要解决Android Studio的decodeStream方法返回的图像以横向方向显示的问题，可以使用Matrix类来对图像进行旋转操作。下面是一个包含代码示例的解决方法：

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
    private ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = findViewById(R.id.imageView);

        // 加载图片资源
        Bitmap bitmap = decodeSampledBitmapFromResource(getResources(), R.drawable.image, 100, 100);

        // 检查图片是否需要旋转
        if (bitmap.getWidth() > bitmap.getHeight()) {
            Matrix matrix = new Matrix();
            matrix.postRotate(90); // 顺时针旋转90度

            // 旋转图片
            bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
        }

        // 显示图片
        imageView.setImageBitmap(bitmap);
    }

    public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);

        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource(res, resId, options);
    }

    public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            while ((halfHeight / inSampleSize) >= reqHeight && (halfWidth / inSampleSize) >= reqWidth) {
                inSampleSize *= 2;
            }
        }

        return inSampleSize;
    }
}

上述代码中，首先使用decodeSampledBitmapFromResource方法来加载图片资源并进行适当缩放。然后，使用Matrix类对图像进行旋转操作，将宽度大于高度的图片顺时针旋转90度。最后，将旋转后的图片显示在ImageView中。