Android WebView无法加载或打开PDF文件，该如何解决？

问题原因 #

WebView默认仅支持渲染HTML等网页资源，无法直接处理PDF文件，因此需要拦截PDF链接并做自定义处理。

实现步骤 #

1. 拦截PDF链接 #

重写WebViewClient的shouldOverrideUrlLoading方法，识别PDF格式的链接并拦截默认处理：

webView.setWebViewClient(new WebViewClient() {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
        String url = request.getUrl().toString();
        // 判断是否为PDF链接
        if (url.endsWith(".pdf")) {
            // 选择需要的处理方式（打开/下载）
            openPdfWithSystemApp(url);
            // downloadPdfFile(url);
            return true;
        }
        return super.shouldOverrideUrlLoading(view, request);
    }
});

2. 方案一：调用系统应用打开PDF #

通过Intent调用手机已有的PDF阅读器打开链接：

private void openPdfWithSystemApp(String pdfUrl) {
    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setDataAndType(Uri.parse(pdfUrl), "application/pdf");
    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    try {
        startActivity(intent);
    } catch (ActivityNotFoundException e) {
        Toast.makeText(this, "未找到可打开PDF的应用，请先安装PDF阅读器", Toast.LENGTH_SHORT).show();
    }
}

3. 方案二：实现PDF下载功能 #

使用系统DownloadManager完成下载，需先添加权限：

第一步：添加权限到AndroidManifest.xml

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="28" />

（注：Android 10及以上使用分区存储，无需WRITE_EXTERNAL_STORAGE权限；若要保存到公共目录，需申请MANAGE_EXTERNAL_STORAGE权限）

第二步：实现下载方法

private void downloadPdfFile(String pdfUrl) {
    DownloadManager.Request request = new DownloadManager.Request(Uri.parse(pdfUrl));
    request.setTitle("PDF下载");
    request.setDescription("正在下载PDF文件");
    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
    // 设置保存到系统下载目录
    request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "downloaded_pdf.pdf");
    
    DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
    if (downloadManager != null) {
        downloadManager.enqueue(request);
        Toast.makeText(this, "开始下载PDF", Toast.LENGTH_SHORT).show();
    }
}

4. 方案三：在WebView内直接加载PDF（可选） #

如果需要在应用内渲染PDF，可使用第三方库（如AndroidPdfViewer）：

第一步：添加依赖到build.gradle(Module)

implementation 'com.github.barteksc:android-pdf-viewer:3.2.0-beta.1'

第二步：布局中添加PDFView

<com.github.barteksc.pdfviewer.PDFView
    android:id="@+id/pdfView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

第三步：修改拦截逻辑，下载并加载PDF

private void loadPdfInApp(String pdfUrl) {
    new AsyncTask<Void, Void, File>() {
        @Override
        protected File doInBackground(Void... voids) {
            try {
                URL url = new URL(pdfUrl);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                File tempFile = new File(getExternalFilesDir(null), "temp_pdf.pdf");
                
                InputStream input = connection.getInputStream();
                FileOutputStream output = new FileOutputStream(tempFile);
                byte[] buffer = new byte[1024];
                int bytesRead;
                while ((bytesRead = input.read(buffer)) != -1) {
                    output.write(buffer, 0, bytesRead);
                }
                output.close();
                input.close();
                return tempFile;
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

        @Override
        protected void onPostExecute(File file) {
            if (file != null && file.exists()) {
                PDFView pdfView = findViewById(R.id.pdfView);
                webView.setVisibility(View.GONE);
                pdfView.setVisibility(View.VISIBLE);
                pdfView.fromFile(file).load();
            } else {
                Toast.makeText(WebViewPage.this, "PDF加载失败", Toast.LENGTH_SHORT).show();
            }
        }
    }.execute();
}

完整修改后的代码 #

public class WebViewPage extends AppCompatActivity {
    WebView webView;
    Button closeweb;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_web_view_page);

        webView = findViewById(R.id.webview);
        closeweb = findViewById(R.id.closeweb);
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);

        webView.setWebViewClient(new WebViewClient() {
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
                String url = request.getUrl().toString();
                if (url.endsWith(".pdf")) {
                    openPdfWithSystemApp(url);
                    // downloadPdfFile(url);
                    return true;
                }
                return super.shouldOverrideUrlLoading(view, request);
            }
        });

        webView.loadUrl("https://www.google.in");
        closeweb.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(WebViewPage.this, HomePage.class);
                startActivity(intent);
            }
        });
    }

    private void openPdfWithSystemApp(String pdfUrl) {
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(Uri.parse(pdfUrl), "application/pdf");
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        try {
            startActivity(intent);
        } catch (ActivityNotFoundException e) {
            Toast.makeText(this, "未找到可打开PDF的应用，请先安装PDF阅读器", Toast.LENGTH_SHORT).show();
        }
    }

    private void downloadPdfFile(String pdfUrl) {
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(pdfUrl));
        request.setTitle("PDF下载");
        request.setDescription("正在下载PDF文件");
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "downloaded_pdf.pdf");
        
        DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
        if (downloadManager != null) {
            downloadManager.enqueue(request);
            Toast.makeText(this, "开始下载PDF", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onBackPressed() {
        if (webView.canGoBack()) {
            webView.goBack();
        } else {
            super.onBackPressed();
        }
    }
}

内容的提问来源于stack exchange，提问作者Abm