Android WebView实现文件下载功能

WebView控制调用相应的WEB页面进行展示。当碰到页面有下载链接的时候，点击上去是一点反应都没有的。原来是因为WebView默认没有开启文件下载的功能，如果要实现文件下载的功能，需要设置WebView的DownloadListener，通过实现自己的DownloadListener来实现文件的下载。具体操作如下：

1、设置WebView的DownloadListener：

 webView.setDownloadListener(new MyWebViewDownLoadListener());

2、实现MyWebViewDownLoadListener这个类，具体可以如下这样：

private class MyWebViewDownLoadListener implements DownloadListener{ 

  @Override
  public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype,
         long contentLength) {
   Log.i("tag", "url="+url);
   Log.i("tag", "userAgent="+userAgent);
   Log.i("tag", "contentDisposition="+contentDisposition);
   Log.i("tag", "mimetype="+mimetype);
   Log.i("tag", "contentLength="+contentLength);
   Uri uri = Uri.parse(url);
   Intent intent = new Intent(Intent.ACTION_VIEW, uri);
   startActivity(intent);
  }
} 

这只是调用系统中已经内置的浏览器进行下载，还没有WebView本身进行的文件下载，不过，这也基本上满足我们的应用场景了。

我在项目中的运用

项目要求这样：
1.需要使用WebView加载一个网页；
2.网页中有文件下载的链接，点击后需要下载文件到SDcard；
3.然后自动打开文件；

下面是具体解决办法
第一步，对WebView进行一系列设置。

WebView webview=(WebView)layout.findViewById(R.id.webview);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.setWebChromeClient(new MyWebChromeClient());
    webview.requestFocus();
//    webview.loadUrl("file:///android_asset/risktest.html");
    webview.loadUrl(jcrs_sub.get(position).addr);
    // 设置web视图客户端
    webview.setWebViewClient(new MyWebViewClient());
    webview.setDownloadListener(new MyWebViewDownLoadListener()); 

//内部类
public class MyWebViewClient extends WebViewClient {
  // 如果页面中链接，如果希望点击链接继续在当前browser中响应，
  // 而不是新开Android的系统browser中响应该链接，必须覆盖 webview的WebViewClient对象。
  public boolean shouldOverviewUrlLoading(WebView view, String url) {
   L.i("shouldOverviewUrlLoading");
   view.loadUrl(url);
   return true;
  } 

  public void onPageStarted(WebView view, String url, Bitmap favicon) {
   L.i("onPageStarted");
   showProgress();
  } 

  public void onPageFinished(WebView view, String url) {
   L.i("onPageFinished");
   closeProgress();
  } 

  public void onReceivedError(WebView view, int errorCode,
    String description, String failingUrl) {
   L.i("onReceivedError");
   closeProgress();
  }
 } 

// 如果不做任何处理，浏览网页，点击系统“Back”键，整个Browser会调用finish()而结束自身，
 // 如果希望浏览的网 页回退而不是推出浏览器，需要在当前Activity中处理并消费掉该Back事件。
 public boolean onKeyDown(int keyCode, KeyEvent event) {
  // if((keyCode==KeyEvent.KEYCODE_BACK)&&webview.canGoBack()){
  // webview.goBack();
  // return true;
  // }
  return false;
} 

第二步，起线程开始下载文件。

//内部类
private class MyWebViewDownLoadListener implements DownloadListener { 

  @Override
  public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype,
         long contentLength) {
   if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
    Toast t=Toast.makeText(mContext, "需要SD卡。", Toast.LENGTH_LONG);
    t.setGravity(Gravity.CENTER, 0, 0);
    t.show();
    return;
   }
   DownloaderTask task=new DownloaderTask();
   task.execute(url);
  } 

 }
 //内部类
 private class DownloaderTask extends AsyncTask<String, Void, String> { 

  public DownloaderTask() {
  } 

  @Override
  protected String doInBackground(String... params) {
   // TODO Auto-generated method stub
   String url=params[0];
//   Log.i("tag", "url="+url);
   String fileName=url.substring(url.lastIndexOf("/")+1);
   fileName=URLDecoder.decode(fileName);
   Log.i("tag", "fileName="+fileName); 

   File directory=Environment.getExternalStorageDirectory();
   File file=new File(directory,fileName);
   if(file.exists()){
    Log.i("tag", "The file has already exists.");
    return fileName;
   }
   try {
    HttpClient client = new DefaultHttpClient();
//    client.getParams().setIntParameter("http.socket.timeout",3000);//设置超时
    HttpGet get = new HttpGet(url);
    HttpResponse response = client.execute(get);
    if(HttpStatus.SC_OK==response.getStatusLine().getStatusCode()){
     HttpEntity entity = response.getEntity();
     InputStream input = entity.getContent(); 

     writeToSDCard(fileName,input); 

     input.close();
//     entity.consumeContent();
     return fileName;
    }else{
     return null;
    }
   } catch (Exception e) {
    e.printStackTrace();
    return null;
   }
  } 

  @Override
  protected void onCancelled() {
   // TODO Auto-generated method stub
   super.onCancelled();
  } 

  @Override
  protected void onPostExecute(String result) {
   // TODO Auto-generated method stub
   super.onPostExecute(result);
   closeProgressDialog();
   if(result==null){
    Toast t=Toast.makeText(mContext, "连接错误！请稍后再试！", Toast.LENGTH_LONG);
    t.setGravity(Gravity.CENTER, 0, 0);
    t.show();
    return;
   } 

   Toast t=Toast.makeText(mContext, "已保存到SD卡。", Toast.LENGTH_LONG);
   t.setGravity(Gravity.CENTER, 0, 0);
   t.show();
   File directory=Environment.getExternalStorageDirectory();
   File file=new File(directory,result);
   Log.i("tag", "Path="+file.getAbsolutePath()); 

   Intent intent = getFileIntent(file); 

   startActivity(intent); 

  } 

  @Override
  protected void onPreExecute() {
   // TODO Auto-generated method stub
   super.onPreExecute();
   showProgressDialog();
  } 

  @Override
  protected void onProgressUpdate(Void... values) {
   // TODO Auto-generated method stub
   super.onProgressUpdate(values);
  } 

} 

第三步，实现一些工具方法。

private ProgressDialog mDialog;
 private void showProgressDialog(){
  if(mDialog==null){
   mDialog = new ProgressDialog(mContext);
   mDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);//设置风格为圆形进度条
   mDialog.setMessage("正在加载 ，请等待...");
   mDialog.setIndeterminate(false);//设置进度条是否为不明确
   mDialog.setCancelable(true);//设置进度条是否可以按退回键取消
   mDialog.setCanceledOnTouchOutside(false);
   mDialog.setOnDismissListener(new OnDismissListener() { 

    @Override
    public void onDismiss(DialogInterface dialog) {
     // TODO Auto-generated method stub
     mDialog=null;
    }
   });
   mDialog.show(); 

  }
 }
 private void closeProgressDialog(){
  if(mDialog!=null){
   mDialog.dismiss();
   mDialog=null;
  }
 }
  public Intent getFileIntent(File file){
//  Uri uri = Uri.parse("http://m.ql18.com.cn/hpf10/1.pdf");
  Uri uri = Uri.fromFile(file);
  String type = getMIMEType(file);
  Log.i("tag", "type="+type);
  Intent intent = new Intent("android.intent.action.VIEW");
  intent.addCategory("android.intent.category.DEFAULT");
  intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
  intent.setDataAndType(uri, type);
  return intent;
  } 

 public void writeToSDCard(String fileName,InputStream input){ 

  if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
   File directory=Environment.getExternalStorageDirectory();
   File file=new File(directory,fileName);
//   if(file.exists()){
//    Log.i("tag", "The file has already exists.");
//    return;
//   }
   try {
    FileOutputStream fos = new FileOutputStream(file);
    byte[] b = new byte[2048];
    int j = 0;
    while ((j = input.read(b)) != -1) {
     fos.write(b, 0, j);
    }
    fos.flush();
    fos.close();
   } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }else{
   Log.i("tag", "NO SDCard.");
  }
 } 

 private String getMIMEType(File f){
  String type="";
  String fName=f.getName();
  /* 取得扩展名 */
  String end=fName.substring(fName.lastIndexOf(".")+1,fName.length()).toLowerCase(); 

  /* 依扩展名的类型决定MimeType */
  if(end.equals("pdf")){
   type = "application/pdf";//
  }
  else if(end.equals("m4a")||end.equals("mp3")||end.equals("mid")||
  end.equals("xmf")||end.equals("ogg")||end.equals("wav")){
  type = "audio/*";
  }
  else if(end.equals("3gp")||end.equals("mp4")){
  type = "video/*";
  }
  else if(end.equals("jpg")||end.equals("gif")||end.equals("png")||
  end.equals("jpeg")||end.equals("bmp")){
  type = "image/*";
  }
  else if(end.equals("apk")){
  /* android.permission.INSTALL_PACKAGES */
  type = "application/vnd.android.package-archive";
  }
//  else if(end.equals("pptx")||end.equals("ppt")){
//  type = "application/vnd.ms-powerpoint";
//  }else if(end.equals("docx")||end.equals("doc")){
//  type = "application/vnd.ms-word";
//  }else if(end.equals("xlsx")||end.equals("xls")){
//  type = "application/vnd.ms-excel";
//  }
  else{
//  /*如果无法直接打开，就跳出软件列表给用户选择 */
  type="*/*";
  }
  return type;
} 

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