Question

尝试下载PDF文件并将其保存在内部存储或共享首选项中并阅读时，我遇到了问题。是否可以在内部存储中下载？我已经从互联网上学到了几个教程，但它并没有起作用。有人可以指导我怎么做吗？非常感谢。

package com.icul.downloadinternal;

import android.content.SharedPreferences;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.preference.PreferenceManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Base64;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.IOException;

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class MainActivity extends AppCompatActivity {

    Button download, read;
    ImageView pdf;
    String url = "https://www.cdc.gov/eval/guide/cdcevalmanual.pdf";

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

        download = (Button) findViewById(R.id.button);
        read = (Button) findViewById(R.id.button2);
        pdf = (ImageView) findViewById(R.id.image);

        download.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    downloadFileSync(url);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        read.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SharedPreferences shre = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
                String previouslyEncodedImage = shre.getString("pdf_data", "");

                if( !previouslyEncodedImage.equalsIgnoreCase("") ){
                    byte[] b = Base64.decode(previouslyEncodedImage, Base64.DEFAULT);
                    Bitmap bitmap = BitmapFactory.decodeByteArray(b, 0 , b.length);
                    pdf.setImageBitmap(bitmap);
                }
                else {
                    Toast.makeText(getApplicationContext(),"No File", Toast.LENGTH_LONG).show();
                }
            }
        });

    }
    public void downloadFileSync(String downloadUrl) throws Exception {

        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(downloadUrl).build();
        Response response = client.newCall(request).execute();
        if (!response.isSuccessful()) {
            throw new IOException("Failed to download file: " + response);
        }

        String encodedImage = Base64.encodeToString(response.body().bytes(), Base64.DEFAULT);
        SharedPreferences shre = PreferenceManager.getDefaultSharedPreferences(this);
        SharedPreferences.Editor edit = shre.edit();
        edit.putString("pdf_data", encodedImage);
        edit.commit();
    }
}

Answer 1

摇篮

compile 'com.squareup.okhttp3:okhttp:3.8.0'

写：

public void downloadFileSync(String downloadUrl) throws Exception {

    OkHttpClient client = new OkHttpClient();
    Request request = new Request.Builder().url(downloadUrl).build();
    Response response = client.newCall(request).execute();
    if (!response.isSuccessful()) {
        throw new IOException("Failed to download file: " + response);
    }
    String encodedImage = Base64.encodeToString( response.body().bytes(), Base64.DEFAULT);

    SharedPreferences shre = 
    PreferenceManager.getDefaultSharedPreferences(this);
    Editor edit=shre.edit();
    edit.putString("pdf_data",encodedImage);
    edit.commit();
 }

阅读：

SharedPreferences shre = PreferenceManager.getDefaultSharedPreferences(this);
String previouslyEncodedImage = shre.getString("pdf_data", "");

if( !previouslyEncodedImage.equalsIgnoreCase("") ){
    byte[] b = Base64.decode(previouslyEncodedImage, Base64.DEFAULT);
    // .....
}

Answer 2

请将以下文件/方法添加到您的项目中

PdfDownloader.java
PDFDownloaderAsyncTask.java

然后使用以下方法 handleViewPdf 来查看pdf：

private void handleViewPdf() {

    File folder = getAppDirectory(context);
    String fileName = "test.pdf";// getPdfFileName(pdfUrl);
    File pdfFile = new File(folder, fileName);

    if(pdfFile.exists() && pdfFile.length() > 0) {
        openPDFFile(context, Uri.fromFile(pdfFile));
    }
    else {
        if(pdfFile.length() == 0) {
            pdfFile.delete();
        }
        try {
            pdfFile.createNewFile();
        }
        catch(IOException e) {
            e.printStackTrace();
        }
        ArrayList<String> fileNameAndURL = new ArrayList<>();
        fileNameAndURL.add(pdfFile.toString());
        fileNameAndURL.add(pdfUrl);
        fileNameAndURL.add(fileName);
        if(pdfDownloaderAsyncTask == null) {
            pdfDownloaderAsyncTask = new PDFDownloaderAsyncTask(context, pdfFile);
        }
        if(hasInternetConnection(context)) {
            if(!pdfDownloaderAsyncTask.isDownloadingPdf()) {
                pdfDownloaderAsyncTask = new PDFDownloaderAsyncTask(context, pdfFile);
                pdfDownloaderAsyncTask.execute(fileNameAndURL);
            }
        }
        else {
            //show error
        }
    }
}

<强> PDFDownloaderAsyncTask.java

    import java.io.File;
    import java.util.ArrayList;

    import android.content.Context;
    import android.net.Uri;
    import android.os.AsyncTask;
    import android.os.Handler;
    import android.text.TextUtils;
    import android.widget.Toast;


    public class PDFDownloaderAsyncTask extends AsyncTask<ArrayList<String>, Void, String> {

        private boolean isDownloadingPdf = false;

        private File    file;
        private Context context;

        public PDFDownloaderAsyncTask(Context context, File file) {

            this.file = file;
            this.context = context;
            this.isDownloadingPdf = false;
        }

        public boolean isDownloadingPdf() {

            return this.isDownloadingPdf;
        }

        @Override
        protected void onPreExecute() {

            super.onPreExecute();
            //show loader etc
        }

        @Override
        protected String doInBackground(ArrayList<String>... params) {

            isDownloadingPdf = true;
            File file = new File(params[0].get(0));
            String fileStatus = PdfDownloader.downloadFile(params[0].get(1), file);
            return fileStatus;
        }

        @Override
        protected void onPostExecute(String result) {

            super.onPostExecute(result);
            Loader.hideLoader();
            if(!TextUtils.isEmpty(result) && result.equalsIgnoreCase(context.getString(R.string.txt_success))) {
                showPdf();
            }
            else {
                isDownloadingPdf = false;
                Toast.makeText(context, context.getString(R.string.error_could_not_download_pdf), Toast.LENGTH_LONG).show();
                file.delete();
            }
        }

        @Override
        protected void onCancelled() {

            isDownloadingPdf = false;
            super.onCancelled();
            //Loader.hideLoader();
        }

        @Override
        protected void onCancelled(String s) {

            isDownloadingPdf = false;
            super.onCancelled(s);
            //Loader.hideLoader();
        }

        private void showPdf() {

            new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {

                    isDownloadingPdf = false;
                    openPDFFile(context, Uri.fromFile(file));
                }
            }, 1000);
        }
    }

<强> PdfDownloader.java

package com.pdf;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class PdfDownloader {
    private static final int MEGABYTE = 1024 * 1024;

    public static String downloadFile(String fileUrl, File directory) {

        String downloadStatus;
        try {

            URL url = new URL(fileUrl);
            HttpURLConnection urlConnection =(HttpURLConnection) url.openConnection();
            urlConnection.connect();

            InputStream inputStream = urlConnection.getInputStream();
            FileOutputStream fileOutputStream = new FileOutputStream(directory);
            int totalSize = urlConnection.getContentLength();

            Log.d("PDF", "Total size: " + totalSize);
            byte[] buffer = new byte[MEGABYTE];
            int bufferLength = 0;
            while((bufferLength = inputStream.read(buffer)) > 0) {
                fileOutputStream.write(buffer, 0, bufferLength);
            }
            downloadStatus = "success";
            fileOutputStream.close();
        }
        catch(FileNotFoundException e) {
            downloadStatus = "FileNotFoundException";
            e.printStackTrace();
        }
        catch(MalformedURLException e) {
            downloadStatus = "MalformedURLException";
            e.printStackTrace();
        }
        catch(IOException e) {
            downloadStatus = "IOException";
            e.printStackTrace();
        }
        Log.d("PDF", "Download Status: " + downloadStatus);
        return downloadStatus;
    }


    public static void openPDFFile(Context context, Uri path) {

        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(path, "application/pdf");
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        try {
            context.startActivity(intent);
        }
        catch(ActivityNotFoundException e) {
            Toast.makeText(context, context.getString(R.string.txt_no_pdf_available), Toast.LENGTH_SHORT).show();
        }
        Loader.hideLoader();
    }

    public static File getAppDirectory(Context context) {

        String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
        File folder = new File(extStorageDirectory, context.getString(R.string.app_folder_name).trim());
        if(!folder.exists()) {
            boolean success = folder.mkdirs();
            Log.d("Directory", "mkdirs():" + success);
        }
        return folder;
    }

}

android studio下载pdf文件并将其保存在sharedpreferences中

2 个答案: