sockets - 在Java ME中使用套接字连接下载二进制文件

Question

我正在尝试使用Java ME Api在我的手机上下载pdf文件(使用SocketConnection)。这个想法是向服务器发送一个HTTP GET请求，并用pdf文件的数据进行回复。但是，我面临的问题是服务器最初会先返回字符串数据(HTTP Headers)，然后再返回二进制数据。我只想存储二进制数据(pdf文件)。

到目前为止，我已经编写了此代码，只要服务器用字符串数据回复，它就可以很好地工作。但是，当它用二进制数据答复时，此代码仍尝试将所有内容存储为字符串，正确存储最初返回的HTTP Headers(不需要)，然后将与我的PDF文件的二进制数据相对应的位乱码。

public void FileDownload() {
    try {
        sc = (SocketConnection) Connector.open("socket://" + hostname + ":" + port);
        OutputStream os = sc.openOutputStream();
        os.write(("GET " + link_to_file_to_be_downloaded + " HTTP/1.0\r\n").getBytes("UTF-8"));
        os.write(("HOST: " + hostname + "\r\n").getBytes("UTF-8"));
        os.write(("\r\n").getBytes("UTF-8"));
        os.flush();
        os.close();

        String url = "file:///E:/Data/" + "binary_data.pdf";
        FileConnection fconn = (FileConnection) Connector.open(url, Connector.READ_WRITE);
        if (!fconn.exists()) {
            fconn.create();
        }
        OutputStream ops = fconn.openOutputStream();
        byte data = 0;
        in = sc.openInputStream();
        data = (byte) in.read();
        while (data != -1) {
            ops.write(data);
            data = (byte) in.read();
        }
        ops.flush();
        ops.close();
        fconn.close();                

    } catch (IOException ex) {
        parent_class.main_form.append("Exception occured while "
                + "downloading file: " + ex.toString() + "\n");
    } finally {
        if (in != null) {
            try {
                in.close();
            } catch (IOException ex) {
                parent_class.main_form.append("Exception occured while "
                        + "downloading file: " + ex.toString() + "\n");
            }
        }
    }
}

这就是使用此代码存储在文件“binary_data.pdf”中的内容-

HTTP/1.1 200 OK
Date: Sun, 25 Mar 2012 07:03:10 GMT
Server: Apache/2.2.14 (Ubuntu)
Last-Modified: Tue, 20 Mar 2012 22:00:45 GMT
ETag: "420050-12bad-4bbb3ce85fd21"
Accept-Ranges: bytes
Content-Length: 76717
Content-Type: application/pdf
Via: 1.0 www.XXX.XXX.org
Connection: close

%PDF-1.4
%????
3 0 obj <<
/Length 4077      
/Filter /FlateDecode
>>
stream
x??ZYs?6~????9U.?#??Udg?M*qYJ???T-4?fq? @Z????<FT?}
lt7??n???_???4?s???????"
3????<???^?V?z??M?z??m?^????V???o??S'm6?????.??/Sx??Y?av?MB?*b^?f??/?IO??B??q??/?(??aT?a?@#??,?%???Z8? ?]??-?\?]??????nw?2?;?????Z?;?[}??????&J=ml??-??V?|??:??"?(?Gf??D??~?QW?U?Z???cP?b???QX

(使用高级 HttpConnection api进行此操作可能会更简单，但是我希望了解所有操作都在最基本的级别上进行，因此我改用了 SocketConnection api。)

简而言之，我希望我的应用程序要做的就是简单地将服务器正确答复的数据解释为字符串或二进制，然后相应地存储二进制文件(可能会丢弃字符串HTTP header )。

Answer 1

我找到了解决方案。以下是工作代码。
我首先将 header 响应存储为字符串。 header 以\r\n\r\n终止(因此，以字节为单位读取直到这些字符)。稍后将(可能)二进制数据分别存储在文件中。

    public String FileDownloadNonPersistently() {
        String server_reply = new String();
        try {
            sc = (SocketConnection) Connector.open("socket://" + hostname + ":" + port);
            os = sc.openOutputStream();
            os.write(("GET " + link_to_file_to_be_downloaded + 
                    " HTTP/1.0\r\n").getBytes("UTF-8"));
            os.write(("HOST: " + hostname + "\r\n").getBytes("UTF-8"));
            os.write(("\r\n").getBytes("UTF-8"));
            os.flush();
            os.close();

            in = sc.openInputStream();
            // 1. Read the response header from server separately beforehand.
            byte data;
            String temp_char = "";
            while (!"\r\n\r\n".equals(temp_char)) {
                data = (byte) in.read();
                server_reply += String.valueOf((char) data);
                if (((char) data) == '\r' || ((char) data) == '\n') {
                    temp_char += String.valueOf((char) data);
                } else {
                    temp_char = "";
                }
            }

            // 2. Recieving the actual data, be it text or binary
            current = 0;
            mybytearray  = new byte[filesize];
            bytesRead = in.read(mybytearray,0,mybytearray.length);
            current = bytesRead;
            do {
                bytesRead = in.read(mybytearray, current,
                       (mybytearray.length-current));
                if(bytesRead >= 0) current += bytesRead;
            } while(bytesRead > -1);

            // Store recieved data to file, if set true from options
            if (tcp_save_downloaded_file == true) {
                // decide an appropriate file name acc. to download link
                String url = "file:///E:/Data/" + "tcp_downloaded_file.pdf";
                FileConnection fconn = (FileConnection) 
                        Connector.open(url, Connector.READ_WRITE);
                if (!fconn.exists()) {      // XXX. what if file already present? overwrite or append mode?
                    fconn.create();
                }
                OutputStream ops = fconn.openOutputStream();
                ops.write(mybytearray, 0 , current);
                ops.flush();
                ops.close();
            }

        } catch (Exception ex) {
            parent_class.main_form.append("Exception occured while "
                    + "downloading file: " + ex.toString() + "\n\n");
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException ex) {
                    parent_class.main_form.append("Exception occured while "
                            + "closing inputstream "
                            + "after downloading file: " + ex.toString() + "\n\n");
                }
            }
            // XXX. see if you need to close the OutputStreams and 
            // SocketConnection as well.
            return server_reply;
        }
    }