把功能强大的Spring EL表达式应用在.net平台

Z时代
2024-01-10
分类：综合

本文内容纲要：

- Spring EL 表达式是什么？ - 为什么要使用SpringEL? - SpringEL 如何使用 - 对象的某个属性获取和重新赋值 - 文字表达式 - Properties, Arrays, Lists, Dictionaries, Indexers - Defining Arrays, Lists and Dictionaries Inline - Methods - Relational operators - Logical operators - Bitwise operators - Mathematical operators - Assignment - Expression lists - Types - Type Registration & Constructors - Variables - The '#this' and '#root' variables - Ternary Operator (If-Then-Else) - List Projection and Selection - Collection Processors and Aggregators - DI Object References(方便和DI容器结合使用) - SpringEL与Autofac容器相结合框架项目的目的 - 支持的标签一览 - 欢迎追求代码极客精神的你来试用和反馈。

Spring EL 表达式是什么？

Spring3中引入了Spring表达式语言—SpringEL,SpEL是一种强大,简洁的装配Bean的方式,他可以通过运行期间执行的表达式将值装配到我们的属性或构造函数当中,更可以调用C#中提供的静态常量,获取外部json xml文件中的的配置值

为什么要使用SpringEL?

可以方便的注入外部配置文件到类的构造方法，属性或者字段，支持注入容器里面的对象的某个属性值，还可以调用对象的方法，功能非常的强大，请看官方文档的例子或者下面我的单元测试例子

SpringEL与Autofac容器相结合框架

el表达式灵活使用能极大提高代码的活性

SpringEL 如何使用

NUGET地址： Install-Package Spring.EL

该项目是从spring.core项目抽取出来的，因为我只想用 EL 功能，其他的功能我都去掉了。

外部暴露的对象有下面几个重要对象
- ExpressionEvaluator 提供了很关键的几个静态方法
public static object GetValue(object root, string expression);
public static object GetValue(object root, string expression, IDictionary variables)
public static void SetValue(object root, string expression, object newValue)
public static void SetValue(object root, string expression, IDictionary variables, object newValue)

Spring官方文档

对象的某个属性获取和重新赋值

文字表达式

[TestMethod]
        public void TestMethod_02()
        {
            string tonyPizza = (string)ExpressionEvaluator.GetValue(null, "'Tony''s Pizza'"); // evals to "Tony's Pizza"
            string helloWorld = (string)ExpressionEvaluator.GetValue(null, "'Hello World'"); // evals to "Hello World"
            double avogadrosNumber = (double)ExpressionEvaluator.GetValue(null, "6.0221415E+23");
            int maxValue = (int)ExpressionEvaluator.GetValue(null, "0x7FFFFFFF");  // evals to 2147483647
            DateTime birthday = (DateTime)ExpressionEvaluator.GetValue(null, "date('1974/08/24')");
            DateTime exactBirthday = (DateTime)ExpressionEvaluator.GetValue(null, " date('19740824T131030', 'yyyyMMddTHHmmss')");
            bool trueValue = (bool)ExpressionEvaluator.GetValue(null, "true");
            object nullValue = ExpressionEvaluator.GetValue(null, "null");
        }

Properties, Arrays, Lists, Dictionaries, Indexers

[TestMethod]
        public void TestMethod_03()
        {
            Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            tesla.PlaceOfBirth.City = "Smiljan";
            string invention = (string)ExpressionEvaluator.GetValue(tesla, "Inventions[2]"); // "Induction motor"
            string name = (string)ExpressionEvaluator.GetValue(tesla, "Members[0].Name"); // "Nikola Tesla"
            string invention1 = (string)ExpressionEvaluator.GetValue(tesla, "Members[0].Inventions[2]"); // "Wireless communication"
            Bar bar = new Bar();
            int val = (int)ExpressionEvaluator.GetValue(bar, "[1]"); // evaluated to 2
            ExpressionEvaluator.SetValue(bar, "[1]", 3);  // set value to 3
        }

Defining Arrays, Lists and Dictionaries Inline

[TestMethod]
        public void TestMethod_05()
        {
            var val = ExpressionEvaluator.GetValue(null, "{1, 2, 3, 4, 5}");
            var val2 = ExpressionEvaluator.GetValue(null, "{'abc', 'xyz'}");
            var val21 = ExpressionEvaluator.GetValue(null, "new int[] {1, 2, 3, 4, 5}");
            var val22 = ExpressionEvaluator.GetValue(null, "#{'key1' : 'Value 1', 'today' : DateTime.Today}");
            var val221 = ExpressionEvaluator.GetValue(null, "#{1 : 'January', 2 : 'February', 3 : 'March'}");
        }

Methods

[TestMethod]
        public void TestMethod_06()
        {
            Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            //string literal
            char[] chars = (char[])ExpressionEvaluator.GetValue(null, "'test'.ToCharArray(1, 2)");  // 't','e'
            //date literal
            int year = (int)ExpressionEvaluator.GetValue(null, "date('1974/08/24').AddYears(31).Year"); // 2005
            // object usage, calculate age of tesla navigating from the IEEE society.
            int age = (int)ExpressionEvaluator.GetValue(tesla, "Members[0].GetAge(date('2005-01-01'))"); // 149 (eww..a big anniversary is coming up ;)
        }

Relational operators

[TestMethod]
        public void TestMethod_07()
        {
            var a1 = ExpressionEvaluator.GetValue(null, "2 == 2");  // true
            var a12 = ExpressionEvaluator.GetValue(null, "date('1974-08-24') != DateTime.Today");  // true
            var a13 = ExpressionEvaluator.GetValue(null, "2 < -5.0"); // false
            var a14 = ExpressionEvaluator.GetValue(null, "DateTime.Today <= date('1974-08-24')"); // false
            var a15 = ExpressionEvaluator.GetValue(null, "'Test' >= 'test'"); // true
            a1 = ExpressionEvaluator.GetValue(null, "3 in {1, 2, 3, 4, 5}");  // true
            a1 = ExpressionEvaluator.GetValue(null, "'Abc' like '[A-Z]b*'");  // true
            a1 = ExpressionEvaluator.GetValue(null, "'Abc' like '?'");  // false
            a1 = ExpressionEvaluator.GetValue(null, "1 between {1, 5}");  // true
            a1 = ExpressionEvaluator.GetValue(null, "'efg' between {'abc', 'xyz'}");  // true
            a1 = ExpressionEvaluator.GetValue(null, "'xyz' is int");  // false
            a1 = ExpressionEvaluator.GetValue(null, "{1, 2, 3, 4, 5} is ArrayList");  // true
            a1 = ExpressionEvaluator.GetValue(null, "'5.0067' matches '^-?\\d+(\\.\\d{2})?$'");  // false
            a1 = ExpressionEvaluator.GetValue(null, @"'5.00' matches '^-?\d+(\.\d{2})?$'"); // true
        }

Logical operators

[TestMethod]
        public void TestMethod_10()
        {
            Inventor ieee = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            // AND
            bool falseValue = (bool)ExpressionEvaluator.GetValue(null, "true and false"); //false
            string expression = @"IsMember('Nikola Tesla') and IsMember('Mihajlo Pupin')";
            bool trueValue = (bool)ExpressionEvaluator.GetValue(ieee, expression);  //true
            // OR
            trueValue = (bool)ExpressionEvaluator.GetValue(null, "true or false");  //true
            expression = @"IsMember('Nikola Tesla') or IsMember('Albert Einstien')";
            trueValue = (bool)ExpressionEvaluator.GetValue(ieee, expression); // true
            // NOT
            falseValue = (bool)ExpressionEvaluator.GetValue(null, "!true");
            // AND and NOT
            expression = @"IsMember('Nikola Tesla') and !IsMember('Mihajlo Pupin')";
            falseValue = (bool)ExpressionEvaluator.GetValue(ieee, expression);
        }

Bitwise operators

[TestMethod]
        public void TestMethod_11()
        {
            // AND
            int result = (int)ExpressionEvaluator.GetValue(null, "1 and 3"); // 1 & 3
            // OR
            result = (int)ExpressionEvaluator.GetValue(null, "1 or 3");  // 1 | 3
            // XOR
            result = (int)ExpressionEvaluator.GetValue(null, "1 xor 3");  // 1 ^ 3
            // NOT
            result = (int)ExpressionEvaluator.GetValue(null, "!1"); // ~1
        }

Mathematical operators

[TestMethod]
        public void TestMethod_12()
        {
            // Addition
            int two = (int)ExpressionEvaluator.GetValue(null, "1 + 1"); // 2
            String testString = (String)ExpressionEvaluator.GetValue(null, "'test' + ' ' + 'string'"); //'test string'
            DateTime dt = (DateTime)ExpressionEvaluator.GetValue(null, "date('1974-08-24') + 5"); // 8/29/1974
            // Subtraction
            int four = (int)ExpressionEvaluator.GetValue(null, "1 - -3"); //4
            Decimal dec = (Decimal)ExpressionEvaluator.GetValue(null, "1000.00m - 1e4"); // 9000.00
            TimeSpan ts = (TimeSpan)ExpressionEvaluator.GetValue(null, "date('2004-08-14') - date('1974-08-24')"); //10948.00:00:00
            // Multiplication
            int six = (int)ExpressionEvaluator.GetValue(null, "-2 * -3"); // 6
            double twentyFour = (double)ExpressionEvaluator.GetValue(null, "2.0 * 3e0 * 4"); // 24
            // Division
            int minusTwo = (int)ExpressionEvaluator.GetValue(null, "6 / -3"); // -2
            var one = ExpressionEvaluator.GetValue(null, "8.0 / 4e0 / 2"); // 1
            // Modulus
            int three = (int)ExpressionEvaluator.GetValue(null, "7 % 4"); // 3
            one = ExpressionEvaluator.GetValue(null, "8.0 % 5e0 % 2"); // 1
            // Exponent
            var sixteen = ExpressionEvaluator.GetValue(null, "-2 ^ 4"); // 16
            // Operator precedence
            var minusFortyFive = ExpressionEvaluator.GetValue(null, "1+2-3*8^2/2/2"); // -45
        }

Assignment

[TestMethod]
        public void TestMethod_13()
        {
            Inventor inventor = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            String aleks = (String)ExpressionEvaluator.GetValue(inventor, "Name = 'Aleksandar Seovic'");
            DateTime dt = (DateTime)ExpressionEvaluator.GetValue(inventor, "DOB = date('1974-08-24')");
        }

Expression lists

[TestMethod]
        public void TestMethod_14()
        {
            Inventor ieee = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            String pupin = (String)ExpressionEvaluator.GetValue(ieee.Members, "([1].Place.City = 'Beograd'; [1].Place.Name = 'Serbia'; [1].Name)");
        }

Types

[TestMethod]
        public void TestMethod_15()
        {
            var a1 = ExpressionEvaluator.GetValue(null, "1 is int");
            var a2 = ExpressionEvaluator.GetValue(null, "DateTime.Today");
            var a3 = ExpressionEvaluator.GetValue(null, "new string[] {'abc', 'efg'}");
            Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            Type dateType = (Type)ExpressionEvaluator.GetValue(null, "T(System.DateTime)");
            Type evalType =
                (Type)ExpressionEvaluator.GetValue(null, "T(Spring.Expressions.ExpressionEvaluator, Spring.EL)");
            bool trueValue = (bool)ExpressionEvaluator.GetValue(tesla, "T(System.DateTime) == DOB.GetType()");
        }

Type Registration & Constructors

[TestMethod]
        public void TestMethod_17()
        {
            Inventor2 tesla = new Inventor2("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            DateTime dt = (DateTime)ExpressionEvaluator.GetValue(null, "new DateTime(1974, 8, 24)");
            // Register Inventor type then create new inventor instance within Add method inside an expression list.
            // Then return the new count of the Members collection.
            TypeRegistry.RegisterType(typeof(PlaceOfBirth));
            int three = (int)ExpressionEvaluator.GetValue(tesla.Members, "( Add(new PlaceOfBirth('Aleksandar Seovic')); Count)");
            TypeRegistry.RegisterType(typeof(Inventor));
            Inventor aleks = (Inventor)ExpressionEvaluator.GetValue(null, "new Inventor('Aleksandar Seovic', date('1974-08-24'), 'Serbian', Inventions = new string[]{'SPELL'})");
        }

Variables

[TestMethod]
        public void TestMethod_19()
        {
            Inventor tesla = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            Dictionary<string, object> vars = new Dictionary<string, object>();
            vars["newName"] = "Mike Tesla2";
            var a = ExpressionEvaluator.GetValue(tesla, "Name = #newName", vars);
            ExpressionEvaluator.GetValue(tesla, "( #oldName = Name; Name = 'Nikola Tesla' )", vars);
            String oldName = (String)vars["oldName"]; // Mike Tesla
            vars["prez"] = "president";
            Inventor2 pupin = (Inventor2)ExpressionEvaluator.GetValue(tesla, "Officers[#prez]", vars);
        }

The '#this' and '#root' variables

[TestMethod]
        public void TestMethod_20()
        {
            Inventor ieee = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            // sets the name of the president and returns its instance
            var a1 = ExpressionEvaluator.GetValue(ieee, "Officers['president'].( #this.Name = 'Nikola Tesla'; #this )");
            var a2 = ExpressionEvaluator.GetValue(ieee, "Officers['president'].( #root.Officers.Remove('president'); #this )");
        }

Ternary Operator (If-Then-Else)

[TestMethod]
        public void TestMethod_21()
        {
            String aTrueString = (String)ExpressionEvaluator.GetValue(null, "false ? 'trueExp' : 'falseExp'"); // trueExp
        }
        [TestMethod]
        public void TestMethod_22()
        {
            Inventor ieee = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            ExpressionEvaluator.SetValue(ieee, "Name", "IEEE");
            Dictionary<string, object> vars = new Dictionary<string, object>();
            vars["queryName"] = "Nikola Tesla";
            string expression = @"IsMember(#queryName)
                      ? #queryName + ' is a member of the ' + Name + ' Society'
                      : #queryName + ' is not a member of the ' + Name + ' Society'";
            String queryResultString = (String)ExpressionEvaluator.GetValue(ieee, expression, vars);
        }

List Projection and Selection

[TestMethod]
        public void TestMethod_23()
        {
            Inventor ieee = new Inventor("Nikola Tesla", new DateTime(1856, 7, 9), "Serbian");
            IList placesOfBirth = (IList)ExpressionEvaluator.GetValue(ieee, "Members.!{Name}"); // { 'Smiljan', 'Idvor' }
            IList serbianInventors = (IList)ExpressionEvaluator.GetValue(ieee, "Members.?{Name == '1'}"); // { tesla, pupin }
            IList sonarInventors = (IList)ExpressionEvaluator.GetValue(ieee, "Members.?{'1' in Inventions}"); // { pupin }
            IList sonarInventorsNames = (IList)ExpressionEvaluator.GetValue(ieee, "Members.?{'1' in Inventions}.!{Name}"); // { 'Mihajlo Pupin' }
            var a1 = ExpressionEvaluator.GetValue(ieee, "Members.^{Name == '1'}.Name");  // 'Nikola Tesla'
            var a3 = ExpressionEvaluator.GetValue(ieee, "Members.${Name == '3'}.Name"); // 'Mihajlo Pupin'
        }

Collection Processors and Aggregators

[TestMethod]
        public void TestMethod_24()
        {
            var a1 = ExpressionEvaluator.GetValue(null, "{1, 5, -3}.count()");  // 3
            var a2 = ExpressionEvaluator.GetValue(null, "count()"); // 0
            a2 = ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.sum()");  // 13 (int)
            a2 = ExpressionEvaluator.GetValue(null, "{5, 5.8, 12.2, 1}.sum()"); // 24.0 (double)
            a2 = ExpressionEvaluator.GetValue(null, "{1, 5, -4, 10}.average()");  // 3
            a2 = ExpressionEvaluator.GetValue(null, "{1, 5, -2, 10}.average()"); // 3.5
            a2 = ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.min()");  // -3
            a2 = ExpressionEvaluator.GetValue(null, "{'abc', 'efg', 'xyz'}.min()"); // 'abc'
            a2 = ExpressionEvaluator.GetValue(null, "{1, 5, -3, 10}.max()");  // 10
            a2 = ExpressionEvaluator.GetValue(null, "{'abc', 'efg', 'xyz'}.max()"); // 'xyz'
            a2 = ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', null, 'abc', 'def', null}.nonNull()");  // { 'abc', 'xyz', 'abc', 'def' }
            a2 = ExpressionEvaluator.GetValue(null,
                "{ 'abc', 'xyz', null, 'abc', 'def', null}.nonNull().distinct().sort()"); // { 'abc', 'def', 'xyz' }
            a2 = ExpressionEvaluator.GetValue(null, "{ 'abc', 'xyz', 'abc', 'def', null, 'def' }.distinct(true).sort()"); // { null, 'abc', 'def', 'xyz' }
            a2 = ExpressionEvaluator.GetValue(null,
                "{ 'abc', 'xyz', 'abc', 'def', null, 'def' }.distinct(false).sort()"); // { 'abc', 'def', 'xyz' }
        }

DI Object References(方便和DI容器结合使用)

[TestMethod]
        public void TestMethod_26()
        {
            Dictionary<string, object> vars = new Dictionary<string, object>();
            vars["_sprint_context_resove_"] = new SprintContextResove((name) =>
            {
                if (name == "Inventor") return new Inventor("a", DateTime.Now, "d");
                return new Inventor2("a", DateTime.Now, "d");
            });
            var IsMember = ExpressionEvaluator.GetValue(null, "@(Inventor).IsMember('Nikola Tesla1')", vars);
        }

SpringEL与Autofac容器相结合框架项目的目的

基于参考 Java的 Spring注解方式开发思想，

所有autofac容器的注册和装配都是依赖标签来完成。

这样一来一方面很容易分清楚哪些是DI 哪些非DI，哪些是拦截器，哪些需要拦截器代码也好看，编程效率能够大大提升。

支持的标签一览

标签名称	使用位置	使用说明
AutoConfiguration	打在class上面	自动装配class里面带有Bean标签的方法
Bean	打在方法上面	配合AutoConfiguration标签使用
Component	打在class上面	自动注册
Autowired	打在构造方法的Parameter，类的Property，类的Field	自动装配
PropertySource	打在class上面	配合Value标签使用，设置Value的数据源，支持json,xml,支持资源内嵌
Value	打在构造方法的Parameter，类的Property，类的Field	静态数据装配(支持SPEL表达式)
Aspect	打在class上面	开启拦截器，默认注册为类拦截器，可以指定接口型拦截器

欢迎追求代码极客精神的你来试用和反馈。

本文内容总结：Spring EL 表达式是什么？，为什么要使用SpringEL?，SpringEL 如何使用，对象的某个属性获取和重新赋值，文字表达式，Properties, Arrays, Lists, Dictionaries, Indexers，Defining Arrays, Lists and Dictionaries Inline，Methods，Relational operators，Logical operators，Bitwise operators，Mathematical operators，Assignment，Expression lists，Types，Type Registration & Constructors，Variables，The '#this' and '#root' variables，Ternary Operator (If-Then-Else)，List Projection and Selection，Collection Processors and Aggregators，DI Object References(方便和DI容器结合使用)，SpringEL与Autofac容器相结合框架项目的目的，支持的标签一览，欢迎追求代码极客精神的你来试用和反馈。，

原文链接：https://www.cnblogs.com/yudongdong/p/11648118.html

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