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