/*
 * Copyright 2002-2018 the original author or authors.
 *
 * 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 org.springframework.expression.spel.ast;

import org.springframework.asm.Label;
import org.springframework.asm.MethodVisitor;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.TypedValue;
import org.springframework.expression.spel.CodeFlow;
import org.springframework.expression.spel.ExpressionState;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

Represents the elvis operator ?:. For an expression "a?:b" if a is not null, the value of the expression is "a", if a is null then the value of the expression is "b".
Author:Andy Clement, Juergen Hoeller
Since:3.0
/** * Represents the elvis operator ?:. For an expression "a?:b" if a is not null, the value * of the expression is "a", if a is null then the value of the expression is "b". * * @author Andy Clement * @author Juergen Hoeller * @since 3.0 */
public class Elvis extends SpelNodeImpl { public Elvis(int pos, SpelNodeImpl... args) { super(pos, args); }
Evaluate the condition and if not null, return it. If it is null, return the other value.
Params:
  • state – the expression state
Throws:
  • EvaluationException – if the condition does not evaluate correctly to a boolean or there is a problem executing the chosen alternative
/** * Evaluate the condition and if not null, return it. * If it is null, return the other value. * @param state the expression state * @throws EvaluationException if the condition does not evaluate correctly * to a boolean or there is a problem executing the chosen alternative */
@Override public TypedValue getValueInternal(ExpressionState state) throws EvaluationException { TypedValue value = this.children[0].getValueInternal(state); // If this check is changed, the generateCode method will need changing too if (!StringUtils.isEmpty(value.getValue())) { return value; } else { TypedValue result = this.children[1].getValueInternal(state); computeExitTypeDescriptor(); return result; } } @Override public String toStringAST() { return getChild(0).toStringAST() + " ?: " + getChild(1).toStringAST(); } @Override public boolean isCompilable() { SpelNodeImpl condition = this.children[0]; SpelNodeImpl ifNullValue = this.children[1]; return (condition.isCompilable() && ifNullValue.isCompilable() && condition.exitTypeDescriptor != null && ifNullValue.exitTypeDescriptor != null); } @Override public void generateCode(MethodVisitor mv, CodeFlow cf) { // exit type descriptor can be null if both components are literal expressions computeExitTypeDescriptor(); cf.enterCompilationScope(); this.children[0].generateCode(mv, cf); String lastDesc = cf.lastDescriptor(); Assert.state(lastDesc != null, "No last descriptor"); CodeFlow.insertBoxIfNecessary(mv, lastDesc.charAt(0)); cf.exitCompilationScope(); Label elseTarget = new Label(); Label endOfIf = new Label(); mv.visitInsn(DUP); mv.visitJumpInsn(IFNULL, elseTarget); // Also check if empty string, as per the code in the interpreted version mv.visitInsn(DUP); mv.visitLdcInsn(""); mv.visitInsn(SWAP); mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "equals", "(Ljava/lang/Object;)Z",false); mv.visitJumpInsn(IFEQ, endOfIf); // if not empty, drop through to elseTarget mv.visitLabel(elseTarget); mv.visitInsn(POP); cf.enterCompilationScope(); this.children[1].generateCode(mv, cf); if (!CodeFlow.isPrimitive(this.exitTypeDescriptor)) { lastDesc = cf.lastDescriptor(); Assert.state(lastDesc != null, "No last descriptor"); CodeFlow.insertBoxIfNecessary(mv, lastDesc.charAt(0)); } cf.exitCompilationScope(); mv.visitLabel(endOfIf); cf.pushDescriptor(this.exitTypeDescriptor); } private void computeExitTypeDescriptor() { if (this.exitTypeDescriptor == null && this.children[0].exitTypeDescriptor != null && this.children[1].exitTypeDescriptor != null) { String conditionDescriptor = this.children[0].exitTypeDescriptor; String ifNullValueDescriptor = this.children[1].exitTypeDescriptor; if (ObjectUtils.nullSafeEquals(conditionDescriptor, ifNullValueDescriptor)) { this.exitTypeDescriptor = conditionDescriptor; } else { // Use the easiest to compute common super type this.exitTypeDescriptor = "Ljava/lang/Object"; } } } }