如何将下载的文件保存在应用程序内存的缓存文件夹中？

我知道之前也曾问过类似的问题，但实际上没有可行的解决方案。我正在通过DownloadManager下载多个PDF文件，我想将这些文件保存到应用程序内存的缓存文件夹中，但找不到任何方法。

这是我的代码：

public class MainActivity extends AppCompatActivity {

    Button btn;
    DownloadManager downloadManager;
    List<String> myList = new ArrayList<String>();

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

        myList.add("https://doc.lagout.org/programmation/Actionscript%20-%20Flash%20-%20Flex%20-%20Air/Flash%20Development%20for%20Android%20Cookbook%20-%20Labrecque%20-%20Packt%20%282011%29/Flash%20Development%20for%20Android%20Cookbook%20-%20Labrecque%20-%20Packt%20%282011%29.pdf");
        myList.add("http://www.csc.kth.se/utbildning/kth/kurser/DD143X/dkand11/Group1Mads/andreas.ulvesand.daniel.eriksson.report.pdf");
        myList.add("http://enos.itcollege.ee/~jpoial/allalaadimised/reading/Android-Programming-Cookbook.pdf");
        myList.add("https://x.coe.phuket.psu.ac.th/warodom/242-320/ebook/9781785883262-ANDROID_PROGRAMMING_FOR_BEGINNERS.pdf");
        myList.add("https://www.cs.cmu.edu/~bam/uicourse/830spring09/BFeiginMobileApplicationDevelopment.pdf");
        myList.add("https://commonsware.com/Android/Android-1_0-CC.pdf");

        btn = findViewById(R.id.download_btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadManager = (DownloadManager)getSystemService(Context.DOWNLOAD_SERVICE);
                for(int i = 0; i < myList.size(); i++) {
                    Uri uri = Uri.parse(myList.get(i));
                    DownloadManager.Request request = new DownloadManager.Request(uri);
                    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                    Long reference = downloadManager.enqueue(request);
                }
            }
        });
    }
}