Question

这里有类似的问题：How to add a schema to a Dataset in Spark?

然而，我面临的问题是我已经预定义了Dataset<Obj1>，我想定义一个与其数据成员匹配的模式。最终目标是能够在两个java对象之间进行连接。

示例代码：

Dataset<Row> rowDataset = spark.getSpark().sqlContext().createDataFrame(rowRDD, schema).toDF();
Dataset<MyObj> objResult = rowDataset.map((MapFunction<Row, MyObj>) row ->
        new MyObj(
                row.getInt(row.fieldIndex("field1")),
                row.isNullAt(row.fieldIndex("field2")) ? "" : row.getString(row.fieldIndex("field2")),
                row.isNullAt(row.fieldIndex("field3")) ? "" : row.getString(row.fieldIndex("field3")),
                row.isNullAt(row.fieldIndex("field4")) ? "" : row.getString(row.fieldIndex("field4"))
        ), Encoders.javaSerialization(MyObj.class));

如果我打印行数据集的架构，我会按预期获得架构：

rowDataset.printSchema();

root
 |-- field1: integer (nullable = false)
 |-- field2: string (nullable = false)
 |-- field3: string (nullable = false)
 |-- field4: string (nullable = false)

如果我打印对象数据集，我将丢失实际架构

objResult.printSchema();

root
 |-- value: binary (nullable = true)

问题是我如何应用Dataset<MyObj>？

的架构

Answer 1

下面是代码片段，我试过并且火花按预期运行，似乎问题的根本原因是地图功能不是其他东西。

 SparkSession session = SparkSession.builder().config(conf).getOrCreate();
        Dataset<Row> ds = session.read().text("<some path>");
        Encoder<Employee> employeeEncode = Encoders.bean(Employee.class);
        ds.map(new MapFunction<Row, Employee>() {
            @Override
            public Employee call(Row value) throws Exception {
                return new Employee(value.getString(0).split(","));
            }
        }, employeeEncode).printSchema();

<强>输出：

root
 |-- age: integer (nullable = true)
 |-- name: string (nullable = true)

//员工Bean

public class Employee {
    public String name;
    public Integer age;
    public Employee(){

    }
    public Employee(String [] args){
        this.name=args[0];
        this.age=Integer.parseInt(args[1]);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}

将模式应用于Spark对象的java对象数据集

1 个答案: