Android为图片添加水印，裁剪图片，旋转图片工具类

public class ImageUtil {

    /**
     * 旋转图片
     * @param angle 旋转角度
     * @param bitmap 要处理的Bitmap
     * @return 处理后的Bitmap
     */
    public static Bitmap rotaingImageView(int angle, Bitmap bitmap)
    {
        // 旋转图片 动作
        Matrix matrix = new Matrix();
        matrix.postRotate(angle);
        // 创建新的图片
        Bitmap resizedBitmap = Bitmap.createBitmap(bitmap, 0, 0,
                bitmap.getWidth(), bitmap.getHeight(), matrix, true);
        if (resizedBitmap != bitmap && !bitmap.isRecycled()){
            bitmap.recycle();
            //bitmap = null;
        }
        return resizedBitmap;
    }

    /**
     * 设置水印图片在左上角
     * @param context
     * @param src
     * @param watermark
     * @param paddingLeft
     * @param paddingTop
     * @return
     */
    public static Bitmap createWaterMaskLeftTop(
            Context context, Bitmap src, Bitmap watermark,
            int paddingLeft, int paddingTop) {
        return createWaterMaskBitmap(src, watermark,
                dp2px(context, paddingLeft), dp2px(context, paddingTop));
    }

    private static Bitmap createWaterMaskBitmap(Bitmap src, Bitmap watermark,
                                                int paddingLeft, int paddingTop) {
        if (src == null) {
            return null;
        }
        int width = src.getWidth();
        int height = src.getHeight();
        //创建一个bitmap
        Bitmap newb = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);// 创建一个新的和SRC长度宽度一样的位图
        //将该图片作为画布
        Canvas canvas = new Canvas(newb);
        //在画布 0，0坐标上开始绘制原始图片
        canvas.drawBitmap(src, 0, 0, null);
        //在画布上绘制水印图片
        canvas.drawBitmap(watermark, paddingLeft, paddingTop, null);
        // 保存
        canvas.save(Canvas.ALL_SAVE_FLAG);
        // 存储
        canvas.restore();
        return newb;
    }

    /**
     * 设置水印图片在右下角
     * @param context
     * @param src
     * @param watermark
     * @param paddingRight
     * @param paddingBottom
     * @return
     */
    public static Bitmap createWaterMaskRightBottom(
            Context context, Bitmap src, Bitmap watermark,
            int paddingRight, int paddingBottom) {
        return createWaterMaskBitmap(src, watermark,
                src.getWidth() - watermark.getWidth() - dp2px(context, paddingRight),
                src.getHeight() - watermark.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 设置水印图片到右上角
     * @param context
     * @param src
     * @param watermark
     * @param paddingRight
     * @param paddingTop
     * @return
     */
    public static Bitmap createWaterMaskRightTop(
            Context context, Bitmap src, Bitmap watermark,
            int paddingRight, int paddingTop) {
        return createWaterMaskBitmap( src, watermark,
                src.getWidth() - watermark.getWidth() - dp2px(context, paddingRight),
                dp2px(context, paddingTop));
    }

    /**
     * 设置水印图片到左下角
     * @param context
     * @param src
     * @param watermark
     * @param paddingLeft
     * @param paddingBottom
     * @return
     */
    public static Bitmap createWaterMaskLeftBottom(
            Context context, Bitmap src, Bitmap watermark,
            int paddingLeft, int paddingBottom) {
        return createWaterMaskBitmap(src, watermark, dp2px(context, paddingLeft),
                src.getHeight() - watermark.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 设置水印图片到中间
     * @param src
     * @param src
     * @param watermark
     * @return
     */
    public static Bitmap createWaterMaskCenter(Bitmap src, Bitmap watermark) {
        return createWaterMaskBitmap(src, watermark,
                (src.getWidth() - watermark.getWidth()) / 2,
                (src.getHeight() - watermark.getHeight()) / 2);
    }

    /**
     * 给图片添加文字到左上角
     * @param context
     * @param bitmap
     * @param text
     * @return
     */
    public static Bitmap drawTextToLeftTop(Context context, Bitmap bitmap, String text,
                                           int size, int color, int paddingLeft, int paddingTop) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds,
                dp2px(context, paddingLeft),
                dp2px(context, paddingTop) + bounds.height());
    }

    /**
     * 绘制文字到右下角
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingRight
     * @param paddingBottom
     * @return
     */
    public static Bitmap drawTextToRightBottom(Context context, Bitmap bitmap, String text,
                                               int size, int color, int paddingRight, int paddingBottom) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds,
                bitmap.getWidth() - bounds.width() - dp2px(context, paddingRight),
                bitmap.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 绘制文字到右上方
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingRight
     * @param paddingTop
     * @return
     */
    public static Bitmap drawTextToRightTop(Context context, Bitmap bitmap, String text,
                                            int size, int color, int paddingRight, int paddingTop) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds,
                bitmap.getWidth() - bounds.width() - dp2px(context, paddingRight),
                dp2px(context, paddingTop) + bounds.height());
    }

    /**
     * 绘制文字到左下方
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @param paddingLeft
     * @param paddingBottom
     * @return
     */
    public static Bitmap drawTextToLeftBottom(Context context, Bitmap bitmap, String text,
                                              int size, int color, int paddingLeft, int paddingBottom) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds,
                dp2px(context, paddingLeft),
                bitmap.getHeight() - dp2px(context, paddingBottom));
    }

    /**
     * 绘制文字到中间
     * @param context
     * @param bitmap
     * @param text
     * @param size
     * @param color
     * @return
     */
    public static Bitmap drawTextToCenter(Context context, Bitmap bitmap, String text,
                                          int size, int color) {
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(color);
        paint.setTextSize(dp2px(context, size));
        Rect bounds = new Rect();
        paint.getTextBounds(text, 0, text.length(), bounds);
        return drawTextToBitmap(context, bitmap, text, paint, bounds,
                (bitmap.getWidth() - bounds.width()) / 2,
                (bitmap.getHeight() + bounds.height()) / 2);
    }

    //图片上绘制文字
    private static Bitmap drawTextToBitmap(Context context, Bitmap bitmap, String text,
                                           Paint paint, Rect bounds, int paddingLeft, int paddingTop) {
        android.graphics.Bitmap.Config bitmapConfig = bitmap.getConfig();

        paint.setDither(true); // 获取跟清晰的图像采样
        paint.setFilterBitmap(true);// 过滤一些
        if (bitmapConfig == null) {
            bitmapConfig = android.graphics.Bitmap.Config.ARGB_8888;
        }
        bitmap = bitmap.copy(bitmapConfig, true);
        Canvas canvas = new Canvas(bitmap);

        canvas.drawText(text, paddingLeft, paddingTop, paint);
        return bitmap;
    }

    /**
     * 缩放图片
     * @param src
     * @param w
     * @param h
     * @return
     */
    public static Bitmap scaleWithWH(Bitmap src, double w, double h) {
        if (w == 0 || h == 0 || src == null) {
            return src;
        } else {
            // 记录src的宽高
            int width = src.getWidth();
            int height = src.getHeight();
            // 创建一个matrix容器
            Matrix matrix = new Matrix();
            // 计算缩放比例
            float scaleWidth = (float) (w / width);
            float scaleHeight = (float) (h / height);
            // 开始缩放
            matrix.postScale(scaleWidth, scaleHeight);
            // 创建缩放后的图片
            return Bitmap.createBitmap(src, 0, 0, width, height, matrix, true);
        }
    }

    /**
     * dip转pix
     * @param context
     * @param dp
     * @return
     */
    public static int dp2px(Context context, float dp) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dp * scale + 0.5f);
    }
}

调取的方法很简单，就不多说了，只列举一个调用的小栗子吧：

Bitmap resultBitmap = ImageUtil.drawTextToRightBottom(context, result.crop(), "哈哈哈", 45, Color.RED, 20, 20);

对，就这么简单。在上面工具类中我都写了注释，以及各个参数代表什么意思都写了。不会的可以留言。