android从网络获取pdf下载显示，并且可以打开本地assets内的pdf文件

最近的项目中需要嵌入一个打开pdf下载查看的功能，研究了一下，这里写出来做一个备忘，顺便可以和大家做一下交流学习。好了，首先我们先考虑一下这个需求：
1.网络下载
2.下载后的保存文件地址
3.通过文件地址展示pdf
没错，就是这么简单：
下面附上代码demo
part1：mainactivity，
这里我先是使用了打开本地的assets文件

public class MainActivity extends AppCompatActivity {
   private Context mContext=this;
   private Button button;
   private Handler handler=new Handler();
   private PDFView pdfView;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_pdf);
       button= (Button) findViewById(R.id.button);
       pdfView = (PDFView) findViewById(R.id.pdfView);

               // 在我这个测试例子中，事先准备一个叫做sample.pdf的pdf大文件放到assets目录下。
               // 从assets文件目录下读取名为 sample.pdf的文件，缺省把该pdf定位到第一页。
               pdfView.fromAsset("sample.pdf").defaultPage(1).onPageChange(new OnPageChangeListener() {

                       @Override
                       public void onPageChanged(int page, int pageCount) {
                               // 当用户在翻页时候将回调。
                               Toast.makeText(getApplicationContext(), page + " / " + pageCount, Toast.LENGTH_SHORT).show();
                           }
                   }).load();

       button.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               Intent intent=new Intent(mContext,DownLoaderActivity.class);
               startActivity(intent);
           }
       });
   }
}

part2：这里是我在点击按钮之后进入的下载并展示页面

public class DownLoaderActivity extends AppCompatActivity 
implements OnPageChangeListener,OnLoadCompleteListener,OnDrawListener {
   private OkHttpClient okHttpClient;
   private ProgressBar progressBar;
   private String url= "https://pic.bincrea.c"+
"om/bc_bg_6D40C91A170D41C182511ABBB8A634A4.pdf";
   private TextView textView;
   private PDFView pdfView;
   private Handler handler = new Handler() {
       @Override
       public void handleMessage(Message msg) {
           super.handleMessage(msg);
           switch (msg.what) {
               case 1:
                   //进度条的值
                   int i = msg.arg1;
                   progressBar.setProgress(i);
           }
           if (msg.arg1==100){
               displayFromFile(new File(Environment.getExternalStorageDirectory().getAbsolutePath(), url.substring(url.lastIndexOf("/") + 1)));
           }
       }
   };
   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_down_loader);
       textView = (TextView) findViewById(R.id.textView);
       progressBar = (ProgressBar) findViewById(R.id.progressBar);
       pdfView = (PDFView) findViewById(R.id.pdfView);
       okHttpClient = new OkHttpClient(
       Request request = new Request.Builder().url(url).build();
       okHttpClient.newCall(request).enqueue(new Callback() {
           @Override
           public void onFailure(Call call, IOException e) {
               Log.d("h_bl", "onFailure");
           }

           @Override
           public void onResponse(Call call, Response response) throws IOException {
               InputStream is = null;
               byte[] buf = new byte[2048];
               int len = 0;
               FileOutputStream fos = null;
               String SDPath = Environment.getExternalStorageDirectory().getAbsolutePath();
               try {
                   is = response.body().byteStream();
                   long total = response.body().contentLength();
                   File file = new File(SDPath, url.substring(url.lastIndexOf("/") + 1));
                   fos = new FileOutputStream(file);
                   long sum = 0;
                   while ((len = is.read(buf)) != -1) {
                       fos.write(buf, 0, len);
                       sum += len;
                       int progress = (int) (sum * 1.0f / total * 100);
                       Log.d("h_bl", "progress=" + progress);
                       Message msg = handler.obtainMessage();
                       msg.what = 1;
                       msg.arg1 = progress;
                       handler.sendMessage(msg);
                   }
                   fos.flush();
                   Log.d("h_bl", "文件下载成功");
               } catch (Exception e) {
               } finally {
                   try {
                       if (is != null)
                           is.close();
                   } catch (IOException e) {
                   }
                   try {
                       if (fos != null)
                           fos.close();
                   } catch (IOException e) {
                   }
               }
           }
       });
   }
   private void displayFromFile( File file ) {
       pdfView.fromFile(file)   //设置pdf文件地址
               .defaultPage(1)         //设置默认显示第1页
               .onPageChange(this)     //设置翻页监听
               .onLoad(this)           //设置加载监听
               .onDraw(this)            //绘图监听
               .showMinimap(false)     //pdf放大的时候，是否在屏幕的右上角生成小地图
               .swipeVertical( false )  //pdf文档翻页是否是垂直翻页，默认是左右滑动翻页
               .enableSwipe(true)   //是否允许翻页，默认是允许翻
               // .pages( 2 ，5  )  //把2  5 过滤掉
               .load();
   }

   @Override
   public void onPageChanged(int page, int pageCount) {
       Toast.makeText( DownLoaderActivity.this , " " + page +
               " / " + pageCount , Toast.LENGTH_SHORT).show();

   }
   /**
    * 加载完成回调
    * @param nbPages  总共的页数
    */
   @Override
   public void loadComplete(int nbPages) {
       Toast.makeText( DownLoaderActivity.this ,  "加载完成" + nbPages  , Toast.LENGTH_SHORT).show();
   }

   @Override
   public void onLayerDrawn(Canvas canvas, float pageWidth, float pageHeight, int displayedPage) {
       // Toast.makeText( MainActivity.this ,  "pageWidth= " + pageWidth + "
       // pageHeight= " + pageHeight + " displayedPage="  + displayedPage , Toast.LENGTH_SHORT).show();
   }

}

具体的布局文件我就不贴了，过于简单，相信你可以1秒钟写完，haha