从SpringBoot源码看资源映射原理

大厂_uFW

于 2025-02-10 11:55:24 发布

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文章标签： spring boot 后端 java

本文链接：https://blog.youkuaiyun.com/2501_90433155/article/details/145547115

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在谈SpringBoot之前，我们先回顾一下SSM中关于资源配置是如何实现的。

在SSM环境下，一般我们可以通过<mvc:resources />节点来配置不拦截静态资源，就像下边这样：

<mvc:resources mapping=“/js/**” location=“/js/” />

<mvc:resources mapping=“/css/**” location=“/css/” />

<mvc:resources mapping=“/img/**” location=“/img/” />

这里的/**表示的是可以匹配任意层级的路径，属于 ant风格表达式 ，感兴趣的小伙伴自行百度了解即可，所以也可以写成下面这样

<mvc:resources mapping=“/**” location=“/” />

上边的这种配置方式是属于XML配置的方式，SpringMVC的配置方式除了XML配置，也是可以通过java代码配置的，只需要我们自己定义一个类，来继WebMvcConfigurationSupport这个类即可，我们看一下WebMvcConfigurationSupport的源码部分：

/**

Override this method to add resource handlers for serving static resources.
@see ResourceHandlerRegistry

protected void addResourceHandlers(ResourceHandlerRegistry registry) {

}

上边的注释写的很清楚，重写这个方法来增加一个静态资源的映射。那么具体怎么写呢？

我们再按照注释看一下ResourceHandlerRegistry的源码，重点看一下对这个类的注释，如下。

To create a resource handler, use {@link #addResourceHandler(String…)} providing the URL path patterns

/ * for which the handler should be invoked to serve static resources (e.g. {@code “/resources/**”}).

大概意思就是为了创建资源的处理器，要调用addResourceHandler方法来提供url的表达式，这个方法是为了服务静态资源的（ps:英语水平也一般，了解大意即可）

然后我们去看addResourceHandler方法：

/**

Add a resource handler for serving static resources based on the specified URL path patterns.
The handler will be invoked for every incoming request that matches to one of the specified
path patterns.
Patterns like {@code "/static/**"} or {@code "/css/{filename:\\w+\\.css}"} are allowed.
See {@link org.springframework.util.AntPathMatcher} for more details on the syntax.
@return a {@link ResourceHandlerRegistration} to use to further configure the
registered resource handler

public ResourceHandlerRegistration addResourceHandler(String… pathPatterns) {

ResourceHandlerRegistration registration = new ResourceHandlerRegistration(pathPatterns);

this.registrations.add(registration);

return registration;

}

我们看到这个方法执行后返回了一个新的类ResourceHandlerRegistration

那我们再来看一下这个类中的核心方法

/**

Add one or more resource locations from which to serve static content.
Each location must point to a valid directory. Multiple locations may
be specified as a comma-separated list, and the locations will be checked
for a given resource in the order specified.
For example, {{@code "/"}, {@code "classpath:/META-INF/public-web-resources/"}}
allows resources to be served both from the web application root and
from any JAR on the classpath that contains a
{@code /META-INF/public-web-resources/} directory, with resources in the
web application root taking precedence.
For {@link org.springframework.core.io.UrlResource URL-based resources}
(e.g. files, HTTP URLs, etc) this method supports a special prefix to
indicate the charset associated with the URL so that relative paths
appended to it can be encoded correctly, e.g.
{@code [charset=Windows-31J]https://example.org/path}.
@return the same {@link ResourceHandlerRegistration} instance, for
chained method invocation

public ResourceHandlerRegistration addResourceLocations(String… resourceLocations) {

this.locationValues.addAll(Arrays.asList(resourceLocations));

return this;

}

上边注释的大意就是增加一个或者多个静态资源路径，并举了一些例子。源码我们就看到这里。

所以我们可以像这样实现资源的映射：

import org.springframework.context.annotation.Configuration;

import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;

import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

/**

@author liumeng
@Date: 2020/9/25 09:20
@Description:

@Configuration

public class SpringMvcConfig extends WebMvcConfigurationSupport {

@Override

protected void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler(“/**”).addResourceLocations(“/”);

}

关于SpringMVC中的资源映射部分就介绍到这，那么我们继续来看SpringBoot的资源映射吧。

SpringBoot的资源映射

===================

其实SpringBoot的资源映射也是一脉相承的，当我们初始化一个SpringBoot项目后，静态资源会默认存在resource/static目录中，那么SpringBoot的底层是怎么实现的呢，接下来我们就去源码里探索一下。

SpringBoot的源码在WebMvcAutoConfiguration这个类中，我们发现了熟悉的代码：

@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)); } }

这里面我们重点看下边这部分

String staticPathPattern = this.mvcProperties.getStaticPathPattern();

if (!registry.hasMappingForPattern(staticPathPattern)) {

customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern) .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))

.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl)); }

我们看一下getStaticPathPattern()方法的实现，发现获得的就是

/**