iOS开发网络编程之断点续传-NSURLConnection

最近在做一个小项目的时候，发现使用NSURLSession或者AFNNetworking进行断点续传时诸多的不便，于是自己封装了一个类来实现断点续传,在程序重新启动时仍然可以继续下载(需自己调用方法)，同时可以在同一时间多次调用该类方法。使用时请注意传入各参数的合理性，方法内部并没有对传入的参数进行修正

主要技术： NSURLConnection、block、NFFileHandle

1、首先，我提供一个类方法，供外界调用。 创建的类名为DownloadService

 //
 //  DownloadService.h
 //  11111
 //
 //  Created by Liu Feng on 14-2-17.
 //  Copyright (c) 2014年 Liu Feng. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 typedef void (^DownloadServiceSuccess)(NSString *savePath);
 typedef void (^DownloadServiceFailure)(NSError *error);

 @interface DownloadService : NSObject
 /**
  *  下载指定URL的资源到路径
  *
  *  @param urlStr   网络资源路径
  *  @param toPath   本地存储文件夹
  *  @param capacity 缓存大小，单位为Mb
  *  @param success  成功时回传本地存储路径
  *  @param failure  失败时回调的错误原因
  */
 + (void)downLoadWithURL:(NSString *)urlStr toDirectory:(NSString *)toDirectory cacheCapacity:(NSUInteger)capacity  success:(DownloadServiceSuccess)success failure:(DownloadServiceFailure)failure;

 @end

2、在.m中实现

 //
 //  DownloadService.m
 //  11111
 //
 //  Created by Liu Feng on 14-2-17.
 //  Copyright (c) 2014年 Liu Feng. All rights reserved.
 //

 #import "DownloadService.h"

 static DownloadService *_download;
 static NSMutableDictionary *_dictPath;
 static NSMutableDictionary *_dictBlock;
 static NSMutableDictionary *_dictHandle;
 static unsigned long long _cacheCapacity; // 缓存
 static NSMutableData *_cacheData;

 typedef void (^myBlcok)(NSString *savePath, NSError *error);

 @interface DownloadService ()<NSURLConnectionDataDelegate>

 @end

 @implementation DownloadService

 + (void)initialize
 {
     _download = [[DownloadService alloc] init];
     _dictPath = [NSMutableDictionary dictionary]; // 存储文件路径
     _dictBlock = [NSMutableDictionary dictionary]; // 存储block
     _dictHandle = [NSMutableDictionary dictionary]; // 存储NSFileHandle对象
     _cacheData = [NSMutableData data]; // 存放缓存
 }

 + (void)downLoadWithURL:(NSString *)urlStr toDirectory:(NSString *)toDirectory cacheCapacity:(NSInteger)capacity success:(DownloadServiceSuccess)success failure:(DownloadServiceFailure)failure{

     // 1. 创建文件
     NSString *fileName = [urlStr lastPathComponent];
     NSString *filePath = [NSString stringWithFormat:@"%@/%@", toDirectory, fileName];

     // 记录文件起始位置
     unsigned long long from = ;
     if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]){ // 已经存在
         from = [[NSData dataWithContentsOfFile:filePath] length];
     }else{ // 不存在，直接创建
         [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
     }

     // url
     NSURL *url = [NSURL URLWithString:urlStr];

     // 请求
     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:5.0f];

     // 设置请求头文件
     NSString *rangeValue = [NSString stringWithFormat:@"bytes=%llu-", from];
     [request addValue:rangeValue forHTTPHeaderField:@"Range"];

     // 创建连接
     NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:_download];

     // 保存文章连接
     _dictPath[connection.description] = filePath;

     // 保存block,用于回调
     myBlcok block = ^(NSString *savePath, NSError *error){
         if (error) {
             if (failure) {
                 failure(error);
             }
         }else{
             if (success) {
                 success(savePath);
             }
         }
     };
     _dictBlock[connection.description] = block;

     // 保存缓存大小
     _cacheCapacity = capacity *  * ;

     // 开始连接
     [connection start];
 }
 /**
  *  接收到服务器响应
  *
  *  @param connection 哪一个连接
  *  @param response   响应对象
  */
 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
 {
     // 取出文章地址
     NSString *filePath = _dictPath[connection.description];

     // 打开文件准备输入
     NSFileHandle *outFile = [NSFileHandle fileHandleForWritingAtPath:filePath];

     // 保存文件操作对象
     _dictHandle[connection.description] = outFile;
 }
 /**
  *  开始接收数据
  *
  *  @param connection 哪一个连接
  *  @param data       二进制数据
  */
 - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
 {
     // 取出文件操作对象
     NSFileHandle *outFile = _dictHandle[connection.description];

     // 移动到文件结尾
     [outFile seekToEndOfFile];

     // 保存数据
     [_cacheData appendData:data];

     if (_cacheData.length >= _cacheCapacity) {
         // 写入文件
         [outFile writeData:data];

         // 清空数据
         [_cacheData setLength:];
     }
 }
 /**
  *  连接出错
  *
  *  @param connection 哪一个连接出错
  *  @param error      错误信息
  */
 - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
 {
     // 取出文件操作对象
     NSFileHandle *outFile = _dictHandle[connection.description];

     // 关闭文件操作
     [outFile closeFile];

     // 回调block
     myBlcok block = _dictBlock[connection.description];

     if (block) {
         block(nil, error);
     }

     // 移除字典中
     [_dictHandle removeObjectForKey:connection.description];
     [_dictPath removeObjectForKey:connection.debugDescription];
     [_dictBlock removeObjectForKey:connection.description];
 }
 /**
  *  结束加载
  *
  *  @param connection 哪一个连接
  */
 - (void)connectionDidFinishLoading:(NSURLConnection *)connection
 {
     // 取出文件操作对象
     NSFileHandle *outFile = _dictHandle[connection.description];

     // 关闭文件操作
     [outFile closeFile];

     // 取出路径
     NSString *savePath = [_dictPath objectForKey:connection.description];

     // 取出block
     myBlcok block = _dictBlock[connection.description];

     // 回调
     if (block) {
         block(savePath, nil);
     }

     // 移除字典中
     [_dictHandle removeObjectForKey:connection.description];
     [_dictPath removeObjectForKey:connection.debugDescription];
     [_dictBlock removeObjectForKey:connection.description];
 }

 @end