iOS開發-Get請求，Post請求，同步請求和異步請求

標題中的Get和Post是請求的兩種方式，同步和異步屬於實現的方法，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，不過隨着時間的進化，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，給你先上一兩個吃着，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, // Unimplemented
    NSURLRequestReloadIgnoringCacheData = 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，此策略多用於離線操作）;

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 stub
		response.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URL
    NSURL *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GET
    
    NSString *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 stub
		request.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URL
    NSURL *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GET
    
    NSString *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 stub
		response.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 stub
		request.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；