/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* 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.falcon.designer.primitive;
import org.apache.commons.lang.NotImplementedException;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.net.URI;
import java.util.Map;
/**
* Actions are components of flows. They encapsulate an atomic
* execution unit in a flow. If an action is dependent on another
* action, then the action wont be started unless the preceding
* action is entirely complete.
*
* Few examples of Actions are
* 1. SSH Action, which executes a shell command on a remote host
* 2. Data Transform Action, which executes a collection of data transformation
* as a single logical unit
*
* There are no restrictions imposed on an Action with respect to the input
* or the output such as in a Transformation.
*/
public abstract class Action extends Primitive {
protected final String type;
protected Action(@Nonnull String type) {
this.type = type;
}
@Nonnull
public String getType() {
return type;
}
/**
* Indicates whether this action has any output or not. If this function
* returns true, then {@link Action#outputKeys()} and {@link Action#outputFile()} ()}
* needs to be implemented by the concrete class.
*
* @return - True if the action has output that any downstream control or action
* can consume, false otherwise.
*/
public abstract boolean hasOutput();
/**
* Are the keys that the action chooses to expose to the external world that
* can either be used to manage the flow control or be used as an input in a subsequent
* action within the context of a flow. Each key that may be output by this
* action would have to declared along with its return type {@link java.sql.Types}.
*
* If an action output key isn't white listed through this with a specific type,
* then default type is assumed {@link java.sql.Types#VARCHAR}. All output keys
* are nullable. If null the flow control can assume default values (which may vary
* depending on the data type. For ex: VARCHAR(""), NUMERIC(0), DATETIME(CURRENTTIME))
*
* @return - Output key name and its corresponding data type. If the output key
* doesn't conform to this data type, the flow may fail at runtime or may safely assume
* default value. The behavior is left to the implementation of the flow compiler
* and scheduler.
*/
@Nullable
public Map<String, Integer> outputKeys() {
if (hasOutput()) {
throw new NotImplementedException(getClass() + "::outputKeys()");
} else {
return null;
}
}
/**
* Returns a file name as URI that can be mapped to generic hadoop file system
* implementation.
*
* @return - Fully qualified file name uri as understood by the hadoop file system.
*/
@Nullable
public URI outputFile() {
if (hasOutput()) {
throw new NotImplementedException(getClass() + "::outputFile()");
} else {
return null;
}
}
}