I solved it.
My Use Case was to see how a SpringBatch project created in STS using :: Spring Boot :: (v1.3.1.RELEASE) was going to behave with the H2 database; to do the latter, I needed to be able to get the H2 console running as well to query the DB results of the batch run.
This is what I did and found out:
Created an Web project in STS using Spring Boot:
Added the following to the pom.xml of the latter:
Added a Spring configuration file as follows to the project:
This solves the Web project deficiencies in STS. If you run the project now, you can access the H2 console as follows: http://localhost:8080/console
Now create a SpringBatch project in STS as follows (the alternative method creates a different template missing most of the classes for persisting data. This method creates 2 projects: one Complete, and the other an initial. Use the Complete in the following.):
The SpringBatch project created with STS uses an in memory H2 database that it CLOSES once the application run ends; once you run it, you can see this in the logging output.
So what we need is to create a new DataSource that overrides the default that ships with the project (if you are interested, just have a look at the log messages and you will see that it uses a default datasource...this is created from:
o.s.j.d.e.EmbeddedDatabaseFactory with the following parameters:
Starting embedded database: url='jdbc:hsqldb:mem:testdb', username='sa')
So, it starts an in memory, and then closes it. You have no chance of seeing the data with the H2 console; it has come and gone.
So, create a DataSource as follows:
You can of course use a properties file to map the parameters, and profiles for different DataSource instances...but I digress.
Now, make sure you set the bit that the red arrow in the picture is pointing to, to a location on your computer where a file can be persisted.
Running the SpringBatch (Complete project) you should now have a db file in that location after it runs (persisting Person data)
Run the Web project you configured previously in these steps, and you WILL :=) see your data, and all the Batch job and step run data (et voila!):
Painful but rewarding. Hope it helps you to really BOOTSTRAP :=)
I have met exactly this problem.
From what you describe, I suppose that you connect your jdbc with the "real" h2 server, but you are connecting on web application to database by the wrong mode (embedded-in-memory mode, aka h2mem). It means that h2 will create a new database in-memory, instead of using your true database stored elsewhere.
Please make sure that when you connect to this database, you use the mode Generic H2 (Server), NOTGeneric H2 (Embedded). You can refer to the picture below.
Version of jar file and installed h2 database should be same.
If in case you have created and populated H2 database table using maven dependency in spring boot, then please do change the JDBC URL as jdbc:h2:mem:testdb while connecting to H2 using web console.
It is an old question, but I came across the same problem. Eventually I found out that the default JDBC URL is pointing a test server rather than my application. After correcting it, I could access the right DB.
I tried with both Generic H2 (Embedded) and the Generic H2 (Server) options, both worked as long as the JDBC URL: is provided correctly.
In grails 4.0.1 the jdbc URL for development is jdbc:h2:mem:devDb. Check your application.yml file for the exact URL.
For the people who are using H2 in embedded(persistent mode) and want to "connect" to it from IntelliJ(other IDEs probably apply too).
Using for example jdbc url as follows: jdbc:h2:./database.h2
Note, that H2 does not allow implicit relative paths, and requires adding explicit ./
Relative paths are relative to current workdir
When you run your application, your workdir is most likely set to your project's root dir
On the other hand, IDE's workdir is most likely not your project's root
Hence, in IDE when "connecting" to your database you need to use absolute path like: jdbc:h2:/Users/me/projects/MyAwesomeProject/database.h2
For some reason IntelliJ by default also adds ;MV_STORE=false. It disables MVStore engine which in fact is currently used by default in H2.
So make sure that both your application and your IDE use the same store engine, as MVStore and PageStore have different file layouts.
Note that you cannot "connect" to your database if your application is using it because of locking. The other way around applies too.
In my case the issue was caused by the fact that I didn't set the h2 username, password in java. Unfortunatelly, Spring didn't display any errors to me, so it was not easy to figure out. Adding this lines to dataSource method helped me fix the issue:
dataSource.setUsername("sa");
dataSource.setPassword("");
Also, I should have specified the schema when creating tables in schema.sql
Selecting Generic H2 (Server) solved for me. We tempted to use default Generic H2 (Embedded) which is wrong.
I am about to make a connection to my database and I am using EJB and JPA. I have recently started doing these technologies so I have some problems understand it all at this point:)
I know that the persistence.xml is needed in order to use JPA. It is the file where I configure how to connect to the database, that I know. However it seems like there are multiple ways of doing it.
What would be the difference (or when should I even use the one alternative over the other?) of defining properties such as username, database, password etc. in the persistence.xml file and in Glassfish? Advantages/disadvantages if any.
Underneath on the image I posted I have JDBC Resources and JDBC Connection Pools. I am a litte confused about the terminology of the two. Why don't we add properties such as username, database, password and so on in the JDBC Resources? Could someone explain the difference between them and what they mean?
JDBC Resources
A JDBC resource (data source) provides applications with a means of
connecting to a database. Typically, the administrator creates a JDBC
resource for each database accessed by the applications deployed in a
domain. (However, more than one JDBC resource can be created for a
database.)
http://download.oracle.com/docs/cd/E19316-01/820-4335/ablih/index.html
I think it strange that we add such properties on the pool but not in the resource, but I probably misunderstand the concepts.
In the "JDBC connection pools" you can create container managed JDBC data sources (with connection pooling capabilities). The data source needs to know about at least the JDBC driver, the JDBC URL, username and password.
In the "JDBC resources" you can bind those container managed JDBC data sources to one or more JNDI names so that they are by JNDI available to the deployed web application.
In the persistence.xml you can specify whether to use a local data source or to use a container managed data source. If you want to use a container managed data source, then you should specify its JNDI name. Using a container managed data source has the advantage that you can share a single data source among multiple web applications. In case of JPA, it has also the advantage that you can make use of JTA (container managed transactions) so that you don't need to call transaction.begin(), commit(), rollback() etc in every method.