Thymeleaf系列二 简单表达式: 变量、消息、Literals、文本、算术、比较和条件表达式

1. 概述

本节主要介绍thymeleaf的语法：简单表达式。包括以下内容：
- 变量表达式：Variable Expressions
- 消息表达式：Message Expressions
- Literals
- 文本操作符： Text operations
- 算术表达式：Arithmetic operations
- 比较操作符：Comparisons and equality
- 条件操作符： Conditional operators

2. 例子

2.1 公共类

User

public class User {    private String name;    private boolean isAdmin;    private String other;    private int age;// set/get 略}

Family

public class Family {    private User father;    private List<User> childList;    // set/get 略}

ExpressionsCtl：Control类
此类初始化测试类，当访问此URL，并转到expressions/simple.html。

@Controller@RequestMapping("/expressions")public class ExpressionsCtl {    /**     * 简单表达式     */    @RequestMapping("/simple")    public String simpleExpressions(ModelMap map){        // 变量表达式：Variable Expressions        User user = new User("simple_name");        user.setAge(new Random().nextInt(100));        map.put("user", user);        return "expressions/simple";    }     ... }

下面的代码都在此simple.html页面中。

2.2 变量表达式(Variable Expressions)

实现功能：

• 简单的表达式
• 变量值和字符串拼接

==================== 变量表达式(Variable Expressions) ===============================<br/><!-- 变量表达式(Variable Expressions)-->${user.name} --> <input type="text" name="userName" value="James Carrot" th:value="${user.name}" /> <br /><!-- 变量值和字符串拼接  -->'The name of the user is ' + ${user.name} --> <span th:text="'The name of the user is ' + ${user.name}" ></span> <br /><br />

输出: “–>”的左边是语法，右边是对应的输出

==================== 变量表达式(Variable Expressions) ===============================${user.name} --> simple_name'The name of the user is ' + ${user.name} --> The name of the user is simple_name 

2.3 消息表达式：Message Expressions

实现功能：

• 直接从属性文件中获取值
• 从属性文件中获取值，并替换占位符

<!-- 消息表达式：Message Expressions --><!-- 直接从属性文件中获取值 -->#{home.welcome} --> <span th:text="#{home.welcome}">Welcome to our grocery store!</span> <br /><!-- 从属性文件中获取值，并替换占位符  -->#{home.welcome.replace(${user.name})} --> <span th:text="#{home.welcome.replace(${user.name})}"></span> <br /><br />

输出: “–>”的左边是语法，右边是对应的输出

=====================消息表达式：Message Expressions =================================#{home.welcome} --> welcome thymeleaf #{home.welcome.replace(${user.name})} --> welcome thymeleaf, simple_name! 

2.4 Literals

实现功能：

• 文本 Text literals
• 数字 Number literals
• 布尔值
• Null值

========================== Literals =======================================<br/><!-- 文本 Text literals: Text literals are just character strings specified between single quotes --><div>  Now you are looking at a <span th:text="'working web application'">template file</span>.</div><!-- 数字 Number literals: 0, 34, 3.0, 12.3,… --><div>仅仅输出数字 th:text="2013" --> <span th:text="2013">1492</span>.</div><div>数字计算 th:text="2013 + 2" --> <span th:text="2013 + 2">1494</span>.</div><!-- 布尔值： Boolean literals: true, false -->${user.isAdmin()} == false --> <span th:if="${user.isAdmin()} == false"> false </span> <br /><!-- Null值： Null literal: null -->${user.other} == null --> <span th:if="${user.other} == null"> null</span><br />

输出: “–>”的左边是语法，右边是对应的输出

========================== Literals =======================================Now you are looking at a working web application.仅仅输出数字 th:text="2013" --> 2013.数字计算 th:text="2013 + 2" --> 2015.${user.isAdmin()} == false --> false ${user.other} == null --> null 

2.5 文本操作符： Text operations

实现功能：

• +:字符串拼接字体串
• 简化字符中拼接操作： Literal substitutions（使用”|”包围字符串，不需要对字符串使用”’”）

<!-- +:字符串拼接字体串 -->'The name of the user is ' + ${user.name} + '_' + ${user.age} --> <span th:text="'The name of the user is ' + ${user.name} + '_' + ${user.age}"> </span> <br/><!-- 简化字符中拼接操作： Literal substitutions（使用"|"包围字符串，不需要对字符串使用"'"） -->|Welcome to our application, ${user.name}!| --> <span th:text="|Welcome to our application, ${user.name}!|"></span> <br />等价于这条语句：<br />'Welcome to our application, ' + ${user.name} + '!' --> <span th:text="'Welcome to our application, ' + ${user.name} + '!'"> </span><br />

输出: “–>”的左边是语法，右边是对应的输出

========================== 文本操作符： Text operations: =================================='The name of the user is ' + ${user.name} + '_' + ${user.age} --> The name of the user is simple_name_52 |Welcome to our application, ${user.name}!| --> Welcome to our application, simple_name! 等价于这条语句：'Welcome to our application, ' + ${user.name} + '!' --> Welcome to our application, simple_name! 

2.6 算术表达式：Arithmetic operations

实现功能：

• 二进制运算符: Binary operators: +, -, *, /, %
• Boolean operations: true,false, !, not
• Binary operators: and, or

<!-- 二进制运算符: Binary operators: +, -, *, /, %  -->${user.age} % 2 == 0 --> <span th:text="${user.age} % 2 == 0"> </span> <br /><!-- Boolean operations: true,false, !, not  -->true --> <span th:text="true"> </span> <br />!(${user.age} % 2 == 0 --> <span th:text="!(${user.age} % 2 == 0)"> </span> <br /><!-- Binary operators: and, or -->(${user.age} % 2 == 0) and true --> <span th:text="(${user.age} % 2 == 0) and true"> </span><br />

输出: “–>”的左边是语法，右边是对应的输出

========================== 算术表达式：Arithmetic operations ==================================${user.age} % 2 == 0 --> true true --> true !(${user.age} % 2 == 0 --> false (${user.age} % 2 == 0) and true --> true

2.7 比较操作符：Comparisons and equality

实现功能：

• 比较符号Comparators: >, <, >=, <= (gt, lt, ge, le)
• Equality operators: ==, != (eq, ne)

========================== 比较操作符：Comparisons and equality ==================================<br/><!-- Comparators: >, <, >=, <= (gt, lt, ge, le) -->${user.age} &gt; 18 --> <span th:if="${user.age} &gt; 18"> 大人 </span> <br /><!-- Equality operators: ==, != (eq, ne) -->${user.age} != 18 --> <span th:if="${user.age} != 18"> 大人_no_equality </span> <br /><br />

输出: “–>”的左边是语法，右边是对应的输出

========================== 比较操作符：Comparisons and equality ==================================${user.age} > 18 --> 大人 ${user.age} != 18 --> 大人_no_equality 

2.8 条件操作符： Conditional operators

实现功能：

• If-then: (if) ? (then)
• If-then-else: (if) ? (then) : (else)
• 如果null值，则使用？:后面的值: Default: (value) ?: (defaultvalue)

<!-- If-then: (if) ? (then) -->${user.age}%2==0 ? 'even' --> <span th:text="${user.age}%2==0 ? 'even'"> </span> <br /><!-- If-then-else: (if) ? (then) : (else)  -->${user.age}%2==0 ? 'even' : 'odd' --> <span th:text="${user.age}%2==0 ? 'even' : 'odd'"> </span> <br /><!-- 如果null值，则使用？:后面的值: Default: (value) ?: (defaultvalue) -->${user.age} ?:'18' --> <span th:text="${user.age} ?:'18'"> </span> <br />

输出: “–>”的左边是语法，右边是对应的输出

========================== 条件操作符： Conditional operators ==================================${user.age}%2==0 ? 'even' --> even ${user.age}%2==0 ? 'even' : 'odd' --> even ${user.age} ?:'18' --> 52 

3. 代码

详细代码见Github