问题
I have a Spring Boot project with multiple databases of different years and these databases have same tables so the only difference is the year (..., DB2016, DB2017). In the controller of the application i need to return data that belong to "different" years. Moreover in future years other databases will be created (eg. in 2018 there's going to be a db named "DB2018"). So my problem is how to switch the connection among databases without creating a new datasource and a new repository every new year. In an other question posted by me (Spring Boot - Same repository and same entity for different databases) the answer was to create different datasources and different repositories for every existing database, but in this case i want to return data from existing databases on the basis of the current year. More specifically:
SomeEntity.java
@Entity(name = "SOMETABLE")
public class SomeEntity implements Serializable {
@Id
@Column(name="ID", nullable=false)
private Integer id;
@Column(name="NAME")
private String name;
}
SomeRepository.java
public interface SomeRepository extends PagingAndSortingRepository<SomeEntity, Integer> {
@Query(nativeQuery= true, value = "SELECT * FROM SOMETABLE WHERE NAME = ?1")
List<SomeEntity> findByName(String name);
}
SomeController.java
@RequestMapping(value="/foo/{name}", method=RequestMethod.GET)
public ResponseEntity<List<SomeEntity>> findByName(@PathVariable("name") String name) {
List<SomeEntity> list = autowiredRepo.findByName(name);
return new ResponseEntity<List<SomeEntity>>(list,HttpStatus.OK);
}
application.properties
spring.datasource.url=jdbc:postgresql://localhost:5432/DB
spring.datasource.username=xxx
spring.datasource.password=xxx
So if the current year is 2017 i want something like this:
int currentyear = Calendar.getInstance().get(Calendar.YEAR);
int oldestDbYear = 2014;
List<SomeEntity> listToReturn = new LinkedList<SomeEntity>();
//the method getProperties is a custom method to get properties from a file
String url = getProperties("application.properties", "spring.datasource.url");
props.setProperty("user", getProperties("application.properties","spring.datasource.username"));
props.setProperty("password", getProperties("application.properties","spring.datasource.password"));
for (int i = currentYear, i>oldestDbYear, i--) {
//this is the connection that must be used by autowiredRepo Repository, but i don't know how to do this.
//So the repository uses different connection for every year.
Connection conn = getConnection(url+year,props);
List<SomeEntity> list_of_specific_year = autowiredRepo.findByName(name);
conn.close;
listToReturn.addAll(list_of_specific_year);
}
return listToReturn;
Hope everithing is clear
回答1:
The thing that is probably most suitable to your needs here is Spring's AbstractRoutingDataSource. You do need to define multiple DataSources but you will only need a single repository. Multiple data sources is not an issue here as there is always a way to create the DataSource beans programatically at run time and register them with the application context.
How it works is you basically register a Map<Object, DataSource> inside your @Configuration class when creating your AbstractRoutingDataSource @Bean and in this case the lookup key would be the year.
Then you need create a class that implements AbstractRoutingDataSource and implement the determineCurrentLookupKey() method. Anytime a database call is made, this method is called in the current context to lookup which DataSource should be returned. In your case it sounds like you simply want to have the year as a @PathVariable in the URL and then as the implementation of determineCurrentLookupKey() grab that @PathVariable out of the URL (e.g in your controller you have mappings like @GetMapping("/{year}/foo/bar/baz")).
HttpServletRequest request = ((ServletRequestAttributes)RequestContextHolder
.getRequestAttributes()).getRequest();
HashMap templateVariables =
(HashMap)request.getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE);
return templateVariables.get("year");
I used this approach when writing a testing tool for a product where there were many instances running on multiple different servers and I wanted a unified programming model from my @Controllers but still wanted it to be hitting the right database for the server/deployment combination in the url. Worked like a charm.
The drawback if you are using Hibernate is that all connections will go through a single SessionFactory which will mean you can't take advantage of Hibernate's 2nd level caching as I understand it, but I guess that depends on your needs.
来源：https://stackoverflow.com/questions/46935382/spring-boot-change-connection-dynamically