四、Spring Boot与Web开发

1.web创建

使用SpringBoot：

1.创建SpringBoot应用，选择需要的模块

2.SpringBoot已经默认将这些场景配置好了，只需要在配置文件中指定少量配置就可以运行起来

3.编写业务代码

自动配置原理

每个场景SpringBoot帮我们配置了什么，能不能修改

xxxxAutoConfiguration:帮我们给容器中自动配置组件
xxxxProperties：配置类来封装配置文件的内容

2.静态资源映射规则

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

WebMvcAutoConfiguration类


@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();
    if (!registry.hasMappingForPattern(staticPathPattern)) {
        customizeResourceHandlerRegistration(
            registry.addResourceHandler(staticPathPattern)
            .addResourceLocations(
                this.resourceProperties.getStaticLocations())
            .setCachePeriod(cachePeriod));
    }
}

//欢迎页映射
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ResourceProperties resourceProperties) {
    return new WelcomePageHandlerMapping(resourceProperties.getWelcomePage(),       this.mvcProperties.getStaticPathPattern());}

//图标映射
@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);
        mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
                                                   faviconRequestHandler()));
        return mapping;
    }

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

}

1.所有/webjars/**，都去classpath:classpath:/META-INF/resources/webjars/

webjars:以jar包方式引入静态资源；

<!-- 引入webjars-->
<dependency>
    <groupId>org.webjars</groupId>
    <artifactId>jquery</artifactId>
    <version>3.4.1</version>
</dependency>

2.“/**”访问当前项目的任何资源(静态资源文件夹)

resources 下是类路径classpath

"classpath:/META-INF/resources/",
"classpath:/resources/",
"classpath:/static/", 
"classpath:/public/"
"/"

3.欢迎页：静态文件夹下所有index.html —>映射为"/**"

4.图标映射：所有的**/favicon.ico 都是在静态资源文件下找；

3.模板引擎

jsp Velocity Freemarker Thymeleaf

SpringBoot推荐的Thymeleaf；

语法简单，功能强大；

1.引入Thymeleaf

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

2.Thymeleaf语法

@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");

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

	public static final String DEFAULT_SUFFIX = ".html";

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

1.导入thymeleaf名称空间

xmlns:th="http://www.thymeleaf.org"

2.thymeleaf语法规则

<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<h1>成功</h1>
<div th:text="${hello }">这是欢迎信息</div>
</body>

3.语法规则

a. th:text 改变当前元素里面的文本内容

th 任意属性替换原生属性 th:id="${}"

[外链图片转存失败(img-Br3V5Q5L-1564008788250)(C:\Users\Administrator\Desktop\GitHub\spring-boot\assets\1563967235138.png)]

b.表达式语法

Simple expressions:
    Variable Expressions: ${...}  获取变量值
    	1.获取对象的属性、调用方法
    	2.使用内置的基本对象
        #ctx : the context object.
        #vars: the context variables.
        #locale : the context locale.
        #request : (only in Web Contexts) the HttpServletRequest object.
        #response : (only in Web Contexts) the HttpServletResponse object.
        #session : (only in Web Contexts) the HttpSession object.
        #servletContext : (only in Web Contexts) the ServletContext object.
        3.内置工具对象
#execInfo : information about the template being processed.
#messages : methods for obtaining externalized messages inside variables expressions, in the same way as they would be obtained using #{…} syntax.
#uris : methods for escaping parts of URLs/URIs Page 20 of 106#conversions : methods for executing the configured conversion service (if any).
#dates : methods for java.util.Date objects: formatting, component extraction, etc.
#calendars : analogous to #dates , but for java.util.Calendar objects.
#numbers : methods for formatting numeric objects.
#strings : methods for String objects: contains, startsWith, prepending/appending, etc.
#objects : methods for objects in general.
#bools : methods for boolean evaluation.
#arrays : methods for arrays.
#lists : methods for lists.
#sets : methods for sets.
#maps : methods for maps.
#aggregates : methods for creating aggregates on arrays or collections.
#ids : methods for dealing with id attributes that might be repeated (for example, as a result of an iteration)
    Selection Variable Expressions: *{...} 变量选择表达式，和${}功能上一样
    	补充:配合 th:object使用
    <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链接
    		@{/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:
    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）
    If-then: (if) ? (then)
    If-then-else: (if) ? (then) : (else)
    Default: (value) ?: (defaultvalue)
Special tokens:（特殊操作）
	No-Operation: _  （无操作）

行内写法：[[ $s e s s i o n . u s e r . n a m e]] - - - > t h : t e x t = "$ {session.user.name}"

4.SpringMvc自动配置

1.SpringMvc自动配置

以下是SpringBoot对springmvc的默认：

Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.
- 自动配置了视图解析器（根据方法返回值，返回view，视图对象决定如何渲染）
- ContentNegotiatingViewResolver组合所有的视图解析器
Support for serving static resources, including support for WebJars (see below).
- 静态资源文件夹路径和webjars
Automatic registration of Converter, GenericConverter, Formatter beans.
- 自动注册：类型转换、格式化器数据
Support for HttpMessageConverters (see below).
- 用来转换http请求和响应 user–json
Automatic registration of MessageCodesResolver (see below).
- 定义错误代码生成规则
Static index.html support.
- 静态首页访问
Custom Favicon support (see below).
- 图标
Automatic use of a ConfigurableWebBindingInitializer bean (see below).
- 请求数据绑定到javabean；数据绑定器；

If you want to keep Spring Boot MVC features, and you just want to add additional MVC configuration (interceptors, formatters, view controllers etc.) you can add your own @Configuration class of type WebMvcConfigurerAdapter, but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter or ExceptionHandlerExceptionResolver you can declare a WebMvcRegistrationsAdapterinstance providing such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

2.扩展SpringMvc

编写一个配置类（@Configuration），是WebMvcConfigurerAdapter类型；不能标注@EnableWebMvc

既保留了所有的自动配置，也能使用我们扩展的配置

//使用WebMvcConfigurerAdapter可以来扩展SpringMvc功能
@Configuration
public class MyMvcConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {

        registry.addViewController("/atguigu").setViewName("success");
    }
}

原理：

1.WebMVCAutoConfiguration是SpringMvc的自动配置类

2.在做其他自动配置时会导入；@import（EnableWebMvcConfiguation.class）

@Configuration
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {

	private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();

	//从容器中获取所有的WebMvcConfigurer
	@Autowired(required = false)
	public void setConfigurers(List<WebMvcConfigurer> configurers) {
		if (!CollectionUtils.isEmpty(configurers)) {
			this.configurers.addWebMvcConfigurers(configurers);
            //一个参考实现：将所有的WebMvcConfigurer相关的配置一起调用；
		}
	}

3.所有容器中webConfig一起起作用

4.我们的配置类一起被调用；

3.全面接管SpringMvc

@EnableWebMvc最原始的框架，全部由自己配置

5.如何修改SpringBoot默认配置

模式：

1.SpringBoot自动配置很多组件时候，先看容器中有没有用户自己配置的（@Bean @Component）如果有就用用户的配置，如果没有，才自动配置；如果有些组件可以有多个（ViewResolver）将用户配置的和自己默认的组合起来；

2.在SpringBoot中会有非常多的xxxConfiguration