NetConnection简介

NetConnection简介

一、“NetConnection”简介：
转述Matrix上zhengyun_ustc所述：“你的HttpConnection是否封装的足够健壮呢？遇到各种情况，你是否有信心应对呢？譬如说，你要请求的Response包实在太大，以至于运营商给你掐了告诉你说超时；譬如说你是不是总要自己写一个线程来专门作http连接？譬如说有一些移动运营商设置了caching proxy servers，妨碍了你的测试。”
为了解决这个问题，一位日本程序员“JAY-F”针对MIDP1.0提供了一种robust的“NetConnection”封装。这个HttpConnnection类负责管理连接并易于使用。
二、“NetConnection”特性：
1. 跨过Proxy-server阻碍：
一些移动网络放置了代理服务器用来提高访问速度，但是它的cache也成为了开发人员测试/调试程序的一大障碍。“NetConnection”类使用一个简单的http request属性将server上的代理功能关闭掉。
2. 使用线程分离的连接模式：
本类可以使用单线程、多线程两种模式运行，只要设置一个简单的标志即可。
3. 支持Http request range：
由于服务商在其网络上可能存在一些针对回应数据最大长度的限制，所以“NetConnection”类提供了构造request URL的功能使回应数据分为多个数据包。从而去除了前面的限制。
三、netConnection是如何实现的？
1。netConnection类结构分析：
此类实现了Runnable接口，其运行模式支持多线程模式：当前只能由一个线程使用资源，其它线程wait。
此类使用了一些静态成员变量：

				
        //当前只能由一个线程使用singleton。
        private static NetConnection singleton = new NetConnection();

        private static HttpConnection httpConn;

        private static String url;

        private static String method;

        private static byte[] data;
                

        private static String contentType;
        

        private static long lowRange;
        

        private static long highRange;
        

        private static boolean disableProxy;
        

        private static boolean detached;
        
        private static byte[] response;

类方法：

//线程run方法
public void run()

//当前运行的线程执行完毕后，通报给其它的由于等待资源而wait状态的线程
private synchronized void forceNotify() 

//当资源正在被其它线程使用时，当前线程进入wait状态
private synchronized void forceWait()

//关闭http连接
private static void severConnection()

由于使用了这些static成员变量，所以一些操作方法需要同步（synchronized）。
2。netConnection核心代码解析：
netConnection类的实现思想很简单，就是设置一些request属性和对于GET方法构造一个特殊的URL。更重要的是其作者对http协议的深入理解、严谨的代码风格值得吾辈学习、研究。这也是本人分析其核心代码的一大原因。

/**
 * 实现了连接逻辑。
 * 调用者可以在分离的线程中使用netConnection类的静态连接。
 * @throws IllegalStateException 如果此方法直接其它类调用则抛出该异常
 */
public void run() {
        
        if (url == null) {
                throw new IllegalStateException("Cannot invoke this method!");
        }

        
        DataOutputStream dos = null;
        DataInputStream dis = null;
        StringBuffer buffer = null;

        try {

                int permissions = 0;
                
                //根据method值，设置Connector的权限（READ/READ_WRITE）
                if (HttpConnection.GET.equals(method)) {
                        permissions = Connector.READ;
                } else if (HttpConnection.POST.equals(method)) {
                        permissions = Connector.READ_WRITE;
                }
                
                //如果关闭server代理功能，则构造noProxyUrl。
                //原理：使用timestamp作为该URL中no-proxy参数值，
                //        致使server视其为client发来的新请求。
                if (disableProxy) {
                        
                        boolean hasQueryParams = false;
                        
                        char[] ca = url.toCharArray();
                        //判断原URL中是否含有参数
                        for (int loop = 0; loop < url.length(); loop++) {
                                
                                if (ca[loop] == '?') {
                                        hasQueryParams = true;
                                        break;
                                }
                        }
                        
                        //由于需要多次字符串拼接，所以使用可提供效率的StringBuffer类
                        StringBuffer noProxyUrl = new StringBuffer();

                        //将原URL内容复制到noProxyUrl
                        noProxyUrl.append(url);

                        //如果原URL中含有参数，
                        //  则需要在noProxyUrl中增加"&"，
                        //  否则直接在noProxyUrl中增加"?"，
                        //  这样做为了后面增加no-proxy参数做准备。
                        if (hasQueryParams) {
                                noProxyUrl.append("&");
                        } else {
                                noProxyUrl.append("?");
                        }

                        //增加no-proxy参数
                        noProxyUrl.append("no-proxy=");
                        noProxyUrl.append(System.currentTimeMillis()); // timestamp
                        
                        //将构造好的noProxyUrl复制到原URL
                        url = noProxyUrl.toString();
                }
                
                

                // 打开Http 连接
                httpConn = (HttpConnection) Connector.open(url, permissions, true);
                //设置request方法
                httpConn.setRequestMethod(method);

                //如果request权限为READ（即request方法为GET），
                //则需要设置http request属性的Range。
                //原理：设置http request属性的Range后的，
                //        server接收到该request后将把response数据分成小部分发回。
                //        从而避免了部分运营商对http response size的限制。
                if (permissions == Connector.READ) {        
                        if (lowRange > -1 && lowRange < highRange) {
                                StringBuffer range = new StringBuffer();
                                
                                range.append("bytes=");
                                range.append(lowRange);
                                range.append("-");
                                range.append(highRange);
                                
                                httpConn.setRequestProperty("Range", range.toString());
                        }
                //否则，request权限为READ_WRITE（即request方法为POST），
                //那么设置request的Content-Type属性。
                } else if (permissions == Connector.READ_WRITE) {
                        // POST request
                        httpConn.setRequestProperty("Content-Type", contentType);
                        dos = httpConn.openDataOutputStream();
                        dos.write(data);
                }
        
        } catch (Exception e) {
        
                exceptionPipe = e;
                //如果程序运行在多线程模式，则在异常发生后需要唤醒其它睡眠的线程继续run
                if (detached) {
                        forceNotify();
                }
                
                return;
                
        } finally {

                try {
                        try {
                                if (dos != null) {
                                        // 关闭dos
                                        dos.close();
                                }
                        } catch (Exception e) {
                                // 如果程序运行在多线程模式，则在异常发生后需要唤醒其它睡眠的线程继续run
                                if (exceptionPipe == null) {
                                        exceptionPipe = e;
                                        
                                        if (detached) {
                                                forceNotify();
                                        }
                                        return;
                                }
                        } finally {
                                dos = null;
                        }
                        
                        // 读取http连接的回应代码
                        int responseCode = httpConn.getResponseCode();
                        
                        //当request方法为GET，并设置了request range时，接收到的回应代码为HTTP_PARTIAL
                        //当request方法为POST，接收到的回应代码为HTTP_OK
                        //如果上述两种回应代码均没有收到，则表明连接失败或者出问题
                        if (responseCode != HttpConnection.HTTP_OK
                                        && responseCode != HttpConnection.HTTP_PARTIAL) {

                                if (exceptionPipe == null) {
                                        StringBuffer errorCode = new StringBuffer();
                                        errorCode.append("Response code from server: ");
                                        errorCode.append(responseCode);
                                        errorCode.append("\nMessage: [");
                                        errorCode.append(httpConn.getResponseMessage());
                                        errorCode.append("]");
                                        
                                        exceptionPipe = new IOException(errorCode.toString());
                                        
                                        if (detached) {
                                                forceNotify();
                                        }
                                        return;
                                }
                        }

                        //如果收到了上述的两种回应代码之一，则可以继续读取server的response数据
                        dis = httpConn.openDataInputStream();

                        //循环读取repsonse数据
                        int ch;
                        buffer = new StringBuffer();
                while ((ch = dis.read()) != -1) {
                        buffer.append((char) ch);
                }

                //将response数据进行必要的编码转换                 
                        response = buffer.toString().getBytes("ISO8859_1");
                        //接收到回应后，表明整个http会话过程结束，线程将结束。
                        //如果程序运行在多线程模式，则此时需要唤醒其它睡眠的线程继续run
                        if (detached) {
                                forceNotify();
                        }
                        
                        return;

                } catch (Exception e) {
                        
                        if (exceptionPipe == null) {
                                exceptionPipe = e;
                                
                                if (detached) {
                                        forceNotify();
                                }
                                
                                return;
                        }
                } finally {
                    
                        try {
                                if (dis != null) {
                                        // 关闭dis
                                        dis.close();
                                }
                        } catch (Exception e) {
                                // 若关闭dis时发生异常，则进行异常处理
                                if (exceptionPipe == null) {
                                        exceptionPipe = e;
                                        
                                        if (detached) {
                                                forceNotify();
                                        }
                                        return;
                                }
                        } finally {
                                dis = null;
                        }
                        
                        try {
                                if (httpConn != null) {
                                        //关闭http连接
                                        httpConn.close();

                                        httpConn = null;
                                }
                        } catch (Exception e) {

                                if (exceptionPipe == null) {
                                        exceptionPipe = e;
                                        
                                        if (detached) {
                                                forceNotify();
                                        }
                                        return;
                                }
                        }
                }
        }
}

五、参考资料：
联系netConnection作者：JAY-F
源代码下载
HTTP/1.1定义