Spring: Using builder pattern to create a bean

You may try to implement FactoryBean interface:

public class HttpFactoryBean implements FactoryBean<HttpClient>{

private String host;
private int port;


public HttpClient getObject() throws Exception {
    return new StdHttpClient.Builder()
                            .host(host)
                            .port(port)
                            .build();
}

public Class<? extends HttpClient> getObjectType() {
    return StdHttpClient.class;
}

public boolean isSingleton() {
    return true;
}

public void setHost(String host) {
    this.host = host;
}

public void setPort(int port) {
    this.port = port;
}}

And add to config following bean definition:

<beans ..."> 
   <bean name="myHttpClient" class="HttpFactoryBean">
       <property name="port" value="8080"/>
       <property name="host" value="localhost"/>
   </bean>
</beans>

Then you can inject this bean to another beans, it will be resolved as StdHttpClient instance.

Please check Spring FactoryBean and FactoryMethod documentation.

I once stumbled on the same issue when I was developing FlexyPool, so this is what I did.

Basically, starting from the following Builder:

public final class Configuration<T extends DataSource> extends ConfigurationProperties<T, Metrics, PoolAdapter<T>> {
 
    public static final long DEFAULT_METRIC_LOG_REPORTER_PERIOD = 5;
 
    public static class Builder<T extends DataSource> {
        private final String uniqueName;
        private final T targetDataSource;
        private final PoolAdapterBuilder<T> poolAdapterBuilder;
        private final MetricsBuilder metricsBuilder;
        private boolean jmxEnabled = true;
        private long metricLogReporterPeriod = DEFAULT_METRIC_LOG_REPORTER_PERIOD;
 
        public Builder(String uniqueName, T targetDataSource, MetricsBuilder metricsBuilder, PoolAdapterBuilder<T> poolAdapterBuilder) {
            this.uniqueName = uniqueName;
            this.targetDataSource = targetDataSource;
            this.metricsBuilder = metricsBuilder;
            this.poolAdapterBuilder = poolAdapterBuilder;
        }
 
        public Builder setJmxEnabled(boolean enableJmx) {
            this.jmxEnabled = enableJmx;
            return this;
        }
 
        public Builder setMetricLogReporterPeriod(long metricLogReporterPeriod) {
            this.metricLogReporterPeriod = metricLogReporterPeriod;
            return this;
        }
 
        public Configuration<T> build() {
            Configuration<T> configuration = new Configuration<T>(uniqueName, targetDataSource);
            configuration.setJmxEnabled(jmxEnabled);
            configuration.setMetricLogReporterPeriod(metricLogReporterPeriod);
            configuration.metrics = metricsBuilder.build(configuration);
            configuration.poolAdapter = poolAdapterBuilder.build(configuration);
            return configuration;
        }
    }
 
    private final T targetDataSource;
    private Metrics metrics;
    private PoolAdapter poolAdapter;
 
    private Configuration(String uniqueName, T targetDataSource) {
        super(uniqueName);
        this.targetDataSource = targetDataSource;
    }
 
    public T getTargetDataSource() {
        return targetDataSource;
    }
 
    public Metrics getMetrics() {
        return metrics;
    }
 
    public PoolAdapter<T> getPoolAdapter() {
        return poolAdapter;
    }
}

Using the Java-based configuration is straight-forward:

@org.springframework.context.annotation.Configuration
public class FlexyDataSourceConfiguration {
 
    @Bean
    public Configuration configuration() {
        return new Configuration.Builder(
                UUID.randomUUID().toString(),
                poolingDataSource,
                CodahaleMetrics.BUILDER,
                BitronixPoolAdapter.BUILDER
        ).build();
    }
}

But you can also use XML-based configuration as well:

<bean id="configurationBuilder" class="com.vladmihalcea.flexypool.config.Configuration$Builder">
    <constructor-arg value="uniqueId"/>
    <constructor-arg ref="poolingDataSource"/>
    <constructor-arg value="#{ T(com.vladmihalcea.flexypool.metric.codahale.CodahaleMetrics).BUILDER }"/>
    <constructor-arg value="#{ T(com.vladmihalcea.flexypool.adaptor.BitronixPoolAdapter).BUILDER }"/>
</bean>
 
<bean id="configuration" factory-bean="configurationBuilder" factory-method="build"/>