// HttpServletRequest

//这里其实是nginx的IP，则本地。
String nginxIP = request.getRemoteAddr();        

//自己设置的自定义Header，为请求clicent端的IP。
String clientIP = request.getHeader("X-Real-IP"); 

import android.util.Log;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MiniFileDownload {

    private static final String TAG = "MiniFileDownload";
    interface DownloadCallBack{
        void onError(Exception e);
        void onOK(File file);
        void onProgress(float progress);
    }
    public static void start(String url, File saveFile, DownloadCallBack callBack) {

        if(saveFile.exists()){
            saveFile.delete();
        }
        if(callBack == null){
            return;
        }
        HttpURLConnection conn;
        try {

            //连接URL服务器
            conn = (HttpURLConnection)new URL(url).openConnection();
            conn.setConnectTimeout(3 * 1000);
            conn.setUseCaches(false);
        } catch (IOException e) {
            e.printStackTrace();
            callBack.onError(e);
            return;
        }

        InputStream is = null;
        BufferedOutputStream bos = null;
        try {

            //判断响应码，如果服务器不响应错误，开始下载。
            if (conn.getResponseCode() != 200){
                Log.e(TAG,"ResponseCode = " + conn.getResponseCode());
                return;
            }
            //获取文件总大小
            int contentLength = conn.getContentLength();
            Log.d(TAG,"content Length = " + contentLength);
            byte[] buffer = new byte[1024];
            int offset = 0 ;
            int len;

            //本地文件输出流
            bos = new BufferedOutputStream( new FileOutputStream(saveFile) );

            //获取输入流
            is = conn.getInputStream();
            //循环读（下载）
            while ((len = is.read(buffer)) != -1) {

                Log.d(TAG,"read buffer len = " + len);
                bos.write(buffer, 0, len);
                offset += len;
                Log.d(TAG,"offset = " + offset + " ;total=" + contentLength);
                //计算进度
                float progress = (float)offset / (float)contentLength;
                Log.d(TAG,"progress = " + progress);
                //更新进度到回调，UI层可以显示下载进度
                callBack.onProgress(progress);
            }
            Log.d(TAG,"ok");
            callBack.onOK(saveFile);
        } catch (IOException e) {
            e.printStackTrace();
            callBack.onError(e);
        }finally {

            //关闭资源
            if(is != null){
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            if(bos != null){
                try {
                    bos.flush();
                    bos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            conn.disconnect();
        }
    }

}

public class TestGridDecoration extends RecyclerView.ItemDecoration{

    private int offset;

    public TestGridDecoration(int offset) {
        this.offset = offset;
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        int childLayoutPosition = parent.getChildLayoutPosition(view);

        //每行的元素数量
        int spanCount = ((GridLayoutManager)parent.getLayoutManager()).getSpanCount();

        //总行数
        int maxRow = state.getItemCount() / spanCount;
        //所处的行号
        int row = childLayoutPosition / spanCount;
        //所处的列号
        int column = childLayoutPosition % spanCount;


        if(row == 0){
            //第一行
            outRect.top = 0;
            outRect.bottom = 0;
        }else if(row == maxRow){
            //最后一行
            outRect.top = offset;
            outRect.bottom = offset;
        }else{
            //中间行
            outRect.top = offset;
            outRect.bottom = 0;
        }


        if(column == 0){
            //第一列
            outRect.left = offset;
            outRect.right = offset / 2;
        }else if(column == spanCount - 1){
            //最后一列
            outRect.left = offset / 2;
            outRect.right = offset;
        }else{
            //中间列
            outRect.left = offset / 2;
            outRect.right = offset / 2;
        }

    }
}