001/* 002 * Copyright 2002-2019 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.expression.spel.ast; 018 019import org.springframework.asm.Label; 020import org.springframework.asm.MethodVisitor; 021import org.springframework.expression.EvaluationException; 022import org.springframework.expression.TypedValue; 023import org.springframework.expression.spel.CodeFlow; 024import org.springframework.expression.spel.ExpressionState; 025import org.springframework.util.Assert; 026import org.springframework.util.ObjectUtils; 027import org.springframework.util.StringUtils; 028 029/** 030 * Represents the elvis operator ?:. For an expression "a?:b" if a is not null, the value 031 * of the expression is "a", if a is null then the value of the expression is "b". 032 * 033 * @author Andy Clement 034 * @author Juergen Hoeller 035 * @since 3.0 036 */ 037public class Elvis extends SpelNodeImpl { 038 039 public Elvis(int startPos, int endPos, SpelNodeImpl... args) { 040 super(startPos, endPos, args); 041 } 042 043 044 /** 045 * Evaluate the condition and if not null, return it. 046 * If it is null, return the other value. 047 * @param state the expression state 048 * @throws EvaluationException if the condition does not evaluate correctly 049 * to a boolean or there is a problem executing the chosen alternative 050 */ 051 @Override 052 public TypedValue getValueInternal(ExpressionState state) throws EvaluationException { 053 TypedValue value = this.children[0].getValueInternal(state); 054 // If this check is changed, the generateCode method will need changing too 055 if (!StringUtils.isEmpty(value.getValue())) { 056 return value; 057 } 058 else { 059 TypedValue result = this.children[1].getValueInternal(state); 060 computeExitTypeDescriptor(); 061 return result; 062 } 063 } 064 065 @Override 066 public String toStringAST() { 067 return getChild(0).toStringAST() + " ?: " + getChild(1).toStringAST(); 068 } 069 070 @Override 071 public boolean isCompilable() { 072 SpelNodeImpl condition = this.children[0]; 073 SpelNodeImpl ifNullValue = this.children[1]; 074 return (condition.isCompilable() && ifNullValue.isCompilable() && 075 condition.exitTypeDescriptor != null && ifNullValue.exitTypeDescriptor != null); 076 } 077 078 @Override 079 public void generateCode(MethodVisitor mv, CodeFlow cf) { 080 // exit type descriptor can be null if both components are literal expressions 081 computeExitTypeDescriptor(); 082 cf.enterCompilationScope(); 083 this.children[0].generateCode(mv, cf); 084 String lastDesc = cf.lastDescriptor(); 085 Assert.state(lastDesc != null, "No last descriptor"); 086 CodeFlow.insertBoxIfNecessary(mv, lastDesc.charAt(0)); 087 cf.exitCompilationScope(); 088 Label elseTarget = new Label(); 089 Label endOfIf = new Label(); 090 mv.visitInsn(DUP); 091 mv.visitJumpInsn(IFNULL, elseTarget); 092 // Also check if empty string, as per the code in the interpreted version 093 mv.visitInsn(DUP); 094 mv.visitLdcInsn(""); 095 mv.visitInsn(SWAP); 096 mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "equals", "(Ljava/lang/Object;)Z",false); 097 mv.visitJumpInsn(IFEQ, endOfIf); // if not empty, drop through to elseTarget 098 mv.visitLabel(elseTarget); 099 mv.visitInsn(POP); 100 cf.enterCompilationScope(); 101 this.children[1].generateCode(mv, cf); 102 if (!CodeFlow.isPrimitive(this.exitTypeDescriptor)) { 103 lastDesc = cf.lastDescriptor(); 104 Assert.state(lastDesc != null, "No last descriptor"); 105 CodeFlow.insertBoxIfNecessary(mv, lastDesc.charAt(0)); 106 } 107 cf.exitCompilationScope(); 108 mv.visitLabel(endOfIf); 109 cf.pushDescriptor(this.exitTypeDescriptor); 110 } 111 112 private void computeExitTypeDescriptor() { 113 if (this.exitTypeDescriptor == null && this.children[0].exitTypeDescriptor != null && 114 this.children[1].exitTypeDescriptor != null) { 115 String conditionDescriptor = this.children[0].exitTypeDescriptor; 116 String ifNullValueDescriptor = this.children[1].exitTypeDescriptor; 117 if (ObjectUtils.nullSafeEquals(conditionDescriptor, ifNullValueDescriptor)) { 118 this.exitTypeDescriptor = conditionDescriptor; 119 } 120 else { 121 // Use the easiest to compute common super type 122 this.exitTypeDescriptor = "Ljava/lang/Object"; 123 } 124 } 125 } 126 127}