標題中的Get和Post是請求的兩種方式，同步和異步屬于實現的方法，Get方式有同步和異步兩種方法，Post同理也有兩種。稍微有點Web知識的，對Get和Post應該不會陌生，常說的請求處理響應，基本上請求的是都是這兩個哥們，Http最開始定義的與服務器交互的方式有八種，不過隨著時間的進化，現在基本上使用的只剩下這兩種，有興趣的可以參考本人之前的博客Http協議中Get和Post的淺談，iOS客戶端需要和服務端打交道，Get和Post是跑不了的，本文中包含iOS代碼和少量Java服務端代碼，開始正題吧.

Get和Post同步請求

Get和Post同步請求的時候最常見的是登錄，輸入各種密碼才能看到的功能，必須是同步，異步在Web上局部刷新的時候用的比較多，比較耗時的時候執行異步請求，可以讓客戶先看到一部分功能，然后慢慢刷新，舉個例子就是餐館吃飯的時候點了十幾個菜，給你先上一兩個吃著，之后給別人上，剩下的慢慢上。大概就是這樣的。弄了幾個按鈕先上圖:

先貼下同步請求的代碼:

//設置URL路徑NSString *urlStr=[NSString stringWithFormat:@"http://localhost:8080/MyWeb/Book?username=%@&password=%@&type=get",@"博客園",@"keso"];urlStr=[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];NSURL *url=[NSURL URLWithString:urlStr];//通過URL設置網絡請求NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];NSError *error=nil;//獲取服務器數據NSData *requestData= [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:&error];if (error) {NSLog(@"錯誤信息:%@",[error localizedDescription]);}else{NSString *result=[[NSString alloc]initWithData:requestData encoding:NSUTF8StringEncoding];NSLog(@"返回結果:%@",result);}

代碼很多，需要解釋一下:

①URL如果有中文無法傳遞，需要編碼一下:

[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

②設置網路請求中的代碼，有兩個參數，最后一個設置請求的時間，這個不用說什么，重點說下緩存策略cachePolicy，系統中的定義如下:

typedef NS_ENUM(NSUInteger, NSURLRequestCachePolicy) {NSURLRequestUseProtocolCachePolicy = 0,NSURLRequestReloadIgnoringLocalCacheData = 1,NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4, // UnimplementedNSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,NSURLRequestReturnCacheDataElseLoad = 2,NSURLRequestReturnCacheDataDontLoad = 3,NSURLRequestReloadRevalidatingCacheData = 5, // Unimplemented };

?NSURLRequestUseProtocolCachePolicy（基礎策略）,NSURLRequestReloadIgnoringLocalCacheData（忽略本地緩存）;

NSURLRequestReloadIgnoringLocalAndRemoteCacheData（無視任何緩存策略，無論是本地的還是遠程的，總是從原地址重新下載）;

NSURLRequestReturnCacheDataElseLoad（首先使用緩存，如果沒有本地緩存，才從原地址下載);

NSURLRequestReturnCacheDataDontLoad（使用本地緩存，從不下載，如果本地沒有緩存，則請求失敗，此策略多用于離線操作）;

NSURLRequestReloadRevalidatingCacheData（如果本地緩存是有效的則不下載，其他任何情況都從原地址重新下載）;

Java服務端代碼:

protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubresponse.setContentType("text/html;charset=utf-8;");PrintWriter out = response.getWriter();System.out.println(request.getParameter("username"));System.out.println(request.getParameter("password"));if (request.getParameter("type") == null) {out.print("默認測試");} else {if (request.getParameter("type").equals("async")) {out.print("異步Get請求");} else {out.print("Get請求");}}}

?最終效果如下:

Post請求的代碼，基本跟Get類型，有注釋，就不多解釋了:

//設置URLNSURL *url=[NSURL URLWithString:@"http://localhost:8080/MyWeb/Book"];//創建請求NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];[request setHTTPMethod:@"POST"];//設置請求方式為POST，默認為GETNSString *param= @"Name=博客園&Address=http://www.cnblogs.com/xiaofeixiang&Type=post";//設置參數NSData *data = [param dataUsingEncoding:NSUTF8StringEncoding];[request setHTTPBody:data];//連接服務器NSData *received = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];NSString *result= [[NSString alloc]initWithData:received encoding:NSUTF8StringEncoding];NSLog(@"%@",result);

　Java服務端代碼:

protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubrequest.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8");PrintWriter out = response.getWriter();System.out.println("姓名:" + request.getParameter("Name"));System.out.println("地址:" + request.getParameter("Address"));System.out.println("類型:" + request.getParameter("Type"));if (request.getParameter("Type").equals("async")) {out.print("異步請求");} else {out.print("Post請求");}}

效果如下:

Get和Post異步請求

異步實現的時候需要實現協議NSURLConnectionDataDelegate，Get異步代碼如下:

//設置URL路徑NSString *urlStr=[NSString stringWithFormat:@"http://localhost:8080/MyWeb/Book?username=%@&password=%s&type=async",@"FlyElephant","keso"];urlStr=[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];NSURL *url=[NSURL URLWithString:urlStr];//創建請求NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];//連接服務器NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];

?實現協議的連接過程的方法:

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{NSHTTPURLResponse *res = (NSHTTPURLResponse *)response;NSLog(@"%@",[res allHeaderFields]);self.myResult = [NSMutableData data]; }接收到服務器傳輸數據的時候調用，此方法根據數據大小執行若干次 -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {[self.myResult appendData:data];}//數據傳輸完成之后執行方法 -(void)connectionDidFinishLoading:(NSURLConnection *)connection{NSString *receiveStr = [[NSString alloc]initWithData:self.myResult encoding:NSUTF8StringEncoding];NSLog(@"%@",receiveStr);}//網絡請求時出現錯誤（斷網，連接超時)執行方法 -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{NSLog(@"%@",[error localizedDescription]); }

異步傳輸的過程數據需要拼接，所以這個時候需要設置一個屬性接收數據:

@property (strong,nonatomic) NSMutableData *myResult;

效果如下:

?

Post異步傳遞代碼:

//設置URLNSURL *url=[NSURL URLWithString:@"http://localhost:8080/MyWeb/Book"];//設置請求NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];[request setHTTPMethod:@"POST"];//設置請求方式為POST，默認為GETNSString *param= @"Name=keso&Address=http://www.cnblogs.com/xiaofeixiang&Type=async";//設置參數NSData *data = [param dataUsingEncoding:NSUTF8StringEncoding];[request setHTTPBody:data];//連接服務器NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];

效果如下:

異步的請求比較簡單，需要的方法都已經被封裝好了，需要注意數據是動態拼接的,請求的代碼都是在Java Servlet中實現的，Java項目中的目錄如下:

Book.java中代碼如下:

import java.io.IOException; import java.io.PrintWriter; import java.net.URLDecoder; import java.net.URLEncoder;import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;/*** Servlet implementation class Book*/ @WebServlet("/Book") public class Book extends HttpServlet {private static final long serialVersionUID = 1L;/*** @see HttpServlet#HttpServlet()*/public Book() {super();// TODO Auto-generated constructor stub}/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse* response)*/protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubresponse.setContentType("text/html;charset=utf-8;");PrintWriter out = response.getWriter();System.out.println(request.getParameter("username"));System.out.println(request.getParameter("password"));if (request.getParameter("type") == null) {out.print("默認測試");} else {if (request.getParameter("type").equals("async")) {out.print("異步Get請求");} else {out.print("Get請求");}}}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse* response)*/protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubrequest.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8");PrintWriter out = response.getWriter();System.out.println("姓名:" + request.getParameter("Name"));System.out.println("地址:" + request.getParameter("Address"));System.out.println("類型:" + request.getParameter("Type"));if (request.getParameter("Type").equals("async")) {out.print("異步Post請求");} else {out.print("Post請求");}}}

Get和Post總結

①同步請求一旦發送，程序將停止用戶交互，直至服務器返回數據完成，才可以進行下一步操作(例如登錄驗證)；

②異步請求不會阻塞主線程，會建立一個新的線程來操作，發出異步請求后，依然可以對UI進行操作，程序可以繼續運行；

③Get請求，將參數直接寫在訪問路徑上，容易被外界看到，安全性不高，地址最多255字節;

④Post請求，將參數放到body里面，安全性高，不易被捕獲；

總結

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