public class RecyclerViewDivider extends RecyclerView.ItemDecoration {
    
    private Paint mPaint;
    //分割线
    private Drawable mDivider;
    //分割线高度，默认是1px
    private int mDividerHeight = 1;
    //列表的方向：LinearLayoutManager.VERTICAL或LinearLayoutManager.HORIZONTAL
    private int mOrientation;

    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

     /**
     *
     * 默认分割线：高度为2px，颜色为灰色
     * 获取属性值，
     *
     * @param context
     * @param orientation  列表方向
     */

    public RecyclerViewDivider(Context context, int orientation){
        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("请输入正确的参数！");
        }
        mOrientation = orientation;
        final TypedArray array = context.obtainStyledAttributes(ATTRS);
        mDivider = array.getDrawable(0);
        array.recycle();
        mDividerHeight = mDivider.getIntrinsicHeight();
    }

    /**
     * 自定义分割线
     *
     * @param context
     * @param orientation 列表方向
     * @param drawableId  分割线图片
     */
    public RecyclerViewDivider(Context context, int orientation, int drawableId) {
        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("请输入正确的参数！");
        }
        mOrientation = orientation;

        mDivider = ContextCompat.getDrawable(context, drawableId);
        mDividerHeight = mDivider.getIntrinsicHeight();
    }

    /**
     * 自定义分割线
     *
     * @param orientation   列表方向
     * @param dividerHeight 分割线高度
     * @param dividerColor  分割线颜色
     */
    public RecyclerViewDivider(int orientation, int dividerHeight, int dividerColor) {

        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("请输入正确的参数！");
        }
        mOrientation = orientation;

        mDividerHeight = dividerHeight;

        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(dividerColor);
        mPaint.setStyle(Paint.Style.FILL);

    }

    //获取分割线尺寸
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

        if (mOrientation == LinearLayoutManager.VERTICAL) {
            outRect.set(0, 0, 0, mDividerHeight);
        } else {
            outRect.set(0, 0, mDividerHeight, 0);
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        if(mOrientation==LinearLayoutManager.VERTICAL){
            drawVerticalLine(c,parent);
        }else{
            drawHorizontalLine(c,parent);
        }
    }

    //为横方向item, 画分割线
    private void drawHorizontalLine(Canvas canvas, RecyclerView parent) {
    
        final int top = parent.getPaddingTop();
        final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom();
        final int childSize = parent.getChildCount();
        for (int i = 0; i < childSize - 1; i++) {
            if ((i+1) % 3 != 0) {
                final View child = parent.getChildAt(i);
                RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
                final int left = child.getRight() + layoutParams.rightMargin;
                final int right = left + mDividerHeight;
                if (mDivider != null) {
                    mDivider.setBounds(left, top, right, bottom);
                    mDivider.draw(canvas);
                }
                if (mPaint != null) {
                    canvas.drawRect(left, top, right, bottom, mPaint);
                }
            }
        }
    }

    //为竖方向item, 画分割线
    private void drawVerticalLine(Canvas canvas, RecyclerView parent) {
    
        final int left = parent.getPaddingLeft();
        final int right = parent.getMeasuredWidth() - parent.getPaddingRight();
        final int childSize = parent.getChildCount();
        for (int i = 0; i < childSize; i++) {
            if (i < childSize -1) {
                final View child = parent.getChildAt(i);
                RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
                final int top = child.getBottom() + layoutParams.bottomMargin;
                final int bottom = top + mDividerHeight;
                LogUtil.e("wsd", child.getTop() + "  " + child.getBottom() + "  " + child.getLeft() + "  " + child.getRight()
                        + "  " + layoutParams.topMargin + "  " + layoutParams.bottomMargin);

                if (mDivider != null) {
                    mDivider.setBounds(left, top, right, bottom);
                    mDivider.draw(canvas);
                }

                if (mPaint != null) {
                    canvas.drawRect(left, top, right, bottom, mPaint);
                }

            }
        }
    }
}


使用
//自定义分割线
 recyclerView.addItemDecoration(new RecyclerViewDivider(LinearLayoutManager.HORIZONTAL,
                ScreenUtils.dip2px(this, 30f), Color.parseColor("#FFFFFF")));
  //默认分割线
  mRecyclerView.addItemDecoration(new RecyclerViewDivider(this, LinearLayoutManager.VERTICAL));