I have a quite complex save process of Spring data JPA repos in one Transaction:
mainRepo.save();
relatedRepo1.save();
relatedRepoOfRelatedRepo1.save();
...
And in the end I call (on mainRepo):
#Modifying
#Query("update mainEntity set finished = true where id = :id")
void setFinishedTrue(#Param("id") UUID id);
I want to guarantee that when setFinishedTrue(id) is called, all the related data are actually on the database because it will start an integration process that requires all needed data is available.
If you are using standard settings JPA will flush data before executing queries. So you are fine.
If you want to be really really really sure you can add an explicit flush operation.
You can do this by either using the JpaRepository.flush operation or by injecting the EntityManager and call flush on it explicitly.
I am writing RESTful services using spring and hibernate. I read many resource in internet, but they did not clarify my doubts. Please explain me in details what are DAO, DTO and Service layers in spring framework? And why usage of these layers is required in spring to develop RESTfull API services.
First off, these concepts are Platform Agnostic and are not exclusive to Spring Framework or any other framework, for that matter.
Data Transfer Object
DTO is an object that carries data between processes. When you're working with a remote interface, each call it is expensive. As a result you need to reduce the number of calls. The solution is to create a Data Transfer Object that can hold all the data for the call. It needs to be serializable to go across the connection. Usually an assembler is used on the server side to transfer data between the DTO and any domain objects. It's often little
more than a bunch of fields and the getters and setters for them.
Data Access Object
A Data Access Object abstracts and encapsulates all access to
the data source. The DAO manages the connection with the data source to
obtain and store data.
The DAO implements the access mechanism required to work with the data source.
The data source could be a persistent store like an RDBMS, or a business service accessed via REST or SOAP.
The DAO abstracts the underlying data access implementation for the Service objects to
enable transparent access to the data source. The Service also delegates
data load and store operations to the DAO.
Service
Service objects are doing the work that the
application needs to do for the domain you're working with. It involves calculations based on inputs and
stored data, validation of any data that comes in from the presentation, and figuring out exactly what data
source logic to dispatch, depending on commands received from the presentation.
A Service Layer defines an application's boundary and its set of available operations from
the perspective of interfacing client layers. It encapsulates the application's business logic, controlling
transactions and coordinating responses in the implementation of its operations.
Recommended References
Martin Fowler has a great book on common Application Architecture Patterns named Patterns of Enterprise Application Architecture. There is also, Core J2EE Patterns that worth looking at.
DAO - Data Access Object:
An object that provides a common interface to perform all database operations like persistence mechanism.
public interface GenericDao<T> {
public T find(Class<T> entityClass, Object id);
public void save(T entity);
public T update(T entity);
public void delete(T entity);
public List<T> findAll(Class<T> entityClass);
}
See this example : Spring – DAO and Service layer
DTO - Data Transfer Object:
An object that carries data between processes in order to reduce the number of method calls means you combine more than one POJO entities in service layer.
For example a GET request /rest/customer/101/orders is to retrieve all the orders for customer id 101 along with customer details hence you need combine entity Customer and entity Orders with details.
Enterprise application is divided into tiers for easy maintenance and development. Tiers are dedicated to particular type of tasks like
presentation layer (UI)
Business layer
Data access layer (DAO, DTO)
Why this design:
Let's pick an example you have an application which reads data from db and performs some business logic on it then present it to user. Now if you want to change your DB let say earlier application was running on Oracle now you want to use mysql so if you don't develop it in tiers you will doing changes everywhere in application. But if you implement DAO in application then this can be done easily
DAO: Data Access Object is design pattern
just provide an interface for accessing data to service layer and provide different implementations for different data sources (Databases, File systems)
Example code:
public interface DaoService {
public boolean create(Object record);
public CustomerTemp findTmp(String id);
public Customer find(String id);
public List getAllTmp();
public List getAll();
public boolean update(Object record);
public boolean delete(Object record);
public User getUser(String email);
public boolean addUser(User user);
}
Service layer using Dao
#Service("checkerService")
public class CheckerServiceImpl implements CheckerService{
#Autowired
#Qualifier("customerService")
private DaoService daoService;
Now i can provide any implementation of DaoService interface.
Service and DTO are also used for separation of concerns.
DTO: The data object that we pass between different processes or within the same process. It can be a wrapper around the actual entity object. Using entity object as is for DTO is not safe and not recommended. Design of this object is based on various factors like simplicity of representation, security of exposing Ids, consumer requirement and so on.
In Spring, DTO can be formed with a simple model/pojo object.
DAO: The object responsible for CRUD operations.
In Spring, this can be an object that implements JPARepository interface, or any bean that connects with database and does a CRUD for us. Please remember your journey from JDBC to Hibernate to Spring data JPA. :)
Service: Core bean for business logic implementation. This object may has DAO object as its dependency. Core business logic for the particular use case will go here.
In Spring, Service object/bean can be created either by annotating the bean with #Service or #Component annotation or simply representing the object as a bean using java configuration. Make sure you inject all the required dependencies into the service bean for its heavy lifting job.
SERVICE LAYER:
It receives the request from controller layer and process the request to Persistence layer
#Controller:It is the annotation which initialize whole controller layer.
#Service:It is the annotation which initialize whole service layer.
#Repository: It is the annotation which initialize whole persistence layer.
DTO:
It is an Data Transfer object which used to pass the properties from service layer to persistence layer.
DAO:
It is an Data Access object. it is also known as persistence layer. In this DAO we receive property values from service layer in DTO object. Here we write an persistence logic to db.
I am just wondering whether using a OneToManyResultSetExtractor or a ResultSetExtractor with Spring Batch's JdbcCursorItemReader?
The issue I have is that the expected RowMapper only deals with one object per row and I have a join sql query that returns many rows per object.
Out of the box, it does not support the use of a ResultSetExtractor. The reason for this is that the wrapping ItemReader is stateful and needs to be able to keep track of how many rows have been consumed (it wouldn't know otherwise). The way that type of functionality is typically done in Spring Batch is by using an ItemProcessor to enrich the object. Your ItemReader would return the one (of the one to many) and then the ItemProcessor would enrich the object with the many. This is a common pattern in batch processing called the driving query pattern. You can read more about it in the Spring Batch documentation here: http://docs.spring.io/spring-batch/trunk/reference/html/patterns.html
That being said, you could also wrap the JdbcCursorItemReader with your own implementation that performs the logic of aggregation for you.
I have a requirement to implement in Spring batch,I need to read from a file and from a DB ,the data needs to be processed and written to an email
I have gone through the spring batch documentation but was unable to find a CHUNKtasklet which would read data from multiple readers
SO essentially I have to read from 2 different sources of data(one from file and another from DB,each will need to have its own mapper)
Regards
Tar
I see two options depending on how the data is structured:
Spring Batch relies heavily on composition when building batch components. One option would be to create a custom composite ItemReader that delegates to a other readers (ones Spring Batch provides or otherwise) and provides the logic to assemble a single object based on the results of those delegated ItemReaders.
You could use an ItemReader to provide the base information (say from a database) and use and ItemProcessor to enrich the item (say reading from a file).
Either of the above are normal ways to handle this type of input scenario.
Currently I'm working on a software that consists of two parts.
One part is a kind of company wide framework for data processing (kind of self written process engine). It uses JTA UserTransactions and calls a sub processor that is written by our project.
Our "sub processor" is an application on it's own. It uses container managed persistence via JPA. (Websphere with OpenJPA)
A typical workflow is:
process engine loads process data -> start user transaction -> calls sub processor -> writes process data -> ends user transaction
We now experience the following wrong behavior:
The user transaction is committed in the process engine, all the meta data of the process is stored into the db BUT the data the entity manager holds inside our sub processor application is not written to the db.
Is there some manual communication necessary to commit the content of our entity manager?
The Problem we observed had nothing to do with JTA and transactions.
We tried to clean a blob column but this was not possible. I will create another question for it.