Spring Boot Web开发与thymeleaf模板引擎

简介：

• 使用Springboot应用，选中需要的模块，
• Spring已经默认将场景配置好了，只需在配置文件中少量配置就可以运行起来
• 自己编写业务代码

自动配置原理

这个场景Springboot帮我们配置了什么、能不能修改呢？能修改哪些配置？

xxxxxAutoConfiguration ：帮我们给容器自动配置组件

xxxproperties 配置类来封装配置文件的内容

Springboot对静态资源的映射规则

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties implements ResourceLoaderAware {
  //可以设置和静态资源有关的参数，缓存时间等

｝
 //webMVC的自动配置
WebMvcAuotConfiguration：
        @Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
            if (!this.resourceProperties.isAddMappings()) {
                logger.debug("Default resource handling disabled");
                return;
            }
            Integer cachePeriod = this.resourceProperties.getCachePeriod();
            if (!registry.hasMappingForPattern("/webjars/**")) {
                customizeResourceHandlerRegistration(
                        registry.addResourceHandler("/webjars/**").addResourceLocations("classpath:/META-INF/resources/webjars/").setCachePeriod(cachePeriod));
            }
            String staticPathPattern = this.mvcProperties.getStaticPathPattern();
              //静态资源文件夹映射
            if (!registry.hasMappingForPattern(staticPathPattern)) {
      customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern).addResourceLocations(this.resourceProperties.getStaticLocations()).setCachePeriod(cachePeriod));
            }
        }

        //配置欢迎页映射  默认识别我们template下的index.html; 页面
        @Bean
        public WelcomePageHandlerMapping welcomePageHandlerMapping(ResourceProperties resourceProperties) {
            return new WelcomePageHandlerMapping(resourceProperties.getWelcomePage(),
                    this.mvcProperties.getStaticPathPattern());
        }

       //配置喜欢的图标 即我们网页标签最左边的图标
        @Configuration
        @ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
        public static class FaviconConfiguration {
            private final ResourceProperties resourceProperties;
            public FaviconConfiguration(ResourceProperties resourceProperties) {this.resourceProperties = resourceProperties;
            }

            @Bean
            public SimpleUrlHandlerMapping faviconHandlerMapping() {
                SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
                mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
                  //所有  **/favicon.ico
               mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",faviconRequestHandler()));
                return mapping;
            }

            @Bean
            public ResourceHttpRequestHandler faviconRequestHandler() {
                ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
                requestHandler.setLocations(this.resourceProperties.getFaviconLocations());
                return requestHandler;
            }
        }

静态资源的映射

• 所有的 /webjars/**  都去 classpath:/META-INF/resources/webjars/ 找资源； webjars：以jar包的方式引入静态资源； http://www.webjars.org/

pom.xml 依赖：

<!--引入jquery-webjar-->在访问的时候只需要写webjars下面资源的名称即可
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>jquery</artifactId>
            <version>3.3.1</version>
        </dependency>

访问地址：localhost:8080/webjars/jquery/3.3.1/jquery.js

• "/**" 访问当前项目的任何资源，都去（静态资源的文件夹）找映射 （以下路径优先级从上往下）

  "classpath:/META-INF/resources/",
  "classpath:/resources/",
  "classpath:/static/",
  "classpath:/public/"
  "/"：当前项目的根路径

  localhost:8080/abc === 默认去静态资源文件夹里面找abc

• 欢迎页； 静态资源文件夹下的所有index.html页面；被"/**"映射；
  • localhost:8080/ 找index页面
• 所有的 **/favicon.ico 都是在静态资源文件下找；

模板引擎

常用的模板引擎有：JSP，Velocity、Freemarker、Thymeleaf

Springboot 推荐使用thymeleaf ，语法更简单，功能更强大。

引入thymeleaf

       <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
       </dependency>
SpringBoot默认的thymeleaf 版本为 2.1.6 ，该版本太低，所以我们需要手动切换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>
SpringBoot 的其他默认版本的依赖也是这样切换，如果需要修改的话，一样的切换思路。

配置上面这两个的时候，启动Springboot 会报错误

An attempt was made to call the method org.thymeleaf.spring5.SpringTemplateEngine.setRenderHiddenMarkersBeforeCheckboxes(Z)V but it does not exist. Its class, org.thymeleaf.spring5.SpringTemplateEngine, is available from the following locations:

jar:file:/E:/springboot/repository/org/thymeleaf/thymeleaf-spring5/3.0.9.RELEASE/thymeleaf-spring5-3.0.9.RELEASE.jar!/org/thymeleaf/spring5/SpringTemplateEngine.class

It was loaded from the following location:

file:/E:/springboot/repository/org/thymeleaf/thymeleaf-spring5/3.0.9.RELEASE/thymeleaf-spring5-3.0.9.RELEASE.jar

Action:

Correct the classpath of your application so that it contains a single, compatible version of org.thymeleaf.spring5.SpringTemplateEngine

修改为以下即可：

thymeleaf的使用

配置：

@ConfigurationProperties(prefix = "spring.thymeleaf")
public class ThymeleafProperties {
    private static final Charset DEFAULT_ENCODING = Charset.forName("UTF-8");
    private static final MimeType DEFAULT_CONTENT_TYPE = MimeType.valueOf("text/html");

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

　　public static final String DEFAULT_PREFIX = "classpath:/templates/";
   public static final String DEFAULT_SUFFIX = ".html"; 

使用：

1，在html 页面上导入thymeleaf的命名空间 ， 不导入也可以，只是在写代码的时候，没有相应的代码提示。

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

thymeleaf的语法

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <h1>成功！</h1>
    <!--th:text 将div里面的文本内容设置为 -->
    <div th:text="${hello}">这是显示欢迎信息</div>
</body>
</html>

语法规则：

1）、th:text；改变当前元素里面的文本内容；

　　　　th：任意html属性；来替换原生属性的值

2）、表达式

Simple expressions:（表达式语法）
    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).

    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>

    Message Expressions: #{...}：获取国际化内容
    Link URL Expressions: @{...}：定义URL；
            @{/order/process(execId=${execId},execType='FAST')}
    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: _