com.alibaba.antx.config.generator.expr.CompositeExpression Maven / Gradle / Ivy
/*
* Copyright (c) 2002-2012 Alibaba Group Holding Limited.
* All rights reserved.
*
* 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.alibaba.antx.config.generator.expr;
import java.util.ArrayList;
import java.util.List;
/**
* 代表一个组合的表达式。
*
* @author Michael Zhou
*/
public class CompositeExpression implements Expression {
private String expr;
private Expression[] expressions;
/**
* 创建一个组合的表达式。
*
* @param expr 表达式字符串
* @param expressions 表达式列表
*/
public CompositeExpression(String expr, List expressions) {
this.expr = expr;
this.expressions = (Expression[]) expressions.toArray(new Expression[expressions.size()]);
}
/**
* 取得表达式字符串表示。
*
* @return 表达式字符串表示
*/
public String getExpressionText() {
return expr;
}
/**
* 在指定的上下文中计算表达式。
*
* @param context 上下文
* @return 表达式的计算结果
*/
public Object evaluate(ExpressionContext context) {
StringBuffer buffer = new StringBuffer();
for (Expression expression : expressions) {
Object value = expression.evaluate(context);
if (value != null) {
buffer.append(value);
}
}
return buffer.toString();
}
/**
* 创建表达式。
*
* - 如果表达式中不包含“
${...}”，则创建ConstantExpression。
* - 如果表达式以“
${”开始，并以“}”结尾，则创建引用表达式。
* - 如果表达式包含“
${...}”，但在此之外还有别的字符，则创建
* CompositeExpression。
*
*
* @param expr 表达式字符串
* @return 表达式
*/
public static Expression parse(String expr) {
int length = expr.length();
int startIndex = expr.indexOf("${");
// 如果表达式不包含${}，则创建constant expression。
if (startIndex < 0) {
return new ConstantExpression(expr);
}
int endIndex = expr.indexOf("}", startIndex + 2);
if (endIndex < 0) {
throw new ExpressionException("Missing '}' character at the end of expression: " + expr);
}
// 如果表达式以${开头，以}结尾，则直接调用factory来创建表达式。
if (startIndex == 0 && endIndex == length - 1) {
return new ReferenceExpression(expr.substring(2, endIndex));
}
// 创建复合的表达式。
List expressions = new ArrayList();
char ch = 0;
int i = 0;
StringBuffer chars = new StringBuffer();
StringBuffer exprBuff = new StringBuffer();
MAIN:
while (i < length) {
ch = expr.charAt(i);
switch (ch) {
case '$': {
if (i + 1 < length) {
++i;
ch = expr.charAt(i);
switch (ch) {
case '$': {
chars.append(ch);
break;
}
case '{': {
if (chars.length() > 0) {
expressions.add(new ConstantExpression(chars.toString()));
chars.delete(0, chars.length());
}
if (i + 1 < length) {
++i;
while (i < length) {
ch = expr.charAt(i);
{
switch (ch) {
case '"': {
exprBuff.append(ch);
++i;
DOUBLE_QUOTE:
while (i < length) {
ch = expr.charAt(i);
boolean escape = false;
switch (ch) {
case '\\': {
escape = true;
++i;
exprBuff.append(ch);
break;
}
case '"': {
++i;
exprBuff.append(ch);
break DOUBLE_QUOTE;
}
default: {
escape = false;
++i;
exprBuff.append(ch);
}
}
}
break;
}
case '\'': {
exprBuff.append(ch);
++i;
SINGLE_QUOTE:
while (i < length) {
ch = expr.charAt(i);
boolean escape = false;
switch (ch) {
case '\\': {
escape = true;
++i;
exprBuff.append(ch);
break;
}
case '\'': {
++i;
exprBuff.append(ch);
break SINGLE_QUOTE;
}
default: {
escape = false;
++i;
exprBuff.append(ch);
}
}
}
break;
}
case '}': {
expressions.add(new ReferenceExpression(exprBuff.toString()));
exprBuff.delete(0, exprBuff.length());
++i;
continue MAIN;
}
default: {
exprBuff.append(ch);
++i;
}
}
}
}
}
break;
}
default:
chars.append(ch);
}
} else {
chars.append(ch);
}
break;
}
default:
chars.append(ch);
}
++i;
}
if (chars.length() > 0) {
expressions.add(new ConstantExpression(chars.toString()));
}
return new CompositeExpression(expr, expressions);
}
}
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