application-dev/web/web-download.md

# 使用Web组件的下载能力

> **说明：**
>
>Web组件的下载功能要求应用通过调用[WebDownloadItem.start](../reference/apis-arkweb/js-apis-webview.md#start11)来指定下载文件的保存路径。值得注意的是，WebDownloadItem.start并非启动下载，下载过程实际上在用户点击页面链接时即已开始。WebDownloadItem.start的作用是将已经下载到临时文件的部分移动到指定目标路径，后续未完成的下载的内容将直接保存到指定目标路径，临时目录位于`/data/storage/el2/base/cache/web/Temp/`。如果决定取消当前下载，应调用[WebDownloadItem.cancel](../reference/apis-arkweb/js-apis-webview.md#cancel11)，此时临时文件将被删除。
>
>如果不希望在WebDownloadItem.start之前将文件下载到临时目录，可以通过WebDownloadItem.cancel中断下载，后续可通过[WebDownloadManager.resumeDownload](../reference/apis-arkweb/js-apis-webview.md#resumedownload11)恢复中断的下载。

## 监听页面触发的下载

通过[setDownloadDelegate()](../reference/apis-arkweb/js-apis-webview.md#setdownloaddelegate11)向Web组件注册一个DownloadDelegate来监听页面触发的下载任务。资源由Web组件来下载，Web组件会通过DownloadDelegate将下载的进度通知给应用。

下面的示例中，在应用的rawfile中创建index.html以及download.html。应用启动后会创建一个Web组件并加载index.html，点击setDownloadDelegate按钮向Web组件注册一个DownloadDelegate，点击页面里的下载按钮的时候会触发一个下载任务，在DownloadDelegate中可以监听到下载的进度。

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // 传入一个下载路径，并开始下载。
              // 如果传入一个不存在的路径，则会下载到默认/data/storage/el2/base/cache/web/目录。
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              // 下载任务的唯一标识。
              console.log("download update guid: " + webDownloadItem.getGuid());
              // 下载的进度。
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              // 当前的下载速度。
              console.log("download update speed: " + webDownloadItem.getCurrentSpeed())
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // 下载任务失败的错误码。
              console.log("download failed last error code: " + webDownloadItem.getLastErrorCode());
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: $rawfile('index.html'), controller: this.controller })
    }
  }
}
```

加载的html文件。
```html
<!-- index.html -->
<!DOCTYPE html>
<html>
<body>
// 点击视频右下方菜单的下载按钮会触发下载任务。
<video controls="controls" width="800px" height="580px"
       src="http://vjs.zencdn.net/v/oceans.mp4"
       type="video/mp4">
</video>
<a href='data:text/html,%3Ch1%3EHello%2C%20World%21%3C%2Fh1%3E' download='download.html'>下载download.html</a>
</body>
</html>
```

待下载的html文件。
```html
<!-- download.html -->
<!DOCTYPE html>
<html>
<body>
<h1>download test</h1>
</body>
</html>
```

## 使用Web组件发起一个下载任务

使用[startDownload()](../reference/apis-arkweb/js-apis-webview.md#startdownload11)接口发起一个下载。
Web组件发起的下载会根据当前显示的url以及Web组件默认的Referrer Policy来计算referrer。

  在下面的示例中，先点击setDownloadDelegate按钮向Web注册一个监听类，然后点击startDownload主动发起了一个下载，
  该下载任务也会通过设置的DownloadDelegate来通知app下载的进度。

```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // 传入一个下载路径，并开始下载。
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update guid: " + webDownloadItem.getGuid());
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            // 这里指定下载地址为 https://www.example.com/，Web组件会发起一个下载任务将该页面下载下来。
            // 开发者需要替换为自己想要下载的内容的地址。
            this.controller.startDownload('https://www.example.com/');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

使用[DocumentViewPicker()](../reference/apis-core-file-kit/js-apis-file-picker.md#documentviewpicker)获取当前示例的默认下载目录，将该目录设置为下载目录。
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
import { picker, fileUri } from  '@kit.CoreFileKit';
@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // 使用DocumentViewPicker()获取当前示例的默认下载目录，将该目录设置为下载目录
              getDownloadPathFromPicker().then((downloadPath) => {
                webDownloadItem.start(downloadPath + '/' + webDownloadItem.getSuggestedFileName());
              });

            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              // 下载任务的唯一标识。
              console.log("download update guid: " + webDownloadItem.getGuid());
              // 下载的进度。
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              // 当前的下载速度。
              console.log("download update speed: " + webDownloadItem.getCurrentSpeed())
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // 下载任务失败的错误码。
              console.log("download failed last error code: " + webDownloadItem.getLastErrorCode());
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Web({ src: $rawfile('index.html'), controller: this.controller })
    }
  }

}
function getDownloadPathFromPicker(): Promise<string> {
  return new Promise<string>(resolve => {
    try {
      const documentSaveOptions = new picker.DocumentSaveOptions();
      documentSaveOptions.pickerMode = picker.DocumentPickerMode.DOWNLOAD
      const documentPicker = new picker.DocumentViewPicker();
      documentPicker.save(documentSaveOptions).then(async (documentSaveResult: Array<string>) => {
        if (documentSaveResult.length <= 0) {
          resolve('');
          return;
        }
        const uriString = documentSaveResult[0];
        if (!uriString) {
          resolve('');
          return;
        }
        const uri = new fileUri.FileUri(uriString);
        resolve(uri.path);
      }).catch((err: BusinessError) => {
        console.error(`ErrorCode: ${err.code},  Message: ${err.message}`);
        resolve('');
      });
    } catch (error) {
      resolve('');
    }
  })
}
```


## 使用Web组件恢复进程退出时未下载完成的任务
在Web组件启动时，可通过[resumeDownload()](../reference/apis-arkweb/js-apis-webview.md#resumedownload11)接口恢复未完成的下载任务。

在以下示例中，通过“record”按钮将当前下载任务保存至持久化文件中，应用重启后，可借助“recovery”按钮恢复持久化的下载任务。示例代码实现了将当前下载任务持久化保存至文件的功能，若需保存多个下载任务，应用可根据需求调整持久化的时机与方式。
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
import { downloadUtil, fileName, filePath } from './downloadUtil'; // downloadUtil.ets 见下文

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  delegate: webview.WebDownloadDelegate = new webview.WebDownloadDelegate();
  download: webview.WebDownloadItem = new webview.WebDownloadItem();
  // 用于记录失败的下载任务。
  failedData: Uint8Array = new Uint8Array();

  build() {
    Column() {
      Button('setDownloadDelegate')
        .onClick(() => {
          try {
            this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // 传入一个下载路径，并开始下载。
              webDownloadItem.start("/data/storage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download update percent complete: " + webDownloadItem.getPercentComplete());
              this.download = webDownloadItem;
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // 序列化失败的下载任务到一个字节数组。
              this.failedData = webDownloadItem.serialize();
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
            webview.WebDownloadManager.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      Button('startDownload')
        .onClick(() => {
          try {
            // 这里指定下载地址为 https://www.example.com/，Web组件会发起一个下载任务将该页面下载下来。
            // 开发者需要替换为自己想要下载的内容的地址。
            this.controller.startDownload('https://www.example.com/');
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      // 将当前的下载任务信息序列化保存，用于后续恢复下载任务。
      // 当前用例仅展示下载一个任务的场景，多任务场景请按需扩展。
      Button('record')
        .onClick(() => {
          try {
            // 保存当前下载数据到持久化文档中。
            downloadUtil.saveDownloadInfo(downloadUtil.uint8ArrayToStr(this.download.serialize()));
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })
      // 从序列化的下载任务信息中，恢复下载任务。
      // 按钮触发时必须保证WebDownloadManager.setDownloadDelegate设置完成。
      Button('recovery')
        .onClick(() => {
          try {
            // 当前默认持久化文件存在，用户根据实际情况增加判断。
            let webDownloadItem =
              webview.WebDownloadItem.deserialize(downloadUtil.strToUint8Array(downloadUtil.readFileSync(filePath, fileName)));
            webview.WebDownloadManager.resumeDownload(webDownloadItem);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }
        })

      Web({ src: 'www.example.com', controller: this.controller })
    }
  }
}
```

下载任务信息持久化工具类文件。
```ts
// downloadUtil.ets
import { util } from '@kit.ArkTS';
import fileStream from '@ohos.file.fs';

const helper = new util.Base64Helper();

export const filePath = getContext().filesDir;
export const fileName = 'demoFile.txt';
export namespace  downloadUtil {

  export function uint8ArrayToStr(uint8Array: Uint8Array): string {
    return helper.encodeToStringSync(uint8Array);
  }

  export function strToUint8Array(str: string): Uint8Array {
    return helper.decodeSync(str);
  }

  export function saveDownloadInfo(downloadInfo: string): void {
    if (!fileExists(filePath)) {
      mkDirectorySync(filePath);
    }

    writeToFileSync(filePath, fileName, downloadInfo);
  }

  export function fileExists(filePath: string): boolean {
    try {
      return fileStream.accessSync(filePath);
    } catch (error) {
      return false;
    }
  }

  export function mkDirectorySync(directoryPath: string, recursion?: boolean): void {
    try {
      fileStream.mkdirSync(directoryPath, recursion ?? false);
    } catch (error) {
      console.error(`mk dir error. err message: ${error.message}, err code: ${error.code}`);
    }
  }

  export function writeToFileSync(dir: string, fileName: string, msg: string): void {
    let file = fileStream.openSync(dir + '/' + fileName, fileStream.OpenMode.WRITE_ONLY | fileStream.OpenMode.CREATE);
    fileStream.writeSync(file.fd, msg);
  }

  export function readFileSync(dir: string, fileName: string): string {
    return fileStream.readTextSync(dir + '/' + fileName);
  }

}
```