6、模板引擎

JSP、Velocity、Freemarker、Thymeleaf

对于模板引擎，SpringBoot推荐的Thymeleaf；

1）、引入

springboot官方文档

官网：https://www.thymeleaf.org/

坐标：

<!--模板引擎-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

切换其版本：

均在GitHub中进行查看

切换thymeleaf版本
<properties>
                <thymeleaf.version>3.0.9.RELEASE</thymeleaf.version>
                <!-- 布局功能的支持程序  thymeleaf3主程序  layout2以上版本 -->
                <!-- thymeleaf2   layout1-->
                <thymeleaf-layout-dialect.version>2.2.2</thymeleaf-layout-dialect.version>
  </properties>

2）、使用

使用规则：

ThymeleafProperties.java

@ConfigurationProperties(
    prefix = "spring.thymeleaf"
)
public class ThymeleafProperties {
    private static final Charset DEFAULT_ENCODING;
    public static final String DEFAULT_PREFIX = "classpath:/templates/";
    public static final String DEFAULT_SUFFIX = ".html";
    private boolean checkTemplate = true;
    private boolean checkTemplateLocation = true;
    private String prefix = "classpath:/templates/";
    private String suffix = ".html";

只要我们把HTML页面放在classpath:/templates/，thymeleaf就能自动渲染；

测试：

@Controller
public class TestController {

    @RequestMapping("/test")
    public  String testThymelea(){
        //classpath:/templates/th.html
        return "th";
    }
}

静态文件

测试结果：

使用案例：

导入命名空间，有提示作用

<html lang="en" xmlns:th="http://www.thymeleaf.org">

语法：

<body>
    th页面！
    th页面！
    
    <!--th:text 将div里面的文本内容设置为 -->
    <div th:text="${th}">th</div>
</body>

关于导入命名空间之后还没有提示：在进行重启

语法规则：

th:text；改变当前元素里面的文本内容；

文档的：

位置

2）、表达式？

文档的

位置

Simple expressions:（表达式语法）
a. Variable Expressions: ${...}：获取变量值；OGNL；
        1）、获取对象的属性、调用方法
        2）、使用内置的基本对象：
    #ctx : the context object.
    #vars: the context variables.
    #locale : the context locale.
    #request : (only in Web Contexts) the HttpServletRequest object.
    #response : (only in Web Contexts) the HttpServletResponse object.
    #session : (only in Web Contexts) the HttpSession object.
    #servletContext : (only in Web Contexts) the ServletContext object.
        ${session.foo}
      3）、内置的一些工具对象：
        #execInfo : information about the template being processed.
        #messages : methods for obtaining externalized messages inside variables expressions,
        #          in the same way as they would be obtained using #{…} syntax.
        #uris : methods for escaping parts of URLs/URIs
        #conversions : methods for executing the configured conversion service (if any).
        #dates : methods for java.util.Date objects: formatting, component extraction, etc.
        #calendars : analogous to #dates , but for java.util.Calendar objects.
        #numbers : methods for formatting numeric objects.
        #strings : methods for String objects: contains, startsWith, prepending/appending, etc.
        #objects : methods for objects in general.
        #bools : methods for boolean evaluation.
        #arrays : methods for arrays.
        #lists : methods for lists.
        #sets : methods for sets.
        #maps : methods for maps.
        #aggregates : methods for creating aggregates on arrays or collections.
        #ids : methods for dealing with id attributes that might be repeated (for example, as a result of an iteration).

b. Selection Variable Expressions: *{...}：选择表达式：和${}在功能上是一样；
        补充：配合 th:object="${session.user}：       
        <div th:object="${session.user}">        
        <p>Name: <span th:text="*{firstName}">Sebastian</span>.</p>            
        <p>Surname: <span th:text="*{lastName}">Pepper</span>.</p>        
        <p>Nationality: <span th:text="*{nationality}">Saturn</span>.</p>        
        </div>    
c. Message Expressions: #{...}：获取国际化内容
d. Link URL Expressions: @{...}：定义URL；              
        @{/order/process(execId=${execId},execType='FAST')}
f. Fragment Expressions: ~{...}：片段引用表达式              
        <div th:insert="~{commons :: main}">...</div>             
    Literals（字面量）    
        Text literals: 'one text' , 'Another one!' ,…   
        Number literals: 0 , 34 , 3.0 , 12.3 ,…    
        Boolean literals: true , false    
        Null literal: null   
        Literal tokens: one , sometext , main ,…
    Text operations:（文本操作）    
        String concatenation: +    Literal substitutions: |The name is ${name}|
    Arithmetic operations:（数学运算）    
        Binary operators: + , - , * , / , %   
        Minus sign (unary operator): -
    Boolean operations:（布尔运算）    
        Binary operators: and , or    Boolean negation (unary operator): ! , not
    Comparisons and equality:（比较运算）  
      Comparators: > , < , >= , <= ( gt , lt , ge , le )    Equality operators: == , != ( eq , ne )
    Conditional operators:条件运算（三元运算符）    
        If-then: (if) ? (then)    If-then-else: (if) ? (then) : (else)    
        Default: (value) ?: (defaultvalue)Special tokens:   
    No-Operation: _

b补充

测试：

   <div th:text="${th}"></div>
    <div th:utext="${th}"></div>

<!--每次遍历都会生成当前这个标签  -->
<p th:text="${th}" th:each="th:${th1}"></p>

@RequestMapping("/test")
public  String testThymelea(Map<Object,Object> map){
    map.put("th","<h2>helloword</h2>");

    String [] t = {"a","b","c"};
    map.put("th1",t);
    return "th";
}