Open pdf by URL and PDFView InputStream

I would like the user to enter the product code (in activity_main.xml ) and click the button.

The screen changes ( view_pdf.xml ), it would download the PDF ( AnsyTask ) and it would open in PDFView by pdfView.fromStream . I use Android Studio and Spring Boot.

MainActivity

public class MainActivity extends AppCompatActivity {
    private ProgressDialog load;
    private TextView codigoModel;
    private Button bt_busca;
    private PDFView pdfView;
    private ProgressDialog loadPdf;

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

        codigoModel = (TextView) findViewById(R.id.codigoModelo);
        bt_busca = (Button) findViewById(R.id.bt_buscar);
        pdfView = (PDFView) findViewById(R.id.pdfView);

        bt_busca.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                setContentView(R.layout.view_pdf);
                chamarAsyncTask(codigoModel.getText().toString());
            }
        });
    }

    private void chamarAsyncTask(String codigoModel) {
        DownloadPdfView downloadPdfView = new DownloadPdfView();
        Log.i("AsyncTask", "AsyncTask senado chamado Thread: " + Thread.currentThread().getName());
        downloadPdfView.execute(codigoModel);
    }

    private class DownloadPdfView extends AsyncTask<String, Void, InputStream> {

        @Override
        protected void onPreExecute() {
            Log.i("AsyncTask", "Exibindo ProgressDialog na tela Thread: " + Thread.currentThread().getName());
            loadPdf = ProgressDialog.show(MainActivity.this, "Por Favor Aguarde ...",
                    "Baixando Desenho ...");

        }

        @Override
        protected InputStream doInBackground(String... params) {
        InputStream inputStream;
        AcessoWebService url = new AcessoWebService();
        String codigo = params[0];
        Log.i("AsyncTask", "Baixando o PDF Thread: " + Thread.currentThread().getName());

        AcessoWebService acessoWebService = new AcessoWebService();
        inputStream = acessoWebService.getApiInputStream("http://192.168.100.100:8080/produto/download/" + codigo);

        return inputStream;
        }

        @Override
        protected void onPostExecute(InputStream inputStream) {
            pdfView.fromStream(inputStream).load();
        }
    }
}  

Web Service Access

    public class AcessoWebService {

    public InputStream getApiInputStream(String url) {

        int codigoResposta;
        HttpURLConnection conexao;
        InputStream inputStream = null;

        try {

            URL apiEnd = new URL(url);
            conexao = (HttpURLConnection) apiEnd.openConnection();
            conexao.setRequestMethod("GET");
            conexao.setReadTimeout(15000);
            conexao.setConnectTimeout(15000);
            conexao.connect();

            codigoResposta = conexao.getResponseCode();
            if (codigoResposta < HttpURLConnection.HTTP_BAD_REQUEST) {
                inputStream = new BufferedInputStream(conexao.getInputStream());
            } else {
                inputStream = conexao.getErrorStream();
            }

            inputStream.close();
            conexao.disconnect();

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return inputStream;
    }
}  

Dependencies

//Add Library
compile 'com.github.barteksc:android-pdf-viewer:2.8.2'
compile 'org.apache.commons:commons-collections4:4.1'  

Exception

E/AndroidRuntime: FATAL EXCEPTION: main
                                                                        Process: br.com.mobile, PID: 16834
                                                                        java.lang.NullPointerException: Attempt to invoke virtual method 'com.github.barteksc.pdfviewer.PDFView$Configurator com.github.barteksc.pdfviewer.PDFView.fromStream(java.io.InputStream)' on a null object reference  
    at br.com.mobile.MainActivity$DownloadPdfView.onPostExecute(MainActivity.java:100)
                                                                            at br.com.mobile.MainActivity$DownloadPdfView.onPostExecute(MainActivity.java:54)