Spring Boot 1 database multiple database users

You have already found the best way to do that task, I mean AbstractRoutingDataSource. If you have fixed number of users it is the simplest way you could use following approach:

public final class RoutingDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        return UserContextHolder.getUserName() + "DataSource";
    }
}

And configuration:

@Bean
@Qualifier("user1DataSource")
public DataSource userOneDataSource() {
    return DataSourceBuilder.create()
            .username("user1")
            .password("pass")
             ...
             .build();
}

@Bean
@Qualifier("user2DataSource")
public DataSource userOneDataSource() {
    return DataSourceBuilder.create()
            .username("user2")
             ...
             .build();
}

@Bean
@Primary
public RoutingDataSource dataSource(Map<String, DataSource> datasources) {
    return new RoutingDataSource().dataSource(datasources);
 }

If you need add users and datasources at runtime you could use somethig like this:

public final class RoutingDataSource extends AbstractRoutingDataSource {
    private final ConcurrentHashMap<String, DataSource> dynamicDataSources = new ConcurrentHashMap<>();

    @Override
    protected Object determineCurrentLookupKey() {
        return UserContextHolder.getUserName() + "_datasource";
    }

    @Override
    protected DataSource determineTargetDataSource() {
        String currentLookupKey = this.determineCurrentLookupKey().toString();
        String userName = UserContextHolder.getUserName();
        String password = UserContextHolder.getPassword();

        return this.dynamicDataSources.computeIfAbsent(currentLookupKey, (key) -> DataSourceBuilder.create()
                .driverClassName("your.driver.class")
                .url("jdbc:same:url/here")
                .username(userName)
                .password(password)
                .build());
    }
}