iOS开发-Get请求，Post请求，同步请求和异步请求

标题中的Get和Post是请求的两种方式，同步和异步属于实现的方法，Get方式有同步和异步两种方法，Post同理也有两种。稍微有点Web知识的，对Get和Post应该不会陌生，常说的请求处理响应，基本上请求的是都是这两个哥们，Http最开始定义的与服务器交互的方式有八种，不过随着时间的进化，现在基本上使用的只剩下这两种，有兴趣的可以参考本人之前的博客Http协议中Get和Post的浅谈，iOS客户端需要和服务端打交道，Get和Post是跑不了的，本文中包含iOS代码和少量Java服务端代码，开始正题吧.

Get和Post同步请求

Get和Post同步请求的时候最常见的是登录，输入各种密码才能看到的功能，必须是同步，异步在Web上局部刷新的时候用的比较多，比较耗时的时候执行异步请求，可以让客户先看到一部分功能，然后慢慢刷新，举个例子就是餐馆吃饭的时候点了十几个菜，给你先上一两个吃着，之后给别人上，剩下的慢慢上。大概就是这样的。弄了几个按钮先上图:

先贴下同步请求的代码:

     //设置URL路径
     NSString *urlStr=[NSString stringWithFormat:@"http://localhost:8080/MyWeb/Book?username=%@&password=%@&type=get",@"博客园",@"keso"];
     urlStr=[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
     NSURL *url=[NSURL URLWithString:urlStr];
    
    //通过URL设置网络请求
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];

    NSError *error=nil;
    //获取服务器数据
    NSData *requestData= [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:&error];
    if (error) {
        NSLog(@"错误信息:%@",[error localizedDescription]);
    }else{
        NSString *result=[[NSString alloc]initWithData:requestData encoding:NSUTF8StringEncoding];
        NSLog(@"返回结果:%@",result);

    }

代码很多，需要解释一下:

①URL如果有中文无法传递，需要编码一下:

[urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

②设置网路请求中的代码，有两个参数，最后一个设置请求的时间，这个不用说什么，重点说下缓存策略cachePolicy，系统中的定义如下:

typedef NS_ENUM(NSUInteger, NSURLRequestCachePolicy)
{
    NSURLRequestUseProtocolCachePolicy = 0,

    NSURLRequestReloadIgnoringLocalCacheData = 1,
    NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4, // Unimplemented
    NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,

    NSURLRequestReturnCacheDataElseLoad = 2,
    NSURLRequestReturnCacheDataDontLoad = 3,

    NSURLRequestReloadRevalidatingCacheData = 5, // Unimplemented
};

 NSURLRequestUseProtocolCachePolicy（基础策略）,NSURLRequestReloadIgnoringLocalCacheData（忽略本地缓存）;

NSURLRequestReloadIgnoringLocalAndRemoteCacheData（无视任何缓存策略，无论是本地的还是远程的，总是从原地址重新下载）;

NSURLRequestReturnCacheDataElseLoad（首先使用缓存，如果没有本地缓存，才从原地址下载);

NSURLRequestReturnCacheDataDontLoad（使用本地缓存，从不下载，如果本地没有缓存，则请求失败，此策略多用于离线操作）;

NSURLRequestReloadRevalidatingCacheData（如果本地缓存是有效的则不下载，其他任何情况都从原地址重新下载）;

Java服务端代码:

	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("默认测试");
		} else {
			if (request.getParameter("type").equals("async")) {
				out.print("异步Get请求");
			} else {
				out.print("Get请求");
			}
		}
	}

 最终效果如下:

Post请求的代码，基本跟Get类型，有注释，就不多解释了:

   //设置URL
    NSURL *url=[NSURL URLWithString:@"http://localhost:8080/MyWeb/Book"];
    //创建请求
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    
    [request setHTTPMethod:@"POST"];//设置请求方式为POST，默认为GET
    
    NSString *param= @"Name=博客园&Address=http://www.cnblogs.com/xiaofeixiang&Type=post";//设置参数
    
    NSData *data = [param dataUsingEncoding:NSUTF8StringEncoding];
    
    [request setHTTPBody:data];
    
    //连接服务器
    NSData *received = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

    NSString *result= [[NSString alloc]initWithData:received encoding:NSUTF8StringEncoding];

    NSLog(@"%@",result);

　Java服务端代码:

	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("类型:" + request.getParameter("Type"));
		if (request.getParameter("Type").equals("async")) {
			out.print("异步请求");
		} else {
			out.print("Post请求");
		}

	}

效果如下:

Get和Post异步请求

异步实现的时候需要实现协议NSURLConnectionDataDelegate，Get异步代码如下:

   //设置URL路径
    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];
    //创建请求
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    
    //连接服务器
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];

 实现协议的连接过程的方法:

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSHTTPURLResponse *res = (NSHTTPURLResponse *)response;
    
    NSLog(@"%@",[res allHeaderFields]);
    
    self.myResult = [NSMutableData data];
}

////接收到服务器传输数据的时候调用，此方法根据数据大小执行若干次
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.myResult appendData:data];
    
}

//数据传输完成之后执行方法
-(void)connectionDidFinishLoading:(NSURLConnection *)connection

{
    NSString *receiveStr = [[NSString alloc]initWithData:self.myResult encoding:NSUTF8StringEncoding];
    
    NSLog(@"%@",receiveStr);
    
}

//网络请求时出现错误（断网，连接超时)执行方法
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error

{
    NSLog(@"%@",[error localizedDescription]);
}

异步传输的过程数据需要拼接，所以这个时候需要设置一个属性接收数据:

@property (strong,nonatomic) NSMutableData *myResult;

效果如下:

Post异步传递代码:

   //设置URL
    NSURL *url=[NSURL URLWithString:@"http://localhost:8080/MyWeb/Book"];
    
    //设置请求
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10];
    
    [request setHTTPMethod:@"POST"];//设置请求方式为POST，默认为GET
    
    NSString *param= @"Name=keso&Address=http://www.cnblogs.com/xiaofeixiang&Type=async";//设置参数
    
    NSData *data = [param dataUsingEncoding:NSUTF8StringEncoding];
    
    [request setHTTPBody:data];
    //连接服务器
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];

效果如下:

异步的请求比较简单，需要的方法都已经被封装好了，需要注意数据是动态拼接的,请求的代码都是在Java Servlet中实现的，Java项目中的目录如下:

Book.java中代码如下:

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("默认测试");
		} else {
			if (request.getParameter("type").equals("async")) {
				out.print("异步Get请求");
			} else {
				out.print("Get请求");
			}
		}
	}

	/**
	 * @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("类型:" + request.getParameter("Type"));
		if (request.getParameter("Type").equals("async")) {
			out.print("异步Post请求");
		} else {
			out.print("Post请求");
		}

	}

}

Get和Post总结

①同步请求一旦发送，程序将停止用户交互，直至服务器返回数据完成，才可以进行下一步操作(例如登录验证)；

②异步请求不会阻塞主线程，会建立一个新的线程来操作，发出异步请求后，依然可以对UI进行操作，程序可以继续运行；

③Get请求，将参数直接写在访问路径上，容易被外界看到，安全性不高，地址最多255字节;

④Post请求，将参数放到body里面，安全性高，不易被捕获；