doc(udf): document Java UDF

ci/scripts/build-other.sh

@@ -13,6 +13,6 @@ cd ..
 
 echo "--- Upload Java artifacts"
 cp java/connector-node/assembly/target/risingwave-connector-1.0.0.tar.gz ./risingwave-connector.tar.gz
-cp java/udf/target/risingwave-udf-example.jar ./risingwave-udf-example.jar
+cp java/udf-example/target/risingwave-udf-example.jar ./risingwave-udf-example.jar
 buildkite-agent artifact upload ./risingwave-connector.tar.gz
 buildkite-agent artifact upload ./risingwave-udf-example.jar

e2e_test/udf/udf.slt

@@ -1,7 +1,7 @@
 # Before running this test:
 #   python3 e2e_test/udf/test.py
 # or:
-#   cd src/udf/java && mvn package && java -jar target/risingwave-udf-example.jar
+#   cd java/udf-example && mvn package && java -jar target/risingwave-udf-example.jar
 
 # Create a function.
 statement ok

java/pom.xml

@@ -9,6 +9,7 @@
     <modules>
         <module>proto</module>
         <module>udf</module>
+        <module>udf-example</module>
         <module>java-binding</module>
         <module>common-utils</module>
         <module>java-binding-integration-test</module>

java/udf-example/README.md

@@ -0,0 +1,8 @@
+## RisingWave Java UDF Example
+
+Make sure you have installed Java 11 and Maven 3 or later.
+
+```sh
+mvn package
+java -jar target/risingwave-udf-example.jar
+```

java/udf-example/pom.xml

@@ -0,0 +1,67 @@
+<?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>com.example</groupId>
+  <artifactId>udf-example</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>udf-example</name>
+  <url>http://maven.apache.org</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.risingwave.java</groupId>
+      <artifactId>risingwave-udf</artifactId>
+      <version>0.0.1</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <version>3.0.0-M6</version>
+        <configuration>
+          <argLine>--add-opens=java.base/java.nio=ALL-UNNAMED</argLine>
+        </configuration>
+      </plugin>
+      <!-- generate an executable for examples -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <version>3.4.2</version>
+        <configuration>
+          <archive>
+            <manifest>
+              <mainClass>com.example.UdfExample</mainClass>
+            </manifest>
+          </archive>
+          <descriptorRefs>
+            <descriptorRef>jar-with-dependencies</descriptorRef>
+          </descriptorRefs>
+          <finalName>risingwave-udf-example</finalName>
+          <appendAssemblyId>false</appendAssemblyId>
+        </configuration>
+        <executions>
+          <execution>
+            <id>udf-example</id>
+            <phase>package</phase>
+            <goals>
+              <goal>single</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

java/udf/src/main/java/com/risingwave/functions/example/UdfExample.java → java/udf-example/src/main/java/com/example/UdfExample.java

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package com.risingwave.functions.example;
+package com.example;
 
 import java.io.IOException;
 import java.math.BigDecimal;
@@ -35,7 +35,6 @@ public static void main(String[] args) throws IOException {
             server.addFunction("int_42", new Int42());
             server.addFunction("gcd", new Gcd());
             server.addFunction("gcd3", new Gcd3());
-            server.addFunction("to_string", new ToString());
             server.addFunction("extract_tcp_info", new ExtractTcpInfo());
             server.addFunction("hex_to_dec", new HexToDec());
             server.addFunction("array_access", new ArrayAccess());
@@ -77,12 +76,6 @@ public int eval(int a, int b, int c) {
         }
     }
 
-    public static class ToString implements ScalarFunction {
-        public String eval(String s) {
-            return s;
-        }
-    }
-
     public static class ExtractTcpInfo implements ScalarFunction {
         public static class TcpPacketInfo {
             public String srcAddr;

java/udf/README.md

@@ -1,8 +1,256 @@
-## How to run example
+# RisingWave Java UDF SDK
 
-Make sure you have installed Java 11 and Maven 3 or later.
+This library provides a Java SDK for creating user-defined functions (UDF) in RisingWave.
+
+## Introduction
+
+RisingWave supports user-defined functions implemented as external functions.
+With the RisingWave Java UDF SDK, users can define custom UDFs using Java and start a Java process as a UDF server.
+RisingWave can then remotely access the UDF server to execute the defined functions.
+
+## Installation
+
+To install the RisingWave Java UDF SDK:
+
+```sh
+git clone https://github.com/risingwavelabs/risingwave.git
+cd risingwave/java/udf
+mvn install
+```
+
+## Creating a New Project
+
+> NOTE: You can also start from the [udf-example](../udf-example) project without creating the project from scratch.
+
+To create a new project using the RisingWave Java UDF SDK, follow these steps:
+
+```sh
+mvn archetype:generate -DgroupId=com.example -DartifactId=udf-example -DarchetypeArtifactId=maven-archetype-quickstart -DarchetypeVersion=1.4 -DinteractiveMode=false
+```
+
+Configure your `pom.xml` file as follows:
+
+```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>com.example</groupId>
+    <artifactId>udf-example</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.risingwave.java</groupId>
+            <artifactId>risingwave-udf</artifactId>
+            <version>0.0.1</version>
+        </dependency>
+    </dependencies>
+</project>
+```
+
+The `--add-opens` flag must be added when running unit tests through Maven:
+
+```xml
+<build>
+    <plugins>
+        <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-surefire-plugin</artifactId>
+            <version>3.0.0-M7</version>
+            <configuration>
+                <argLine>--add-opens=java.base/java.nio=ALL-UNNAMED</argLine>
+            </configuration>
+        </plugin>
+    </plugins>
+</build>
+```
+
+## Scalar Functions
+
+A user-defined scalar function maps zero, one, or multiple scalar values to a new scalar value. 
+
+In order to define a scalar function, one has to create a new class that implements the `ScalarFunction`
+interface in `com.risingwave.functions` and implement exactly one evaluation method named `eval(...)`.
+This method must be declared public and non-static.
+
+Any [data type](#data-types) listed in the data types section can be used as a parameter or return type of an evaluation method.
+
+Here's an example of a scalar function that calculates the greatest common divisor (GCD) of two integers:
+
+```java
+import com.risingwave.functions.ScalarFunction;
+
+public class Gcd implements ScalarFunction {
+    public int eval(int a, int b) {
+        while (b != 0) {
+            int temp = b;
+            b = a % b;
+            a = temp;
+        }
+        return a;
+    }
+}
+```
+
+> **NOTE:** Differences with Flink
+> 1. The `ScalarFunction` is an interface instead of an abstract class.
+> 2. Multiple overloaded `eval` methods are not supported.
+> 3. Variable arguments such as `eval(Integer...)` are not supported.
+
+## Table Functions
+
+A user-defined table function maps zero, one, or multiple scalar values to one or multiple
+rows (structured types). 
+
+In order to define a table function, one has to create a new class that implements the `TableFunction`
+interface in `com.risingwave.functions` and implement exactly one evaluation method named `eval(...)`. 
+This method must be declared public and non-static.
+
+The return type must be an `Iterator` of any [data type](#data-types) listed in the data types section.
+Similar to scalar functions, input and output data types are automatically extracted using reflection.
+This includes the generic argument T of the return value for determining an output data type.
+
+Here's an example of a table function that generates a series of integers:
+
+```java
+import com.risingwave.functions.TableFunction;
+
+public class Series implements TableFunction {
+    public Iterator<Integer> eval(int n) {
+        return java.util.stream.IntStream.range(0, n).iterator();
+    }
+}
+```
+
+> **NOTE:** Differences with Flink
+> 1. The `TableFunction` is an interface instead of an abstract class. It has no generic arguments.
+> 2. Instead of calling `collect` to emit a row, the `eval` method returns an `Iterator` of the output rows.
+> 3. Multiple overloaded `eval` methods are not supported.
+> 4. Variable arguments such as `eval(Integer...)` are not supported.
+> 5. In SQL, table functions can be used in the `FROM` clause directly. `JOIN LATERAL TABLE` is not supported.
+
+## UDF Server
+
+To create a UDF server and register functions:
+
+```java
+import com.risingwave.functions.UdfServer;
+
+public class App {
+    public static void main(String[] args) {
+        try (var server = new UdfServer("0.0.0.0", 8815)) {
+            // register functions
+            server.addFunction("gcd", new Gcd());
+            server.addFunction("series", new Series());
+            // start the server
+            server.start();
+            server.awaitTermination();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}
+```
+
+To run the UDF server, execute the following command:
 
 ```sh
-mvn package
-java -jar target/risingwave-udf-example.jar
+_JAVA_OPTIONS="--add-opens=java.base/java.nio=ALL-UNNAMED" mvn exec:java -Dexec.mainClass="com.example.App"
+```
+
+## Creating Functions in RisingWave
+
+```sql
+create function gcd(int, int) returns int
+language java as gcd using link 'http://localhost:8815';
+
+create function series(int) returns table (x int)
+language java as series using link 'http://localhost:8815';
+```
+
+For more detailed information and examples, please refer to the official RisingWave [documentation](https://www.risingwave.dev/docs/current/user-defined-functions/#4-declare-your-functions-in-risingwave).
+
+## Using Functions in RisingWave
+
+Once the user-defined functions are created in RisingWave, you can use them in SQL queries just like any built-in functions. Here are a few examples:
+
+```sql
+select gcd(25, 15);
+
+select * from series(10);
 ```
+
+## Data Types
+
+The RisingWave Java UDF SDK supports the following data types:
+
+| SQL Type  | Java Type          | Notes              |
+| --------- | ------------------ | ------------------ |
+| SMALLINT  | short, Short       |                    |
+| INT       | int, Integer       |                    |
+| BIGINT    | long, Long         |                    |
+| FLOAT     | float, Float       |                    |
+| DOUBLE    | double, Double     |                    |
+| DECIMAL   | BigDecimal         |                    |
+| VARCHAR   | String             |                    |
+| BYTEA     | byte[]             |                    |
+| JSONB     | String             | Use `@DataTypeHint("JSONB") String` as the type. See [example](#jsonb). |
+| JSONB[]   | String[]           | Use `@DataTypeHint("JSONB[]") String[]` as the type. |
+| STRUCT<>  | user-defined class | Define a data class as the type. See [example](#struct-type). |
+| ...others |                    | Not supported yet. |
+
+### JSONB
+
+```java
+import com.google.gson.Gson;
+
+// Returns the i-th element of a JSON array.
+public class JsonbAccess implements ScalarFunction {
+    static Gson gson = new Gson();
+
+    public @DataTypeHint("JSONB") String eval(@DataTypeHint("JSONB") String json, int index) {
+        if (json == null)
+            return null;
+        var array = gson.fromJson(json, Object[].class);
+        if (index >= array.length || index < 0)
+            return null;
+        var obj = array[index];
+        return gson.toJson(obj);
+    }
+}
+```
+
+```sql
+create function jsonb_access(jsonb, int) returns jsonb
+language java as jsonb_access using link 'http://localhost:8815';
+```
+
+### Struct Type
+
+```java
+// Split a socket address into host and port.
+public static class IpPort implements ScalarFunction {
+    public static class SocketAddr {
+        public String host;
+        public short port;
+    }
+
+    public SocketAddr eval(String addr) {
+        var socketAddr = new SocketAddr();
+        var parts = addr.split(":");
+        socketAddr.host = parts[0];
+        socketAddr.port = Short.parseShort(parts[1]);
+        return socketAddr;
+    }
+}
+```
+
+```sql
+create function ip_port(varchar) returns struct<host varchar, port smallint>
+language java as ip_port using link 'http://localhost:8815';
+```
+
+## Full Example
+
+You can checkout [udf-example](../udf-example) and use it as a template to create your own UDFs.