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baeldung - Coding and Testing Stuff: Introduction to WebJars

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二03 | 时间 2016 | 作者 红领巾 ] 0人收藏点击收藏

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1. Overview

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

Simply put, WebJars are client side dependenciespackaged 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 .

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:

Wecan explicitly and easily manage the client-side dependencies in JVM-based web applications Wecan use them with any commonly usedbuild tool, eg: Maven, Gradle, etc 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 :

<dependency>
<groupId>org.webjars</groupId>
<artifactId>bootstrap</artifactId>
<version>3.3.7-1</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.1.1</version>
</dependency>

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

Note: You can check the latestversionof the Twitter Bootstrap and the jQuery dependencies on Maven Central.

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.

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.

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

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry
.addResourceHandler("/webjars/**")
.addResourceLocations("/webjars/");
}
}

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.

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

<dependency>
<groupId>org.webjars</groupId>
<artifactId>webjars-locator</artifactId>
<version>0.30</version>
</dependency>

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 HTMLwelcome page to our application (this is index.html ):

<html>
<head>
<title>WebJars Demo</title>
</head>
<body>
</body>
</html>

Now we can useTwitter Bootstrap and jQuery in the project let’s useboth in our welcome page, starting with 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.

We’ll add a bootstrap alert into our page:

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

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

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

Nowwe need to add jQuery and bootstrap.min.js for the close button functionality, so add them insidebody 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:

<html>
<head>
<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" />
</head>
<body>
<div class="container"><br/><div class="alert alert-success"> <a href="#" class="close" data-dismiss="alert" aria-label="close">×</a> <strong>Success!</strong> It is working as we expected.</div&

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