GennericUDF的实现例子
时间: 2023-08-12 16:27:03 浏览: 38
以下是一个计算两个数相加的GennericUDF的实现例子:
```java
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.exec.UDFReturnType;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.io.IntWritable;
public class AddUDF extends GenericUDF {
private IntWritable result = new IntWritable();
@Override
public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
// 检查参数数量是否正确
if (arguments.length != 2) {
throw new UDFArgumentLengthException("AddUDF takes exactly two arguments");
}
// 检查参数类型是否正确
if (!arguments[0].getTypeName().equals("int") || !arguments[1].getTypeName().equals("int")) {
throw new UDFArgumentTypeException(0, "AddUDF takes two integer arguments");
}
// 定义函数返回类型为int
return PrimitiveObjectInspectorFactory.writableIntObjectInspector;
}
@Override
public Object evaluate(DeferredObject[] arguments) throws HiveException {
// 获取两个参数的值
int a = (int) arguments[0].get();
int b = (int) arguments[1].get();
// 计算结果
result.set(a + b);
return result;
}
@Override
public String getDisplayString(String[] children) {
return "AddUDF(" + children[0] + ", " + children[1] + ")";
}
@Override
public UDFReturnType getReturnType() {
// 定义函数返回类型为int
return UDFReturnType.INT;
}
}
```
这个例子中,我们定义了一个名为AddUDF的GennericUDF,它接收两个int类型的参数,并返回它们的和。在initialize()方法中,我们检查了参数数量和类型是否正确,并定义了函数的返回类型为int。在evaluate()方法中,我们获取了两个参数的值并计算它们的和,最后将结果封装到IntWritable对象中并返回。在getDisplayString()方法中,我们定义了函数在Hive中的显示名称。
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