廢話就不多說了直接看下怎麼實現

1.新增相關的許可權，裝置API大於6.0時需要主動申請許可權

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />

//裝置API大於6.0時，主動申請許可權
    private void requestPermission(Activity context) {
        if (Build.VERSION
 
.SDK_INT >= Build.VERSION_CODES.M) {
            if (ContextCompat.checkSelfPermission(context, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                    != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(context, new String[]{Manifest.permission.WRITE
 
_EXTERNAL_STORAGE,
                        Manifest.permission.READ_EXTERNAL_STORAGE}, 0);

            }
        }
    }

2.連線伺服器獲取檔案

    /**
     * 從伺服器下載檔案
     * @param path 下載檔案的地址
     * @param FileName 檔名字
     */
    public static void downLoad(final String path, final String FileName) {
        new
 
 Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    URL url = new URL(path);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    con.setReadTimeout(5000);
                    con.setConnectTimeout(5000);
                    con.setRequestProperty("Charset", "UTF-8");
                    con.setRequestMethod("GET");
                    if (con.getResponseCode() == 200) {
                        InputStream is = con.getInputStream();//獲取輸入流
                        FileOutputStream fileOutputStream = null;//檔案輸出流
                        if (is != null) {
                            FileUtils fileUtils = new FileUtils();
                            fileOutputStream = new FileOutputStream(fileUtils.createFile(FileName));//指定檔案儲存路徑，程式碼看下一步
                            byte[] buf = new byte[1024];
                            int ch;
                            while ((ch = is.read(buf)) != -1) {
                                fileOutputStream.write(buf, 0, ch);//將獲取到的流寫入檔案中
                            }
                        }
                        if (fileOutputStream != null) {
                            fileOutputStream.flush();
                            fileOutputStream.close();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

3.建立檔案儲存路徑

public class FileUtils {
    private String path = Environment.getExternalStorageDirectory().toString() + "/shidoe";

    public FileUtils() {
        File file = new File(path);
        /**
         *如果資料夾不存在就建立
         */
        if (!file.exists()) {
            file.mkdirs();
        }
    }

    /**
     * 建立一個檔案
     * @param FileName 檔名
     * @return
     */
    public File createFile(String FileName) {
        return new File(path, FileName);
    }
}

4.下載示例

downLoad("http://www.shidoe.com/shidoe/Edition/upfile/04.png", "che.png");//下載完成後就可以在手機目錄裡檢視到了

5.動態獲取需要儲存檔案的檔名

//獲取 / 最後一次出現的位置，然後位置+1擷取剩餘的就是檔名了
String s = "http://www.shidoe.com/shidoe/Edition/upfile/04.png";
        int i = s.lastIndexOf("/");
        String FileName= s.substring(i + 1);

6.載入剛下載好的圖片顯示在介面上還是非常easy的

 private void loadImage() {
        String path = Environment.getExternalStorageDirectory().toString() + "/shidoe";
        try {
            Bitmap bmp = BitmapFactory.decodeStream(new FileInputStream(new File(path, "che.png")));
            iv.setImageBitmap(bmp);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

如果幫到了你就幫忙頂一下吧