【1】是什么
WebJars是将web前端资源（js，css等）打成jar包文件，然后借助Maven工具，以jar包形式对web前端资源进行统一依赖管理，保证这些Web资源版本唯一性。WebJars的jar包部署在Maven中央仓库上。
官网地址 ： https://www.webjars.org/
【2】WebJars使用
在官网首页，找到资源文件对应的maven依赖，写入项目pom.xml文件，然后在页面引用即可。
如下图所示，引入JQuery和Bootstrap：
pom.xml文件如下所示：
<!--引入jquery-webjar-->
<dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.3.1</version>
</dependency>
<!--引入bootstrap-->
<dependency>
<groupId>org.webjars</groupId>
<artifactId>bootstrap</artifactId>
<version>4.0.0</version>
</dependency>引入的jar包如下：
【3】SpringBoot对WebJars支持
查看WebMWebMVCAutoConfiguration源码如下：
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
if (!this.resourceProperties.isAddMappings()) {
logger.debug("Default resource handling disabled");
return;
}
Integer cachePeriod = this.resourceProperties.getCachePeriod();
//注意这里，对webjars支持
if (!registry.hasMappingForPattern("/webjars/**")) {
customizeResourceHandlerRegistration(
registry.addResourceHandler("/webjars/**")
.addResourceLocations(
"classpath:/META-INF/resources/webjars/")
.setCachePeriod(cachePeriod));
}
//这里是对静态资源的映射支持
String staticPathPattern = this.mvcProperties.getStaticPathPattern();
if (!registry.hasMappingForPattern(staticPathPattern)) {
customizeResourceHandlerRegistration(
registry.addResourceHandler(staticPathPattern)
.addResourceLocations(
this.resourceProperties.getStaticLocations())
.setCachePeriod(cachePeriod));
}
}
其中如下代码说明SpringBoot如何对WebJars进行支持：
所有 /webjars/**都去 classpath:/META-INF/resources/webjars/ 找资源；
//注意这里，对webjars支持
if (!registry.hasMappingForPattern("/webjars/**")) {
customizeResourceHandlerRegistration(
registry.addResourceHandler("/webjars/**")
.addResourceLocations(
"classpath:/META-INF/resources/webjars/")
.setCachePeriod(cachePeriod));
}【4】页面使用
页面引入如下：
<link rel="stylesheet" href="/webjars/bootstrap/4.0.0/css/bootstrap.css" />
<script src="/webjars/jquery/3.3.1/jquery.js"></script>
<script src="/webjars/bootstrap/4.0.0/js/bootstrap.js"></script>如上所示，路径中是需要添加版本号的，这是很不友好的，下面去掉版本号。
pom.xml添加依赖如下：
<dependency>
<groupId>org.webjars</groupId>
<artifactId>webjars-locator</artifactId>
<version>0.32</version>
</dependency>
对应的类-WebJarsResourceResolver如下：
- WebJarsResourceResolver 的作用是可以让页面引用省略 webjar 的版本。
package org.springframework.web.servlet.resource;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import org.webjars.WebJarAssetLocator;
import org.springframework.core.io.Resource;
/**
* A {@code ResourceResolver} that delegates to the chain to locate a resource and then
* attempts to find a matching versioned resource contained in a WebJar JAR file.
*
* <p>This allows WebJars.org users to write version agnostic paths in their templates,
* like {@code <script src="/jquery/jquery.min.js"/>}.
* This path will be resolved to the unique version {@code <script src="/jquery/1.2.0/jquery.min.js"/>},
* which is a better fit for HTTP caching and version management in applications.
*
* <p>This also resolves resources for version agnostic HTTP requests {@code "GET /jquery/jquery.min.js"}.
*
* <p>This resolver requires the "org.webjars:webjars-locator" library on classpath,
* and is automatically registered if that library is present.
*
* @author Brian Clozel
* @since 4.2
* @see org.springframework.web.servlet.config.annotation.ResourceChainRegistration
* @see <a href="http://www.webjars.org">webjars.org</a>
*/
public class WebJarsResourceResolver extends AbstractResourceResolver {
private final static String WEBJARS_LOCATION = "META-INF/resources/webjars/";//默认去该路径下寻找
private final static int WEBJARS_LOCATION_LENGTH = WEBJARS_LOCATION.length();
private final WebJarAssetLocator webJarAssetLocator;
/**
* Create a {@code WebJarsResourceResolver} with a default {@code WebJarAssetLocator} instance.
*/
public WebJarsResourceResolver() {
this(new WebJarAssetLocator());
}
/**
* Create a {@code WebJarsResourceResolver} with a custom {@code WebJarAssetLocator} instance,
* e.g. with a custom index.
* @since 4.3
*/
public WebJarsResourceResolver(WebJarAssetLocator webJarAssetLocator) {
this.webJarAssetLocator = webJarAssetLocator;
}
@Override
protected Resource resolveResourceInternal(HttpServletRequest request, String requestPath,
List<? extends Resource> locations, ResourceResolverChain chain) {
Resource resolved = chain.resolveResource(request, requestPath, locations);
if (resolved == null) {
String webJarResourcePath = findWebJarResourcePath(requestPath);
if (webJarResourcePath != null) {
return chain.resolveResource(request, webJarResourcePath, locations);
}
}
return resolved;
}
@Override
protected String resolveUrlPathInternal(String resourceUrlPath,
List<? extends Resource> locations, ResourceResolverChain chain) {
String path = chain.resolveUrlPath(resourceUrlPath, locations);
if (path == null) {
String webJarResourcePath = findWebJarResourcePath(resourceUrlPath);
if (webJarResourcePath != null) {
return chain.resolveUrlPath(webJarResourcePath, locations);
}
}
return path;
}
// 这里获取请求对应的项目中实际资源路径，
//返回结果如：bootstrap/4.0.0/css/bootstrap.css
protected String findWebJarResourcePath(String path) {
int startOffset = (path.startsWith("/") ? 1 : 0);
int endOffset = path.indexOf("/", 1);
if (endOffset != -1) {
String webjar = path.substring(startOffset, endOffset);
String partialPath = path.substring(endOffset + 1);
String webJarPath = webJarAssetLocator.getFullPathExact(webjar, partialPath);
if (webJarPath != null) {
return webJarPath.substring(WEBJARS_LOCATION_LENGTH);
}
}
return null;
}
}页面引用修改如下：
<link rel="stylesheet" href="/webjars/bootstrap/css/bootstrap.css" />
<script src="/webjars/jquery/jquery.js"></script>
<script src="/webjars/bootstrap/js/bootstrap.js"></script>此时，使用两种形式(带版本号和不带版本号)的请求都可以正确获取资源！