Presto 聚合函数（UDAF） 开发详细步骤

1.加入相关依赖：

packaging>presto-plugin         0.208                     com.facebook.presto         presto-spi         ${presto.verison}         provided                          com.google.guava         guava         11.0.2               com.facebook.presto      presto-maven-plugin      0.3     true

2.创建sum类：

@AggregationFunction("sumdouble") @Description("this is a double sum function") public final class DoubleSumAggregation {     private DoubleSumAggregation() {}       @InputFunction     public static void input(@AggregationState NullableDoubleState state, @SqlType(StandardTypes.DOUBLE) double value)     {         state.setNull(false);         state.setDouble(state.getDouble() + value);     }       @CombineFunction     public static void combine(@AggregationState NullableDoubleState state, @AggregationState NullableDoubleState otherState)     {         if (state.isNull()) {             state.setNull(false);             state.setDouble(otherState.getDouble());             return;         }           state.setDouble(state.getDouble() + otherState.getDouble());     }       @OutputFunction(StandardTypes.DOUBLE)     public static void output(@AggregationState NullableDoubleState state, BlockBuilder out)     {         NullableDoubleState.write(DoubleType.DOUBLE, state, out);     } }

说明：

@AggregationFunction("sumdouble"):聚合函数的名称，会在你的使用show functions；命令的时候显示出来

@Description():想要别人更了解你的函数，你可以 增加一下描述信息

@InputFunction:标志着这个静态方法为聚合的入口，输入方法，注意没有返回值

@CombineFunction：合并函数可以把其他块的数据进行合并，必须

@OutputFunction(输出类型)：标志输出方法，得到最终的结果

2.创建NullableDoubleState.class

官方代码：

@AccumulatorStateMetadata(stateSerializerClass = NullableDoubleStateSerializer.class) public interface NullableDoubleState         extends AccumulatorState {     double getDouble();       void setDouble(double value);       @InitialBooleanValue(true)     boolean isNull();       void setNull(boolean value);       static void write(Type type, NullableDoubleState state, BlockBuilder out)     {         if (state.isNull()) {             out.appendNull();         }         else {             type.writeDouble(out, state.getDouble());         }     } }

注意：其他类型，写法类似

3.编写注册类

/**  * 插件注册类  */ public class FunctionsPlugin implements Plugin {     @Override     public Set> getFunctions() {         return ImmutableSet.>builder()                 .add(DoubleSumAggregation.class)                 .build();     } }

注意：这个类最好和DoubleSumAggregation.class放到一个package下

4.容易被忽视的部分

在resource下创建META-INF/services目录，并创建文件名为com.facebook.presto.spi.Plugin的文件，并添加内容：

xxx.xxx.xxx.FunctionsPlugin

5.打包

mvn clean package

6.把xxx.zip解压到${PRESTOHOME}/plugin

>unzip ${projectdir}/target/xxx.zip -d ${PRESTOHOME}/plugin

注意：需要解压到所有节点上

7.重启之后就可以用