public void url2bitmap(String url) {
        Bitmap bm = null;
        try {
            URL iconUrl = new URL(url);
            URLConnection conn = iconUrl.openConnection();
            HttpURLConnection http = (HttpURLConnection) conn;
            int length = http.getContentLength();
            conn.connect();
            // 获得图像的字符流
            InputStream is = conn.getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is, length);
            bm = BitmapFactory.decodeStream(bis);
            bis.close();
            is.close();
            if (bm != null) {
                save2Album(bm,url);
            }
        } catch (Exception e) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    showToastMessage("保存失败");
                }
            });
            e.printStackTrace();
        }
    }

    private void save2Album(Bitmap bitmap, String picUrl) {
        File appDir = new File(Environment.getExternalStorageDirectory(), System.currentTimeMillis() + ".png");
        if (!appDir.exists()) appDir.mkdir();
        String[] str = picUrl.split("/");
        String fileName = str[str.length - 1];
        File file = new File(appDir, fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
            onSaveSuccess(file);
        } catch (IOException e) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                  showToastMessage("保存失败");
                }
            });
            e.printStackTrace();
        }
    }

    private void onSaveSuccess(final File file) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.fromFile(file)));
                showToastMessage("保存成功");
            }
        });
    }

Url 转化为Bitmap

 private static Bitmap bitmap;
    public static Bitmap getBitmap(final String url) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                URL imageurl = null;

                try {
                    imageurl = new URL(url);
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                }
                try {
                    HttpURLConnection conn = (HttpURLConnection)imageurl.openConnection();
                    conn.setDoInput(true);
                    conn.connect();
                    InputStream is = conn.getInputStream();
                    bitmap = BitmapFactory.decodeStream(is);
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        return bitmap;
    }