download.java

new APIRequest( new APIClient(HomeActivity.this), APP_SERVER+"/download_pdf", APIRequest.GET)
            .withDefaultParams(defaultParamsHashMap())
            .addParam("format", "json")
            .addParam("id", pdfId)
            .addHeaderParam("Referer", APP_REFERER);
            .startDownload(CACHE_ID, DOWNLOAD_FOLDER, new APIDataRequestHandler(){
                
                @Override
                public void before(){
                    showProgressBar();
                }
                
                @Override
                public void after(){
                    showPDF();
                    hideProgressBar();
                }
                
                @Override
                public void onException(Exception e) {
                    e.printStackTrace();
                }
                
                @Override
                public void onResponse(File data) {
                    mapFilePathToPage(data.getAbsolutePath(), PAGE_NUMBER)
                }
                
                @Override
                public void onProgressUpdate(int changed){
                    updateProgressBar(changed)
                }
                
            });