<groupId>org.example</groupId>
<artifactId>hive-udf</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>

<!-- https://mvnrepository.com/artifact/org.apache.hive/hive-exec -->
<dependency>
 <groupId>org.apache.hive</groupId>
 <artifactId>hive-exec</artifactId>
 <version>3.1.3</version>
 <exclusions>
 <exclusion>
 <groupId>org.pentaho</groupId>
 <artifactId>*</artifactId>
 </exclusion>
 </exclusions>
</dependency>

package org.example;

import org.apache.hadoop.hive.ql.exec.UDF;

public class nvl extends UDF {
 public String evaluate(final String s) {
 if (s == null) { return null; }
 return s + ":HelloWorld";
 }
}

package org.example;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDFUtils;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;

@Description(name = "nvl",
        value = "nvl(value, default_value) - Returns default value if value is null else returns value",
        extended = "Example: SELECT nvl(null, default_value);")
public class MyUDF extends GenericUDF {

    private GenericUDFUtils.ReturnObjectInspectorResolver returnOIResolver;
    private ObjectInspector[] argumentOIs;

    /**
     * Determine the return type based on the parameter types of the function.
     */
    public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        argumentOIs = arguments;
        if(arguments.length != 2) {
            throw new UDFArgumentException("The operator 'NVL' accepts 2 arguments.");
        }
        returnOIResolver = new GenericUDFUtils.ReturnObjectInspectorResolver(true);
        if(!(returnOIResolver.update(arguments[0]) && returnOIResolver.update(arguments[1]))) {
            throw new UDFArgumentTypeException(2, "The 1st and 2nd args of function NLV should have the same type, "
                    + "but they are different: \\""+arguments[0].getTypeName()+"\\" and \\"" + arguments[1].getTypeName() + "\\"");
        }
        return returnOIResolver.get();
    }

    /**
     * Calculate the result. The final result’s data type will be determined based on the return type specified in the initialize method.
     */
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        Object retVal = returnOIResolver.convertIfNecessary(arguments[0].get(), argumentOIs[0]);
        if(retVal == null) {
            retVal = returnOIResolver.convertIfNecessary(arguments[1].get(), argumentOIs[1]);
        }
        return retVal;
    }

    /**
     * Get the string to display in the explain
     */
    public String getDisplayString(String[] children) {
        StringBuilder builder = new StringBuilder();
        builder.append("if ");
        builder.append(children[0]);
        builder.append(" is null ");
        builder.append("returns ");
        builder.append(children[1]);
        return builder.toString();
    }
}

mvn clean package -DskipTests

scp ./target/hive-udf-1.0-SNAPSHOT.jar root@${master_public_ip}:/usr/local/service/hive

su hadoop
hadoop fs -put ./hive-udf-1.0-SNAPSHOT.jar /

hadoop fs -ls /
Found 5 items
drwxr-xr-x - hadoop supergroup 0 2023-08-22 09:20 /data
drwxrwx--- - hadoop supergroup 0 2023-08-22 09:20 /emr
-rw-r--r-- 2 hadoop supergroup 3235 2023-08-22 15:39 /hive-udf-1.0-SNAPSHOT.jar
drwx-wx-wx - hadoop supergroup 0 2023-08-22 09:20 /tmp
drwxr-xr-x - hadoop supergroup 0 2023-08-22 09:20 /user

hive

hive> create function nvl as "org.example.MyUDF" using jar "hdfs:///hive-udf-1.0-SNAPSHOT.jar";

Added [/data/emr/hive/tmp/1b0f12a6-3406-4700-8227-37dec721297b_resources/hive-udf-1.0-SNAPSHOT.jar] to class path
Added resources: [hdfs:///hive-udf-1.0-SNAPSHOT.jar]
OK
Time taken: 1.549 seconds

hive> select nvl("tur", "def");
OK
tur
Time taken:0.344 seconds, Fetched:1 row(s)
hive> select nvl(null, "def");
OK
def
Time taken:0.471 seconds, Fetched:1 row(s)