Spring：使用构建器模式创建bean

Question

我使用ektorp连接到CouchDB。

构建ektorp HttpClient实例的方法是使用构建器模式：

HttpClient httpClient = new StdHttpClient.Builder()
                                .host("mychouchdbhost")
                                .port(4455)
                                .build();

我对Spring比较陌生。请告诉我如何在我的上下文中配置HttpClient以通过Builder创建它。

一种方法是使用@Configuration。还有其他选择吗？

Answer 1

您可以尝试实现FactoryBean接口：

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;
}}

并添加到以下bean定义的配置：

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

然后你可以将这个bean注入另一个bean，它将被解析为StdHttpClient实例。

Answer 2

我曾经偶然发现同样的问题，当我开发flexy-pool (a reactive connection pool sizing utility)时，所以我用基于Java和基于xml的例子编写了an article。

基本上，从以下Builder开始：

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;
    }
}

使用基于Java的配置是直截了当的：

@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();
    }
}

但您也可以使用基于XML的配置：

<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"/>

Answer 3

请检查Spring FactoryBean和FactoryMethod文档。

Answer 4

虽然不明确你的情况;如果它通过标准bean模式set方法公开属性，则可以扩展构建器。即如果我们以org.apache.httpcomponents:httpclient HttpClientBuilder为例，我们可以得到以下结果：

public class HttpClientFactoryBean
        extends HttpClientBuilder
        implements InitializingBean,
                   FactoryBean<HttpClient> {

    private HttpClient value;

    @Override
    public void afterPropertiesSet() throws Exception {
        this.value = build();
    }

    @Override
    public HttpClient getObject() throws Exception {
        return value;
    }

    @Override
    public Class<?> getObjectType() {
        return HttpClient.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

}

现在，工厂bean可以访问HttpClientBuilder公开的任何方法。现在可以进行如下配置：

<beans id="httpClient" class="com.drunkendev.factory.HttpClientFactoryBean">
  <beans name="defaultCredentialsProvider" ref="credentialsProvider"/>
  <beans name="targetAuthenticationStrategy">
    <util:constant static-field="org.apache.http.impl.client.TargetAuthenticationStrategy.INSTANCE"/>
  </beans>
</beans>