org.apache.flink.table.api.TableException: Only the first field can reference an atomic type.

异常

Exception in thread "main" org.apache.flink.table.api.TableException: Only the first field can reference an atomic type.
    at org.apache.flink.table.api.TableEnvironment.$anonfun$getFieldInfo$7(TableEnvironment.scala:1117)
    at scala.collection.TraversableLike.$anonfun$flatMap$1(TraversableLike.scala:240)
    at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:32)
    at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:29)
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:194)
    at scala.collection.TraversableLike.flatMap(TraversableLike.scala:240)
    at scala.collection.TraversableLike.flatMap$(TraversableLike.scala:237)
    at scala.collection.mutable.ArrayOps$ofRef.flatMap(ArrayOps.scala:194)
    at org.apache.flink.table.api.TableEnvironment.getFieldInfo(TableEnvironment.scala:1112)
    at org.apache.flink.table.api.BatchTableEnvironment.registerDataSetInternal(BatchTableEnvironment.scala:423)
    at org.apache.flink.table.api.java.BatchTableEnvironment.registerDataSet(BatchTableEnvironment.scala:129)
    at com.tt.study.sql.WordCountSql.main(WordCountSql.java:33)

maven依赖

	<properties>
        <flink.version>1.7.2</flink.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-java</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-table_2.12</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-scala_2.12</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-streaming-scala_2.12</artifactId>
            <version>${flink.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-streaming-java_2.12</artifactId>
            <version>${flink.version}</version>
        </dependency>
    </dependencies>

flink sql实例

import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.table.api.Table;
import org.apache.flink.table.api.TableEnvironment;
import org.apache.flink.table.api.java.BatchTableEnvironment;
import java.util.ArrayList;
import java.util.List;

public class WordCountSql {
    public static void main(String[] args) throws Exception {
        ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
        BatchTableEnvironment tEnv = TableEnvironment.getTableEnvironment(env);

        List<WC> list = new ArrayList<>();
        String wordsStr = "Hello Flink Hello immoc";
        String[] words = wordsStr.split("\\W+");
        for (String word : words){
            WC wc = new WC(word, 1);
            list.add(wc);
        }

        DataSet<WC> input = env.fromCollection(list);
        tEnv.registerDataSet("WordCount", input,"word, frequency");
        Table table = tEnv.sqlQuery("select word, sum(frequency) as frequency from WordCount group by word");

        DataSet<WC> result = tEnv.toDataSet(table, WC.class);
        result.print();
    }
    
    public static class WC {
        String word;
        long frequency;

        public WC() {
        }

        public WC(String word, long count) {
            this.word = word;
            this.frequency = count;
        }

        @Override
        public String toString() {
            return "WC{" +
                    "word='" + word + '\'' +
                    ", frequency=" + frequency +
                    '}';
        }
    }
}

方案

参考网上方案加了依赖、和Bean的无参构造方法后异常仍然存在。于是查看官方的样例 ，仔细对比代码实现。发现样例的静态类属性是public，于是在WC类中生成get、set方法，或者用lombok包的@Data后，异常得以解决。

SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
WC{word='Hello', frequency=2}
WC{word='immoc', frequency=1}
WC{word='Flink', frequency=1}
Disconnected from the target VM, address: '127.0.0.1:58738', transport: 'socket'

Process finished with exit code 0