Android Webview shouldInterceptRequest: Advanced Features

Imagine this: you’re loading a webpage in your Android app’s WebView, and suddenly, ads, unnecessary data, or even pop-ups start to clog up your user experience. Sounds annoying, right? Thankfully, shouldInterceptRequest is here to help. In this guide, we’ll dive into how you can use shouldInterceptRequest to take control over every single request that goes through your WebView in Android. Whether you want to block ads, add authentication, or just cache some content for speed, you’re in the right place.

What is shouldInterceptRequest, and Why Should You Care?

At its core, shouldInterceptRequest is like a gatekeeper for every network request your WebView makes. When a page inside your WebView tries to fetch any resource (like images, scripts, or styles), shouldInterceptRequest lets you intercept the request, inspect it, and decide whether to allow, modify, or block it entirely.

Here’s how to set up a basic shouldInterceptRequest in a CustomWebViewClient:

class CustomWebViewClient : WebViewClient() {
    override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
        // Your custom logic goes here
        return super.shouldInterceptRequest(view, request)
    }
}

Redirecting and Modifying Requests

Imagine you want to load a cached version of a resource or redirect a URL to save bandwidth. With shouldInterceptRequest, you can easily swap out the requested resource for a different one.

override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
    val url = request?.url.toString()
    if (url.contains("example.com/ad")) {
        return WebResourceResponse(
            "text/plain", "utf-8",
            ByteArrayInputStream("".toByteArray())
        )
    }
    return super.shouldInterceptRequest(view, request)
}

Tip: Don’t go overboard with redirects. Redirecting multiple requests can slow down your WebView’s performance, especially on low-end devices.

Don’t go overboard with redirects. Redirecting multiple requests can slow down your WebView’s performance, especially on low-end devices.

Ad Blocking in WebView

Let’s face it, ads are everywhere, and sometimes they can overwhelm the user experience. By using shouldInterceptRequest, you can block those pesky ads based on their URLs.

val blockedUrls = listOf("adserver.com", "trackersite.com")
override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
    val url = request?.url.toString()
    if (blockedUrls.any { url.contains(it) }) {
        return WebResourceResponse("text/plain", "utf-8", ByteArrayInputStream("".toByteArray()))
    }
    return super.shouldInterceptRequest(view, request)
}

In this example, we use a simple list of blocked URLs. If the requested URL matches any in the list, we return an empty response, effectively blocking the ad.

Data Compression: Save Bandwidth

If your app loads lots of data-heavy resources, you can reduce bandwidth by compressing the data before sending it. Here’s how you can set up gzip compression:

override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
    val connection = URL(request?.url.toString()).openConnection()
    connection.setRequestProperty("Accept-Encoding", "gzip")

    val inputStream = if (connection.getHeaderField("Content-Encoding") == "gzip") {
        GZIPInputStream(connection.getInputStream())
    } else {
        connection.getInputStream()
    }

    return WebResourceResponse(
        "text/html", "utf-8", inputStream
    )
}

Why Compress?

Compression can save bandwidth and reduce loading times, which is crucial for users with limited data plans or in areas with slow connections.

Caching Resources Locally

Let’s say you want to load some resources only once and cache them for later use. This approach can significantly improve performance, especially if your app uses the same resources repeatedly.

override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
    val url = request?.url.toString()
    val cachedResponse = getFromCache(url)

    return if (cachedResponse != null) {
        WebResourceResponse("text/html", "utf-8", ByteArrayInputStream(cachedResponse))
    } else {
        super.shouldInterceptRequest(view, request)
    }
}

private fun getFromCache(url: String): ByteArray? {
    // Implement caching logic here
    return null
}

In this example, getFromCache attempts to fetch the requested resource from local storage. If it finds it, it returns the cached response; otherwise, it allows the request to proceed normally.

Adding Authentication Headers

For resources that require authentication, like APIs, you can include custom headers with your requests. Here’s how:

override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
    val connection = URL(request?.url.toString()).openConnection() as HttpURLConnection
    connection.setRequestProperty("Authorization", "Bearer YOUR_TOKEN")

    val inputStream = connection.inputStream
    return WebResourceResponse(
        "text/html", "utf-8", inputStream
    )
}

In this example, we’re adding an Authorization header to each request. This is particularly useful when accessing secure resources.

Using shouldInterceptRequest with Android’s WebView unlocks a world of possibilities for controlling, optimizing, and securing your in-app web browsing experience. Whether you’re blocking ads, compressing data, caching resources, or adding authentication, these techniques can dramatically improve both performance and user experience. Play around with these tips, and don’t forget to keep the user experience in mind while customizing your WebView.