Camel - Aggregator Hello World

Camel Aggregator提供開發人員能夠將大量訊息合成一個的功能。假設你的系統會接受外來通知，並將內容寫進資料庫中；一次連線寫一筆資料會比較快，還是透過一次連線寫入五筆資料快呢? 正常來說，一次連線寫入五筆同屬性資料會是比較快的。它與Throttler的最大區別在於，Throttler限制了client的請求，而Aggreator則是收集起來一次請求。因此，如果使用Aggreator，你的程式必須要有對應的處理方式。

我將透過HTTP GET請求/events/{id}做為範例，說明如何使用Aggregator去將單位時間內的請求，以{id}去分組並Aggredate成各別分組訊息。本篇文章中使用到兩個RouteBuilder，分別為RestRouteBuilder與AggregatorGroupRouteBuilder。RestRouteBuilder負責REST核心相關設定，可參考先前文章。接下來直接說明AggregatorGroupRouteBuilder。

package org.tonylin.practice.camel.aggregator;
 
import static com.google.common.base.Preconditions.checkState;
 
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.processor.aggregate.GroupedExchangeAggregationStrategy;
 
public class AggregatorGroupRouteBuilder extends RouteBuilder {
 
	private final static String GET_EVENTS = "GET_EVENTS";
 
	private Object eventHandler;
	private int period = 500;
 
	public AggregatorGroupRouteBuilder(Object eventHandler) {
		this.eventHandler = eventHandler;
 
	}
 
	public void setPeriod(int period) {
		this.period = period;
	}
 
	@Override
	public void configure() throws Exception {
		checkState(eventHandler!=null, "Can't find eventHandler");
 
		rest("/events/{id}").get().route().id(GET_EVENTS)
		.aggregate(new GroupedExchangeAggregationStrategy())
		.header("id")
		.completionInterval(period)
		.bean(eventHandler).endRest();
	}
}

• aggregate(new GroupedExchangeAggregationStrategy()): 使用GroupedExchangeAggregationStrategy去做aggregate，aggregate的內容為Exchange。如果有任何條件限制，要以Exchange去操作。
• header(“id”): 與aggregate一起使用，代表以header id去分組，在這裡就是屬於event的id。
• completionInterval(period): 做aggregate的單位時間。
• bean(eventHandler): 請求的處理者，必須要有能力處理aggregate後的訊息。

Camel Aggregator提供了很多細部操作，你也可以根據自身需求做AggregationStrategy，這部分以後有機會再分享。接下來讓我們透過單元測試展示效果。

測試有兩個目標，testGroupedExchange用以確認aggregate group後的結果，另外一個testCompletionInterval則是確認單位時間設定的作用。以下為程式碼主要結構，主要測試程式碼稍後做說明:

package org.tonylin.practice.camel.aggregator;
 
import static com.google.common.base.Preconditions.checkState;
 
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
 
import org.apache.camel.Exchange;
import org.apache.camel.Handler;
import org.apache.camel.RoutesBuilder;
import org.apache.camel.test.junit4.CamelTestSupport;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClientBuilder;
import org.junit.Test;
import org.tonylin.practice.camel.rest.RestRouteBuilder;
 
public class AggregatorGroupRouteBuilderTest extends CamelTestSupport  {
 
	private RestHandler hander = new RestHandler();
 
	private HttpClient client = HttpClientBuilder.create().build();
 
	@Override
	protected RoutesBuilder[] createRouteBuilders() throws Exception {
		AggregatorGroupRouteBuilder aggregatorGroupRouteBuilder = new AggregatorGroupRouteBuilder(hander);
		aggregatorGroupRouteBuilder.setPeriod(500);
 
		return new RoutesBuilder[] {
				new RestRouteBuilder(),
				aggregatorGroupRouteBuilder
		};
	}
 
	@Test
	public void testGroupedExchange() throws Exception {
		// skip
	}
	@Test
	public void testCompletionInterval() throws Exception {
		// skip
	}
}

• Camel - Aggregator