/*
* Copyright 2002-2014 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.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
* @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.
* @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 (!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();
this.children[0].generateCode(mv, cf);
Label elseTarget = new Label();
Label endOfIf = new Label();
mv.visitInsn(DUP);
mv.visitJumpInsn(IFNULL, elseTarget);
mv.visitJumpInsn(GOTO, endOfIf);
mv.visitLabel(elseTarget);
mv.visitInsn(POP);
this.children[1].generateCode(mv, cf);
if (!CodeFlow.isPrimitive(this.exitTypeDescriptor)) {
CodeFlow.insertBoxIfNecessary(mv, cf.lastDescriptor().charAt(0));
}
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 (conditionDescriptor.equals(ifNullValueDescriptor)) {
this.exitTypeDescriptor = conditionDescriptor;
}
else if (conditionDescriptor.equals("Ljava/lang/Object") && !CodeFlow.isPrimitive(ifNullValueDescriptor)) {
this.exitTypeDescriptor = ifNullValueDescriptor;
}
else if (ifNullValueDescriptor.equals("Ljava/lang/Object") && !CodeFlow.isPrimitive(conditionDescriptor)) {
this.exitTypeDescriptor = conditionDescriptor;
}
else {
// Use the easiest to compute common super type
this.exitTypeDescriptor = "Ljava/lang/Object";
}
}
}
}