Create a User-Defined Function with Confluent Cloud for Apache Flink

A user-defined function (UDF) extends the capabilities of Confluent Cloud for Apache Flink® and enables you to implement custom logic beyond what is supported by SQL. For example, you can implement functions like encoding and decoding a string, performing geospatial calculations, encrypting and decrypting fields, or reusing an existing library or code from a third-party supplier.

Confluent Cloud for Apache Flink supports UDFs written in Java. Package your custom function and its dependencies into a JAR file and upload it as an artifact to Confluent Cloud. Register the function in a Flink database by using the CREATE FUNCTION statement, and invoke your UDF in Flink SQL or the Table API. Confluent Cloud provides the infrastructure to run your code.

The following steps show how to implement a simple user-defined scalar function, upload it to Confluent Cloud, and use it in a Flink SQL statement.

• Step 1: Build the uber jar
• Step 2: Upload the jar as a Flink artifact
• Step 3: Register the UDF
• Step 4: Use the UDF in a Flink SQL query
• Step 5: Implement UDF logging (optional)
• Step 6: Delete the UDF

After you build and run the scalar function, try building a table function.

For more code examples, see Flink UDF Java Examples.

Prerequisites

You need the following prerequisites to use Confluent Cloud for Apache Flink.

• Access to Confluent Cloud.

• The organization ID, environment ID, and compute pool ID for your organization.

• The OrganizationAdmin, EnvironmentAdmin, or FlinkAdmin role for creating compute pools, or the FlinkDeveloper role if you already have a compute pool. If you don’t have the appropriate role, reach out to your OrganizationAdmin or EnvironmentAdmin.

• The Confluent CLI. To use the Flink SQL shell, update to the latest version of the Confluent CLI by running the following command:

  confluent update --yes
  

  If you used homebrew to install the Confluent CLI, update the CLI by using the brew upgrade command, instead of confluent update.

  For more information, see Confluent CLI.

• A provisioned Flink compute pool in Confluent Cloud.

• Apache Maven software project management tool (see Installing Apache Maven)

• Java 11 to Java 17

• Sufficient permissions to upload and invoke UDFs in Confluent Cloud. For more information, see Flink RBAC.

• If using the Table API only, Flink versions 1.18.x and 1.19.x of flink-table-api-java are supported.

Step 1: Build the uber jar

In this section, you compile a simple Java class, named TShirtSizingIsSmaller into a jar file. The project is based on the ScalarFunction class in the Flink Table API. The TShirtSizingIsSmaller.java class has an eval function that compares two T-shirt sizes and returns the smaller size.

1. Copy the following project object model into a file named pom.xml.

   Important

   You can’t use your own Flink-related jars. If you package Flink core dependencies as part of the jar, you may break the dependency.

   Also, this example shows how to capture all dependencies greedily, possibly including more than needed. As an alternative, you can optimize on artifact size by listing all dependencies and including their transitive dependencies.

   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>example</groupId>
       <artifactId>udf_example</artifactId>
       <version>1.0</version>
   
       <properties>
           <maven.compiler.source>11</maven.compiler.source>
           <maven.compiler.target>11</maven.compiler.target>
           <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
       </properties>
   
       <dependencies>
           <dependency>
               <groupId>org.apache.flink</groupId>
               <artifactId>flink-table-api-java</artifactId>
               <version>1.18.1</version>
               <scope>provided</scope>
           </dependency>
   
           <!-- Dependencies -->
   
       </dependencies>
   
       <build>
           <sourceDirectory>./example</sourceDirectory>
           <plugins>
               <plugin>
                   <groupId>org.apache.maven.plugins</groupId>
                   <artifactId>maven-shade-plugin</artifactId>
                   <version>3.6.0</version>
                   <configuration>
                       <artifactSet>
                           <includes>
                               <!-- Include all UDF dependencies and their transitive dependencies here. -->
                               <!-- This example shows how to capture all of them greedily. -->
                               <include>*:*</include>
                           </includes>
                       </artifactSet>
                       <filters>
                           <filter>
                               <artifact>*</artifact>
                               <excludes>
                                   <!-- Do not copy the signatures in the META-INF folder.
                                   Otherwise, this might cause SecurityExceptions when using the JAR. -->
                                   <exclude>META-INF/*.SF</exclude>
                                   <exclude>META-INF/*.DSA</exclude>
                                   <exclude>META-INF/*.RSA</exclude>
                               </excludes>
                           </filter>
                       </filters>
                   </configuration>
                   <executions>
                       <execution>
                           <phase>package</phase>
                           <goals>
                               <goal>shade</goal>
                           </goals>
                       </execution>
                   </executions>
               </plugin>
           </plugins>
       </build>
   </project>
   

2. Create a directory named “example”.

   mkdir example
   

3. In the example directory, create a file named TShirtSizingIsSmaller.java.

   touch example/TShirtSizingIsSmaller.java
   

4. Copy the following code into TShirtSizingIsSmaller.java.

   package com.example.my;
   
   import org.apache.flink.table.functions.ScalarFunction;
   
   import java.util.Arrays;
   import java.util.List;
   import java.util.stream.IntStream;
   
   /** TShirt sizing function for demo. */
   public class TShirtSizingIsSmaller extends ScalarFunction {
      public static final String NAME = "IS_SMALLER";
   
      private static final List<Size> ORDERED_SIZES =
               Arrays.asList(
                     new Size("X-Small", "XS"),
                     new Size("Small", "S"),
                     new Size("Medium", "M"),
                     new Size("Large", "L"),
                     new Size("X-Large", "XL"),
                     new Size("XX-Large", "XXL"));
   
      public boolean eval(String shirt1, String shirt2) {
         int size1 = findSize(shirt1);
         int size2 = findSize(shirt2);
         // If either can't be found just say false rather than throw an error
         if (size1 == -1 || size2 == -1) {
               return false;
         }
         return size1 < size2;
      }
   
      private int findSize(String shirt) {
         return IntStream.range(0, ORDERED_SIZES.size())
                  .filter(
                           i -> {
                              Size s = ORDERED_SIZES.get(i);
                              return s.name.equalsIgnoreCase(shirt)
                                       || s.abbreviation.equalsIgnoreCase(shirt);
                           })
                  .findFirst()
                  .orElse(-1);
      }
   
      private static class Size {
         private final String name;
         private final String abbreviation;
   
         public Size(String name, String abbreviation) {
               this.name = name;
               this.abbreviation = abbreviation;
         }
      }
   }
   

5. Run the following command to build the jar file.

   mvn clean package
   

6. Run the following command to check the contents of your jar.

   jar -tf target/udf_example-1.0.jar | grep -i TShirtSizingIsSmaller
   

   Your output should resemble:

   com/example/my/TShirtSizingIsSmaller$Size.class
   com/example/my/TShirtSizingIsSmaller.class
   

Step 2: Upload the jar as a Flink artifact

You can use the Confluent Cloud Console, the Confluent CLI, or the REST API to upload your UDF.

Confluent Cloud ConsoleConfluent CLIREST API

1. Log in to Confluent Cloud and navigate to your Flink workspace.
2. Navigate to the environment where you want to run the UDF.
3. Click Flink, in the Flink page, click Artifacts.
4. Click Upload artifact to open the upload pane.
5. In the Cloud provider dropdown, select AWS, and in the Region dropdown, select the cloud region.
6. Click Upload your JAR file and navigate to the location of your JAR file, which in the current example is target/udf_example-1.0.jar.
7. When your JAR file is uploaded, it appears in the Artifacts list. In the list, click the row for your UDF artifact to open the details pane.

Step 3: Register the UDF

UDFs are registered inside a Flink database, which means that you must specify the Confluent Cloud environment (Flink catalog) and Kafka cluster (Flink database) where you want to use the UDF.

You can use the Confluent Cloud Console, the Confluent CLI, the Confluent Terraform provider, or the REST API to register your UDF.

Confluent Cloud ConsoleConfluent CLITerraformREST API

1. In the Flink page, click Compute pools.
2. In the tile for the compute pool where you want to run the UDF, click Open SQL workspace.
3. In the Use catalog dropdown, select the environment where you want to run the UDF.
4. In the Use database dropdown, select Kafka cluster that you want to run the UDF.

• In Cloud Console or the Confluent CLI, run the CREATE FUNCTION statement to register your UDF in the current catalog and database. Substitute your UDF’s values for <artifact-id> and <version-id>.

  CREATE FUNCTION is_smaller
    AS 'com.example.my.TShirtSizingIsSmaller'
    USING JAR 'confluent-artifact://<artifact-id>/<version-id>';
  

  Your output should resemble:

  Function 'is_smaller' created.
  

Step 4: Use the UDF in a Flink SQL query

Once it is registered, your UDF is available to use in queries.

1. Run the following statement to view the UDFs in the current database.

   SHOW USER FUNCTIONS;
   

   Your output should resemble:

   +---------------+
   | function name |
   +---------------+
   | is_smaller    |
   +---------------+
   

2. Run the following statement to create a sizes table.

   CREATE TABLE sizes (
     `size_1` STRING,
     `size_2` STRING
   );
   

3. Run the following statement to populate the sizes table with values.

   INSERT INTO sizes VALUES
     ('XL', 'L'),
     ('small', 'L'),
     ('M', 'L'),
     ('XXL', 'XL');
   

4. Run the following statement to view the rows in the sizes table.

   SELECT * FROM sizes;
   

   Your output should resemble:

   size_1 size_2
   XL     L
   small  L
   M      L
   XXL    XL
   

5. Run the following statement to execute the is_smaller function on the data in the sizes table.

   SELECT size_1, size_2, IS_SMALLER (size_1, size_2)
     AS is_smaller
     FROM sizes;
   

   Your output should resemble:

   size_1 size_2 is_smaller
   XL     L      FALSE
   small  L      TRUE
   M      L      TRUE
   XXL    XL     FALSE
   

Step 5: Implement UDF logging (optional)

If you want to log UDF status messages to a Kafka topic, follow the steps in Enable UDF Logging.

Step 6: Delete the UDF

When you’re finished using the UDF, you can delete it from the current database.

You can use the Confluent Cloud Console, the Confluent CLI, the Confluent Terraform provider, or the REST API to delete your UDF.

Drop the function

1. Run the following statement to remove the is_smaller function from the current database.

   DROP FUNCTION is_smaller;
   

   Your output should resemble:

   Function 'is_smaller' dropped.
   

   Currently running statements are not affected and continue running.

2. Exit the Flink shell.

   exit;
   

Delete the JAR artifact

Confluent Cloud ConsoleConfluent CLITerraformREST API

1. Navigate to the environment where your UDF is registered.
2. Click Flink, and in the Flink page, click Artifacts.
3. In the artifacts list, find the UDF you want to delete.
4. In the Actions column, click the icon, and in the context menu, select Delete artifact.
5. In the confirmation dialog, type “udf_example”, and click Confirm. The “Artifact deleted successfully” message appears.

Implement a user-defined table function

In the previous steps, you implemented a UDF with a simple scalar function. Confluent Cloud for Apache Flink also supports user-defined table functions (UDTFs), which take multiple scalar values as input arguments and return multiple rows as output, instead of a single value.

The following steps show how to implement a simple UDTF, upload it to Confluent Cloud, and use it in a Flink SQL statement.

• Step 1: Build the uber jar
• Step 2: Upload the UDTF jar as a Flink artifact
• Step 3: Register the UDTF
• Step 4: Use the UDTF in a Flink SQL query

Step 1: Build the uber jar

In this section, you compile a simple Java class, named SplitFunction into a jar file, similar to the previous section. The class is based on the TableFunction class in the Flink Table API. The SplitFunction.java class has an eval function that uses the Java split method to break up a string into words and returns the words as columns in a row.

1. In the example directory, create a file named SplitFunction.java.

   touch example/SplitFunction.java
   

2. Copy the following code into SplitFunction.java.

   package com.example.my;
   
   import org.apache.flink.table.annotation.DataTypeHint;
   import org.apache.flink.table.annotation.FunctionHint;
   import org.apache.flink.table.api.*;
   import org.apache.flink.table.functions.TableFunction;
   import org.apache.flink.types.Row;
   import static org.apache.flink.table.api.Expressions.*;
   
   @FunctionHint(output = @DataTypeHint("ROW<word STRING>"))
   public class SplitFunction extends TableFunction<Row> {
   
      public void eval(String str, String delimiter) {
         for (String s : str.split(delimiter)) {
            // use collect(...) to emit a row
            collect(Row.of(s));
         }
      }
   }
   

3. Run the following command to build the jar file. You can use the POM file from the previous section.

   mvn clean package
   

4. Run the following command to check the contents of your jar.

   jar -tf target/udf_example-1.0.jar | grep -i SplitFunction
   

   Your output should resemble:

   com/example/my/SplitFunction.class
   

Step 2: Upload the UDTF jar as a Flink artifact

Confluent Cloud ConsoleConfluent CLI

1. Log in to Confluent Cloud and navigate to your Flink workspace.
2. Navigate to the environment where you want to run the UDF.
3. Click Flink, in the Flink page, click Artifacts.
4. Click Upload artifact to open the upload pane.
5. In the Cloud provider dropdown, select AWS, and in the Region dropdown, select the cloud region.
6. Click Upload your JAR file and navigate to the location of your JAR file, which in the current example is target/udf_example-1.0.jar.
7. When your JAR file is uploaded, it appears in the Artifacts list. In the list, click the row for your UDF artifact to open the details pane.

Step 3: Register the UDTF

1. In the Flink shell or the Cloud Console, specify the catalog and database (environment and cluster) where you want to use the UDTF, as you did in the previous section.

2. Run the CREATE FUNCTION statement to register your UDTF in the current catalog and database. Substitute your UDTF’s values for <artifact-id> and <version-id>.

   CREATE FUNCTION split_string
     AS 'com.example.my.SplitFunction'
     USING JAR 'confluent-artifact://<artifact-id>/<version-id>';
   

   Your output should resemble:

   Function 'split_string' created.
   

Step 4: Use the UDTF in a Flink SQL query

Once it is registered, your UDTF is available to use in queries.

1. Run the following statement to view the UDFs in the current database.

   SHOW USER FUNCTIONS;
   

   Your output should resemble:

   +---------------+
   | Function Name |
   +---------------+
   | split_string  |
   +---------------+
   

2. Run the following statement to execute the split_string function.

   SELECT * FROM (VALUES 'A;B', 'C;D;E;F') as T(f), LATERAL TABLE(split_string(f, ';'))
   

   Your output should resemble:

   f        word
   A;B      A
   A;B      B
   C;D;E;F  C
   C;D;E;F  D
   C;D;E;F  E
   C;D;E;F  F
   

3. When you’re done with the example UDTF, drop the function and delete the JAR artifact as you did in Step 6: Delete the UDF.

Related content

• Enable UDF Logging
• confluent flink artifact create
• CREATE FUNCTION Statement
• Artifacts endpoints
• Flink UDF Java Examples

Note

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