esper安裝與示例

1. esper的安裝：

在 http://esper.codehaus.org/esper/download/download.html 這裏下載esper壓縮包。解壓縮之後獲得文件夾 esper-4.x.x，在該文件夾根目錄有 esper-4.x.x.jar，這就是我們需要用到的esper庫，將其加入到項目中。值得注意的是，使用esper不僅僅需要這個jar文件，還需要esper所依賴的其他的庫。我們還需要將 esper-4.x.x/esper/lib 文件夾內的4個jar文件同樣加入項目，這樣才能正常使用 esper。

2. 詳細安裝方法：

已經安裝好esper的同學可以直接跳至第三步。由於本人剛剛學習Java，對於Java的對於第三方庫的使用非常不瞭解。所以費了老半天勁纔將esper引入項目，其實很簡單。(1) 將esper-4.x.x.jar 文件拖入eclipse的項目中，選擇“Copy File”。(2) 右擊項目名 => Properties => Libraries => Add JARs => 選擇 esper-4.x.x.jar => OK ，這樣，esper就安裝好了。(3) 同樣的辦法引入 esper-4.x.x/esper/lib 文件夾內的另外4個jar文件。之後，esper就可以使用了。

3. esper簡單實例

import com.espertech.esper.client.*;
import java.util.Random;
import java.util.Date;

public class exampleMain {

    public static class Tick {
        String symbol;
        Double price;
        Date timeStamp;

        public Tick(String s, double p, long t) {
            symbol = s;
            price = p;
            timeStamp = new Date(t);
        }
        public double getPrice() {return price;}
        public String getSymbol() {return symbol;}
        public Date getTimeStamp() {return timeStamp;}

        @Override
        public String toString() {
            return "Price: " + price.toString() + " time: " + timeStamp.toString();
        }
    }

    private static Random generator = new Random();

    public static void GenerateRandomTick(EPRuntime cepRT) {

        double price = (double) generator.nextInt(10);
        long timeStamp = System.currentTimeMillis();
        String symbol = "AAPL";
        Tick tick = new Tick(symbol, price, timeStamp);
        System.out.println("Sending tick:" + tick);
        cepRT.sendEvent(tick);

    }

    public static class CEPListener implements UpdateListener {

        public void update(EventBean[] newData, EventBean[] oldData) {
            System.out.println("Event received: " + newData[0].getUnderlying());
        }
    }

    public static void main(String[] args) {

//The Configuration is meant only as an initialization-time object.
        Configuration cepConfig = new Configuration();
        cepConfig.addEventType("StockTick", Tick.class.getName());
        EPServiceProvider cep = EPServiceProviderManager.getProvider("myCEPEngine", cepConfig);
        EPRuntime cepRT = cep.getEPRuntime();

        EPAdministrator cepAdm = cep.getEPAdministrator();
        EPStatement cepStatement = cepAdm.createEPL("select * from " +
                "StockTick(symbol='AAPL').win:length(2) " +
                "having avg(price) > 6.0");

        cepStatement.addListener(new CEPListener());

       // We generate a few ticks...
        for (int i = 0; i < 5; i++) {
            GenerateRandomTick(cepRT);
        }
    }
}

輸出：

log4j:WARN No appenders could be found for logger (com.espertech.esper.epl.metric.MetricReportingPath).
log4j:WARN Please initialize the log4j system properly.
Sending tick:Price: 6.0 time: Tue Jul 21 01:11:15 CEST 2009
Sending tick:Price: 0.0 time: Tue Jul 21 01:11:15 CEST 2009
Sending tick:Price: 7.0 time: Tue Jul 21 01:11:15 CEST 2009
Sending tick:Price: 4.0 time: Tue Jul 21 01:11:15 CEST 2009
Sending tick:Price: 9.0 time: Tue Jul 21 01:11:15 CEST 2009
Event received: Price: 9.0 time: Tue Jul 21 01:11:15 CEST 2009

好了。esper可以使用了。