blink udtf的实战

实时计算支持三种自定义函数（UDX），分别是：

UDF（User Defined Function）自定义标量函数，输入一条记录的0个、1个或者多个值，返回一个值。
UDAF（User Defined Aggregation Function）自定义聚合函数，将多条记录聚合成一条值。
UDTF（User Defined Table Function）自定义表值函数，能将多条记录转换后再输出，输出记录的个数和输入记录数不需要一一对应，也是唯一能返回多个字段的自定义函数。

本文档通过使用UDTF解析字节数组成多个字段
如存储的是{"name":"Alice", "age":13, "grade":"A"}的字节数组，通过UDTF 变成三列name,age,grade 值分别为 Alice,13,A

1 UDTF


import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import org.apache.flink.api.common.typeinfo.BasicTypeInfo;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.java.typeutils.RowTypeInfo;
import org.apache.flink.shaded.calcite.com.google.common.collect.Lists;
import org.apache.flink.table.api.functions.TableFunction;
import org.apache.flink.table.api.types.DataType;
import org.apache.flink.table.api.types.TypeInfoWrappedDataType;
import org.apache.flink.types.Row;

import java.nio.charset.Charset;
import java.util.List;

public class kafkaUDTF extends TableFunction<Row> {

    public kafkaUDTF() {

    }

    private List<Class> clazzes = Lists.newArrayList();
    private List<String> fieldName = Lists.newArrayList();

    public kafkaUDTF(String... args) {
        for (String arg : args) {
            if (arg.contains(",")) {
//将 "VARCHAR" 转换为 String.class, "INTEGER" 转为 Integer.class等
                clazzes.add(ClassUtil.stringConvertClass(arg.split(",")[1]));
                fieldName.add(arg.split(",")[0]);
            }
        }
    }
    public static void main(String[] args) {
        kafkaUDTF kafkaUDTF = new kafkaUDTF("name,VARCHAR", "age,INTEGER", "grade,VARCHAR");
        kafkaUDTF.eval("{\"name\":\"Alice\", \"age\":13,  \"grade\":\"A\"}".getBytes());
    }

    public void eval(byte[] message) {
        String mess = new String(message, Charset.forName("UTF-8"));
        JSONObject json = JSON.parseObject(mess);
        Row row = new Row(fieldName.size());
        for (int i = 0; i < fieldName.size(); i++) {
            row.setField(i, json.get(fieldName.get(i)));
        }
        collect(row);
    }

    @Override
    // 如果返回值是Row，就必须重载实现这个方法，显式地告诉系统返回的字段类型
    public DataType getResultType(Object[] arguments, Class[] argTypes) {
        TypeInformation[] typeInformations = new TypeInformation[clazzes.size()];

        for (int i = 0; i < clazzes.size(); i++) {
            typeInformations[i] = BasicTypeInfo.of(clazzes.get(i));
        }
        RowTypeInfo rowType = new RowTypeInfo(typeInformations);
        return new TypeInfoWrappedDataType(rowType);
    }

}

2. Main

 StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
StreamTableEnvironment tableEnv = TableEnvironment.getTableEnvironment(env);
  DataStreamSource<byte[]> byteSource = env.fromElements("{\"name\":\"Alice\", \"age\":13,  \"grade\":\"A\"}".getBytes());
        Table byteSourceTable = tableEnv.fromDataStream(byteSource, "message");

        tableEnv.registerTable("b", byteSourceTable);
        tableEnv.registerFunction("kafkaUDTF", new kafkaUDTF("name,VARCHAR", "age,INTEGER", "grade,VARCHAR"));

        Table res1 = tableEnv.sqlQuery("select  T.name, T.age, T.grade\n" +
                "from b as S\n" +
                "LEFT JOIN LATERAL TABLE(kafkaUDTF(message)) as T(name, age, grade) ON TRUE");
        res1.writeToSink(new PrintTableSink(TimeZone.getDefault()));
        tableEnv.execute();

//打印结果为 task-1> (+)Alice,13,A

3. 依赖

 <dependency>
            <groupId>com.alibaba.blink</groupId>
            <artifactId>flink-core</artifactId>
            <version>1.5.1</version>
            <type>pom</type>
        </dependency>
        <dependency>
            <groupId>com.alibaba.blink</groupId>
            <artifactId>flink-streaming-java_2.11</artifactId>
            <version>1.5.1</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba.blink</groupId>
            <artifactId>flink-streaming-scala_2.11</artifactId>
            <version>1.5.1</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba.blink</groupId>
            <artifactId>flink-table_2.11</artifactId>
            <version>1.5.1</version>
        </dependency>
<dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.9</version>
        </dependency>

4.扩展性

由于blink 的kafka source只支持字节数组，可通过这个UDTF从字节数组解析出想要的字段。