Siddhi Function Extension consumes zero or more parameters for each event and output a single attribute as an output. This could be used to manipulate event attributes to generate new attribute like Function operator.
To implement a custom function extension, create a class extending "org.wso2.siddhi.core.executor.function.FunctionExecutor" and create an appropriate .siddhiext extension mapping file, compile the class, and build the jar containing the .class and .siddhiext files. Add them to the Siddhi class path. In a scenario where they are run on WSO2 DAS add the jar to the <DAS_HOME>/repository/components/dropins directory.
For example, if you have created with namespace "math" and function name "sin" can be referred in the query as follows:
from InValueStream select math:sin(inValue) as sinValue insert into OutMediationStream;
Note
From CEP 3.0.0 onwards, FunctionExecutor is supposed to be used for writing both custom expressions and conditions.
Sample implementation of a custom function extension can be found below;
/*
* Copyright (c) 2015, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
*
* WSO2 Inc. licenses this file to you under the Apache License,
* Version 2.0 (the "License"); you may not use this file except
* in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.wso2.siddhi.extension.math;
import org.wso2.siddhi.core.config.ExecutionPlanContext;
import org.wso2.siddhi.core.exception.ExecutionPlanRuntimeException;
import org.wso2.siddhi.core.executor.ExpressionExecutor;
import org.wso2.siddhi.core.executor.function.FunctionExecutor;
import org.wso2.siddhi.query.api.definition.Attribute;
import org.wso2.siddhi.query.api.exception.ExecutionPlanValidationException;
/*
* sin(a);
* Returns the sine of a (a is in radians).
* Accept Type(s) :DOUBLE/INT/FLOAT/LONG
* Return Type(s): DOUBLE
*/
public class SinFunctionExtension extends FunctionExecutor {
/**
* The initialization method for SinFunctionExtension, this method will be called before the other methods
*
* @param attributeExpressionExecutors the executors of each function parameter
* @param executionPlanContext the context of the execution plan
*/
@Override
protected void init(ExpressionExecutor[] attributeExpressionExecutors, ExecutionPlanContext executionPlanContext) {
if (attributeExpressionExecutors.length != 1) {
throw new ExecutionPlanValidationException("Invalid no of arguments passed to math:sin() function, " +
"required 1, but found " + attributeExpressionExecutors.length);
}
Attribute.Type attributeType = attributeExpressionExecutors[0].getReturnType();
if (!((attributeType == Attribute.Type.DOUBLE)
|| (attributeType == Attribute.Type.INT)
|| (attributeType == Attribute.Type.FLOAT)
|| (attributeType == Attribute.Type.LONG))) {
throw new ExecutionPlanValidationException("Invalid parameter type found for the argument of math:sin() function, " +
"required " + Attribute.Type.INT + " or " + Attribute.Type.LONG +
" or " + Attribute.Type.FLOAT + " or " + Attribute.Type.DOUBLE +
", but found " + attributeType.toString());
}
}
/**
* The main execution method which will be called upon event arrival
* when there are more than one function parameter
*
* @param data the runtime values of function parameters
* @return the function result
*/
@Override
protected Object execute(Object[] data) {
return null;
}
/**
* The main execution method which will be called upon event arrival
* when there are zero or one function parameter
*
* @param data null if the function parameter count is zero or
* runtime data value of the function parameter
* @return the function result
*/
@Override
protected Object execute(Object data) {
if (data != null) {
//type-conversion
if (data instanceof Integer) {
int inputInt = (Integer) data;
return Math.sin((double) inputInt);
} else if (data instanceof Long) {
long inputLong = (Long) data;
return Math.sin((double) inputLong);
} else if (data instanceof Float) {
float inputFloat = (Float) data;
return Math.sin((double) inputFloat);
} else if (data instanceof Double) {
return Math.sin((Double) data);
}
} else {
throw new ExecutionPlanRuntimeException("Input to the math:sin() function cannot be null");
}
return null;
}
/**
* This will be called only once and this can be used to acquire
* required resources for the processing element.
* This will be called after initializing the system and before
* starting to process the events.
*/
@Override
public void start() {
//Implement start logic to acquire relevant resources
}
/**
* This will be called only once and this can be used to release
* the acquired resources for processing.
* This will be called before shutting down the system.
*/
@Override
public void stop() {
//Implement stop logic to release the acquired resources
}
@Override
public Attribute.Type getReturnType() {
return Attribute.Type.DOUBLE;
}
/**
* Used to collect the serializable state of the processing element, that need to be
* persisted for the reconstructing the element to the same state on a different point of time
*
* @return stateful objects of the processing element as an array
*/
@Override
public Object[] currentState() {
return null;
}
/**
* Used to restore serialized state of the processing element, for reconstructing
* the element to the same state as if was on a previous point of time.
*
* @param state the stateful objects of the element as an array on
* the same order provided by currentState().
*/
@Override
public void restoreState(Object[] state) {
//Implement restore state logic.
}
}
Sample math.siddhiext extension mapping file for the custom function extension can be found below;
# # Copyright (c) 2015, WSO2 Inc. (http://www.wso2.org) All Rights Reserved. # # WSO2 Inc. licenses this file to you under the Apache License, # Version 2.0 (the "License"); you may not use this file except # in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, # software distributed under the License is distributed on an # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY # KIND, either express or implied. See the License for the # specific language governing permissions and limitations # under the License. # sin=org.wso2.siddhi.extension.math.SinFunctionExtension