sepl文档阅读
This commit is contained in:
@@ -13,6 +13,34 @@
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- [为field指定默认值](#为field指定默认值)
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- [通过setter为field指定默认值](#通过setter为field指定默认值)
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- [@Autowired方法和构造器](#autowired方法和构造器)
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- [Spel语法](#spel语法)
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- [字面量表达式](#字面量表达式)
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- [字符串类型字面量](#字符串类型字面量)
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- [Properties,Array,List,Map,Indexer](#propertiesarraylistmapindexer)
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- [访问属性](#访问属性)
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- [Array](#array)
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- [Map](#map)
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- [列表表示](#列表表示)
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- [数组构建](#数组构建)
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- [方法调用](#方法调用)
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- [操作符](#操作符)
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- [关系操作符](#关系操作符)
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- [instanceof操作符和matches操作符](#instanceof操作符和matches操作符)
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- [逻辑操作符](#逻辑操作符)
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- [数学运算符](#数学运算符)
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- [赋值运算符](#赋值运算符)
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- [类型操作符](#类型操作符)
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- [构造方法](#构造方法)
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- [变量](#变量)
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- [#this and #root](#this-and-root)
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- [方法注册](#方法注册)
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- [引用bean对象](#引用bean对象)
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- [三元操作符](#三元操作符)
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- [Elvis Operator](#elvis-operator)
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- [空安全操作符](#空安全操作符)
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- [集合过滤操作符](#集合过滤操作符)
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- [集合映射](#集合映射)
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- [表达式模板](#表达式模板)
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# Spel
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@@ -192,6 +220,385 @@ public class MovieRecommender {
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}
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```
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## Spel语法
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### 字面量表达式
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字面量表达式支持字符串、数值（整数、实数、十六进制数）、boolean类型和null。
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#### 字符串类型字面量
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其中字符串类型的字面量通过单引号包围，如果想要将单引号本身放入字符串字面量中，可以使用两个单引号：
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```java
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// 该值为h''h
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parser.parseExpression("'h''''h'").getValue()
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```
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字面量的使用如下所示：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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// evals to "Hello World"
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String helloWorld = (String) parser.parseExpression("'Hello World'").getValue();
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double avogadrosNumber = (Double) parser.parseExpression("6.0221415E+23").getValue();
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// evals to 2147483647
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int maxValue = (Integer) parser.parseExpression("0x7FFFFFFF").getValue();
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boolean trueValue = (Boolean) parser.parseExpression("true").getValue();
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Object nullValue = parser.parseExpression("null").getValue();
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```
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### Properties,Array,List,Map,Indexer
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#### 访问属性
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```java
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int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);
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String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);
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```
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属性名的第一个字符不区分大小写。
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#### Array
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可以通过方括号来访问array和list中的元素内容：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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// Inventions Array
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StandardEvaluationContext teslaContext = new StandardEvaluationContext(tesla);
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// evaluates to "Induction motor"
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String invention = parser.parseExpression("inventions[3]").getValue(teslaContext,
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String.class);
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// Members List
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StandardEvaluationContext societyContext = new StandardEvaluationContext(ieee);
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// evaluates to "Nikola Tesla"
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String name = parser.parseExpression("Members[0].Name").getValue(societyContext, String.class);
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// List and Array navigation
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// evaluates to "Wireless communication"
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String invention = parser.parseExpression("Members[0].Inventions[6]").getValue(societyContext,String.class);
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```
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#### Map
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map中的值可以在方括号中指定字面量key来访问，示例如下所示：
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```java
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// Officer's Dictionary
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Inventor pupin = parser.parseExpression("Officers['president']").getValue(societyContext,Inventor.class);
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// evaluates to "Idvor"
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String city =
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parser.parseExpression("Officers['president'].PlaceOfBirth.City").getValue(societyContext,
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String.class);
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// setting values
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parser.parseExpression("Officers['advisors'][0].PlaceOfBirth.Country").setValue(societyContext,"Croatia");
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```
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#### 列表表示
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列表可以直接通过如下方式来表示：
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```java
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// evaluates to a Java list containing the four numbers
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List numbers = (List) parser.parseExpression("{1,2,3,4}").getValue(context);
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List listOfLists = (List) parser.parseExpression("{{'a','b'},{'x','y'}}").getValue(context);
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```
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#### 数组构建
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spel表达式中数组构建可以使用java语法：
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```java
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int[] numbers1 = (int[]) parser.parseExpression("new int[4]").getValue(context);
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// Array with initializer
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int[] numbers2 = (int[]) parser.parseExpression("new int[]{1,2,3}").getValue(context);
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// Multi dimensional array
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int[][] numbers3 = (int[][]) parser.parseExpression("new int[4][5]").getValue(context);
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```
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### 方法调用
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表达式中方法调用也可以使用java中的语法：
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```java
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// string literal, evaluates to "bc"
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String c = parser.parseExpression("'abc'.substring(2, 3)").getValue(String.class);
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// evaluates to true
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boolean isMember = parser.parseExpression("isMember('Mihajlo Pupin')").getValue(societyContext, Boolean.class);
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```
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### 操作符
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#### 关系操作符
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关系操作符示例如下：
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```java
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// evaluates to true
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boolean trueValue = parser.parseExpression("2 == 2").getValue(Boolean.class);
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// evaluates to false
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boolean falseValue = parser.parseExpression("2 < -5.0").getValue(Boolean.class);
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// evaluates to true
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boolean trueValue = parser.parseExpression("'black' < 'block'").getValue(Boolean.class);
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```
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与null比较时的规则：
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- 任何值都比null大，`X>null`永远为true
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- 没有任何值比null小，`X<null`永远为false
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#### instanceof操作符和matches操作符
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```java
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// evaluates to false
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boolean falseValue = parser.parseExpression("'xyz' instanceof T(int)").getValue(Boolean.class);
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// evaluates to true
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boolean trueValue =
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parser.parseExpression("'5.00' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
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//evaluates to false
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boolean falseValue =
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parser.parseExpression("'5.0067' matches '^-?\\d+(\\.\\d{2})?$'").getValue(Boolean.class);
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```
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#### 逻辑操作符
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逻辑操作符支持and、or、not
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```java
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// -- AND --
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// evaluates to false
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boolean falseValue = parser.parseExpression("true and false").getValue(Boolean.class);
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// evaluates to true
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String expression = "isMember('Nikola Tesla') and isMember('Mihajlo Pupin')";
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boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);
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// -- OR --
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// evaluates to true
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boolean trueValue = parser.parseExpression("true or false").getValue(Boolean.class);
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// evaluates to true
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String expression = "isMember('Nikola Tesla') or isMember('Albert Einstein')";
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boolean trueValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);
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// -- NOT --
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// evaluates to false
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boolean falseValue = parser.parseExpression("!true").getValue(Boolean.class);
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// -- AND and NOT --
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String expression = "isMember('Nikola Tesla') and !isMember('Mihajlo Pupin')";
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boolean falseValue = parser.parseExpression(expression).getValue(societyContext, Boolean.class);
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```
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#### 数学运算符
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```java
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// Addition
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int two = parser.parseExpression("1 + 1").getValue(Integer.class); // 2
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String testString =
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parser.parseExpression("'test' + ' ' + 'string'").getValue(String.class); // 'test string'
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// Subtraction
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int four = parser.parseExpression("1 - -3").getValue(Integer.class); // 4
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double d = parser.parseExpression("1000.00 - 1e4").getValue(Double.class); // -9000
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// Multiplication
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int six = parser.parseExpression("-2 * -3").getValue(Integer.class); // 6
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double twentyFour = parser.parseExpression("2.0 * 3e0 * 4").getValue(Double.class); // 24.0
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// Division
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int minusTwo = parser.parseExpression("6 / -3").getValue(Integer.class); // -2
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double one = parser.parseExpression("8.0 / 4e0 / 2").getValue(Double.class); // 1.0
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// Modulus
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int three = parser.parseExpression("7 % 4").getValue(Integer.class); // 3
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int one = parser.parseExpression("8 / 5 % 2").getValue(Integer.class); // 1
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// Operator precedence
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int minusTwentyOne = parser.parseExpression("1+2-3*8").getValue(Integer.class); // -21
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```
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#### 赋值运算符
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```java
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Inventor inventor = new Inventor();
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StandardEvaluationContext inventorContext = new StandardEvaluationContext(inventor);
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parser.parseExpression("Name").setValue(inventorContext, "Alexander Seovic2");
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// alternatively
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String aleks = parser.parseExpression("Name = 'Alexandar Seovic'").getValue(inventorContext,
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String.class);
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```
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#### 类型操作符
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T操作符会获取一个class对象，在传入T的类型为java.lang下类时，不用指定全类名，否则应指定全类名.
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类中的静态方法也可以通过该操作符进行调用：
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```java
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Class dateClass = parser.parseExpression("T(java.util.Date)").getValue(Class.class);
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Class stringClass = parser.parseExpression("T(String)").getValue(Class.class);
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boolean trueValue =
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parser.parseExpression("T(java.math.RoundingMode).CEILING < T(java.math.RoundingMode).FLOOR")
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.getValue(Boolean.class);
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```
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#### 构造方法
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可以通过new操作符来调用构造方法，在调用构造方法需要指定全类名，但是基类和String可以不指定全类名：
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```java
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Inventor einstein =
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p.parseExpression("new org.spring.samples.spel.inventor.Inventor('Albert Einstein',
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'German')")
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.getValue(Inventor.class);
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//create new inventor instance within add method of List
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p.parseExpression("Members.add(new org.spring.samples.spel.inventor.Inventor('Albert Einstein',
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'German'))")
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.getValue(societyContext);
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```
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### 变量
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可以通过`#argName`语法来引用变量，可以通过`StandardEvaluationContext.setVariable`方法来设置变量：
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```java
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Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
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StandardEvaluationContext context = new StandardEvaluationContext(tesla);
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context.setVariable("newName", "Mike Tesla");
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parser.parseExpression("Name = #newName").getValue(context);
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System.out.println(tesla.getName()) // "Mike Tesla"
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```
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#### #this and #root
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#this变量一直都是被定义的，用于引用当前评估对象，#root变量也是一直都被定义的，引用root context对象。
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```java
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// create an array of integers
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List<Integer> primes = new ArrayList<Integer>();
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primes.addAll(Arrays.asList(2,3,5,7,11,13,17));
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// create parser and set variable 'primes' as the array of integers
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ExpressionParser parser = new SpelExpressionParser();
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StandardEvaluationContext context = new StandardEvaluationContext();
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context.setVariable("primes",primes);
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// all prime numbers > 10 from the list (using selection ?{...})
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// evaluates to [11, 13, 17]
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List<Integer> primesGreaterThanTen =
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(List<Integer>) parser.parseExpression("#primes.?[#this>10]").getValue(context);
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```
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### 方法注册
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可以向StandardEvaluationContext中注册方法，注册的方法可以在spel中使用：
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```java
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public abstract class StringUtils {
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public static String reverseString(String input) {
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StringBuilder backwards = new StringBuilder();
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for (int i = 0; i < input.length(); i++)
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backwards.append(input.charAt(input.length() - 1 - i));
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}
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return backwards.toString();
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}
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}
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```
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注册方法到context中：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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StandardEvaluationContext context = new StandardEvaluationContext();
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context.registerFunction("reverseString",
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StringUtils.class.getDeclaredMethod("reverseString",
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new Class[] { String.class }));
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String helloWorldReversed =
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parser.parseExpression("#reverseString('hello')").getValue(context, String.class);
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```
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### 引用bean对象
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如果为context配置了bean resolver，可以通过`@`语法来查询bean对象：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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StandardEvaluationContext context = new StandardEvaluationContext();
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context.setBeanResolver(new MyBeanResolver());
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// This will end up calling resolve(context,"foo") on MyBeanResolver during evaluation
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Object bean = parser.parseExpression("@foo").getValue(context);
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```
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### 三元操作符
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```java
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parser.parseExpression("Name").setValue(societyContext, "IEEE");
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societyContext.setVariable("queryName", "Nikola Tesla");
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expression = "isMember(#queryName)? #queryName + ' is a member of the ' " +
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"+ Name + ' Society' : #queryName + ' is not a member of the ' + Name + ' Society'";
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String queryResultString =
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parser.parseExpression(expression).getValue(societyContext, String.class);
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// queryResultString = "Nikola Tesla is a member of the IEEE Society"
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```
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### Elvis Operator
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类似于`Optional.ofNullable(var).orElse()`,`?:`表达式可以达成同样效果：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
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StandardEvaluationContext context = new StandardEvaluationContext(tesla);
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String name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, String.class);
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System.out.println(name); // Nikola Tesla
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tesla.setName(null);
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name = parser.parseExpression("Name?:'Elvis Presley'").getValue(context, String.class);
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System.out.println(name); // Elvis Presley
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```
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### 空安全操作符
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`?.`操作符和js中的类似：
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```java
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ExpressionParser parser = new SpelExpressionParser();
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Inventor tesla = new Inventor("Nikola Tesla", "Serbian");
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tesla.setPlaceOfBirth(new PlaceOfBirth("Smiljan"));
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StandardEvaluationContext context = new StandardEvaluationContext(tesla);
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String city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, String.class);
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System.out.println(city); // Smiljan
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tesla.setPlaceOfBirth(null);
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city = parser.parseExpression("PlaceOfBirth?.City").getValue(context, String.class);
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System.out.println(city); // null - does not throw NullPointerException!!!
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```
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### 集合过滤操作符
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`?[selectionExpression]`可以完成集合的过滤，该操作符可以同时针对list和map，在针对map操作时，操作的是`Map.Entry`，entry的key和value都可以作为属性访问。
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```java
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// 针对list
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List<Inventor> list = (List<Inventor>)
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parser.parseExpression("Members.?[Nationality == 'Serbian']").getValue(societyContext);
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// 针对map
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Map newMap = parser.parseExpression("map.?[value<27]").getValue();
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```
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### 集合映射
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类似于Stream.map，spel支持集合映射操作符
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```java
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// returns [ 'Smiljan', 'Idvor' ]
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// 将Inventor集合映射为city集合
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List placesOfBirth = (List)parser.parseExpression("Members.![placeOfBirth.city]");
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```
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### 表达式模板
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表达式模板允许将字面量文本和一个或多个评估component混合在一起，评估块语法类似于`${}`
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```java
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String randomPhrase =
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parser.parseExpression("random number is #{T(java.lang.Math).random()}",
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new TemplateParserContext()).getValue(String.class);
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// evaluates to "random number is 0.7038186818312008"
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```
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Reference in New Issue
Block a user