Change database schema during runtime based on logged in user

Assumptions

Because I don’t have the reputation yet to post a comment below your question, my answer is based on the following assumptions:

• The current schema name to be used for the current user is accessible through a Spring JSR-330 Provider like private javax.inject.Provider<User> user; String schema = user.get().getSchema();. This is ideally a ThreadLocal-based proxy.

• To build a DataSource which is fully configured in a way you need it requires the same properties. Every time. The only thing which is different is the schema name. (It would easily possible to obtain other different parameters as well, but this would be too much for this answer)

• Each schema is already set up with the needed DDL, so there is no need for hibernate to create tables or something else

• Each database schema looks completely the same except for its name

• You need to reuse a DataSource every time the corresponding user makes a request to your application. But you don’t want to have every DataSource of every user permanently in the memory.

My solution idea

Use a combination of ThreadLocal proxys to get the schema name and a Singleton-DataSource which behaves different on every user request. This solution is inspired by your hint to AbstractRoutingDataSource, Meherzad’s comments and own experience.

A dynamic DataSource

I suggest to facilitate the AbstractDataSource of Spring and implement it like the AbstractRoutingDataSource. Instead of a static Map-like approach we use a Guava Cache to get an easy to use cache.

public class UserSchemaAwareRoutingDataSource extends AbstractDataSource {
    private @Inject javax.inject.Provider<User> user;
    private @Inject Environment env;
    private LoadingCache<String, DataSource> dataSources = createCache();

    @Override
    public Connection getConnection() throws SQLException {
        return determineTargetDataSource().getConnection();
    }

    @Override
    public Connection getConnection(String username, String password) throws SQLException {
        return determineTargetDataSource().getConnection(username, password);
    }

    private DataSource determineTargetDataSource() {
        String schema = user.get().getSchema();
        return dataSources.get(schema);
    }

    private LoadingCache<String, DataSource> createCache() {
        return CacheBuilder.newBuilder()
           .maximumSize(100)
           .expireAfterWrite(10, TimeUnit.MINUTES)
           .build(
               new CacheLoader<String, DataSource>() {
                 public DataSource load(String key) throws AnyException {
                   return buildDataSourceForSchema(key);
                 }
               });
    }

    private DataSource buildDataSourceForSchema(String schema) {
        // e.g. of property: "jdbc:postgresql://localhost:5432/mydatabase?currentSchema="
        String url = env.getRequiredProperty("spring.datasource.url") + schema;
        return DataSourceBuilder.create()
            .driverClassName(env.getRequiredProperty("spring.datasource.driverClassName"))
            [...]
            .url(url)
            .build();
    }
}

Now you have a `DataSource´ which acts different for every user. Once a DataSource is created it’s gonna be cached for 10 minutes. That’s it.

Make the application aware of our dynamic DataSource

The place to integrate our newly created DataSource is the DataSource singleton known to the spring context and used in all beans e.g. the EntityManagerFactory

So we need an equivalent to this:

@Primary
@Bean(name = "dataSource")
@ConfigurationProperties(prefix="spring.datasource")
public DataSource dataSource() {
    return DataSourceBuilder.create().build();
}

but it has to be more dynamic, than a plain property based DataSourceBuilder:

@Primary
@Bean(name = "dataSource")
public UserSchemaAwareRoutingDataSource dataSource() {
    return new UserSchemaAwareRoutingDataSource();
}

Conclusion

We have a transparent dynamic DataSource which uses the correct DataSource everytime.

Open questions

• What to do, when no user is logged in? Is there no database access allowed?
• Who sets up the schemes?

Disclaimer

I haven’t tested this code!

EDIT:
To implement a Provider<CustomUserDetails> with Spring you need to define this as prototype. You can utilize Springs support of JSR-330 and Spring Securitys SecurityContextHolder:

@Bean @Scope("prototype")
public CustomUserDetails customUserDetails() {
    return return (CustomUserDetails) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
}

You don’t need a RequestInterceptor, the UserProvider or the controller code to update the user anymore.

Does this help?

EDIT2
Just for the record: do NOT reference the CustomUserDetails bean directly. Since this is a prototype, Spring will try to create a proxy for the class CustomUserDetails, which is not a good idea in our case. So just use Providers to access this bean. Or make it an interface.