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013SpringBoot之静态资源映射规则

013SpringBoot之静态资源映射规则

作者: 编程界的小学生 | 来源:发表于2018-05-30 14:11 被阅读49次

一、说在前面的话

我们之间介绍过SpringBoot自动配置的原理,基本上是如下:

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;

具体可参考【SpringBoot之自动配置原理解析】

二、静态资源映射规则

1、对哪些目录映射?

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

2、什么意思?

就我们在上面五个目录下放静态资源(比如:a.js等),可以直接访问(http://localhost:8080/a.js),类似于以前web项目的webapp下;放到其他目录下无法被访问。

3、为什么是那几个目录?

3.1、看源码

我们一起来读下源码,这个是SpringBoot自动配置的WebMvcAutoConfiguration.java类来帮我们干的。

@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));
    }
}

3.2、分析源码

我们重点分析后半截,前半截后面会介绍。

// staticPathPattern是/**
String staticPathPattern = this.mvcProperties.getStaticPathPattern();
if (!registry.hasMappingForPattern(staticPathPattern)) {
    customizeResourceHandlerRegistration(
            registry.addResourceHandler(staticPathPattern)
                    .addResourceLocations(
                            this.resourceProperties.getStaticLocations())
            .setCachePeriod(cachePeriod));
}
this.resourceProperties.getStaticLocations()
========>
ResourceProperties
public String[] getStaticLocations() {
    return this.staticLocations;
}
========>
private String[] staticLocations = RESOURCE_LOCATIONS;
========>
private static final String[] RESOURCE_LOCATIONS;
private static final String[] SERVLET_RESOURCE_LOCATIONS = { "/" };
private static final String[] CLASSPATH_RESOURCE_LOCATIONS = {
            "classpath:/META-INF/resources/", "classpath:/resources/",
            "classpath:/static/", "classpath:/public/" };
========>
static {
    // 可以看到如下是对上面两个数组进行复制操作到一个新数组上,也就是合并。
    RESOURCE_LOCATIONS = new String[CLASSPATH_RESOURCE_LOCATIONS.length
            + SERVLET_RESOURCE_LOCATIONS.length];
    System.arraycopy(SERVLET_RESOURCE_LOCATIONS, 0, RESOURCE_LOCATIONS, 0,
            SERVLET_RESOURCE_LOCATIONS.length);
    System.arraycopy(CLASSPATH_RESOURCE_LOCATIONS, 0, RESOURCE_LOCATIONS,
            SERVLET_RESOURCE_LOCATIONS.length, CLASSPATH_RESOURCE_LOCATIONS.length);
}

所以上述代码经过我的翻译后成为了如下样子:

registry.addResourceHandler("/**").addResourceLocations(
    "classpath:/META-INF/resources/", "classpath:/resources/",
            "classpath:/static/", "classpath:/public/", "/")
    // 设置缓存时间
    .setCachePeriod(cachePeriod));

3.3、一句话概括

WebMvcAutoConfiguration类自动为我们注册了如下目录为静态资源目录,也就是说直接可访问到资源的目录。

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

优先级从上到下。

所以,如果static里面有个index.html,public下面也有个index.html,则优先会加载static下面的index.html,因为优先级!

4、默认首页

PS:就是直接输入ip:port/项目名称默认进入的页面。

4.1、看源码

WebMvcAutoConfiguration.java

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

4.2、分析源码

resourceProperties.getWelcomePage()
========>
public Resource getWelcomePage() {
    // 遍历默认静态资源目录后面拼接个index.html的数组
    // 比如:[/static/index.html, /public/index.html等等]
    for (String location : getStaticWelcomePageLocations()) {
        Resource resource = this.resourceLoader.getResource(location);
        try {
            if (resource.exists()) {
                resource.getURL();
                return resource;
            }
        }
        catch (Exception ex) {
            // Ignore
        }
    }
    return null;
}
========>
// 下面这段代码通俗易懂,就是给默认静态资源目录后面拼接个index.html并返回,比如:/static/index.html
private String[] getStaticWelcomePageLocations() {
    String[] result = new String[this.staticLocations.length];
    for (int i = 0; i < result.length; i++) {
        String location = this.staticLocations[i];
        if (!location.endsWith("/")) {
            location = location + "/";
        }
        result[i] = location + "index.html";
    }
    return result;
}

所以上述代码经过我的翻译后成为了如下样子:

return new WelcomePageHandlerMapping(
    "classpath:/META-INF/resources/index.html",
    "classpath:/resources/index.html",
    "classpath:/static/index.html",
    "classpath:/public/index.html",
    "/index.html"
    , "/**");

4.3、一句话概括

WebMvcAutoConfiguration类自动为我们注册了如下文件为默认首页。

classpath:/META-INF/resources/index.html
classpath:/resources/index.html
classpath:/static/index.html 
classpath:/public/index.html
/index.html

优先级从上到下。

所以,如果static里面有个index.html,public下面也有个index.html,则优先会加载static下面的index.html,因为优先级!

5、favicon.ico

PS:就是 image.png

这个图标。

5.1、看源码

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

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

}

5.2、分析源码

// 首先可以看到的是可以设置是否生效,通过参数spring.mvc.favicon.enabled来配置,若无此参数,则默认是生效的。
@ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
========》
// 可以看到所有的**/favicon.ico都是在faviconRequestHandler()这个方法里找。
mapping.setUrlMap(Collections.singletonMap("**/favicon.ico", faviconRequestHandler()));
========》
faviconRequestHandler().this.resourceProperties.getFaviconLocations()
// 就是之前的五个静态资源文件夹。    
List<Resource> getFaviconLocations() {
    List<Resource> locations = new ArrayList<Resource>(
            this.staticLocations.length + 1);
    if (this.resourceLoader != null) {
        for (String location : this.staticLocations) {
            locations.add(this.resourceLoader.getResource(location));
        }
    }
    locations.add(new ClassPathResource("/"));
    return Collections.unmodifiableList(locations);
}    

5.3、一句话概括

只要把favicon.ico放到如下目录下,就会自动生效。

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

6、webjars

6.1、看源码

WebMvcAutoConfiguration

@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));
    }
}

6.2、分析源码

这次我们来分析前半截。

Integer cachePeriod = this.resourceProperties.getCachePeriod();
if (!registry.hasMappingForPattern("/webjars/**")) {
    customizeResourceHandlerRegistration(
            registry.addResourceHandler("/webjars/**")
                    .addResourceLocations(
                            "classpath:/META-INF/resources/webjars/")
            .setCachePeriod(cachePeriod));
}

6.3、一句话概括

所有/webjars/**都从classpath:/META-INF/resources/webjars/路径下去找对应的静态资源。

6.4、什么是webjars?

就是以jar包的方式引入静态资源。

官网地址:http://www.webjars.org/。类似于maven仓库。

image.png

我们可以做个例子,将jquery引入到项目中

<dependency>
    <groupId>org.webjars</groupId>
    <artifactId>jquery</artifactId>
    <version>3.3.1</version>
</dependency>

看项目依赖

image.png

会自动为我们引入jquery,要怎么使用呢?我们上面说过:

所有/webjars/*都从classpath:/META-INF/resources/webjars/路径下去找对应的静态资源。

所以我们启动项目,访问:http://localhost:8080/webjars/jquery/3.3.1/jquery.js即可。

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