com.streamsets.pipeline.api.el.ELEval Maven / Gradle / Ivy
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/*
* Copyright 2017 StreamSets Inc.
*
* Licensed 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 com.streamsets.pipeline.api.el;
import com.streamsets.pipeline.api.impl.Utils;
/**
* An ELEval instance evaluates Java EL expressions.
*
* In the context of a specific stage configuration, the ELEval uses the EL functions and EL constants
* defined in the configuration.
*
* @see com.streamsets.pipeline.api.Stage.ELContext
*/
public abstract class ELEval {
private static final ThreadLocal VARIABLES_IN_SCOPE_TL = new ThreadLocal<>();
/**
* Returns the stage configuration associated with the ELEval instance.
*
* @return the stage configuration associated with the ELEval instance.
*/
public abstract String getConfigName();
/**
* Returns an empty ELVars instance.
*
* @return an empty ELVars instance.
*/
public abstract ELVars createVariables();
/**
* Evaluates an EL.
*
* IMPORTANT: This is method is used by the implementation. It is not available for stages.
*
* @param vars the variables to be available for the evaluation.
* @param el the EL string to evaluate.
* @param returnType the class the EL evaluates to.
* @return the evaluated EL as an instance of the specified return type.
* @throws ELEvalException if the EL could not be evaluated.
*/
protected abstract T evaluate(ELVars vars, String el, Class returnType) throws ELEvalException;
/**
* Evaluates an EL.
*
* @param vars the variables to be available for the evaluation.
* @param el the EL string to evaluate.
* @param returnType the class the EL evaluates to.
* @return the evaluated EL as an instance of the specified return type.
* @throws ELEvalException if the EL could not be evaluated.
*/
public T eval(ELVars vars, String el, Class returnType) throws ELEvalException {
Utils.checkNotNull(vars, "vars");
Utils.checkNotNull(el, "expression");
Utils.checkNotNull(returnType, "returnType");
VARIABLES_IN_SCOPE_TL.set(vars);
try {
return evaluate(vars, el, returnType);
} finally {
VARIABLES_IN_SCOPE_TL.set(null);
}
}
/**
* Returns the ELVars in scope while an EL is being evaluated.
*
* EL functions should use this method to get hold of the ELVars used to invoke the {@link #eval} method.
* @return the ELVars in scope while an EL is being evaluated.
*/
public static ELVars getVariablesInScope() {
return VARIABLES_IN_SCOPE_TL.get();
}
}