如何从服务器检索pdf文件并在应用程序中显示以及如何？

Question

如何在 android 中将 pdf 文件转换为 Base64 以及如何使用 json(HTTPURLConection) 从服务器中检索 pdf 文件？

Answer 1

您可以使用

在 android 中将 PDF 转换为 base64

File dir = Environment.getExternalStorageDirectory();
    File yourFile = new File(dir, "path/to/the/file/inside/the/sdcard.ext");
    String encodeFileToBase64Binary = encodeFileToBase64Binary(yourFile);

    private static String encodeFileToBase64Binary(File fileName) throws IOException {
          byte[] bytes = loadFile(fileName);
          byte[] encoded = Base64.encodeBase64(bytes);
          String encodedString = new String(encoded);
          return encodedString;
     }

你可以参考这个链接来解决你的第二个问题Retrieve PDF from server

Answer 2

You can download a PDF fie from server using following Code..


avtivity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.aman.pdfserver.MainActivity">

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="15dp"
        android:text="download"
        android:onClick="download" />

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentRight="true"
        android:layout_below="@+id/button1"
        android:layout_marginTop="38dp"
        android:text="view"
        android:onClick="view" />

</RelativeLayout>


MainActivity.java


    package com.example.aman.pdfserver;

    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import java.io.File;
    import java.io.IOException;

    import android.app.Activity;
    import android.app.ProgressDialog;
    import android.content.ActivityNotFoundException;
    import android.content.Intent;
    import android.net.Uri;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.os.Environment;
    import android.util.Log;
    import android.view.View;
    import android.widget.Toast;

    public class MainActivity extends AppCompatActivity {

        // Progress dialog
        private ProgressDialog pDialog;

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

            pDialog = new ProgressDialog(this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
        }


        public void download(View v)
        {
            new DownloadFile().execute("http://maven.apache.org/maven-1.x/maven.pdf", "maven.pdf");
        }

        public void view(View v)
        {
            File pdfFile = new File(Environment.getExternalStorageDirectory() + "/testthreepdf/" + "maven.pdf");  // -> filename = maven.pdf
            Uri path = Uri.fromFile(pdfFile);
            Intent pdfIntent = new Intent(Intent.ACTION_VIEW);
            pdfIntent.setDataAndType(path, "application/pdf");
            pdfIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

            try{
                startActivity(pdfIntent);
            }catch(ActivityNotFoundException e){
                Toast.makeText(MainActivity.this, "No Application available to view PDF", Toast.LENGTH_SHORT).show();
            }
        }

        private class DownloadFile extends AsyncTask<String, Void, Void>{

            @Override
            protected Void doInBackground(String... strings) {
                String fileUrl = strings[0];   // -> http://maven.apache.org/maven-1.x/maven.pdf
                String fileName = strings[1];  // -> maven.pdf
                String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
                File folder = new File(extStorageDirectory, "testthreepdf");
                folder.mkdir();

                File pdfFile = new File(folder, fileName);

                try{
                    pdfFile.createNewFile();
                }catch (IOException e){
                    e.printStackTrace();
                }
                FileDownloader.downloadFile(fileUrl, pdfFile);
                return null;
            }
        }


    }


FileDownloader.java


package com.example.aman.pdfserver;

/**
 * Created by Aman on 13-12-2016.
 */

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 FileDownloader {
    private static final int  MEGABYTE = 1024 * 1024;

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

            byte[] buffer = new byte[MEGABYTE];
            int bufferLength = 0;
            while((bufferLength = inputStream.read(buffer))>0 ){
                fileOutputStream.write(buffer, 0, bufferLength);
            }
            fileOutputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}