HTTP定义了一种在服务器和客户端之间传递数据的途径。
URL定义了一种唯一标示资源在网络中位置的途径。
REQUESTS 和 RESPONSES：
客户端先建立一个TCP连接，然后发送一个请求。服务器受到请求处理后发送一个响应向客户端传递数据。然后客户端可以继续发送请求或者关闭这个TCP连接。
HTTPS：
在TCP连接建立后，发送请求之前，需要建立一个一个SSL会话。
request方法和它们的用途
注意：想server发送大量数据需要用POST，因为GET仅支持发送少量数据（8KB）。
iOS的NSURLRequest和它的子类NSMutableURLRequest提供了建立HTTP请求的方法。
NSURLResponse 和 它的子类NSHTTPURLResponse 处理返回的数据。
URL：
Protocol包括HTTP、FTP和file。
URL编码：
NSString *urlString = @"http://myhost.com?query=This is a question";
NSString *encoded = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSURL用来管理URL。
IOS HTTP APIS：
涉及到下面一些类：
NSURL, NSURLRequest, NSURLConnection, 和 NSURLResponse.
1、NSURL
NSURL可以定义本地文件和网络文件
NSURL *url = [NSURL urlWithString:@"http://www.google.com"];
NSData *data = [NSData dataWithContentsOfURL:url];
NSURL定义了很多访问器：
if (url.port == nil) {
NSLog(@"Port is nil"); } else { NSLog(@"Port is not nil"); }
2、NSURLRequest
创建了NSURL后，就可以用NSURLRequest建立请求了：
NSURL *url = [NSURL URLWithString: @"https://gdata.youtube.com/feeds/api/standardfeeds/top_rated"]; if (url == nil) { NSLog(@"Invalid URL");
return; } NSURLRequest *request = [NSURLRequest requestWithURL:url];
if (request == nil) { NSLog(@"Invalid Request"); return; }
NSMutableURLRequest是NSURLRequest 的子类，提供了改变请求的属性的方法：
NSURL *url = [NSURL urlWithString@"http://server.com/postme"];
NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
[req setHTTPMethod:@"POST"]; [req setHTTPBody:[@"Post body" dataUsingEncoding:NSUTF8StringEncoding]];
如果你要发送一个图片或者视频，那么用需要用NSInputStream，它没有把数据全部加在到内存。
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; NSInputStream *inStream = [NSInputStream inputStreamWithFileAtPath:srcFilePath]; [request setHTTPBodyStream:inStream]; [request setHTTPMethod:@"POST"];
3、NSURLResponse
4、NSURLConnection
提供了初始化、开始、和取消一个连接。
发送同步请求：
- (NSArray *) doSyncRequest:(NSString *)urlString { // make the NSURL object from the string NSURL *url = [NSURL URLWithString:urlString]; // Create the request object with a 30 second timeout and a cache policy to always retrieve the // feed regardless of cachability. NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:30.0]; // Send the request and wait for a response NSHTTPURLResponse *response; NSError *error; NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error]; // check for an error if (error != nil) { NSLog(@"Error on load = %@", [error localizedDescription]); return nil; } // check the HTTP status if ([response isKindOfClass:[NSHTTPURLResponse class]]) { NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response; if (httpResponse.statusCode != 200) { return nil; } NSLog(@"Headers: %@", [httpResponse allHeaderFields]); } // Parse the data returned into an NSDictionary NSDictionary *dictionary = [XMLReader dictionaryForXMLData:data error:&error]; // Dump the dictionary to the log file NSLog(@"feed = %@", dictionary); NSArray *entries =[self getEntriesArray:dictionary]; // return the list if items from the feed. return entries; }
Queued Asynchronous Requests：
- (void) doQueuedRequest:(NSString *)urlString delegate:(id)delegate { // make the NSURL object NSURL *url = [NSURL URLWithString:urlString]; // create the request object with a no cache policy and a 30 second timeout. NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:30.0]; // If the queue doesn't exist, create one. if (queue == nil) { queue = [[NSOperationQueue alloc] init]; } // send the request and specify the code to execute when the request completes or fails. [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) { if (error != nil) { NSLog(@"Error on load = %@", [error localizedDescription]); } else { // check the HTTP status if ([response isKindOfClass:[NSHTTPURLResponse class]]) { NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response; if (httpResponse.statusCode != 200) { return; } NSLog(@"Headers: %@", [httpResponse allHeaderFields]); } // parse the results and make a dictionary NSDictionary *dictionary = [XMLReader dictionaryForXMLData:data error:&error]; NSLog(@"feed = %@", dictionary); // get the dictionary entries. NSArray *entries =[self getEntriesArray:dictionary]; // call the delegate if ([delegate respondsToSelector:@selector(setVideos:)]) { [delegate performSelectorOnMainThread:@selector(setVideos:) withObject:entries waitUntilDone:YES]; } } }]; }
NSURLConnection start方法和Delegate：
GET：
NSURL *url=[[ NSURL alloc ] initWithString :urlString]; NSMutableURLRequest *request=[[NSMutableURLRequest alloc ] init ]; NSURLConnection *connection = [[ NSURLConnection alloc ] initWithRequest :request delegate : self ]; if (connection) { [connection start]; } else { NSLog ( @"sorry" ); } /* * NSURLConnectionDataDelegate */ - (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse *)response {
[activityIndicator startAnimating]; //UIActivityIndicatorView NSLog(@"Did Receive Response %@", response); responseData = [[NSMutableData alloc]init]; } - (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data { //NSLog(@"Did Receive Data %@", data); [responseData appendData:data]; //NSMutableData } - (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error { NSLog(@"Did Fail"); } - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
[activityIndicator stopAnimating];
NSLog(@"Did Finish"); // Do something with responseData }
POST：
//initialize new mutable data NSMutableData *data = [[NSMutableData alloc] init]; self.receivedData = data; //initialize url that is going to be fetched. NSURL *url = [NSURL URLWithString:@"http://www.snee.com/xml/crud/posttest.cgi"]; //initialize a request from url NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[url standardizedURL]]; //set http method [request setHTTPMethod:@"POST"]; //initialize a post data NSString *postData = [[NSString alloc] initWithString:@"fname=example&lname=example"]; //set request content type we MUST set this value. [request setValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"]; //set post data of request [request setHTTPBody:[postData dataUsingEncoding:NSUTF8StringEncoding]]; //initialize a connection from request NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; self.connection = connection; //start the connection [connection start];
异步请求：
异步请求需要一个run loop来操作代理对象，GCD和NSOperationQueue默认并没有run loop，所以如果你想在后台发起一个HTTP请求，必须确保有run loop。
NSURLConnection connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO]; [connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode]; [connection start];
上面的代码是在主线程运行，如果想在其他线程运行，可以在其他线程新建一个run loop，并绑定到connection。