Introduction to WebJars – WebJars简介

最后修改: 2016年 10月 16日


1. Overview


This tutorial introduces WebJars and how to use them in a Java application.


Simply put, WebJars are client side dependencies packaged into JAR archive files. They work with most JVM containers and web frameworks.


Here’s a few popular WebJars: Twitter Bootstrap, jQuery, Angular JS, Chart.js etc; a full list is available on the official website.

这里有几个流行的WebJars。Twitter Bootstrap, jQuery, Angular JS, Chart.js等;完整的列表可在官方网站找到。

2. Why Use WebJars?


This question has a very simple answer – because it’s easy.


Manually adding and managing client side dependencies often results in difficult to maintain codebases.


Also, most Java developers prefer to use Maven and Gradle as build and dependency management tools.


The main problem WebJars solves is making client side dependencies available on Maven Central and usable in any standard Maven project.


Here are a few interesting advantages of WebJars:


  1. We can explicitly and easily manage the client-side dependencies in JVM-based web applications
  2. We can use them with any commonly used build tool, eg: Maven, Gradle, etc
  3. WebJars behave like any other Maven dependency – which means that we get transitive dependencies as well

3. The Maven Dependency


Let’s jump right into it and add Twitter Bootstrap and jQuery to pom.xml:

让我们直接跳进去,把Twitter Bootstrap和jQuery添加到pom.xml


Now Twitter Bootstrap and jQuery are available on the project classpath; we can simply reference them and use them in our application.

现在Twitter Bootstrap和jQuery在项目的classpath中可用;我们可以简单地引用它们并在我们的应用程序中使用它们。

Note: You can check the latest version of the Twitter Bootstrap and the jQuery dependencies on Maven Central.

注意:您可以在Maven中心查看最新版本的Twitter BootstrapjQuery依赖项。

4. The Simple App


With these two WebJar dependencies defined, let’s now set up a simple Spring MVC project to be able to use the client-side dependencies.

在定义了这两个WebJar依赖项之后,我们现在来设置一个简单的Spring MVC项目,以便能够使用客户端依赖项。

Before we get to that however, it’s important to understand that WebJars have nothing to do with Spring, and we’re only using Spring here because it’s a very quick and simple way to set up an MVC project.


Here’s a good place to start to set up the Spring MVC and Spring Boot project.

这里是设置Spring MVC和Spring Boot项目的一个好地方

And, with the simple projet set up, we’ll define a some mappings for our new client dependencies:


public class WebConfig implements WebMvcConfigurer {

    public void addResourceHandlers(ResourceHandlerRegistry registry) {

We can of course do that via XML as well:


<mvc:resources mapping="/webjars/**" location="/webjars/"/>

5. Version-Agnostic Dependencies


When using Spring Framework version 4.2 or higher, it will automatically detect the webjars-locator library on the classpath and use it to automatically resolve the version of any WebJars assets.

当使用Spring Framework 4.2或更高版本时,它将自动检测classpath上的webjars-locator库,并使用它来自动解析任何WebJars资产的版本。

In order to enable this feature, we’ll add the webjars-locator library as a dependency of the application:



In this case, we can reference the WebJars assets without using the version; see next section for a couple actual examples.


6. WebJars on the Client


Let’s add a simple plain HTML welcome page to our application (this is index.html):


        <title>WebJars Demo</title>

Now we can use Twitter Bootstrap and jQuery in the project – let’s use both in our welcome page, starting with Bootstrap:

现在我们可以在项目中使用Twitter Bootstrap和jQuery–让我们在欢迎页面中使用这两种工具,首先是Bootstrap。

<script src="/webjars/bootstrap/3.3.7-1/js/bootstrap.min.js"></script>

For a version-agnostic approach:


<script src="/webjars/bootstrap/js/bootstrap.min.js"></script>

Add jQuery:


<script src="/webjars/jquery/3.1.1/jquery.min.js"></script>

And the version-agnostic approach:


<script src="/webjars/jquery/jquery.min.js"></script>

7. Testing

Now that we’ve added Twitter Bootstrap and jQuery in our HTML page, let’s test them.

现在我们已经在HTML页面中加入了Twitter Bootstrap和jQuery,让我们来测试一下它们。

We’ll add a bootstrap alert into our page:


<div class="container"><br/>
    <div class="alert alert-success">         
        <strong>Success!> It is working as we expected.

Note that some basic understanding of Twitter Bootstrap is assumed here; here’s the getting started guides on the official.

请注意,这里假定对Twitter Bootstrap有一些基本了解;这里有官方的入门指南

This will show an alert as shown below, which means we have successfully added Twitter Bootstrap to our classpath.

这将显示一个警报,如下所示,这意味着我们已经成功地将Twitter Bootstrap添加到我们的classpath。

Let’s use jQuery now. We’ll add a close button to this alert:


<a href="#" class="close" data-dismiss="alert" aria-label="close">×</a>

Now we need to add jQuery and bootstrap.min.js for the close button functionality, so add them inside body tag of index.html, as below:


<script src="/webjars/jquery/3.1.1/jquery.min.js"></script>
<script src="/webjars/bootstrap/3.3.7-1/js/bootstrap.min.js"></script>

Note: If you are using version-agnostic approach, be sure to remove only the version from the path, otherwise, relative imports may not work:


<script src="/webjars/jquery/jquery.min.js"></script>
<script src="/webjars/bootstrap/js/bootstrap.min.js"></script>

This is how our final welcome page should look like:


        <script src="/webjars/jquery/3.1.1/jquery.min.js"></script>
        <script src="/webjars/bootstrap/3.3.7-1/js/bootstrap.min.js"></script>
        <title>WebJars Demo</title>
        <link rel="stylesheet" 
          href="/webjars/bootstrap/3.3.7-1/css/bootstrap.min.css" />
        <div class="container"><br/>
            <div class="alert alert-success">
                <a href="#" class="close" data-dismiss="alert" 
                <strong>Success!> It is working as we expected.

This is how the application should look like. (And the alert should disappear when clicking the close button.)



8. Conclusion


In this quick article, we focused on the basics of using WebJars in a JVM-based project, which makes development and maintenance a lot easier.


We implemented a Spring Boot backed project and used Twitter Bootstrap and jQuery in our project using WebJars.

我们实现了一个支持Spring Boot的项目,并在项目中使用了WebJars的Twitter Bootstrap和jQuery。

The source code of the above-used example can be found in the Github project – this is a Maven project, so it should be easy to import and build.

上述例子的源代码可以在Github项目中找到 – 这是一个Maven项目,所以应该很容易导入和构建。