Introduction

The WebClient represent the browser if you work with HtmlUnit. To start using HtmlUnit you have to in instantiate a new WebClient - like starting the browser in the real world.

    try (final WebClient webClient = new WebClient()) {
        // no you have a running browser and you can start doing real things
        // like going to a web page
        final HtmlPage page = webClient.getPage("https://htmlunit.sourceforge.io/");
    }
}

Imitating a specific browser

Often you will want to simulate a specific browser. This is done by passing a com.gargoylesoftware.htmlunit.BrowserVersion into the WebClient constructor. Constants have been provided for some common browsers but you can create your own specific version by instantiating a BrowserVersion.

@Test
public void homePage_Firefox() throws Exception {
    try (final WebClient webClient = new WebClient(BrowserVersion.FIREFOX)) {
        final HtmlPage page = webClient.getPage("https://htmlunit.sourceforge.io/");
        Assert.assertEquals("HtmlUnit – Welcome to HtmlUnit", page.getTitleText());
    }
}

Specifying this BrowserVersion will change the user agent header that is sent up to the server and will change the behavior of some of the JavaScript.

Using the options to adjust the browser

There are various options available to make fine grained adjustments to the browser.

@Test
public void homePage_Firefox() throws Exception {
    try (final WebClient webClient = new WebClient(BrowserVersion.FIREFOX)) {
         // disable javascript
         webClient.getOptions().setJavaScriptEnabled(false);
         // disable css support
         webClient.getOptions().setCssEnabled(false);

        final HtmlPage page = webClient.getPage("https://htmlunit.sourceforge.io/");
        Assert.assertEquals("HtmlUnit – Welcome to HtmlUnit", page.getTitleText());
    }
}

The default values for most options are similar to the default values of real browsers - but (as always) there is one important exception:
HtmlUnit stops the Javascript execution at the first unhandled exception - Browsers do not stop. You can change this by changing the throwExceptionOnScriptError option to false.

@Test
public void homePage_Firefox() throws Exception {
    try (final WebClient webClient = new WebClient(BrowserVersion.FIREFOX)) {
         // procced with the js execution on unhandled js errors
         webClient.getOptions().setThrowExceptionOnScriptError(false);

        final HtmlPage page = webClient.getPage("https://htmlunit.sourceforge.io/");
        Assert.assertEquals("HtmlUnit – Welcome to HtmlUnit", page.getTitleText());
    }
}

For a complete list and more details please have a look at the WebClientOptions API.

Using handlers

There are many handlers used by the WebClient for special purposes. These Handlers are implementing specific interfaces and you are able to replace them with your own implementations. Default implementations are also available.

Polyfills

The number of javascript API's supported by the browsers seems to increase every day. Because of the limited development resources of the HtmlUnit projcet, being on track with this is really hard.
But there are alrady many polyfills available (to add API support for older borwsers). The idea is to use some of these polyfills to add the missing API's.
Starting with version 2.59.0 HtmlUnit supports the integration of polyfills; there is a dedicated option for every supported polyfill (disabled per default) and if enabled, the polifyll is automatically loaded.

@Test
public void fetchSupport() throws Exception {
    try (final WebClient webClient = new WebClient(BrowserVersion.FIREFOX)) {
         // enable fetch api polyfill
         webClient.getOptions().setFetchPolyfillEnabled(true);

        final HtmlPage page = webClient.getPage(....);
    }
}

webClient.getOptions().setFetchPolyfillEnabled(true);

webClient.getOptions().setProxyPolyfillEnabled(true);