Spark Java编程使用方法

Java

如何使用map

• Use lambda syntax

JavaDStream<String> lines = messages.map(s -> s.substring(0, 5))

• Implement the Function interfaces

// Function[T1, R]
JavaDStream<String> lines = messages.map(new Function<String, String>() {
    // call(v1: T1): R
    public String call(String s) {
        return s.substring(0, 5);
    }
});

class GetLength implements Function<String, int> {
    public Inter call(String s) { return s.length(); }
}
JavaDStream<String> lineLengths = lines.map(new GetLength())

如何使用reduce

• Use lambda syntax

int totalLength = lineLengths.reduce((a, b) -> a + b)

• Implement the Function interfaces

// Function2[T1, T2, R]
int totalLength = lineLengths.reduce(new Function2<Integer, Integer, Integer>() {
  public Integer call(Integer a, Integer b) { return a + b; }
});

class Sum implements Function2<Integer, Integer, Integer> {
  public Integer call(Integer a, Integer b) { return a + b; }
}
int totalLength = lineLengths.reduce(new Sum());

如何使用reduceByKey

• Use lambda syntax

JavaPairDStream<String, Integer> wordCounts = wordCount.reduceByKey((a, b) -> a + b);

• Implement the Function interfaces

// Function2[T1, T2, R]
JavaPairDStream<String, Integer> wordCounts = wordCount.reduceByKey(
    new Function2<Integer, Integer, Integer>() {
    @Override
    public Integer call(Integer i1, Integer i2) {
      return i1 + i2;
    }
});

如何使用flatMap

• Use lambda syntax

JavaDStream<String> words = lines.flatMap(x -> Lists.newArrayList(x.split(" ")));

• Implement the Function interfaces

// FlatMapFunction[T, R]
JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
    // call(t: T): Iterator[R]
    public Iterable<String> call(String x) {
        return Lists.newArrayList(SPACE.split(x));
    }
});

如何使用mapPartitions

• Use lambda syntax

JavaDStream<Tuple2<String, String>> mapLines = lines.mapPartitions(parts -> {
    List<Tuple2<String, String>> list = new ArrayList<Tuple2<String, String>>();
    while(parts.hasNext()){
        String msg = parts.next();
        String ip = msg.split(" ")[0];
        String domain = msg.split(" ")[1];
        list.add(new Tuple2<String, String>(ip, domain));
    };
    return list;
});

• Implement the Function interfaces

// FlatMapFunction[T, R]
JavaDStream<Tuple2<String, String>> mapLines = lines.mapPartitions(
    new FlatMapFunction<Iterator<String>, Tuple2<String, String>>() {
        List<Tuple2<String, String>> list = new ArrayList<Tuple2<String, String>>();
        // call(t: T): Iterator[R]
        public Iterable<Tuple2<String, String>> call(Iterator<String> s){
            while(s.hasNext()){
                String msg = s.next();
                String ip = msg.split(" ")[0];
                String domain = msg.split(" ")[1];
                list.add(new Tuple2<String, String>(ip, domain));
            }
            return list;
        }
    }
);

如何使用mapToPair

• Use lambda syntax

JavaPairDStream<String, Integer> wordCounts = words.mapToPair(s -> new Tuple2(s, 1));

• Implement the Function interfaces

// PairFunction[T, K, V]
JavaPairDStream<String, Integer> wordCounts = words.mapToPair(
    new PairFunction<String, String, Integer>() {
        // call(t: T): (K, V)
        public Tuple2<String, Integer> call(String s) {
            return new Tuple2<String, Integer>(s, 1);
        }
});