Apache Flink 是一個分布式流處理框架，用于實時處理無界和有界數據流

1. 簡單的流處理：

import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;

public class SimpleStreamProcessing {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        DataStream<String> source = env.fromElements("Hello", "Flink", "on", "Ubuntu");

        DataStream<String> processed = source.map(s -> s.toUpperCase());

        processed.print();

        env.execute("Simple Stream Processing Example");
    }
}

2. 計算單詞頻率：

import org.apache.flink.api.common.functions.FlatMapFunction;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.util.Collector;

public class WordCountExample {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        DataStream<String> source = env.fromElements("Hello", "Flink", "on", "Ubuntu", "is", "awesome");

        DataStream<Tuple2<String, Integer>> wordCounts = source
                .flatMap(new FlatMapFunction<String, Tuple2<String, Integer>>() {
                    @Override
                    public void flatMap(String value, Collector<Tuple2<String, Integer>> out) {
                        String[] words = value.split("\\s+");
                        for (String word : words) {
                            out.collect(new Tuple2<>(word, 1));
                        }
                    }
                })
                .keyBy(0)
                .sum(1);

        wordCounts.print();

        env.execute("Word Count Example");
    }
}

3. 使用窗口函數計算滾動平均值：

import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;

public class RollingAverageExample {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        DataStream<Double> source = env.fromElements(1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0);

        DataStream<Double> rollingAverage = source
                .timeWindowAll(Time.seconds(3))
                .reduce((value1, value2) -> value1 + value2)
                .map(sum -> sum / 3);

        rollingAverage.print();

        env.execute("Rolling Average Example");
    }
}

要運行這些示例，請確保已安裝 Java 開發工具包（JDK）并正確配置了 Flink。然后，將示例代碼保存為 Java 文件（例如 SimpleStreamProcessing.java），并使用以下命令編譯和運行：

javac -cp /path/to/flink/lib/*: SimpleStreamProcessing.java
java -cp /path/to/flink/lib/*: SimpleStreamProcessing.class SimpleStreamProcessing

請注意，您需要根據實際情況替換 /path/to/flink/lib/ 為 Flink 安裝目錄中 lib 文件夾的路徑。