我正在尝试编写一个应用程序来从 URL 下载 PDF，将它们存储在 SD 上，然后由 Adob​​e PDF 阅读器或其他应用程序(能够打开 PDF)打开。

到目前为止，我已经“成功下载并存储在SD卡上”(但每次我尝试用PDF阅读器打开PDF时，阅读器都会崩溃并说出现意外错误)，例如http://maven.apache.org/maven-1.x/maven.pdf

这是我的下载器的代码:

//........code set ui stuff
//........code set ui stuff
     new DownloadFile().execute(fileUrl, fileName); 


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;
        }
    }



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.setRequestMethod("GET");
            urlConnection.setDoOutput(true);
            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();
        }
    }
}

在 Debug模式下，我可以看到应用下载它并将此 PDF 存储在/storage/sdcard/testpdf/maven.pdf 上。但是，我猜该文件可能在下载过程中以某种方式损坏，因此无法正常打开...

这是我打算如何用另一个阅读器应用程序打开它的代码:

File pdfFile = new File(Environment.getExternalStorageDirectory() + "/testthreepdf/" + fileName);  // -> 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(documentActivity, "No Application available to view PDF", Toast.LENGTH_SHORT).show();
                    }

最佳答案

您好，问题出在 FileDownloader 类中

 urlConnection.setRequestMethod("GET");
    urlConnection.setDoOutput(true);

您需要删除以上两行，一切都会正常工作。如果问题按预期工作，请将问题标记为已回答。

同一问题的最新解决方案已更新Android PDF Write / Read using Android 9 (API level 28)

用屏幕截图附加工作代码。

MainActivity.java

package com.example.downloadread;

import java.io.File;
import java.io.IOException;

import android.app.Activity;
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.view.Menu;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    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.downloadread;

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.setRequestMethod("GET");
            //urlConnection.setDoOutput(true);
            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();
        }
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.downloadread"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="18" />
    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
    <uses-permission android:name="android.permission.READ_PHONE_STATE"></uses-permission>
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.downloadread.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    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=".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>

关于Android 从 URL 下载 PDF，然后使用 PDF 阅读器打开它，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24740228/