如何使用Java套接字HTTP / 1.1请求下载图像？

Question

我正在尝试使用java.net.Socket不带java.net.URL外部库的图像进行下载。这是我所拥有的，我不确定什么不起作用。

        String domain = "www.manchester.edu";
        String path = "/images/default-source/default-album/slide1.jpg";
        Socket socket = new Socket(domain,80);

        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())));
        out.println("" +
                "Get "+path+" HTTP/1.1\n" +
                "Host: "+domain+"\n"+
                "");
        out.println();
        out.flush();

        BufferedImage image = ImageIO.read(socket.getInputStream());

为了查看流中正在发生什么，请将该BufferedImage行交换为：

    BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    String inputLine;
    while ((inputLine = in.readLine()) != null && inputLine.trim() != "0") {
       System.out.println(inputLine);
    }

大概该ImageIO.read(...)方法在套接字输入流中不希望使用HTTP标头。但是我不确定如何删除标题。我试着用读取标题行，BufferedReader然后将套接字输入流传递给，ImageIO.read(...)但这没有用。

这是打印的字符串BufferedReader：

HTTP/1.1 200 OK
Cache-Control: public, max-age=7776000
Content-Length: 96876
Content-Type: image/jpeg
Expires: Thu, 04 Feb 2016 21:36:46 GMT
Last-Modified: Tue, 15 Sep 2015 14:23:40 GMT
Server: Microsoft-IIS/8.5
content-disposition: inline; filename=slide1.jpg
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Fri, 06 Nov 2015 21:36:46 GMT

����...

末尾的不可打印字符似乎表明标题之后是某种图像。但是如何将其转换为a java.awt.image.BufferedImage或a
javafx.scene.image.Image？后者有一个接受输入流的构造函数，我已经尝试过了，但是它不起作用（因为http标头？）。这个问题与此类似，但是我试图创建一个图像而不是一个文件。

Answer 1

使用BufferedReader有误，原因有两个：

1. 它将字节转换为String，然后再转换回字节以将其发送到输出流。转换可能（可能会）导致数据丢失；
2. 它解析了太多字节，您无法控制它。

您需要通过手术来解决此问题，创建一个所需大小的字节缓冲区，并使用an
InputStream根据自己的条件逐字节读取流。另外，由于您知道HTTP标头的结尾为“ \ r \ n \ r \ n”（或13 10 13
10字节），因此可以扫描自己的缓冲区以查找此模式并采取相应的措施。

最好的选择是将图像下载到文件中，然后使用ImageIO从本地文件中读取图像。

    // Initialize the streams.
    final FileOutputStream fileOutputStream = new FileOutputStream(file);
    final InputStream inputStream = socket.getInputStream();

    // Header end flag.
    boolean headerEnded = false;

    byte[] bytes = new byte[2048];
    int length;
    while ((length = inputStream.read(bytes)) != -1) {
        // If the end of the header had already been reached, write the bytes to the file as normal.
        if (headerEnded)
            fileOutputStream.write(bytes, 0, length);

        // This locates the end of the header by comparing the current byte as well as the next 3 bytes
        // with the HTTP header end "\r\n\r\n" (which in integer representation would be 13 10 13 10).
        // If the end of the header is reached, the flag is set to true and the remaining data in the
        // currently buffered byte array is written into the file.
        else {
            for (int i = 0; i < 2045; i++) {
                if (bytes[i] == 13 && bytes[i + 1] == 10 && bytes[i + 2] == 13 && bytes[i + 3] == 10) {
                    headerEnded = true;
                    fileOutputStream.write(bytes, i+4 , 2048-i-4);
                    break;
                }
            }
        }
    }
    inputStream.close();
    fileOutputStream.close();