Enterprise Java
The Builder pattern and the Spring framework
Introduction
I like to make use of the builder pattern whenever an object has both mandatory and optional properties. But building objects is usually the Spring framework responsibility, so let’s see how you can employ it using both Java and XML-based Spring configurations.
A Builder example
Let’s start from the following Builder class.
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; } }
Java-based configuration
If you’re using Spring Java-based configuration then this is how you’d do it:
@org.springframework.context.annotation.Configuration public class FlexyDataSourceConfiguration { @Autowired private PoolingDataSource poolingDataSource; @Bean public Configuration configuration() { return new Configuration.Builder( UUID.randomUUID().toString(), poolingDataSource, CodahaleMetrics.BUILDER, BitronixPoolAdapter.BUILDER ).build(); } @Bean(initMethod = "start", destroyMethod = "stop") public FlexyPoolDataSource dataSource() { Configuration configuration = configuration(); return new FlexyPoolDataSource(configuration, new IncrementPoolOnTimeoutConnectionAcquiringStrategy.Builder(5), new RetryConnectionAcquiringStrategy.Builder(2) ); } }
XML-based configuration
The XML-based configuration is more verbose and not as intuitive as the Java-based configuration:
<bean id="configurationBuilder" class="com.vladmihalcea.flexypool.config.Configuration$Builder"> <constructor-arg value="uniqueId"/> <constructor-arg ref="poolingDataSource"/> <constructor-arg value="#{ T(com.vladmihalcea.flexypool.metric.codahale.CodahaleMetrics).BUILDER }"/> <constructor-arg value="#{ T(com.vladmihalcea.flexypool.adaptor.BitronixPoolAdapter).BUILDER }"/> </bean> <bean id="configuration" factory-bean="configurationBuilder" factory-method="build"/> <bean id="dataSource" class="com.vladmihalcea.flexypool.FlexyPoolDataSource" init-method="start" destroy-method="stop"> <constructor-arg ref="configuration"/> <constructor-arg> <array> <bean class="com.vladmihalcea.flexypool.strategy.IncrementPoolOnTimeoutConnectionAcquiringStrategy$Builder"> <constructor-arg value="5"/> </bean> <bean class="com.vladmihalcea.flexypool.strategy.RetryConnectionAcquiringStrategy$Builder"> <constructor-arg value="2"/> </bean> </array> </constructor-arg> </bean>
Conclusion
You can make use of the Builder pattern no matter the Spring configuration mode you’ve already chosen. If you have doubts about it’s usefulness, here are three compelling reasons you should be aware of.
Reference: | The Builder pattern and the Spring framework from our JCG partner Vlad Mihalcea at the Vlad Mihalcea’s Blog blog. |
hi Vlad,
I need a small help.I have a bean that need a uniqueid as constructor argument.
I tried using but it didnot work.
any ideas
Please ask the question on StackOverflow, and send me a link to it.