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ExpressionEvaluatorEngine.java
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ExpressionEvaluatorEngine.java
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package com.expression.evaluator.engine;
import com.expression.evaluator.api.EvaluatorExpressionException;
import com.expression.evaluator.entity.User;
import com.expression.evaluator.operator.Operator;
import com.expression.evaluator.operator.OperatorFactory;
import com.expression.evaluator.operator.OperatorNames;
import com.expression.evaluator.tree.Node;
import com.expression.evaluator.tree.Operand;
import org.apache.log4j.Logger;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Objects;
/**
* @author rohitkumar
* creation date 22/07/18
* project name expression-evaluator
*/
public abstract class ExpressionEvaluatorEngine {
private static final Logger LOGGER = Logger.getLogger(ExpressionEvaluatorEngine.class);
/**
* @implNote This util method evaluates the expression on the given Entity.
* Format - [ OPERATOR, OPERAND, COMPARISON_VALUE(S) ]
* ["AND", ["EQ", "user.address.city", "Los Angeles"], ["GT", "user.age", 35]]
* @param user
* @param expression
* @return true or false
*/
public static boolean evaluateExpression(User user, ArrayList<Object> expression) throws EvaluatorExpressionException {
LOGGER.debug("Evaluating expression :: "+expression+" on User :: "+user);
/**
* Build Expression tree using the expression.
*/
Node root = buildTree(user, expression);
/**
* Evaluate the expression tree.
*/
Object result = evaluateExpressionTree(root);
return (Boolean) result;
}
/**
* @implNote Evaluate expression tree using Post order traversal.
* @param root
* @return true or false
*/
private static Object evaluateExpressionTree(Node root) {
if (root != null) {
/**
* leaf node will contains the operand and substitution values..
*/
if (root.getLeft() == null && root.getRight() == null) {
return root.getOperand();
}
/**
* Evaluate left subtree.
*/
Object left = evaluateExpressionTree(root.getLeft());
/**
* Evaluate right subtree.
*/
Object right = evaluateExpressionTree(root.getRight());
/**
* Since All non leaf nodes are Operator, Now evaluate the operator.
*/
if (left instanceof Operand && right instanceof Operand) {
return root.getOperator().execute(((Operand)left).getValue(), ((Operand)right).getValue());
} else if (left instanceof Operand && !(right instanceof Operand)) {
/**
* expression - ["AND", ["EQ", "user.address.city", "Los Angeles"], false]
*/
return root.getOperator().execute(((Operand)left).getValue(), right);
} else if (!(left instanceof Operand) && (right instanceof Operand)) {
/**
* expression - ["AND", ["EQ", "user.address.city", "Los Angeles"], false]
*/
return root.getOperator().execute(left, ((Operand)right).getValue());
} else {
return root.getOperator().execute(left, right);
}
}
return false;
}
/**
* @implNote Build Binary Tree of {@link com.expression.evaluator.operator.Operator} and {@link com.expression.evaluator.tree.Operand} using Pre order Traversal.
* Format - [ OPERATOR, OPERAND, COMPARISON_VALUE(S) ]
* ["AND", ["EQ", "user.address.city", "Los Angeles"], ["GT", "user.age", 35]]
* ["OR", ["IN", "event.category", ["infant", "child", "teen"]], ["LT", "user.age", 18]]
* @param user
* @param expression
* @return root node of the tree.
*/
private static Node buildTree(User user, ArrayList<Object> expression) throws EvaluatorExpressionException {
Node root = null;
if (expression != null) {
/**
* Check whether its operator or not
*/
Object value = expression.get(0);
if (OperatorNames.isOperator(value.toString())) {
Operator operator = OperatorFactory.getOperator(value.toString());
if (Objects.isNull(operator)) {
throw new EvaluatorExpressionException("Invalid Operator Name,"+value.toString());
}
root = new Node(operator);
}
if ( (expression.get(1) instanceof ArrayList) && isExpression((ArrayList<Object>) expression.get(1))) {
/**
* sub-expression, recursive call
*/
root.setLeft(buildTree(user, (ArrayList<Object>) expression.get(1)));
} else {
/**
* "user.address.city" , "event.category"
*/
Operand operand = buildOperandFromExpression(user, expression.get(1));
Node leftNode = new Node(operand);
root.setLeft(leftNode);
}
if ( (expression.get(2) instanceof ArrayList) && isExpression((ArrayList<Object>) expression.get(2))) {
/**
* sub-expression, recursive call
*/
root.setRight(buildTree(user, (ArrayList<Object>) expression.get(2)));
} else {
/**
* Substitution-Values
*/
Node rightNode = new Node(new Operand(expression.get(2)));
root.setRight(rightNode);
}
}
return root;
}
/**
* @implNote Build operand from given expression using the {@link User}
* @param user
* @param expression
* @return Operand
*/
private static Operand buildOperandFromExpression(User user, Object expression) throws EvaluatorExpressionException {
if ( !(expression instanceof String)) {
throw new EvaluatorExpressionException("Invalid Operand Name,"+expression.toString());
}
String [] values = ((String) expression).split("\\.");
Object operandValue = user;
String userClassName = User.class.getSimpleName().toLowerCase();
boolean classNameFound = false;
for (String value : values) {
value = value.toLowerCase();
/**
* To handle cases where operand is like - "user.address.city"
*/
if (!classNameFound && userClassName.contains(value)) {
classNameFound = true;
continue;
} else {
for (Method method : operandValue.getClass().getDeclaredMethods()) {
if (method.getName().toLowerCase().contains("get"+value)) {
try {
operandValue = method.invoke(operandValue, null);
break;
} catch (Exception e) {
throw new EvaluatorExpressionException("Invalid Operand Name,"+expression.toString()+e.getLocalizedMessage());
}
}
}
}
}
Operand operand = new Operand(operandValue);
return operand;
}
/**
* @implNote Its must be in FORMAT - [ OPERATOR, OPERAND, COMPARISON_VALUE(S) ]
* @param expression
* @return
*/
public static boolean isExpression(ArrayList<Object> expression) {
int length = expression.size();
if (length != 3) {
return false;
}
Object value1 = expression.get(0);
if (!OperatorNames.isOperator(value1.toString())) {
return false;
}
return true;
}
}