为什么Java没有从InputStream中正确地重新创建这个图像？

Question

我用各种方式看待这个问题......问题是我最终编写完美的字节数,文件非常相似 - 但有些字节不同.我在Scite中打开了Java生成的文件以及原始文件,即使它们很接近,它们也不一样.有没有什么办法解决这一问题？我已经尝试过尽一切可能 - 我使用了不同的包装器,读取器,编写器和采用字节数组的不同方法(或将其作为字符 - 尝试两者)并将其制作成文件.

有关测试的图片位于http://www.google.com/images/srpr/nav_logo13.png.这是代码:

import java.awt.Image;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

import javax.imageio.ImageIO;

public class ImgExample
{

    private String address = "http://www.google.com";
    /**
     * Returns a 3 dimensional array that holds the RGB values of each pixel at the position of the current
     * webcam picture. For example, getPicture()[1][2][3] is the pixel at (2,1) and the BLUE value.
     * [row][col][0] is alpha
     * [row][col][1] is red
     * [row][col][2] is green
     * [row][col][3] is blue
     */
    public int[][][] getPicture()
    {
        Image camera = null;
        try {
            int maxChars = 35000;
            //The image in question is 28,736 bytes, but I want to make sure it's bigger
            //for testing purposes as in my case, it's an image stream so it's unpredictable
            byte[] buffer = new byte[maxChars];
            //create the connection
            HttpURLConnection conn = (HttpURLConnection)(new URL(this.address+"/images/srpr/nav_logo13.png")).openConnection();
            conn.setUseCaches(false);
            //wrap a buffer around our input stream
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            int bytesRead = 0;
            while ( bytesRead < maxChars && reader.ready() )
            {
                //reader.read returns an int - I'm assuming this is okay?
                buffer[bytesRead] = (byte)reader.read();
                bytesRead++;
                if ( !reader.ready() )
                {
                    //This is here to make sure the stream has time to download the next segment
                    Thread.sleep(10);
                }
            }
            reader.close();

            //Great, write out the file for viewing
            File writeOutFile = new File("testgoog.png");
            if ( writeOutFile.exists() )
            {
                writeOutFile.delete();
                writeOutFile.createNewFile();
            }
            FileOutputStream fout = new FileOutputStream(writeOutFile, false);
            //FileWriter fout = new FileWriter(writeOutFile, false);
            //needed to make sure I was actually reading 100% of the file in question
            System.out.println("Bytes read = "+bytesRead);
            //write out the byte buffer from the first byte to the end of all the chars read
            fout.write(buffer, 0, bytesRead);
            fout.flush();
            fout.close();

            //Finally use a byte stream to create an image
            ByteArrayInputStream byteImgStream = new ByteArrayInputStream(buffer);
            camera = ImageIO.read(byteImgStream);
            byteImgStream.close();
        } catch ( Exception e ) { e.printStackTrace(); }
        return ImgExample.imageToPixels(camera);
    }

    public static int[][][] imageToPixels (Image image)
    {
        //there's a bunch of code here that works in the real program, no worries
        //it creates a 3d arr that goes [x][y][alpha, r, g, b val]
        //e.g. imageToPixels(camera)[1][2][3] gives the pixel's blue value for row 1 col 2
        return new int[][][]{{{-1,-1,-1}}};
    }

    public static void main(String[] args)
    {
        ImgExample ex = new ImgExample();
        ex.getPicture();
    }
}

Answer 1

我看到的问题是你正在使用Readers.在Java中,Readers用于处理字符流,而不是二进制流,并且它所做的字符转换很可能是在改变你的字节.

相反,你应该直接read()从InputStream. InputStream的read()将阻塞,直到数据是可用的,但返回-1到达流的末尾时.

编辑:您还可以将InputStream包装在一个BufferedInputStream.