hive udtf 怎么写
时间: 2023-08-02 14:13:22 浏览: 89
Hive UDTF(User-Defined Table-Generating Function)是一种自定义函数,可以用于生成表格数据。下面是编写Hive UDTF的基本步骤:
1. 继承Hive UDTF类(org.apache.hadoop.hive.ql.udtf.generic.GenericUDTF)。
2. 实现一个或多个方法,例如initialize()、process()和close()。
3. 在process()方法中生成输出数据并使用forward()方法将其发送到Hive中。
4. 定义输入参数和输出列的元数据。可以使用@UDFType、@UDF和@Description注解来指定元数据。
5. 将UDTF打包成JAR文件并将其添加到Hive的CLASSPATH中。
6. 在Hive中创建函数并使用它。
下面是一个示例UDTF,它将输入字符串拆分为单词并将每个单词输出为一行:
```
import org.apache.hadoop.hive.ql.udtf.generic.GenericUDTF;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;
import org.apache.hadoop.hive.serde2.objectinspector.StandardListObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import java.util.ArrayList;
public class SplitUDTF extends GenericUDTF {
private final ArrayList<Object[]> output = new ArrayList<>();
@Override
public StructObjectInspector initialize(ObjectInspector[] args) throws UDFArgumentException {
if (args.length != 1) {
throw new UDFArgumentException("SplitUDTF takes exactly one argument");
}
if (args[0].getCategory() != ObjectInspector.Category.PRIMITIVE
|| !args[0].getTypeName().equals("string")) {
throw new UDFArgumentException("SplitUDTF takes a string as its argument");
}
final StandardListObjectInspector outputOI = ObjectInspectorFactory.getStandardListObjectInspector(
PrimitiveObjectInspectorFactory.javaStringObjectInspector);
return ObjectInspectorFactory.getStandardStructObjectInspector(
new ArrayList<String>() {{ add("word"); }},
new ArrayList<ObjectInspector>() {{ add(outputOI); }});
}
@Override
public void process(Object[] args) throws HiveException {
final String input = args[0].toString();
final String[] words = input.split("\\s+");
for (final String word: words) {
output.add(new Object[] { word });
}
}
@Override
public void close() throws HiveException {
for (final Object[] row: output) {
forward(row);
}
}
}
```
使用@UDFType、@UDF和@Description注解指定元数据:
```
@UDFType(deterministic = true)
@UDF(
name = "split",
description = "Splits a string into words",
returnType = "array<string>",
extended = "Example: SELECT split('hello world') AS words FROM table")
public class SplitUDTF extends GenericUDTF {
...
}
```
在Hive中创建函数并使用它:
```
ADD JAR /path/to/split-udtf.jar;
CREATE FUNCTION split AS 'SplitUDTF';
SELECT split('hello world') AS words;
```
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