Flink UDF函数（Function）

接口Function -》接口FilterFunction、MapFunction、FlatMapFunction、ReduceFunction、CoMapFunction
自定义Function，实现以上函数，并重写内部的方法。

ds.reduce(new myFunction());

class myFunction implements ReduceFunction<SensorReading>() {
            @Override
            public SensorReading reduce(SensorReading value1, SensorReading value2) throws Exception {
                return new SensorReading(value1.getId(), value2.getTimestamp(), Math.max(value1.getTemperature(),value2.getTemperature()));
            }
        })

或者写成匿名类

        DataStream result = keyedStream.reduce(new ReduceFunction<SensorReading>() {
            @Override
            public SensorReading reduce(SensorReading value1, SensorReading value2) throws Exception {
                return new SensorReading(value1.getId(), value2.getTimestamp(), Math.max(value1.getTemperature(),value2.getTemperature()));
            }
        });

3. lambda函数

 DataStream result = keyedStream.reduce(（v1, v2） -> v1+v2 );

4,Rich Function
RichMapFunction
RichFlapMapFunction
RichFilterFunction
…
与常规函数不同的是，可以获取运行环境上下文，并通过生命周期方法实现更复杂功能。
生命周期方法:

• open(), 算子如map执行前会被调用
• close(), 清理工作
• getRuntimeContext() ，运行时上下文，如并行度、

 class MyFunction extends RichMapFunction<SensorReading, Tuple2<String, Integer>> {
        @Override
        public void setRuntimeContext(RuntimeContext t) {
            super.setRuntimeContext(t);
        }

        @Override
        public RuntimeContext getRuntimeContext() {
            return super.getRuntimeContext();
        }

        @Override
        public IterationRuntimeContext getIterationRuntimeContext() {
            return super.getIterationRuntimeContext();
        }

        @Override
        public void open(Configuration parameters) throws Exception {
            super.open(parameters);
        }

        @Override
        public void close() throws Exception {
            super.close();
        }

        @Override
        public Tuple2<String, Integer> map(SensorReading value) throws Exception {
        value
            return null;
        }
    }