SpringBoot之Web开发

转 作者 张小翔 | 发表于 | 分类于 2017级

使用 SpringBoot：

  1. 创建 SpringBoot 应用，选中需要的模块

  2. SpringBoot 默认将这些场景自动配置好，只需要在配置文件中指定少量配置

  3. 自己编写业务逻辑代码

SpringBoot 对静态资源的映射规则

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// org/springframework/boot/autoconfigure/web/ResourceProperties.java
@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {
    // 可以设置与静态资源有关的设置，例如缓冲时间等
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// org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration.java
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    if (!this.resourceProperties.isAddMappings()) {
        logger.debug("Default resource handling disabled");
        return;
    }
    Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
    CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
    if (!registry.hasMappingForPattern("/webjars/**")) {
        customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
                                             .addResourceLocations("classpath:/META-INF/resources/webjars/")
                                             .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
    }
    String staticPathPattern = this.mvcProperties.getStaticPathPattern();
    if (!registry.hasMappingForPattern(staticPathPattern)) {
        customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
                                             .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
                                             .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
    }
}

// 配置首页
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext) {
    return new WelcomePageHandlerMapping(new TemplateAvailabilityProviders(applicationContext),
                                         applicationContext, getWelcomePage(), this.mvcProperties.getStaticPathPattern());
}

// 配置喜欢的图标
@Configuration
@ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
public static class FaviconConfiguration implements ResourceLoaderAware {

    private final ResourceProperties resourceProperties;

    private ResourceLoader resourceLoader;

    public FaviconConfiguration(ResourceProperties resourceProperties) {
        this.resourceProperties = resourceProperties;
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    @Bean
    public SimpleUrlHandlerMapping faviconHandlerMapping() {
        SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
        mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
      
 // 在静态文件夹中寻找
        mapping.setUrlMap(Collections.singletonMap("**/favicon.ico", faviconRequestHandler()));
        return mapping;
    }

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

    private List<Resource> resolveFaviconLocations() {
        String[] staticLocations = getResourceLocations(this.resourceProperties.getStaticLocations());
        List<Resource> locations = new ArrayList<>(staticLocations.length + 1);
        Arrays.stream(staticLocations).map(this.resourceLoader::getResource).forEach(locations::add);
        locations.add(new ClassPathResource("/"));
        return Collections.unmodifiableList(locations);
    }

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

    webjars：以 jar 包的方式引入静态资源；

    在 webjars 这个网站上可以使用 maven 导入常用 js 库的 webjar

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    <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，对应

    • classpath:/META-INF/resources/
    • classpath:/resources/
    • classpath:/static/
    • classpath:/public/
    • /：当前项目根路径
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    public class ResourceProperties {

        private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
                                                                      "classpath:/resources/", "classpath:/static/", "classpath:/public/" };

        /**
     * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
     * /resources/, /static/, /public/].
     */
        private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

  3. 欢迎页面的映射

  4. 页面图标映射（可能需要清除浏览器缓存 - Chrome 插件或者 Shift+F5）

    需要放在映射路径的根目录下才可以。

By default, resources are mapped on /**, but you can tune that with the spring.mvc.static-path-pattern property. For instance, relocating all resources to /resources/** can be achieved as follows:

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spring.mvc.static-path-pattern=/resources/**

You can also customize the static resource locations by using the spring.resources.static-locations property (replacing the default values with a list of directory locations). The root Servlet context path, "/", is automatically added as a location as well.

In addition to the “standard” static resource locations mentioned earlier, a special case is made for Webjars content. Any resources with a path in/webjars/** are served from jar files if they are packaged in the Webjars format.

[Tip]
Do not use the src/main/webapp directory if your application is packaged as a jar. Although this directory is a common standard, it works only with war packaging, and it is silently ignored by most build tools if you generate a jar.

模板引擎

Jsp、Thymeleaf、Velocity、Freemarker …

SpringBoot 如果以 jar 的形式打包，而且由于 SpringBoot 使用的是内嵌的 Tomcat ，所以 SpringBoot 推荐使用 Thymeleaf.

引入Thymeleaf

pom.xml

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

Thymeleaf 语法

自动配置的默认规则：

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@ConfigurationProperties(prefix = "spring.thymeleaf")
public class ThymeleafProperties {

private static final Charset DEFAULT_ENCODING = StandardCharsets.UTF_8;

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

public static final String DEFAULT_SUFFIX = ".html";

只要把 html 放在 classpath:/templates/ 后，Thymeleaf 就会自动渲染。

使用：

  1. 导入 thymeleaf 名称空间：

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

  2. 使用语法

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    <!DOCTYPE html>
    <html lang="zh" xmlns:th="http://www.thymeleaf.org">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        <h1>SUCCESS</h1>
        <!-- 将 div 的内容设置为... -->
        <div th:text="${hello}">这是显示欢迎数据</div>
    </body>
    </html>

语法规则

  • 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

    对应的行内写法：

    • th:text => [[]]
    • th:utext => [()]

  • 表达式

    Simple expressions:（表达式语法）

    • Variable Expressions: ${...}

      • 获取对象的属性，调用方法

      • 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.

      • 使用内置的工具对象

        • #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#{} 功能相同，补充使用：配置 th:object 使用，可以直接引用 th:object 的属性

  • Message Expressions: #{...}

    获取国际化内容

  • Link URL Expressions: @{...}

    定义 url，里面可以使用变量等值

  • Fragment Expressions: ~{...}

    片段引用表达式

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）

  • If-then: (if) ? (then)

  • If-then-else: (if) ? (then) : (else)

  • Default: (value) ?: (defaultvalue)

Special tokens:

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  • No-Operation: _