自定义udf函数（一进一出）

1. 添加maven依赖

一、pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
 
    <groupId>org.example</groupId>
    <artifactId>hive_function</artifactId>
    <version>1.0-SNAPSHOT</version>
 
    <dependencies>
        <dependency>
            <groupId>org.apache.hive</groupId>
            <artifactId>hive-exec</artifactId>
            <version>2.3.8</version>
            <!--排除依赖中的某个jar包-->
            <exclusions>
                <exclusion>
                    <groupId>org.pentaho</groupId>
                    <artifactId>pentaho-aggdesigner-algorithm</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>
</project>

二、自定义一个length()函数

package udf;
 
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.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.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorUtils;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.StringObjectInspector;
 
/**
 * 要求：自定义一个length()函数
 * 1. 继承GenericUDF类，
 * 2. 重写两个核心方法
 */
public class MyLength extends GenericUDF {
    /**
     * 初始化方法
     * @param arguments 是输入参数的类型检查器数组
     * @return 返回类型检查器
     * @throws UDFArgumentException
     */
    public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
        // 1. 长度是否合法
        if (arguments.length != 1) {
            throw new UDFArgumentLengthException("there can be at most one parameter");
        }
 
        // 2. 检查参数类型是否合法
        ObjectInspector inspector = arguments[0];
        if (!(inspector instanceof StringObjectInspector)) {
            throw new UDFArgumentTypeException(0, "paramter type is not string");
        }
 
        // 3. 返回一个函数执行完成的类型检查器 int类型的检查器
        return PrimitiveObjectInspectorFactory.javaIntObjectInspector;
    }
 
    /**
     * 函数的执行逻辑
     * @param arguments
     * @return
     * @throws HiveException
     */
    public Object evaluate(DeferredObject[] arguments) throws HiveException {
        DeferredObject argument = arguments[0];
        Object value = argument.get();
        String str = value.toString();
        return str.length();
    }
 
    public String getDisplayString(String[] strings) {
        return null;
    }
}

三、打jar包

四、创建临时函数

hive (test)> create temporary function mylength as "udf.MyLength" using jar "hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar";
Added [/tmp/ce2bebf9-ddf7-443f-badd-2d4f147960bf_resources/hive_function-1.0-SNAPSHOT.jar] to class path
Added resources: [hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar]
OK
Time taken: 0.995 seconds
 
 
hive (test)> show functions;
OK
tab_name
 
 
hive (test)> desc function extended mylength;
OK
tab_name
There is no documentation for function 'mylength'
Function class:udf.MyLength
Function type:TEMPORARY
Resource:hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar
Time taken: 0.008 seconds, Fetched: 4 row(s)
 
 
hive (test)> show create table page_ad;
OK
createtab_stmt
CREATE TABLE `page_ad`(
  `page` string, 
  `aids` string)
ROW FORMAT SERDE 
  'org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe' 
WITH SERDEPROPERTIES ( 
  'field.delim'=',', 
  'line.delim'='\n', 
  'serialization.format'=',') 
STORED AS INPUTFORMAT 
  'org.apache.hadoop.mapred.TextInputFormat' 
OUTPUTFORMAT 
  'org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat'
LOCATION
  'hdfs://node1:9000/user/hive/warehouse/test.db/page_ad'
TBLPROPERTIES (
  'transient_lastDdlTime'='1659523482')
Time taken: 0.108 seconds, Fetched: 17 row(s)
 
 
hive (test)> select mylength(aids) from page_ad;
OK
_c0
13
16
19
Time taken: 0.38 seconds, Fetched: 3 row(s)

五、创建永久函数

hive (default)> create function mylength as "udf.MyLength" using jar "hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar";
Added [/tmp/ac2a0a66-3121-4e8e-8faf-039a09419d7c_resources/hive_function-1.0-SNAPSHOT.jar] to class path
Added resources: [hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar]
OK
Time taken: 0.396 seconds

注意

1. 临时函数：只有当前连接会话可以使用，重建一个hive的连接会话，临时函数失效
2. 永久函数：不管连接多少次，函数都可以使用，临时函数可以使用show functions查询，永久函数无法使用改命令查询
   但是可以在hive的元数据库的FUNCS表中找到我们自己新建的永久函数
3. 临时函数和永久函数都是和数据库挂钩的，如果在别的数据库中使用这个自定义函数，必须带上数据库的名字

# 在default数据库中创建的永久函数
hive (default)> create function mylength as "udf.MyLength" using jar "hdfs://node1:9000/hive_function-1.0-SNAPSHOT.jar";
 
 
hive (default)> select mylength(name) from student_partition;
OK
_c0
Time taken: 1.421 seconds
 
 
hive (default)> use test;
OK
Time taken: 0.02 seconds
 
 
hive (test)> select mylength(aids) from page_ad;
FAILED: SemanticException [Error 10011]: Invalid function mylength
 
 
# 必须带上数据库的名字
hive (test)> select default.mylength(aids) from page_ad;
OK
_c0
13
16
19
Time taken: 0.154 seconds, Fetched: 3 row(s)