How do I create beans programmatically in Spring Boot?

How about creating your beans and ask Spring Boot to inject values into it?

Something like

@Bean
@ConfigurationProperties("ds.client1")
public DataSource dataSourceClient1() {
    DataSourceBuilder.create().build();
}

@Bean
@ConfigurationProperties("ds.client2")
public DataSource dataSourceClient2() {
    DataSourceBuilder.create().build();
}

Then, any setting in the ds.client1 namespace belongs to the first data source (i.e. ds.client1.password is the data source password for that DataSource).

But maybe you don't know how much data sources you'll have? This is getting more complicated, especially if you need to inject those dynamic data sources in other objects. If you only need to lookup them by name, you could register them yourself as singletons. Here is an example that works

@ConfigurationProperties(prefix = "ds")
public class DataSourceSettings implements BeanFactoryAware {

    private List<String> clients = new ArrayList<>();

    private BeanFactory beanFactory;

    public List<String> getClients() {
        return clients;
    }

    public void setClients(List<String> clients) {
        this.clients = clients;
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }

    @PostConstruct
    public void configure() {
        Map<String, String> clientDataSources = new HashMap<String, String>();
        for (String client : clients) {
            // extract client name
            String[] parts = client.split("\\|");
            String clientName = parts[0];
            String url = parts[1];
            // client to datasource mapping
            String dsName = url.substring(url.lastIndexOf("/") + 1);
            if (clientName.contains(",")) {
                // multiple clients with same datasource
                String[] clientList = clientName.split(",");
                for (String c : clientList) {
                    clientDataSources.put(c, url);
                }
            }
            else {
                 clientDataSources.put(clientName, url);
            }
        }
        Assert.state(beanFactory instanceof ConfigurableBeanFactory, "wrong bean factory type");
        ConfigurableBeanFactory configurableBeanFactory = (ConfigurableBeanFactory) beanFactory;
        for (Map.Entry<String, String> entry : clientDataSources.entrySet()) {
            DataSource dataSource = createDataSource(entry.getValue());
            configurableBeanFactory.registerSingleton(entry.getKey(), dataSource);
        }
    }

    private DataSource createDataSource(String url) {
        return DataSourceBuilder.create().url(url).build();
    }
}

Note that those beans are only available by bean name lookup. Let me know if that works out for you.

I created an example project on github to demonstrate your usecase.

https://github.com/lhotari/dynamic-datasources

I implemented a ImportBeanDefinitionRegistrar to add the beans. You can get a hold of the configuration by implementing EnvironmentAware. There might be other ways to achieve your goal, but this was the way I used in GspAutoConfiguration to register beans dynamicly. GspAutoConfiguration makes Grails GSP available in Spring Boot applications.

Here's the relevant configuration class in the dynamic-datasource sample: https://github.com/lhotari/dynamic-datasources/blob/master/src/main/groovy/sample/DynamicDataSourcesConfiguration.java

package sample;

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

import org.springframework.beans.FatalBeanException;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.boot.bind.PropertiesConfigurationFactory;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.jdbc.datasource.SingleConnectionDataSource;
import org.springframework.validation.BindException;

@Configuration
public class DynamicDataSourcesConfiguration implements ImportBeanDefinitionRegistrar, EnvironmentAware {
    private ConfigurableEnvironment environment;
    private static Map<String, Object> defaultDsProperties = new HashMap<String, Object>() {
        {
            put("suppressClose", true);
            put("username", "sa");
            put("password", "");
            put("driverClassName", "org.h2.Driver");
        }
    };

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = (ConfigurableEnvironment)environment;
    }

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        DataSourceSettings settings = resolveSettings();
        for (Entry<String, String> entry : settings.clientDataSources().entrySet()) {
            createDsBean(registry, entry.getKey(), entry.getValue());
        }
    }

    private void createDsBean(BeanDefinitionRegistry registry, String beanName, String jdbcUrl) {
        GenericBeanDefinition beanDefinition = createBeanDefinition(SingleConnectionDataSource.class);
        beanDefinition.getPropertyValues().addPropertyValues(defaultDsProperties).addPropertyValue("url", jdbcUrl);
        registry.registerBeanDefinition(beanName, beanDefinition);
    }

    private GenericBeanDefinition createBeanDefinition(Class<?> beanClass) {
        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(beanClass);
        beanDefinition.setAutowireMode(GenericBeanDefinition.AUTOWIRE_NO);
        return beanDefinition;
    }

    private DataSourceSettings resolveSettings() {
        DataSourceSettings settings = new DataSourceSettings();
        PropertiesConfigurationFactory<Object> factory = new PropertiesConfigurationFactory<Object>(settings);
        factory.setTargetName("ds");
        factory.setPropertySources(environment.getPropertySources());
        factory.setConversionService(environment.getConversionService());
        try {
            factory.bindPropertiesToTarget();
        }
        catch (BindException ex) {
            throw new FatalBeanException("Could not bind DataSourceSettings properties", ex);
        }
        return settings;
    }

}