org.apache.flink.table.api.functions.UserDefinedFunction Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
* regarding copyright ownership. The ASF 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.apache.flink.table.api.functions;
import org.apache.flink.table.functions.utils.UserDefinedFunctionUtils;
import org.apache.commons.codec.digest.DigestUtils;
import java.io.Serializable;
/**
* Base class for all user-defined functions such as scalar functions, table functions,
* or aggregation functions.
*/
public abstract class UserDefinedFunction implements Serializable {
/**
* Setup method for user-defined function. It can be used for initialization work.
*
* By default, this method does nothing.
*/
public void open(FunctionContext context) throws Exception {
}
/**
* Tear-down method for user-defined function. It can be used for clean up work.
*
*
By default, this method does nothing.
*/
public void close() throws Exception {
}
/**
* @return true if a call to this function is guaranteed to always return
* the same result given the same parameters; true is assumed by default
* if user's function is not pure functional, like random(), date(), now()...
* isDeterministic must return false
*/
public boolean isDeterministic() {
return true;
}
public final String functionIdentifier() throws Exception {
String md5 = DigestUtils.md5Hex(UserDefinedFunctionUtils.serialize(this));
return getClass().getCanonicalName().replace('.', '$').concat("$").concat(md5);
}
/**
* User can use this function to name function for visualization and logging.
*/
public String toString() {
return getClass().getSimpleName();
}
}