# Class (WebSchemeHandler)
Represents a **WebSchemeHandler** object used to intercept requests for a specific scheme.
> **NOTE**
>
> - The initial APIs of this module are supported since API version 9. Updates will be marked with a superscript to indicate their earliest API version.
>
> - The initial APIs of this class are supported since API version 12.
>
> - You can preview how this component looks on a real device, but not in DevEco Studio Previewer.
## Module to Import
```ts
import { webview } from '@kit.ArkWeb';
```
## onRequestStart12+
onRequestStart(callback: (request: WebSchemeHandlerRequest, handler: WebResourceHandler) => boolean): void
Called when a request starts. In this callback, you can determine whether to intercept the request. If **false** is returned, the request is not intercepted and the handler is invalid. If **true** is returned, the request is intercepted.
**System capability**: SystemCapability.Web.Webview.Core
**Parameters**
| Name | Type | Mandatory| Description |
| -------- | -------------------- | ---- | ---------- |
| callback | (request: [WebSchemeHandlerRequest](./arkts-apis-webview-WebSchemeHandlerRequest.md), handler: [WebResourceHandler](./arkts-apis-webview-WebResourceHandler.md)) => boolean | Yes| Callback invoked when a request for the specified scheme starts. **request** represents a request. **handler** provides the custom response header and response body for the **Web** component. The return value indicates whether the request is intercepted.|
**Error codes**
For details about the error codes, see [Webview Error Codes](errorcode-webview.md).
| Error Code| Error Message |
| -------- | ------------------------------------- |
| 401 | Parameter error. Possible causes: 1. Mandatory parameters are left unspecified. 2. Incorrect parameter types. |
**Example**
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
import { buffer } from '@kit.ArkTS';
import { WebNetErrorList } from '@ohos.web.netErrorList';
@Entry
@Component
struct WebComponent {
controller: webview.WebviewController = new webview.WebviewController();
schemeHandler: webview.WebSchemeHandler = new webview.WebSchemeHandler();
htmlData: string = "Source:source
";
build() {
Column() {
Web({ src: 'https://www.example.com', controller: this.controller })
.onControllerAttached(() => {
try {
this.schemeHandler.onRequestStart((request: webview.WebSchemeHandlerRequest, resourceHandler: webview.WebResourceHandler) => {
console.log("[schemeHandler] onRequestStart");
try {
console.log("[schemeHandler] onRequestStart url:" + request.getRequestUrl());
console.log("[schemeHandler] onRequestStart method:" + request.getRequestMethod());
console.log("[schemeHandler] onRequestStart referrer:" + request.getReferrer());
console.log("[schemeHandler] onRequestStart isMainFrame:" + request.isMainFrame());
console.log("[schemeHandler] onRequestStart hasGesture:" + request.hasGesture());
console.log("[schemeHandler] onRequestStart header size:" + request.getHeader().length);
console.log("[schemeHandler] onRequestStart resource type:" + request.getRequestResourceType());
console.log("[schemeHandler] onRequestStart frame url:" + request.getFrameUrl());
let header = request.getHeader();
for (let i = 0; i < header.length; i++) {
console.log("[schemeHandler] onRequestStart header:" + header[i].headerKey + " " + header[i].headerValue);
}
let stream = request.getHttpBodyStream();
if (stream) {
console.log("[schemeHandler] onRequestStart has http body stream");
} else {
console.log("[schemeHandler] onRequestStart has no http body stream");
}
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
if (request.getRequestUrl().endsWith("example.com")) {
return false;
}
let response = new webview.WebSchemeHandlerResponse();
try {
response.setNetErrorCode(WebNetErrorList.NET_OK);
response.setStatus(200);
response.setStatusText("OK");
response.setMimeType("text/html");
response.setEncoding("utf-8");
response.setHeaderByName("header1", "value1", false);
} catch (error) {
console.error(`[schemeHandler] ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
// Before calling didFinish or didFail, call didReceiveResponse to send a response header to this request.
let buf = buffer.from(this.htmlData)
try {
if (buf.length == 0) {
console.log("[schemeHandler] length 0");
resourceHandler.didReceiveResponse(response);
// If the value of buf.length is 0 in normal cases, call resourceHandler.didFinish(). Otherwise, call resourceHandler.didFail().
resourceHandler.didFail(WebNetErrorList.ERR_FAILED);
} else {
console.log("[schemeHandler] length 1");
resourceHandler.didReceiveResponse(response);
resourceHandler.didReceiveResponseBody(buf.buffer);
resourceHandler.didFinish();
}
} catch (error) {
console.error(`[schemeHandler] ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
return true;
})
this.schemeHandler.onRequestStop((request: webview.WebSchemeHandlerRequest) => {
console.log("[schemeHandler] onRequestStop");
});
this.controller.setWebSchemeHandler('https', this.schemeHandler);
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
})
.javaScriptAccess(true)
.domStorageAccess(true)
}
}
}
```
## onRequestStop12+
onRequestStop(callback: Callback\): void
Called when a request is complete, under the prerequisite that the request is indicated as intercepted in the **onRequestStart** callback. Specifically, this callback is invoked in the following cases:
1. The **WebResourceHandler** object calls **didFail** or **didFinish**.
2. The request is interrupted due to other reasons.
**System capability**: SystemCapability.Web.Webview.Core
**Parameters**
| Name | Type | Mandatory| Description |
| -------- | -------------------- | ---- | ---------- |
| callback | Callback\<[WebSchemeHandlerRequest](./arkts-apis-webview-WebSchemeHandlerRequest.md)\> | Yes | Callback invoked when the request is complete.|
**Error codes**
For details about the error codes, see [Webview Error Codes](errorcode-webview.md).
| Error Code| Error Message |
| -------- | ------------------------------------- |
| 401 | Invalid input parameter. |
**Example**
For the complete sample code, see [onRequestStart](#onrequeststart12).